Race car suspension Class

[Ranger Mike]

wyld
please read post 301 on page 13 and 1399 on page 56
i will fire up the computer and get details on what info the software needs when looking at rear end

 

[chop6259]

Hey RM,

Every time I have a question I always revisit this forum (have intermittently frequented since 2014). I know you are a big proponent for the performance trends software and that is my next investment. While I'm budgeting the cash for this I do have a question.

While I was mapping out the rear suspension of my dirt late model I was thinking about instant centers. On the dirt cars we do have birdcages on both sides of the rear axle which is where my question lies. In order to calculate the instant centers of the rear end you have to use the lower bars for sure. Although, I'm not sure if you would use any other links to capture the instant centers. Both sides upper bars are angled in the positive direction so you would get no convergence other than aft axle. The lift arm is level at static so that wouldn't be the correct option either. The one given i have is that obviously we do have a positive anti-squat value on the left rear given that it hikes as soon as throttle is applied. Would you suggest just using the just lower bar to map out instant center? I've consulted all of the textbooks I have and have not found much in the way of instant center calculation for this scenario. I'm interested in the theory as it seems to help me conceptualize my direction, execution and optimization.

Also, do you have any reference that would help me understand the math of the instant center? I see a lot of articles referencing 100% but I'm not understanding what the base value and calculated value is that would yield your specific percentage.

I've done a ton of work mapping and optimizing lift bar (torque arm) application and optimization. This is the next piece to the puzzle.

Keep in mind that on a dirt late model you have a live axle decoupled suspension, so the typical anti-squat calculations you would normally find in textbooks for 3-link suspensions etc. do not apply. You basically have four sources of anti-squat in a typical dirt late model utilizing a 4-link rear suspension.

The forces generated by the 5th arm lift bar, the forces generated by the left set of four bar links, the forces generated by the right set of four bar links, and the forces generated by the j-bar. The 5th arm forces are a direct response from axle wrap, so that reaction force is pretty straight forward. You then have to determine the instant centers for both the j-bar system of links and the left and right four bar systems of links.

The anti-squat from the j-bar system is generated by taking a moment about that systems IC from the lateral forces at each of the rear tires. The left and right four bar links are determined by taking a moment about their ICs as well. The force you use is the force that is generated at the axle tube by the rotating tire. This approach is only valid because the 4-bar links systems (via the rotating birdcages) are decoupled from the axle tube.

Keep in mind that these calculations on their own are pretty useless other than for conceptual purposes. They should be used in a large set of equations that define the vehicle as a whole, where the anti-squat forces are but a small part of the overall picture. As for your question about how to determine the 4-bar link instant centers. You would have to project the links onto a two dimensional plane (i.e. a sideview) and find the intersection of the projected lines from the top and bottom 4 link bar. It will be below the ground plane and behind the tire CP on the left rear for example.

 

[Ranger Mike]

excellent reply Chop
Anti squat is a production automobile parameter to try to get some performance out of the grocery getter car design and of little value in a tunable purpose built race car. All you have to know on Rear IC is longer is better.
I suggest you work on mapping the rear end rotation on roll and measure pitch and yaw as well. know how much each link changes the set up and learn WHY. Software on the rear end just uses the lower arm mount points and the older version i have does not address diet car set ups.

 

[UFO]

RM Thanks for all you do for this forum. There is no other with so much interesting info. I would like to give some of my thoughts on dirt late model suspension. Please refer to the drawing below. This is weight transfer to the rear on straight forward acceleration without consideration to the dampers and a few other forces.

With acceleration we only have to worry about forces from one end of the car, the rear. Unlike decell and lateral G forces which have resisting forces from all four corners. Similarly to lateral there are six major things to consider after the wheel base and the center of gravity height are established. They are the elastometric weight transfer, geometric transfer, which consists of the height of the forward drive force compared to the height of the center of gravity of the sprung mass, the jacking effect of the forward drive force, and the lift of the torque control device on the rear axle. The last is the aero drag height, center, and magnitude, and down force location, and magnitude. On a track that has o lot of speed change in the straight the aero will be the dominating forces at the end and the others will dominate off the turn where the acceleration rate is much higher. All will be varied dynamically with changes suspension height and velocity.

This straight forward acceleration may never happen to some short tracks, especially if you run the inside where the straight is rounded by running up to the wall in the center. We must normally consider a combination of lateral and longitudinal on most parts of the track, which makes things much more interesting.

We know we cannot change the total weight transfer to the rear without changing center of gravity height, wheel base, or acceleration. We cannot change them easily, but we can control, to some extent how much is handled by the left and right rear. On tracks that have a lot of bite you are not off the throttle much at all. On tracks that are low traction you are going from low throttle to high coming off the turn putting the rear suspension through a lot more travel with high anti squat. In that case I think anti squat is very important. That is because as you get on the throttle the mass of the sprung weight is moving away from the track and the opposite reaction is pushing the rear axle into the track. This does not last long, only as the frame is moving up but it does give a head start on the traction cycle. When you hit the throttle there is only static weight on the rear and as the car moves forward weight is transferred to the rear giving more traction and allowing more acceleration. This cycle keeps building off the turn, but can have a head start with anti squat before it starts to accelerate forward.

Aero down force also increases with velocity. With a late model having a high horsepower to weight ratio you can afford to lift that wide body and spoiler as far up in the air as you can, but now that is limited by the rules. Another help in the turns is the high degree of roll of the body which directs the aero down force on an angle, putting more on the inside tire. The late models have gone to a ton of dynamic cross weight by standing on the left trailing arms. That makes a lot of inside weight, traction, and drive. They then use a lot of rear steer to help turn and this also puts the car on an angle to the direction of travel, but the rear wheels more in the direction of travel not breaking traction as much. That helps maintain the forward drive, and also makes the body side panel deflect the air helping resist centripetal force. This setup is geared more to a slick track.

