Race car suspension Class

[THORPE]

Quick question on anti dive on dirt oval
This is a Rc car btw.

I'm reading in circle track mag where anti-dive on right front and pro-dive on left helps promote turn in.

I accidentally got them backwards on my setup and fought a bad push all night when letting off at the end of the straight. I found my stupid mistake the next day.

From my understanding anti dive only loads the tire initially then the spring takes Ove from there.
So it's beneficial to load the rf tire initially into turn then try to get equal loading from setup through the rest of the turn?

 

[Ranger Mike]

Thorpe..it happens..but you found it!..great..pls read post # 314 on page 20.
Anti dive is used to keep the front end from diving when you are braking in a turn. Looking at the front end from the side of the car you will note different mount angles of the upper and lower A-arms. The problem is that you run into mechanical bind and start to lock up the pivoting of the A-arms. You run into large caster changes due to this as well.


Personally, I like a car with zero anti dive and like the suspension to be parallel with the track and minimal deflection. I try to minimize things like bump steer, rear steer, camber build. I like Ackermann and lots of it if the track radius warrants it. I like to use the suspension to tune the car. By this i mean I prefer to dial in the car with Spring rates and narrow it to optimum with ARB ( sway bar tuning) Then I really fine tune with shock adjustments. When anti dive and rear / roll steer and other factors come in I get confused and it takes too long to separate out what is causing what. If you can do all the heavy lifting in the garage when you are doing the initial build chances are you can dial it in a lot quicker at the tune and test. You had better not spend time at the race making major spring rate changes etc...if you do..you better go back top square one..my opinion

 

[missile07]

Ranger Mike...First of all I love reading all these posts & the help you have been offering us racers!

On your last posts I noticed you said you like to minimize things like bump steer, rear steer, & camber build...we run 4 link modifieds on dirt and we have been playing with cutting back on rear steer. Other than trial & error is there any info out there on evening out rear steer

 

[Ranger Mike]

Missile07 --Thanks for the kind words..pls. see post # 116 on page 8
When using a very trick 4 link rear suspension using roll over steer adds a big advantage on the dirt track surface. It allows the rear to roll into the corner without breaking traction. To review, when the rear rolls, if the outside wheel base grows longer than the inside wheel base we have roll over steer. This is because of the different in 4 link angles. I think if you start with left upper link at 13 degrees uphill, the rt upper link at 17 degrees uphill, and both lower links at 5 degrees down hill, it is a good base line. Make sure the rear end is straight and has not become bent thru wrecks and crashes.

 

[missile07]

We have been trying to figure out a way to properly measure at full drop the difference in the right & left. At full drop the left side is leading 3.5 inches more than the right. For the past couple of race nights we have shortened the right side bars up to 1 inch. Driver seems to think its helping him from the center off...but I am almost convinced that this is a band aid fix for something else.

 

[Ranger Mike]

i am n Kentucky today...will be back at home base tommorow. I think you have a roll understeer at center off. I agree that there could be something else off. Is is possibel to post the rear end settings on the 4 links?
What are the scale readings at each wheel? Have you read tires with pyrometer lately?

 

[missile07]

Well I don't have the settings right in front of me but I can post what I know...

Bar lengths

LR top 16"
LR bottom 12"

RR top 16" shortened to 15.75"
RR bottom 12" shortened to 11.75"

Bar Angles @ Ride Height

LR top 24-26 degree (chassis manufacturer recommendation)
LR lower 5 degree
RR upper 18-20 degree
RR lower 0-2 degree

As far as the wheel rates I would be lying if I said an exact number but he was running 120 lbs of LR bite & about 55% rear. The last night we were able to race I did pyro the tires and the RR was about 10-15 degrees hotter on both of the final two runs. Car hasn't finished out of the top 5 since June but just missing something.

 

[Ranger Mike]

not having my notes with me, i think you got just a tic too much roll understeer. My guess is to take 2 to 3 degrees out of top right upper link and read tires..if the temp drops a few degrees and car is better...may have found some of the problem...small changes ...dont do anything dramatic...

