- #1,156
Vintageracer13
- 45
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Sorry Mike I think I found my answer in #954 lol
Race car suspension Class
- Automotive
- Thread starter Ranger Mike
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- Car Class Race Suspension
In summary,-The stock car suspension is important for understanding the complexity of a Formula Cars suspension.-When designing a (front) suspension, geometry layout is critical.-spindle choice and dimensions, kingpin and steering inclination, wheel offset, frame height, car track width, camber change curve, static roll center height and location and roll axis location are major factors.-The first critical thing to do is to establish the roll center height and lateral location. The roll center is established by fixed points and angles of the A-arms. These pivot points and angles also establish the camber gain and bump steer.-I have used Suspension Analyzer for years on Super late Model stock cars as
- #1,157
Vintageracer13
- 45
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Good Morning All! I just finished measuring my front roll center after making a new panhard bar. I'm at 2 inches to the right. Not where I wanted to be but much better than where I started. I have a little more work to do on the front end and then I can put the chassis on the ground and get a rough idea of where the height will be.
- #1,158
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vinny, just an educated guess..nothing concrete but you may be ok at 2 inch since the panhard bar angle can be tweeked big time. Look at the angle form the rc to the tire contact patch and study up on how changing the panhard bar angle will effect handling. ifin you get too clise the 45 degree angle to contact patch you may start carrying the left front tire..looks great but racing a three legged stool will wear out the tires quicker..but boy does it look ' hot dog"
- #1,159
Vintageracer13
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Is there truth to the theory if you angle on side of the panhard bar down that side will be forced down?
- #1,160
Vintageracer13
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Ranger Mike,
I talked to the people at perf trends and they told me they are 2 months from a version of the software that will work with the straight front axle. Bob Bolles told me his will work with it so that will be my next major purchase.
I talked to the people at perf trends and they told me they are 2 months from a version of the software that will work with the straight front axle. Bob Bolles told me his will work with it so that will be my next major purchase.
- #1,161
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on paved track cars the panhard bar is usually mounted to the axle on the left side of center line and to chassis on the right side. Longer is better and means less RC movement during total chassis roll. When the p-bar is “ level” both tires will carry equal load caused by chassis roll. if we munt the p-bar on chassis on left side then to the axle on the right side we create too much traction and will push. The angle the bar slants will load that side more and take away from the other side and may lift the left front tire. Just draw out the force vectors and look at the angles. The p-bar mount on the right side chassis is pulling the axle during roll. If the p-bar is level then both tires will be pulled to the outside. If the right side chassis mount is lower than the axle mount then the body will jam the right tire more and cause the left tire to unload a little.look at the rc to tire contact patch. what is the angle?
- #1,162
Vintageracer13
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Sorry Mike I'm referring to the front axle so if I understand you correctly the side that the bar is angled towards will carry more of the load. I ask this because with a beam axle it is difficult to get heat on the left front tire. I often thought if I could build a thinner axle that would bend I could get better loading on that corner.
- #1,163
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correct..front or rear pnhard bar work the same.. draw out the force vectors...you need more static left sid weight to warm up the left ft tire or stiffer rt rear spring
- #1,164
Vintageracer13
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Will do. Thank you!
- #1,165
Wylde
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So I ran a 3 link modified "B-Mod" for a while and noticed that a lot of guys had a really short panhard bar and ran it with a lot of angle. From your explanation that would mean that they would load the right tire more than the left and their roll center would migrate faster. Is that correct?
Regardless we ran a long panhard bar with 1-3" of rake it in and the car was always smooth. It liked to come up on the bars slower but was super consistent and never developed a push. I believe this was due to the fact that the roll center did not migrate near as quickly and kept both tires in the traction equally. Needless to say we won a lot of races with it and they were all scratching their heads at how the more "old school" technology was beating them.
Regardless we ran a long panhard bar with 1-3" of rake it in and the car was always smooth. It liked to come up on the bars slower but was super consistent and never developed a push. I believe this was due to the fact that the roll center did not migrate near as quickly and kept both tires in the traction equally. Needless to say we won a lot of races with it and they were all scratching their heads at how the more "old school" technology was beating them.