The drawing shows how links and torque arm effect loading on the rear axle and unload the springs with acceleration. The gain in down force on the rear tire is not in addition to weight transfer from acceleration but part of it. The drawing shows a static position, the instant center and force direction and magnitude are changing dynamically and constantly. These are the basic forces, there are more involved.

I think I ran on long enough for one post. Please let me know any opinions on this.

 

[Ranger Mike]

ufo
i got halfway thru your post above, and stopped. was replying to each item but it became readily apparent you have not read thru this long 62 page class. if you had you would have seen my posts addressing each and every aspect you chose to comment on. i suggest you read and revisit your post.

 

[berkeman]

ufo
i got halfway thru your post above, and stopped. was replying to each item but it became readily apparent you have not read thru this long 62 page class. if you had you would have seen my posts addressing each and every aspect you chose to comment on. i suggest you read and revisit your post.

One tip for @UFO -- You can use the SEARCH feature in the upper right corner to search just this thread for keywords or phrases. Just pull down the "Everywhere" default for where to search, and change it to "This thread".

 

[UFO]

Thanks for the tip Berkeman. That is a cool tool to get around on this forum.

RM, sorry I didn't mean to be repetitive, this is the first time I ever posted on a forum. I'm a slow reader and started reading this a long time ago and also have a good memory, but it's short so I don't remember it all. I did go back and review a few things.

I was just trying to respond to Wylde's post and had other info to help make my point. I also disagreed somewhat with the point that anti squat didn't apply much to racing, I think it does on late models on certain tracks. I didn't expect a response to everything. There were some points that I don't recall seeing in earlier posts like the angle of the side of the car to the travel path, the force change from roll degree, anti squat and traction cycle, distribution of left and right loading under acc., the difference in anti squat effect on a tacky verses a slick track, and dynamic cross weight jacking from standing on the rods.

RM what is your opinion on the center of gravity calculations using the whole car, I think it should be on the sprung mass only. On a solid axle car there is nothing you can do to change the transfer or distribution of the weight of the axles so if you want to know total transfer, they should be calculated separately. This should move the CoG up a little, this is the only mass rotating around the roll center. To get more accurate weight transfer calculations, CoG lateral movement, fuel slosh, and tire spring rate should be considered.

 

[jack action]

With acceleration we only have to worry about forces from one end of the car, the rear.

Ignoring the front suspension in acceleration? Tell that to a drag racer.

We know we cannot change the total weight transfer to the rear without changing center of gravity height, wheel base, or acceleration.

True.

That is because as you get on the throttle the mass of the sprung weight is moving away from the track and the opposite reaction is pushing the rear axle into the track.

You seem to think that the fact that the sprung mass is moving, that it is somehow adding some vertical force. It does not. (Any extra vertical force would come from the increase in CG height, which would increase the weight transfer)

When you hit the throttle there is only static weight on the rear and as the car moves forward weight is transferred to the rear giving more traction and allowing more acceleration. This cycle keeps building off the turn,

You seem to think that the weight transfer is slowly building under a given acceleration. It does not. It is instantaneous. If the acceleration is there, the weight transfer must also be there.

Also, the car doesn't need to move to have a weight transfer. You can have an acceleration at a zero velocity (car stopped) and the weight transfer will be there. Of course, with an acceleration, the car will not be stopped for long.

RM what is your opinion on the center of gravity calculations using the whole car, I think it should be on the sprung mass only. [...] This should move the CoG up a little, this is the only mass rotating around the roll center.

I think this come from the fact that you think that the weight transfer is influenced by the body motion. Again, it is not (other than CG height change). The unsprung mass is accelerated and it will contribute to the horizontal inertial force acting at the CG (creating a moment about the ground, where the equal and opposing traction force lies), which in turn will be compensated by a reaction moment coming from the axles, i.e the weight transfer.

The keyword here is moment. I think @Ranger Mike hates the term weight transfer because ... there is no weight transferred. There is a moment that compensates for (or adds to) the weight supported at each corner.

The fact that the suspension moves is only a matter of knowing in what proportion (% anti-squat, % anti-lift) does the weight transfer goes through the solid links of the suspension or through the unrestricted spring.

 

[Ranger Mike]

thanks Jack, was watching goat screw at Daytona..what a waste..
my hang up is as stated. I hate the term.

Please read post 563 on page 23 on CoG
228 on page 10
470 on page 19
676 on page 28 and
811 on page 33 - this one is my rant on weight transfer!On this post ifin you don't do the homework, you don't get the trophy.

 

[berkeman]

thanks Jack, was watching goat screw at Daytona..what a waste..

Yeah, no kidding. I gave up after a couple of hours -- looked like the rain would postpone it until today and also give tome for more car repairs...

 

[UFO]

UFO said:
With acceleration we only have to worry about forces from one end of the car, t

jack action said:
Ignoring the front suspension in acceleration? Tell that to a drag racer.

UFO
Unless you have front or four wheel drive the front is not contributing to forward acceleration. It does enter in with controlling left to right distribution of loads, it has nothing to do with jacking forces from acceleration, which is what the discussion was about.

jack action said:
You seem to think that the fact that the sprung mass is moving, that it is somehow adding some vertical force. It does not. (Any extra vertical force would come from the increase in CG height, which would increase the weight transfer)

UFO
You are going to have to talk to Newton about that, the third law of motion goes something like when any object puts a force on another object it will have an equal and opposite reaction on the first object. So when the sprung mass is forced up by the rear the rear will have that same force pushing down on it, and this is in addition to acceleration weight transfer.

jack action said:
You seem to think that the weight transfer is slowly building under a given acceleration. It does not. It is instantaneous. If the acceleration is there, the weight transfer must also be there.