 

[THORPE]

Thanks for the reply. I'll start over on that anti dive and work on other factors as you suggest.
I'm goin way back and check more into roll center too. I moved mine down and to the right for last night. I got more turn in. I was carrying the left rear going in. I stiffened up both front springs and it help.

From what I'm starting to understand, lowering my RC even lower in the front will counter lifting the LR correct?

 

[Ranger Mike]

Thorpe ...great...now your getting it. When you dropped the ft RC you lengthened the lever between the CG and RC so stiffer springs were required to counter the body roll. You got more turn in becuase you used the weight transfer to plant the right front tire better and this gave you more cornering ability.. Excellent. The Lft rear was lifting at turn in BEFORE YOU CHANGED SPRINGS as expected because the right front was loading more and thus unloading the left rear. Also you reduced the " jacking effect" caused by the tire contact patch and RC that tries to lift the left front; hence left rear as well. Montitor the tire temps,,,LR spring change may be in order too? Your camber build should be reduced as a result as well which is a good thing so tire temps should tell you this too. Glad to hear about the change in handling..keep it going!

 

[Ranger Mike]

Anti Dive

I was in a manufacturing facility last week and saw the 2013 Dodge Viper chassis. That car had huge Anti Dive. On the front the upper A-Arm mounts were more or less parallel with the ground but the lower mounts were significantly angled. Rear was like this as well but not as dramatic. If you think about it Detroit thinking is to have the car go straight when you mash the brake pedal so anti dive throws a lot of caster into the front geometry when in dive. The motion of the lower A-Arm moves the bottom of the spindle forward with upward movement and this adds caster which makes the car go straight under braking. Since the arc of travel is “ straight” up as a true race cars front end would be, this adds to spring rate somewhat. Anyway, that’s the rationale as far as I can figure it...

 

[THORPE]

Thorpe ...great...now your getting it. When you dropped the ft RC you lengthened the lever between the CG and RC so stiffer springs were required to counter the body roll. You got more turn in becuase you used the weight transfer to plant the right front tire better and this gave you more cornering ability.. Excellent. The Lft rear was lifting at turn in BEFORE YOU CHANGED SPRINGS as expected because the right front was loading more and thus unloading the left rear. Also you reduced the " jacking effect" caused by the tire contact patch and RC that tries to lift the left front; hence left rear as well. Montitor the tire temps,,,LR spring change may be in order too? Your camber build should be reduced as a result as well which is a good thing so tire temps should tell you this too. Glad to hear about the change in handling..keep it going!

Thanks for the info. I've learned a lot from this thread. Mostly you.

Just to make sure I have my head right, when u say possible lr spring change you mean stiffer correct?

We don't really have a way to measure tire temps on these small scale cars. I may can use an infrared temp gauge that we check engine temps with but I haven't tried that before.


I'm going back to review your spring info. This weekend I ran a split in the front springs. Stiffer lf. Equal in rear both stiffer than front.

The rear Rc is a bit higher than front. I have fully independent and adjustable a arms in rear to play with.

 

[Ranger Mike]

correct on left rear needing stiffer spring to keep the tire in contact with the track. Typically you will have non equal springs on rear too if you are set up to turn left. You could do it with wedge but a tad stiffer spring will do it too.

 

[John LNZ]

Hi Mike. I am a new member to this forum. I am a racecar fabricator in New Zealand. Have found your posts on this site really interesting as I am very much into the physics and the effects it has on racecar set up and construction. I build various types of cars for dirt oval racing exclusively on 1/4 mile tracks. These are spaceframe cars which are classed as "Super Saloons" in NZ and are unique to NZ but similar to a late model with late model front suspension with a sprint car type rear end and tyres. My initial question to you is could you please explain the physics behind moving the LR wheel further out on a slick track as we are struggling for forward bite. I notice a lot of guys are doing this and would like to understand the physics behind it. Many thanks

 

[Ranger Mike]