- #1,166
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Wylde, without knowing all the specs, i would say you are spot on. Longer bars move in shorter arcs which means the RC would have minimum movement. Those short p-bars and J bars will really throw in some chassis jacking. Also running a small degree of angle (rake) means the tires are pretty equal loading. Old school got to be old school caz it worked then and will work now.
good advice from you and thanks
rm
good advice from you and thanks
rm
- #1,167
Vintageracer13
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Ranger Mike what is your opinion on using different length trailing arms on the left and right side? I have 34.5 inch long arms and I was considering shortening up the
Left side. This would allow easier mounting of the front bracket.
Left side. This would allow easier mounting of the front bracket.
- #1,168
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On 3 link paved track trailing arms, two things.
The 3rd link mounting is just as important.
Post # 81 page 6
#253 pg 13
#312 pg 16
#707 pg 36
- Keep them equal length. Do not have different length trail arms on the car. (exception id dirt cars with ½ “difference to build more rear roll steer)
- Longer is better. Nasar uses 51 inch truck arm length. Typical 3 link tail arm length is 20” preferred length is 24”. Too short of a length means brake hop.
The 3rd link mounting is just as important.
Post # 81 page 6
#253 pg 13
#312 pg 16
#707 pg 36
- #1,169
Wylde
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Just out of curiosity, does any car on asphalt use a lift arm rather than a pull bar for their 3rd link?
- #1,170
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you can pretty much bet that every trick and wrinkle wil be tried by a crew chief to get an edge on the competition so yes..this bar issued and every other version as well
- #1,171
drobbie
- 36
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It is very commonly used in Tour-type Modifieds in the Northeast. They are commonly referred to as a Torque Arm. Depending on the car manufacturer and the driver preference they are mounted on ether side off the rear end.I have one on the car we recently purchased.Wylde said:
- #1,172
Vintageracer13
- 45
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drobbie you haven't raced with it yet? I looked at the Neuline at PRI and it looked pretty interesting as far as adjustability
- #1,173
drobbie
- 36
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Not in this car. I have in the past when I crewed for several NASCAR Whelen Modified teams. The ones we use have a rod end attach to the chassis and a rubber biscuit to absorb the shock under acceleration and deceleration.Vintageracer13 said:
- #1,174
Vintageracer13
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So what is your take on them? Thw Whelen Mods seems to be high horsepower with big sticky tires. My application is small hard tires and much lower horsepoer.
- #1,175
drobbie
- 36
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I think they can be very effective if they are set up right. Just like a pull bar, you need ensure its positioned left to right correctly, has the right amount of wrap up, etc. One of the things I think it does excel in is if you adjust the length you can increase or decrease the amount of effect it has lifting the chassis.Vintageracer13 said:
- #1,176
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You guys are really making me work this week!
I had to go to the hauler and dig out Short Track Chassis Set up by Duke Southard to get the third link low down. See attached pic - Note the use of the pull rod and rubber donut to tune in acceleration You must use a damper ( in this case coil over shock) to limit brake hop with this setup. This set up is for really big gummy slicks when you have big horsepower to use up. It looks like what you found under the old Gassers and Altered at the drag strip. Max traction but they did not worry about wheel hop since they had a parachute.
In our situation we have hard spec tires and somewhat limited horsepower compared to a full blown Modified or Sprint Car.
Let us understand what happens to the rear tires when cornering. Please look and study post # 1126 page 57. The tire contact patch at 0 slip angle to 8 degree slip angle. A we go over 8 degree slip angle we lose traction and spin out.
A no rear steer car will have its rear tires go into shear ( where the contact patch adhesion is less than the slippage area) quicker than a race car set up to have rear roll over steer.
As I said before the dirt track super late models run huge rear roll over steer. Watch or look at a photo of one of these beasts at turn entry. The left rear wheel axle center cover is almost at front of the sheet metal wheel well. The left side wheel base shrunk up as the right side wheel base grew.