Also, the car doesn't need to move to have a weight transfer. You can have an acceleration at a zero velocity (car stopped) and the weight transfer will be there. Of course, with an acceleration, the car will not be stopped for long.

UFO
In real life there are very few things that are instantaneous the same here. The acceleration depends on traction, traction depends on load, load from transfer depends on acceleration and so on is the cycle. It also takes time to torsionaly flex the tire, wind up the axle, pitch the sprung mass, and compress and extend the springs and then the traction cycle.

Unless you have an external acceleration or force acting on the car you cannot have weight transfer without movement. The cars acceleration is from engine power put to the wheels, unlike gravity or lateral force from turning, which can act on it without movement if it has a equal resisting force in the opposite direction.

jack action said:
I think this come from the fact that you think that the weight transfer is influenced by the body motion. Again, it is not (other than CG height change). The unsprung mass is accelerated and it will contribute to the horizontal inertial force acting at the CG (creating a moment about the ground, where the equal and opposing traction force lies), which in turn will be compensated by a reaction moment coming from the axles, i.e the weight transfer.

The keyword here is moment. I think @Ranger Mike hates the term weight transfer because ... there is no weight transferred. There is a moment that compensates for (or adds to) the weight supported at each corner.

The fact that the suspension moves is only a matter of knowing in what proportion (% anti-squat, % anti-lift) does the weight transfer goes through the solid links of the suspension or through the unrestricted spring.

UFO
Well, I think you're wrong again, some of what you said is ok, but you're not looking at everything. The moment about the tire contact patch is only for overturning and geometric forces. The other moment is about the roll center, which the sprung mass CoG is rotating. Here is what's happening, on cars that have a lot of body roll, there can be a lot of lateral movement of the CoG which will transfer weight to the outside (RM this is real weight transfer along with fuel and oil slosh).

Technically weight is the force from gravity only, but most consider how the loads change from the resultant force from gravity and other acceleration forces and call it weight transfer, nothings simple!
Beside the formentioned there is other real weight transfer that is from placing the car on a well banked turn. Put the scales under it and the inside will be heaver.

 

[Tom.G]

Me thinks somebody has never seen a car, with the brakes solidly applied, move around when engine power is applied to the drive train.

There is not only the side-to-side rocking from engine torque, but also, depending on the direction of driveshaft rotation, the front or the back suspension will rise.

 

[Ranger Mike]

jack action said:
Ignoring the front suspension in acceleration? Tell that to a drag racer.

UFO
Unless you have front or four wheel drive the front is not contributing to forward acceleration. It does enter in with controlling left to right distribution of loads, it has nothing to do with jacking forces from acceleration, which is what the discussion was about.
Any Race car driver will tell you, front end lift has to be controlled on acceleration. It is a major tuning point to get the car to hook up.

jack action said:
You seem to think that the fact that the sprung mass is moving, that it is somehow adding some vertical force. It does not. (Any extra vertical force would come from the increase in CG height, which would increase the weight transfer)

UFO
You are going to have to talk to Newton about that, the third law of motion goes something like when any object puts a force on another object it will have an equal and opposite reaction on the first object. So when the sprung mass is forced up by the rear the rear will have that same force pushing down on it, and this is in addition to acceleration weight transfer.
This race car suspension class in posted in Physics Forum for a reason. We use the correct terminology to understand how things work or don’t work at the track. Inventing new words or posting non supported opinions is legal here but do not expect an answer.



There are no participation trophies in RACING. Only the winner gets one.

jack action said:
You seem to think that the weight transfer is slowly building under a given acceleration. It does not. It is instantaneous. If the acceleration is there, the weight transfer must also be there.

Also, the car doesn't need to move to have a weight transfer. You can have an acceleration at a zero velocity (car stopped) and the weight transfer will be there. Of course, with an acceleration, the car will not be stopped for long.

UFO
In real life there are very few things that are instantaneous the same here. The acceleration depends on traction, traction depends on load, load from transfer depends on acceleration and so on is the cycle. It also takes time to torsionaly flex the tire, wind up the axle, pitch the sprung mass, and compress and extend the springs and then the traction cycle.

Unless you have an external acceleration or force acting on the car you cannot have weight transfer without movement. The cars acceleration is from engine power put to the wheels, unlike gravity or lateral force from turning, which can act on it without movement if it has a equal resisting force in the opposite direction.

Obviously did not read the recommended posts I noted.
jack action said:
I think this come from the fact that you think that the weight transfer is influenced by the body motion. Again, it is not (other than CG height change). The unsprung mass is accelerated and it will contribute to the horizontal inertial force acting at the CG (creating a moment about the ground, where the equal and opposing traction force lies), which in turn will be compensated by a reaction moment coming from the axles, i.e the weight transfer.

The keyword here is moment. I think @Ranger Mike hates the term weight transfer because ... there is no weight transferred. There is a moment that compensates for (or adds to) the weight supported at each corner.

The fact that the suspension moves is only a matter of knowing in what proportion (% anti-squat, % anti-lift) does the weight transfer goes through the solid links of the suspension or through the unrestricted spring.

UFO
Well, I think you're wrong again, some of what you said is ok, but you're not looking at everything. The moment about the tire contact patch is only for overturning and geometric forces. The other moment is about the roll center, which the sprung mass CoG is rotating. Here is what's happening, on cars that have a lot of body roll, there can be a lot of lateral movement of the CoG which will transfer weight to the outside (RM this is real weight transfer along with fuel and oil slosh).