Thanks John..means a lot when we get reports from the other side of the world...and I was the guy who thought the internet was a FAD...
we went thru this on page 26 of this forum with a fellow running a drawf car...wider is better in that you have more cornering ability in that for a given set up you will transfer less weight and the tires can better accommodate the weight that is transferred. Also the Left rear to right front leverage is improved slightly...and thus side bite off the turn with a tad more wedge..read the whole page as we had a good debate on this...
General Rule of thumb - 1 inch lower COG transfers 3 to 4 % less weight. 1 inch wider car transfers 1 to 1 1/2 % less weight.
Assume we have a race car with 66 inch wide rear track and we add 100 weight to the ballast and we locate this weight 20 inch from the center line of the left rear tire. 20" divided by 66" = 37% of the added weight will go to the right and 63 % will go to the left side of the car ( diagonal weight is not in this calculation). Now if we increase the track width on t he left side by one inch we have 21" divided by 67" = 31% right side weight and 68 % left side weight. (from Short track chassis set up by Duke Southard)

 

[THORPE]

Ranger mike:

What do you feel is more important On dirt oval?

Getting shocks to work perfectly with spring rate for each corner of the car

or

Using dampening to control weight transfer.

This is to settle argument.
I feel like proper spring selection should be used to control weight transfer and dampening should be used to control that particular spring

 

[THORPE]

To specify:

Using front tie down shocks and a lr with stiff bump and light rebound.

 

[Ranger Mike]

The purpose of a shock is to dampen the kinetic energy stored in the spring during weight transfer. Specifically the shock converts this vertical energy to heat energy by creating resistance to movement within the shock. Shocks control the RATE of weight transferred during cornering. Shocks have nothing to do with the amount of weight transferred during cornering. They can affect how quickly the weight is transferred. So using shocks dampening to control weight transfer is not exactly correct. Using the dampening to control the RATE of weight transfer is correct.
The amount of weight transferred is dependent on the center of gravity, roll axis and roll rates. Where the weight is transferred is dependent on the spring rates. How quickly this weight is transferred is controlled by the shocks. So Thorpe, you are a little closer to the true purpose of the shock than the other fellow..my opinion. And you are right on with the tie down scenario in that you are tuning the chassis regarding rate of transfer after you get the spring rate real close to perfect!

 

[THORPE]

Thanks for the info. We just agreed to disagree lol.

What I'm looking for this weekend is s small bit of tire loading control by change in transfer rate.

On a med bank track with decent grip.
I plan to run:

Rf lf Soft.
Lr 2 rates higher than front.
Rr one rate up from front.

Then stiffer bump and rebound in both lf and lr.

From what I understand stiffer lf bump and lr rebound unloads lr tire load sooner on entry and takes cross weight out.
Then stiffer lf and lr bump adds cross weight on exit.

My hope is to be slightly loose entry and slightly tight off witch fits my driving style.

 

[THORPE]

Btw this spring setup has been very close with equal dampening all 4 corners

 

[Ranger Mike]

All things are relative so i would make small changes like when you are on on a wet tacky or very tight track you want to loosen the chassis up on corner entry. Use a tie down shock on the Left front. This let's the left ft. drop down easily at corner entry and takes weight off the RR tire. This makes the car pivot around the Left Ft which makes it easier to steer in the the corner. The tie down shock delays weight transfers off the lefty front. In the middle of the corner when the chassis is transferring weight to the RR., it keeps the LF tied down to prevent a quick weight transfer to t he right rear. A stiffer LR shock with stiffer rebound holds the weight on the LR longer at corner entry not allowing as quick a transfer to the RT FT tire.

 

[THORPE]

Ok I see where you are going with this and it makes sense. Thank you for your time.

I got off track a little after reading this article about initial weight transitions.

http://www.circletrack.com/chassistech/ctrp_1210_adjusting_for_transitions_fine_tuning_your_shocks/

 

[THORPE]

All things are relative so i would make small changes like when you are on on a wet tacky or very tight track you want to loosen the chassis up on corner entry. Use a tie down shock on the Left front. This let's the left ft. drop down easily at corner entry and takes weight off the RR tire. This makes the car pivot around the Left Ft which makes it easier to steer in the the corner. The tie down shock delays weight transfers off the lefty front. In the middle of the corner when the chassis is transferring weight to the RR., it keeps the LF tied down to prevent a quick weight transfer to t he right rear. A stiffer LR shock with stiffer rebound holds the weight on the LR longer at corner entry not allowing as quick a transfer to the RT FT tire.

I did exactly this ^^^^ yesterday for practice and absolutely love it.