Now paved track cars do not use a lot of this for to do so would quickly burn off the rear tires.
The typical set up on a 3 link rear end set up is to have both bottom links ( trailing arms) equal length and running up hill by 5 degrees. This cranks in about 1/4 to 1/2 inch wheel base change.Herb Adams wrote in his book Chassis Engineering that you can set up the rear end to angle to the left ( inside of the track) and adjust the trail arms to take way the induced under steer. See trail arms per attached pic below. I personally have under steer in any way shape or form so am just making you aware of this. Get his book and explore it if you like.
This brings us to the 3rd link. I noted above in post # 1168 page 59 about the 3rd link.
Please read these and the mount location is critical to get equal loading on both tires. As mentioned we once ran a 3rd link that ended at he drives gas pedal.
Spring link and rubber biscuit setups are supposed to ease tire shock when you mash the go pedal. True but there is a more important factor that is not apparent.
The race car goes into the turn and the body rolls causing the wheel base to grow on the right side. As the car accelerates the body settles and the roll over steer goes away.
The cushion rubber grommet or spring top connector bar maintains this roll over steer a tad bit longer than a solid non cushion top link. You stay in roll over steer a little bit longer.
Your tires maintain more tire contact than the less roll over steer car so you are hooked up and moving.
Small advantage but races are won on smaller things..savvy?
I had to go to the hauler and dig out Short Track Chassis Set up by Duke Southard to get the third link low down. See attached pic - Note the use of the pull rod and rubber donut to tune in acceleration You must use a damper ( in this case coil over shock) to limit brake hop with this setup. This set up is for really big gummy slicks when you have big horsepower to use up. It looks like what you found under the old Gassers and Altered at the drag strip. Max traction but they did not worry about wheel hop since they had a parachute.
In our situation we have hard spec tires and somewhat limited horsepower compared to a full blown Modified or Sprint Car.
Let us understand what happens to the rear tires when cornering. Please look and study post # 1126 page 57. The tire contact patch at 0 slip angle to 8 degree slip angle. A we go over 8 degree slip angle we lose traction and spin out.
A no rear steer car will have its rear tires go into shear ( where the contact patch adhesion is less than the slippage area) quicker than a race car set up to have rear roll over steer.
As I said before the dirt track super late models run huge rear roll over steer. Watch or look at a photo of one of these beasts at turn entry. The left rear wheel axle center cover is almost at front of the sheet metal wheel well. The left side wheel base shrunk up as the right side wheel base grew.
Now paved track cars do not use a lot of this for to do so would quickly burn off the rear tires.
The typical set up on a 3 link rear end set up is to have both bottom links ( trailing arms) equal length and running up hill by 5 degrees. This cranks in about 1/4 to 1/2 inch wheel base change.Herb Adams wrote in his book Chassis Engineering that you can set up the rear end to angle to the left ( inside of the track) and adjust the trail arms to take way the induced under steer. See trail arms per attached pic below. I personally have under steer in any way shape or form so am just making you aware of this. Get his book and explore it if you like.
This brings us to the 3rd link. I noted above in post # 1168 page 59 about the 3rd link.
Please read these and the mount location is critical to get equal loading on both tires. As mentioned we once ran a 3rd link that ended at he drives gas pedal.
Spring link and rubber biscuit setups are supposed to ease tire shock when you mash the go pedal. True but there is a more important factor that is not apparent.
The race car goes into the turn and the body rolls causing the wheel base to grow on the right side. As the car accelerates the body settles and the roll over steer goes away.
The cushion rubber grommet or spring top connector bar maintains this roll over steer a tad bit longer than a solid non cushion top link. You stay in roll over steer a little bit longer.
Your tires maintain more tire contact than the less roll over steer car so you are hooked up and moving.
Small advantage but races are won on smaller things..savvy?
Attachments
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- #1,177
Vintageracer13
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That makes sense to me Mike. I have repositioned my 3rd link mounting to take into account the mass percentage and after reading all the material I discovered I ran way too much angle.