Technically weight is the force from gravity only, but most consider how the loads change from the resultant force from gravity and other acceleration forces and call it weight transfer, nothings simple!
Beside the formentioned there is other real weight transfer that is from placing the car on a well banked turn. Put the scales under it and the inside will be heaver.



Again with the “weight transfer” ..and racers wonder why I keep harping on this myth…



I got to measure all that “real weight transfer” on a full fuel cell and in my dry sump oil pan. Should be huge.



Anyway, you are welcome to comment but we are not compelled to reply.

 

[UFO]

Me thinks somebody has never seen a car, with the brakes solidly applied, move around when engine power is applied to the drive train.

There is not only the side-to-side rocking from engine torque, but also, depending on the direction of driveshaft rotation, the front or the back suspension will rise.

Hi Tom.G, I am not so sure I know what you are referring to, I guess it's about acceleration forces on a car sitting still. I will try to explain, what I think happens, better. If a car is sitting still out of gear, on scales, and you snap the throttle, with a, from the front, CW rotating engine. The weight on the right side of the car would increase. This is from the opposite reaction of rest of the car twisting it in the opposite direction of the rapidly accelerating rotating mass in the engine. This is short lived. There may also be a slight gain or loss from the cooling fan if turning depending on the direction it is deflected away from the car.

With a solid rear axle, brakes locked, Trans in and output same direction, and full engine torque applied. The axial torque on the rear housing, up in the front, will be engine torque times trans gear ratio times rear gear ratio. The rear would not have any of this axial torque transmitted to the frame. The forward torque of the axle would be canceled by the rearward torque of the housing, all balanced in the rear as a unit, assuming the brake caliper brackets are fastened to the housing and not on floaters.

The other toque transmitted to the rear from the drive shaft twisting the rear down on the left and up on the right. The magnitude of this will be engine torque times the trans ratio of the gear you are in. This, of coarse, has a opposite reaction applied to the frame by the engine, of the same magnitude. This torque lifts the frame on the left and down on the right. Some of the force gained on the left wheel will be taken off the left rear spring and the opposite on the right rear. Only part of the load change at the axle is made up by the spring force from length change. The rest of it is applied to the front springs from frame roll.

The proportion of the torque handled by the front and rear depends on the roll couple distribution between the front and rear. The bottom line is you may have some corner weight change, but the total front, total rear, total left, and total right will be the same as static

 

[Tom.G]

I think you forgot about the drive shaft pinion in the rear end climbing up on the now-stationary ring gear.

I once had a motorcycle with a driveshaft that when you popped the clutch, the back of the frame would come up and boot you in the behind! (Kinda tough on the passenger too.)

 

[UFO]

Ranger Mike said
I got to measure all that “real weight transfer” on a full fuel cell and in my dry sump oil pan. Should be huge.

UFO
Hi RM, That would be nice if we could run a whole race and still have a full tank of fuel, that wouldn't make the guy at the fuel truck happy. I'm sure you know a lot of the Saturday night racers running 25 lap features go out with a half tank of fuel. Let's take a 25 x 20 foot print 40 gal. tank that is half full of alcohol, on a flat track, pulling 1G of lateral force. Well, that's moving 140 lbs 6'' to the right, not only shifting, but carrying some inertia into the right side of the tank. It may even move more then that depending on how high it's mounted and how much roll is happening. That's why you should have slosh control. Yeah, I know that's the extreme in one direction, but your example was in the other. I thought dry sump systems have oil tanks? I know they're narrow and tall and the oil doesn't move much.

Anyway, you are welcome to comment but we are not compelled to reply

RM I don't need a comment on everything. I made some points that may spark some interest, readers can agree or not, they can comment or not, If they disagree, they can state their case and maybe discuss it further. Maybe one of us will change our mind, Isn't that how we can all learn from this forum? Isn't that what it's for?Either way this is a pretty good informative forum and I appreciate all the work you put into it.

 

[UFO]

I think you forgot about the drive shaft pinion in the rear end climbing up on the now-stationary ring gear.

I once had a motorcycle with a drive shaft that when you popped the clutch, the back of the frame would come up and boot you in the behind! (Kinda tough on the passenger too.)

Tom .G Hi, I never really got into motorcycle suspension dynamics and don't know how they're linked. It looks like you're popping the clutch to take off. I was talking about having the brakes locked up. Yes, I was the rear rapping up in the front. You have to look at it like the wheel is welded to the end of the axle tube. The axle tube And the axle shaft are trying to rotate in opposite directions and balance each other out which leaves the axle housing not attempting to rotate in either direction. After thinking about it a little more there may be a little movement from the axle twist, relative to how long and thin they are compared to torque applied. I still think the rotation would happen the inside of the axle shaft and the ring gear and the housing will not move

 

[UFO]

jack action said:
Ignoring the front suspension in acceleration? Tell that to a drag racer.

@UFO
Unless you have front or four wheel drive the front is not contributing to forward acceleration. It does enter in with controlling left to right distribution of loads, it has nothing to do with jacking forces from acceleration, which is what the discussion was about.@Ranger Mike said
Any Race car driver will tell you, front end lift has to be controlled on acceleration. It is a major tuning point to get the car to hook up.

I think you guys are missing the point, I never said that the front isn't a valuable tool to get balance and control acceleration, especially coming off a turn when there is still some lateral force. The point was that there is only one end of car supplying torque to the tire and pushing on the track. Sorry for the confusion.
With a drag car I think the car would be faster with the front tires just off the ground, all the weight on the drive tires. And also all of the drive shaft torque on the rear and reaction on the frame would be very close to balanced on the rear tires. The problem is you'll have no control with steering so, better get some weight on the front

 

[Ranger Mike]

whoa up there UF
I have to step in here as you are putting out some dangerous information.