Also found a problem I've been fighting for while now. My upper links.
When I drew out the geometry I must have misinterpreted something and had the inner links higher. Thought I was lowering my rc but instead had raised it.

Made the swap real quick to lower them and WOW. All I can say. It was that great. Finally made everything I've been working towards come together for a great setup.

Thank you for your knowledge you are willing to share on here I know it has helped me tremendously

 

[Ranger Mike]

Thanks for the kind words..Ifin we were racing each other on the same track I doubt I would be as Christian...seriously I appreciate it.
I hope everyone realizes I have sourced some pretty good books and if everyone bought these, they would we able to figure things out..all I do is save a little time in the process and hopefully do not impart BAD advice that screws up some ones good set up...Like Jimmy Johnson just demonstrated, you have to FINISH to win. So this winter is the time to check and inspect every nut and bolt on the car. When in doubt ,,replace it!

 

[Ranger Mike]

Real good questions hear. Stagger – on open diff car , it is a waste of effort. The differential is doing its job and tire size will not impact the drive motion at all with this setup. Are you running stock diff or Ford 9 inch model?
But...you can use stagger on right front to add or take out wedge or cross weight. So when you are tire matching keep this in mind and 1/2 inch will do some good for you. Now back to the spring thing...wedge bolts or jack bolts are for at the track FINE TUNING ...period. If you go to the track without knowing where your Roll Center is and what's base line spring rate be you have no business cranking on a stupid jack bolt!..
You have restrictive rules on weight jack bolts..ok..use the stagger to tune it. You can buy spring rubbers to add more rate.
Sway bars ( anti roll bars) ..get as many different ones as will fit and know their spring rates and swap these out at the track until you figure out proper spring package. Shocks...you should have a good base line on these but I assume nothing and we can revisit later. Not knowing all the rules you face all I can do is suggest.

I recommend you spend the $ 100 for Roll Center software. Measure the car, find out where the Roll center is.. Next , before you do anything, look at the rules to see if you can change the roll center height, legally. As a minimum, change the Front RC location to offset it to the right to plant some down force on the right front tire. Then see if you can drop the front RC and still keep it 3 to 3.5 inch to the right. When we drop the RC we kill off camber build and the jacking effect on the right front. Rear RC should come down as well and again depends on rules and you can get different spring heights and spring rates as the software tells you.

Next work on eliminating bump steer and know your camber build curve over +/- 3 inch travel.
More tips are to concentrate your efforts on going after big chunks of things like horsepower. Do look at a trick 2 barrel carb ( why put on a 4 bbl. carb when the tires can't possibly hook up.)
Hedders are good, after market ignition is good if..if... you have battery big enough to run the car all night without the alternator. I like a point eliminator type distributor kit like a photo cell and straight coil..no CD ignition. Simple and easy to trouble shoot at the track. In fact , forget roller rocker arms, big intake valves, trick engine stuff.. just the basics..keep cost down for more tire money. Spend it on brake caliper upgrades and better lighter rotors. Add brake bias pedal so you can dial in front to rear brake bias. Eliminate all the rubber suspension bushings and replace with brass or aluminum. But I am sure you fellows are already on top of this..my point is to show the newbies some areas to improve..economically..

 

[mustngthundr]

I'll be at IMIS- and the ARS chassis seminar

 

[mustngthundr]

I haven't been to it yet either, but iv heard there's lots of good info. I'm looking forward to it

 

[missile07]

Which roll center software package do you prefer? I have been looking at the Performance trends & Auto-Ware. Both look similar but Auto-ware looks more up to date and more user friendly.

 

[Ranger Mike]

suspension software

I use performance trends and recommend you call Kevin Gertgen, who I have worked with since 1999.

BTW..i am honored to be nominated for an award on Engineering Forum poll

Threads in Forum : 2012 PF Member Awards

...thanks guys, I appreciate the votes!

 

[Ranger Mike]

Auto Ware software is a good product from what I can see..