Have you ever been on a race team pit crew?
No experienced round track racer will race with a half full fuel cell. Why. Simply watch video below. In the old days ( 1950s and 1960’s) I saw many a race car explode on impact before fuel cells were required. It is not pretty.

This top off the tank myth , custom or ritual carried over to the fuel cell days but still remains strong on the round track circuit. Drivers are extremely superstitious and just because the fuel cell says it will not explode, don’t mean the racer will believe this.
So he tops it off. You down size the tank to give you the minimum of fuel required to complete the race ( with potential caution laps) and fill it to the top before each race outing.

Todays fuel cell has foam inside the rubber bladder. This foam prevents fuel movement in the bladder and we do not have fuel SLOSH. No way, no how!

I have seen fuel cells catch fire because of metal piercing the cell tub and bladder. Fuel cell life is 4 to 5 years and you have serious safety concerns racing an old bladder. Additionally the foam in the fuel cell will deteriorate and clog your fuel pump and fuel filter.
Who in their right mind would run a 40 gallon fuel cell on a short track 1/3 mile 20 lap race? Nascar has 17.5 gallon fuel cell limit for DAYTONA! Most local race tracks have 22 gallon maximum limit on fuel cells.

Most Saturday night warriors will run a 8 gallon to 15 gallon fuel cell depending on if they run an occasional ½ mile track. A 20 gallon cell is too big and a waste of space.

Where you going to mount this 40 gallon monster? Where you going to race it?

 

[UFO]

whoa up there UF
I have to step in here as you are putting out some dangerous information.

Have you ever been on a race team pit crew?

RM If you read to the bottom it said it was the extreme, that's not dangerous it's more like history. I don't know who is running 40 gal. tanks today, but back in the day it was commonplace with at least the northeast Modifieds. They were poly tanks, called drop tanks because they were L shaped and dropped down behind the rear. They were mostly used for alcohol. I think today there is a lot of 24 gal. fuel cells in use, but some tracks don't require them, at least for alcohol. The foam in the tank doesn't let the fuel hit the side and bounce back, but the fuel still moves to the side, just takes a little longer to get there, it dampens the flow

I still don't understand your point about filling your tank and not running it half full. If you use a half tank of fuel in a race, you start out with a full tank at the end your running it half full. If you fill it up half way your running it half full in the beginning and empty at the end. No one I know puts more fuel in then they need for the race, unless the need some to make weight. And that's not done much because it is better to locate lead ballast where it is most needed for chassis tunning.

As for your question, the answer is yes.

 

[Ranger Mike]

opps

 

[Steve2]

Ranger Mike - On page 58, you discuss brake floaters as it is used in oval track racing. What's your opinion on using brake floaters in road racing to improve rear braking? I don't recall ever seeing it used there. Would it be worth the effort or have adverse effects on corner entry?

 

[LogicIndustries]

Who in their right mind would run a 40 gallon fuel cell on a short track 1/3 mile 20 lap race? Nascar has 17.5 gallon fuel cell limit for DAYTONA! Most local race tracks have 22 gallon maximum limit on fuel cells.

Most Saturday night warriors will run a 8 gallon to 15 gallon fuel cell depending on if they run an occasional ½ mile track. A 20 gallon cell is too big and a waste of space.

Where you going to mount this 40 gallon monster? Where you going to race it?

Not that it was a good idea, but we ran a methanol modified with a 32 gal tank back in the late 90's all over short tracks in MO, and basically every car ran the same setup. Big rectangular poly tank, NO foam, specifically to promote slosh and help turn the car in on entry.

Did it work? Yeah, I think so. Was it smart? Probably not, but I lived through it. In fact, I never saw a fuel fire once in those cars (not just my car, I mean I never saw one of them burn anywhere). That don't mean it's not possible, just means I never saw it happen.

Anyway, he's not super far off base with the size and shape of fuel cells used back in the day. I don't know of the big cells are as common now as they were back then, but I will note that every mfg still makes that same poly bladder cell that I used to run, and a pretty neat wedge shaped one too, both 32 gallons, both without foam.

Not saying you're wrong about anything, just saying that folks did used to run cells that big without foam on short tracks, and probably still do.

 

[Ranger Mike]

Steve

I absolutely do thing brake floaters are the hot set up on left and right turn tracks. Especially if in a stock class with very rigid rules. The improved grip, heat dissipation and life extending properties are a great advantage. I also thing you have to get the computer software to find the true roll center and its path under compression and rebound. (Where have we heard this one before). Running totally stock is exactly that but there should be enough room to slide the brake floater thing thru on safety. You have latitude to change ball joints so get the adjustable height type to take care of roll center. You want no offset and no migration when in compression and rebound so try to get it as close to zero as possible. I also thing hydraulic spring centering perches or coil spring torsion thrust bearings are excellent way to add more grip and lower the lap time. Let the tech boys try to find these! Check and fix any bump steer. Big fix if you got mucho bump steer. All of these will add grip and reduce lap timers when you are out cone killing at the local autocross event.
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https://eibach.com/us/c-119-motorsp...ing-accessories-torsion-release-bearings.html
bump steer video

Logic – Great point on safety - we all did dumb stuff like using beer barrel gas tanks but thank the Racing Gods for that one rule mandating Fuel tank foam cells. I hate rules but can sure “ live” with that one.

 

[Steve2]

Thanks Mike - I agree with all your suggestions, but I apparently didn't write my question clearly. I was talking about floating calipers on the axle housing and having a radius rod to the chassis. I know it's used in dirt track and some other oval racing, but how about road racing - such as SCCA GT classes?

 

[Ranger Mike]

Why not use brake floaters on road race cars? Same reason majority of asphalt racers do not use 4 link setups on their cars.

In road racing we spend all efforts in keeping things symmetric. That’s why the roll center is “ centered “ and rolls as close to centerline as possible. Left to right side weight is equal. This is to best handle the various track turn radius and angles encountered. I have seen drivers bias one side more than the other if the track had 6 right turns and 7 left turns. To me, if you get in a wreck, is it worth taking the extra time to replace the longer radius rods or links instead of replacing the identical length piece? I think the “ keep everything neutral” tune is the way to go. You can have too many options to pick from some times and if time is critical, less options are better. Its got a push, where is it coming from??

Brake floaters as discussed on page 58 are great for a 4 link dirt setup. These racers want huge body roll in one direction and massive induced roll steer. In this case , adding one or two control rods to link the brake calipers makes sense.

Yes road racing cars can use it too but it is added expense and maintenance to keep the bird cages free and floating. Is it really worth the headache?

Deal with the Elephant first, not the piss ant. my opinion. I like your idea though. Can be an edge!

 

[Ranger Mike]

Why use coil spring thrust bearings if the shock travel is only 1 to 2 inches? If you have hard Spec tires, this is exactly where you have very small shock (wheel) movements and this is when grip is generated or lost. The racer that can maintain minimum tire download CHANGE wins. The thrust bearings allow the spring to axially twist (all coil springs twist as they compress) as it compresses without causing ANY Changes - chassis bind, increase spring rate, etc. As a spring is compressed, the helix angle decreases. This causes the spring ends to try to rotate around the spring axis. If we have the old school non flat spring end jammed into the old Chevy A-Arm pocket we have huge twist force and SPRING BEND. This throws big changes in the overall spring rate. By going to the flat end coil spring, we reduce this twist force and degree of bend but now have friction of the flat spring end twisting against the metal spring cup. Heat and friction follow and the heat adds up on a 20 lap race. Since neither end is allowed to rotate freely , then one end or the other will have to slip on the perch face. This extra rotation of the spring end coil slippage across the perch face takes energy, and takes it in an unpredictable manner. It is true that on the surface the amount of energy may seem small and insignificant, but it can actually make a discernable difference. We add bearing at both ends of the flat spring and we eliminate spring bend and reduce to very small the friction we had. Racing tip – soak these in chain saw bar oil for an hour then assemble. Do not use grease. Keep squeeze bottle of chain saw bar oil to squirt once a month.
I quote from Hyperco - Optimum race car suspension components must be designed for consistent performance, an infinite fatigue life and absolute minimum weight. At Hyperco, we look at every aspect of design. Is it as light as possible? Is it the optimal design that can be produced? We continue to research and develop materials and techniques to further our product line in the areas of performance and weight savings. Through our research and development efforts, we've designed a collection of new and innovative components. They are designed, tested and manufactured with the same attention to detail that has made our other products winners on the race track ensuring that these components also provide a Performance Advantage. In racing, tire grip and low wear rate, are critical for maximum performance. Unfortunately, one of the common characteristics of coil springs is that they do not naturally distribute their load evenly around the face of their end coils thus generating a lateral load. The lateral force creates a bending load in the shock absorber, significantly increasing its friction; the result is lower tire grip and increased wear. The Hyperco/ICP Hydraulic Load Centering Spring Perches substantially improve performance by allowing the spring forces to remain centered on the damper and eliminate lateral loads. By precise shaping of the sealing wall of both the perch and cylinder body, the perch can freely tilt as needed to evenly distribute the load over the face of the perch. The result, a reduction of bending load on the shock absorber of up to 96% along with an enhancement in mechanical grip at the tire.
We used these on the Formula car as well as the thrust bearings. On a road course – lap time was 0.200 second per lap from previous race weekend (coil over Penske shocks, same tires) . I would guess on round track , using only the thrust bearings , worth shaving at least 0.100 second lap time.

 

[Ranger Mike]

Anti Squat - revisited
Personally , I am not into ANTI anything on a race car. Adding in Anti Dive, anti squat, droop limiters etc.. to a poor performing race car to keep it from pushing is at best a Band-Aid if you think about it ...you are trying to treat the problem not the cause. I am a big believer in using a cars suspension to deal with weight transfer. I don't even like roll steer but in some classes, its all you can do to make the most with a bad situation. We all know why unsprung weight is so evil. You cannot control it. So, with that line of thought, sprung weight is " good" because we can control it..right? So how best to control the weight transfer? Springs and shocks and ARB (sway bar). Remember, Too much anti squat means BRAKE HOP

Above is 10 year old statement and you can teach an old dog new tricks..I believe in roll rear steer big time now. And if your rules dictate hard spec tires, look at anti squat. Not so much on sticky tire classes.

Draw a horizontal line thru the COG parallel with the ground

On front end, draw a vertical line from the ground thru the front axle center up to horizontal COG line. Now at this point, draw a line to the rear tire contact patch.

This is the 100% anti squat line. You want your rear IC at this line or a little over it.https://www.google.com/search?clien...placement#kpvalbx=_u5OfYbeLN4aYptQPjYewuAU121

If the IC is on the line connecting the rear tire patch with a line between the CG and the front axle centerline you have 100% anti squat. If the line falls below this point you have less than 100% anti squat. Study the illustration.
Study the attached. Less anti squat means the forces are pushing toward the front of the car by pulling at the CG at a 40° angle. The plus anti squat vector pushes to lift the front end and pulling the CG thru a 45° angle.