I think Kevin and the Performsnce Trends software is a little more advanced in that it has the higher end capabities of watching dive and roll dynamically and can use data loggers to collect the data input..plus i have many legacy programs already form over the years...

any serious racer needs at least one of these to find Roll Center and adjust accordingly

my opinion

 

[Ranger Mike]

Street stock rear ARB

A lot of you sent private messages to me about running in very restrictive stock classes and what “ advantages” you can make over competition.
One area often overlooked is the Rear ARB or Sway Bar. We have discussed the Soft Spring Big Bar set up in pretty great detail in previous posts here.
The whole idea of using a BIG Bar on the rear is to permit spring squat and thus more traction coming off the corners. Since you are forced to run hard spec tires, any advantage to putting more traction down will be a great advantage 9 all other things considered.)

A quick review of the ARB - sometimes also called anti-sway bars or anti-roll bars. Their purpose in life is to try to keep the car's body from "rolling" in a left turn.
When you are inside the car, you know that your body gets pulled toward the outside of the turn. The So the right part of the car on the outside of the turn gets pushed down toward the road and the left side part of the car on the inside of the turn rises up. In other words, the body of the car "rolls" 10 or 20 or 30 degrees toward the outside of the turn. If you take a turn fast enough, the tires on the inside of the turn actually rise off the road and the car flips over.

Too much Roll is bad. It tends to put more weight on the outside tires and less weigh on the inside tires, reducing traction. Proper amount of body roll will load the right front tire and assist in improving traction through the turn. Ideally, we would like the body of the car to remain flat through a turn so that the weight stays distributed evenly on all four tires.

ARB tries to keep the car's body flat by moving force from one side of the body to another. When you go into a turn, the front suspension member of the outside of the turn gets pushed upward. The arm of the ARB gets pushed upward, and this applies torsion to the middle section. The torsion moves the arm at the other end of the rod, and this causes the suspension on the other side of the car to compress. The car's body tends to stay flat in the turn.

If you have too much ARB, you tend to lose independence between the suspension members on both sides of the car. When one wheel hits a bump, the ARB transmits the bump to the other side of the car as well, which is not what you want. The ideal is to find a setting that reduces body roll but does not hurt the independence of the front or rear springs.

Back to the “ street Stock “ set up. If we replace the spindly stock “ sway bar’ with a much beefier one, and we switched to much softer rear springs, we still control the body roll and at mid turn after the weight transfer has zeroed out, we can point the car and jump on the throttle much quicker since we wil be loading the rear tires to more of a degree than with our previous set up. Just something to think of when its snowing out side..

 

[Ranger Mike]

Excellent points..pls look at page 2 on how we figured weight that was transferred and look at page 20 for rear motion rates.. We really got to be on top of the front ‘ spring rates’ ( and ARB) to control roll and proper rt ft wheel loading.. the rear...well... we are not talking about a heck of a lot of transfer...i.e. we got a 3100 pound street stocker...going into a medium to high bank turn..
on stock hard tires...for the sake of this discussion we assume we corner at 1.3 G...way high but the figure is common in prior posts so here is the math..
3100 pound car times .35 means 1085 weight transfer up front and left to right. We figured that 75% is going up front so 75% of 1085 is 814 pounds...so both springs and the ARB have to handle 272 pounds with motion rate is figured in...mean while we have 25 % of 1085 pounds or 271 pounds going from left to right in the rear. This is not a lot of weight for the springs to handle. In fact , if we add in the rear ARB we have 271 / 3 = 90 pounds for each spring and the ARB to deal with.
Typical ( per post 308 page 20) Ford 9 inch rear end has a .688 Motion Rate (MR)... so we have the formula WR = (MR x MR) x SR (spring rate).. just FYI...a .688 MR squared is .473
so if we want to handle 90 pounds of weight with each spring ( ARB calculated separately but to have same effectiveness) the math is
90= .473 x SR so...SR= 90 / .473 or 190 lbs. spring...typical stocker run 250# or so Rear springs WITH OUT the ARB.

So you see , the opportunity of using the rear ARB to counter left to right roll and potential for rear squat to really hook up the tires is pretty good.One rumor from the NASCAR side of the house was the rear ARB was mounted in such a way as to close the skirt gap of the skirting on both sides of the new Car of Tommorow..AT SPEED...which is very difficult to detect when going thru tech inspection. Somebody talked and now the ARB links have to be perdendicular to the ground as viewed from all sides. Seems some enterprising team chief figured out if you can seal up the skirting better than the other guy, you got more grip going into the corner and could run deeper..so...if you use some really compliant mounting bushings and angled them ...?