The IC acts like a moment arm or level. It should remain in one location. The farther to the front the instant center the less the IC location will change during rear end movement up and down / sideways during cornering and acceleration. The shorter the IC distance of frt mount point to is the to rear top link mount point the dartier the car will be because the IC is moving more and makes the car feel unsteerable to the driver. In side view, the lines of constant percent anti-squat all pass through the rear tire patch. The greater the slope, the higher the percentage of anti-squat. The location of the IC is determined by the intersection of 2 lines; one drawn through the pivot points of the upper link and the other drawn through the pivot points of the lower link. When the lower link is kept horizontal (or nearly so) and IC adjustments are made with the upper link, a raising of the front of the upper link causes the intersection of the link lines to move forward and fall on a line of less percent anti-squat; a lowering of the front of the upper link causes the intersection to move backward and fall on a line of greater percent anti squat.

So, a shorter IC...UNDER THE CONDITIONS JUST DESCRIBED...would move the anti squat value closer to...or perhaps in excess of...100%. At values over 100%, the car is said to have more bite or grip.

With a longer IC, there is less anti squat and the rear of the car is seen to squat on launch. The front of the car will always rise, of course, but that visible squat at the rear is accompanied by additional rise at the front. This additional rise is the result of a low anti squat value and NOT the result of the long IC.
IC length and the COG - Remember, our goal is to use lift to counteract weight transfer and plant the rear tires with downforce on acceleration.

Let's say your IC length is directly under your C/G location. This makes lifting the front of the car relatively easy. Moving the IC forward of the C/G location makes it much harder to gain lift at the rear due to the angle between the C/G and the IC, no matter how close you are to the neutral (100%) line.
One time we had a top link that was anchored to the chassis by the drivers right foot..LLLLLoooonnngg bar. Basically that is the only benefit. Less IC migration with longer top link. Top link down hill angle is between 5 and 7 degrees. On asphalt cars with sticky tires Lower links should be level with the pavement and longer is better here too. 20 “ typical , 24” is better. Hard spec tires means you have to add angle to the lower arms. Emods with hard spec tires need more bite and 5 degree up hill is typical. More than 5 degrees will promote quick hook up but not maintain grip down the straights as well and the 5 degree is a good compromise to grip off the turn and not wear out the rear tires.Illustrations from Herb Adams book Chassis Engineering – excellent read

 

[Ranger Mike]

If we work thur the Figure 9-8 we see the same vector made up of horizontal and vertical forces like on the dog chain below. Assume the tires project 100 pounds force. Disregard effects of anti squat on downforce load for the purpose of understanding. More anti squat acting on 45° angle means Vert. Force of 71 lbs and Hor. Force of 71 lbs. With the forces acting thru the 40° less anti squat vectors we have Vert. Force of 64 lbs. and Horz. Force of 76 lbs. ​

Example of way over 100% anti squat is a drag car doing a wheelie off the christmas tree. Anti squat trys to lift the front of the race car​

​

Below from www.physicsclassroom.com​

Determining the Components of a Vector​

The task of determining the amount of influence of a single vector in a given direction involves the use of trigonometric functions. The use of these functions to determine the components of a single vector was also discussed in Lesson 1 of this unit. As a quick review, let's consider the use of SOH CAH TOA to determine the components of force acting upon Fido. Assume that the chain is exerting a 60 N force upon Fido at an angle of 40 degrees above the horizontal. A quick sketch of the situation reveals that to determine the vertical component of force, the sine function can be used and to determine the horizontal component of force, the cosine function can be used. The solution to this problem is shown below.

​

 

[Ranger Mike]

3/8 mile paved track late model BBSS setup
This email was sent to me and driver wants to have it posted to help other racers. I am keeping his name and address private but thank him for permitting the sharing of this project. We will be going thru the set up process changing from a ½ mile track package to a 3/8 mile setup. Driver walked the 3/8 track and majority of cars there are BBSS so the track is not that bumpy to take air off the car. Note - you do not need the latest greatest new chassis to be super competitive.

Note this is a Big Bar Soft Spring setup.

He says -
I have a ~2005 Port City straight rail asphalt
Late Model. It is a BBSS chassis.
Here is how the car was setup to run a ½ mile asphalt track with sweeping flat turns. The car turned its fastest lap ever with this setup and was on rails. The car was scaled after the race (topped off fuel). Here are those numbers;TOTAL WEIGHT = 2702 lbs.
% Left = 57.8
% Rear = 49.8
% Diagonal = 55.2
*Swaybar Unhooked
RIDE HEIGHTS
LF = 4" RF = 4" RR = 4-1/2" LR= Floats
CORNER WEIGHTS, SPRING RATES, ETC.
LF = 713 lbs (26.4%) 180 lb spring. Camber +5½°
Caster +2°
RF = 642 lbs (23.8%) 185 lb spring. Camber -1½°
Caster +4°
LR = 850 lbs (31.5%) 225 lb spring.
RR = 497 lbs (18.4%) 400 lb spring.
SWAY BAR
1⅜" splined w/ 13" arms. Calculated @ ~532 lb.
SHOCKS
LF = S7Z RUSH7 16-2 COB
RF = 33-253015 RUSH DIRT LATE MODEL 12-2
LR = F4-B46-0210-HO RUSH7 6-1.5
RR = F4-B46-0210-HO RUSH7 4-3
************Going forward, I will be racing this car on a ⅜ mile asphalt track. The whole track has 12° banking. The radius of both turns is ~161', which would be a diameter of ~322'.
Would you be able to put together a baseline setup package for this track?
Ie. Spring rates that will work with my 1⅜" sway bar (which I calc'ed at a rate of ~ 532 lbs), camber, caster, etc.