 

[Ranger Mike]

Metric chassis rear steer tips

Again many of you have messaged me on advice on gaining an advantage “ legally”.
I looked up my notes from flogging the old GM metric chassis during my door flapper days. I was into chassis measurements big time and wanted to MAP the rear end movement relative to ride height and was trying to understand what was happening when the car was in the turn.
I found that by setting the chassis on stands and mapping the rear end movement using 3 inches of right rear down and 1 inch left rear up, the metric chassis pulled the right rear tire forward almost 3/8 inch more than the left. This was AFTER I loosened the bolts holding the trail arms ..etc... as the stock serrated teeth bound up the components when “ properly tightened”. Anyway, this movement when rolling into a turn, would have the effect of tightening the car on corner exit or anytime the power was applied. I learned three things here. 1. Stock rubber bushings flex and can be to your advantage. 2. I had to free up the components to swing free when race ready and replacing the inner metal spacer that had teeth with a smaller diameter non toothed spacer was a must. Also I replaced the stock bushing bolt nuts with lock nuts at could be run down tight and then backed off a turn to prevent bind. 3. As the venerable Stroker Mcgurk once said..” If some is good and more is better then too much is just enough “ so I went on to see how much flex I could get out of the rubber bushing. More on this later.

You have to measure your car to find out where you are relative to where you want to go. If the rear axle pivots so the right-rear pulls forward, this will tighten the car. If the left rear pulls forward, the car will be looser.

Roll steer can be affected by using very soft rubber bushings. I tried the old tire softener trick but it seriously and quickly deteriorated the bushing and was a mess. With softer bushings on the right rear lower trailing arm, you have roll steer loosening the car on entry. This would reverse with the power on and tightens up the car on corner exit. The soft bushing allows the right rear wheel to pull rearward under braking. With acceleration, the right rear will push forward and this tightens the car on corner exit.

You can soften these bushings by drilling holes in them parallel to the bolt. This permits more compressibility..
Before you loosen up all your bushings, you better think about it.

If you want more roll steer to tighten up the car on corner exit you would soften the bushings on the right lower trailing arm. This compresses the wheel base on that side during acceleration by pulling the right rear forward. It would then steer to the inside. Softening the left side lower trailing arm bushings would offset much of the right side compression. This would loosen the car. Softening both might be an aid to forward traction because the rear end bottom mounting points ( trailing arms) shorten up and thus move forward in the chassis adding weight to the rear tires and more traction.
Beware- If you are using roll steer to tighten the car on corner exit, it may loosen the car on corner entry.

So why do all this...so you have an advantage over the other racer who looks at other areas for an advantage, The rules say stock trail arms and mounting locations and in some cases, no eccentric bolts...so...think about it...you could get up to 1/2 inch movement that could make all the difference.

 

[Ranger Mike]

Happy New Year and you got the best present possible...yeah I agree. Shock location half way between the mount point and Ball Joint will be pretty in effective. The closer to the BJ the better and if rules say you got to run stock location on the shocks...run a racing shock. And you MUST run a shock ( damper) to complete the proper susension. In some cases we need to run a tie down shock to keep transferred weight where we want. Stock location is not excatly racing ideal but as a minimum you need a shock and automotive engineers spent millions on designing the set up and it is a compromise for ride comfort, performance and economy of manufacture.

Stock shocks will not stand up to the abuse of racing. We run Penske 3 way shcoks and have to rebuild every year. The shock oil deteriorates and the thin metal shims wear out. You get a lot of heat when you dampen the suspension and this is the main culprit.

 

[Ranger Mike]

street stock racing shock

Speedway Motors has a bunch of racing shocks specifically for your class..I like this one myself..affordable and who is going to claim your " used shocks" for $ 50.00..never seems to happen..make sure you paint them same as your original shocks and smear a lot of grease and dirt on them...

http://www.speedwaymotors.com/QA1-S...-size-Camaro-Extra-Heavy-8-Valving,31463.html