3/8 mile track rules - American Racer tires AR153 10 inch slicks

-Total weight will be Increasing to 2800 lbs. in 2022
- NO bump stops.
- 4" ride height.
- 58% max left side weight.***CURRENT CHASSIS CONFIGURATION***
NOV 27, 2021
Take note these numbers are with INCORRECT TIRE STAGGER. These numbers are with;
Front Stagger = 2¾"
Rear Stagger = 2½"
This was the only combination I had available.
One of the top teams suggested I run;
1½" FRONT STAGGER.
3" REAR STAGGER.
I previously did the math and 3" rear
stagger is about right.
TOTAL WEIGHT "RACE READY" = 2747 lbs.
Left = 57.0% (1567 lbs)
Rear = 49.3% (1357 lbs)
Diagonal = 54.2%* (1491 lbs)
*Swaybar Preloaded one (1) turn
LR BITE +311 lbs
FRAME RIDE HEIGHTS:
LF = 4" RF = 4"
LR= ~4" (floats) RR = 4-1/2"
CORNER WEIGHTS, SPRING RATES, ETC.
LF = 733 lbs (26.7%) 180 lb spring. Camber +5½°
Caster +2°
RF = 657 lbs (23.9%) 185 lb spring. Camber -3°
Caster +4°
LR = 834 lbs (30.4%) 225 spring rate
RR = 523 lbs (19.0%) 400 spring rate
SWAY BAR
1⅜" DIAMETER, SPLINED.
3 PIECE W/13" ARMS.
CALCULATED @ ~532 LBS.
SHOCKS (BILSTEIN)
LF = S7Z RUSH7 16-2 COB
RF = 33-253015 RUSH DIRT LM 12-2
LR = F4-B46-0210-HO RUSH7 6-1.5
RR = F4-B46-0210-HO RUSH7 4-3
TIRE PRESSURES COLD
LF = 12 psi
RF = 18 psi
LR = 10 - 12 psi
RR = 18 psiInitially, my final rear gear ratio will be 6.02.
I do expect that to change.
A 6600 RPM rev limiting chip is currently installed. Could go to 7000 RPM in the future. Any more would be pushing past what the camshaft has to offer. No sense in beating a dead horse!

 

[Ranger Mike]

Driver did not know where the front Roll Center was so he bought a software package and measured it. Was 1.7 inch height and located 4.5 inch to the right of car centerline. This meant the car was a rocket for a few laps then fell off due to heat build up on tires. The jacking effect carried the left front tire thru the turns like the old Modifieds did with the straight axle. Super cool to watch but not the " hot setup".
Driver is working on benchmarking the car and correcting the roll centers.

 

[Ranger Mike]

Driver went and rechecked his work. found the Front roll center was really 3.5 inch height. This is a wet sump engine with iron heads so 2.5" is about the max height. We have spec slicks on 12° track so we need vertical downforce not shear force. A lower RC will give us this. BBSS means we do not have a lot of body roll but, the body will provide some downforce by downloading on the right front tire ( momentum in the turn). Where else will the momentum go? From the COG thru the RC and to the right front tire and sideways in shear. The trick is to use the downforce to plant the Rt ft tire with proper ARB (sway bar) and springs.

 

[Ranger Mike]

Steve Smith in his great book Paved Track Big Bar Soft Sprig Setups outlined the whole thing. Buy the book.
He states you need Anti-dive which is 3 1/2 to 4 ° on right front and 1 1/2 to 2 ° on left front. I can almost guarantee you that you are running an after market chassis like Howe or Port City, the lower A-arm mounts are parallel to the track (same height front and back).

You need the right front upper A-arm mount point on the front 1/2" higher than the rear (HEIGHT FROM THE GROUND)

you need the left upper A-arm mounts so that the front mount is 1/4" higher than the rear

The left has less anti-dive than the right so forward load transfer compresses the left front corner easier than the right and it does it quicker, helps place weight on the left front tire at corner entry. Shock rebound at left front and stiffer right rear spring help hold down the left front. If we use a right front compression shock it holds cross weight and we have a push. Note in photo the lever distance of IC to COG.

My opinion is that a mechanical means to handle momentum (aka weight transfer) is far better than high dollar shocks and labor intensive spring swaps. This is why we need to tackle this first then fix the roll center location.

 

[Ranger Mike]

Measured the Port City chassis. As found the front top A-Arm mounts were taller in the rear than the front (mount points relative to ground) exactly what we do not want for anti-dive. Fixed these and roll center now off big time as expected. Front roll center now 2.1" height and offset 14.2" to the left of centerline.
After playing with the Circle Track Analyzer the new Roll Center is 2.4" height and 2.9" offset to the right and looks pretty good in 2" dive, 1/2° roll. Got this by adding height to the ball joints.

 

[Ranger Mike]

Why we need rear roll over steer

Note the left figure below is standard Port city set up with rear end square to the car centerline.
The right figure is a rear steer car and note the turning radius is a lot shorter axis.

Roll over steer allows the car to roll around a corner without breaking traction. Breaking traction occurs when forward grip stops and the tire goes into shear sliding sideways. This is one reason you use Stagger and it helps to a point. But at some point all locked rear ends lose traction and you have to hit the brakes or spin out. With no rear roll steer the tire has to break traction to turn. When you have roll over steer the rear end steers the car and no side slip is required. Forward traction is maintained and the rear end is steered.

When I see two famous car book authors Steve Smith ( his illustrations and my sketched up mess) and Herb Adams ( his scan of page in Chassis Engineering) say in print that this works, I have to believe it. Even more than that, just look at a dirt late model race. You can see the wheelbase shrink on the drivers side with body roll.

My sketched up illustrations are very simplified. I should draw in the 26° axle angle of the right side wheel but you get the idea. Shorter turn radius and pivot turn point a lot closer to the COG means better turning relative to the competition.