- #1,178
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Vinny , great detective work. you should be a lot better hooking up those spec tires now. good job!
- #1,179
Vintageracer13
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All you guys get the credit Mike. I had over 20 degrees of angle in the 3rd link
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- #1,180
Wylde
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20 degrees? Sounds like you were running dirt not asphalt!
An old engineer I used to race against ran modifieds for a long time in the 90's and 2000's (Him and I had a pretty good rivalry on the track but were great friends off track). This was when 3 link modifieds were still the hot ticket in our area at least. One day he was telling me that he used to run the right side trailing arms flat or even downhill when the track got really slick. From your second picture and the annotation under it, there was a statement saying if you can dial in roll over steer on entry and roll under steer on exit that's where it is fastest. This makes a lot more sense now why he would run a downhill angle on the rr trailing arm. I might have to try that out on my dad's B-Mod to see what exactly it does.
Thanks for the info RM. Glad we can keep you busy during this gloomy winter!
An old engineer I used to race against ran modifieds for a long time in the 90's and 2000's (Him and I had a pretty good rivalry on the track but were great friends off track). This was when 3 link modifieds were still the hot ticket in our area at least. One day he was telling me that he used to run the right side trailing arms flat or even downhill when the track got really slick. From your second picture and the annotation under it, there was a statement saying if you can dial in roll over steer on entry and roll under steer on exit that's where it is fastest. This makes a lot more sense now why he would run a downhill angle on the rr trailing arm. I might have to try that out on my dad's B-Mod to see what exactly it does.
Thanks for the info RM. Glad we can keep you busy during this gloomy winter!
- #1,181
Vintageracer13
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Yes Wylde I got caught up in the monkey see monkey do game. It wasn't until I started reading the pages here that I realized how many things I didn't understand about setup. I'm very excited for the start of the season because I will have a new car handling wise compared to last season!
- #1,182
smever2
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Just finished up modeling my RC for my dirt late model. Numbers seem odd compared to what I have read in the forum, but I have remeasured them a few different ways and they repeat. Secondly I measured camber in the model and it is spot on to the actual measurement. Take a look at the picture and see what y'all think. http://imgur.com/a/VbWel
- #1,183
smever2
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- #1,184
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smever. what software program is this? The Roll center height looks to be about 3.125" height, but too much to the right .. looks to be about twice the typical offset.
- #1,185
Dirtracer8
- 15
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I am subscribed to this thread.
60 pages of wisdom and real world theory!
Can't thank you guys enough!
60 pages of wisdom and real world theory!
Can't thank you guys enough!
- #1,186
smever2
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I built this in solidworks. It took a little while now configurable model. Next I will try to find the rear and get both in the same 3D sketch. So my RC height should be around 3" from the ground and 4" right of CL?
- #1,187
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i would think that is a good start point. Also where does the Rc migrate to in roll and dive?
- #1,188
Vintageracer13
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Ranger Mike I have a small splined sway bar that I am going to use on my car. It will contact the bottom of the axle on the left side and I plan on using an adjuster on the right side to tighten it. Because of the right side shock location I was thinking of mounting the adjuster to the backside of the axle but this would effectively make the right arm shorter. What are your thoughts on this?
- #1,189
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Back in the 1960s I was crewing on a Ford team. No one was running ARBs then. I was devouring every car magazine I could glom onto. We picked up a pick up truck ARB (sway bar) and mounted it to the top frame hoop rail that ran from the firewall to front end over the radiator and back to the fire wall. Same rail the shocks mounted to. We cobbled up a couple of links to run down and attach to the top A-Arms. Worked real good.
Is your set up going to be perfect..no...but I can tell you it will work.
All things being relative, the ARB will cut down body roll and you can go softer on the front springs, lower the car a little and pick up maybe a second quicker lap time. Go for it.
Is your set up going to be perfect..no...but I can tell you it will work.
All things being relative, the ARB will cut down body roll and you can go softer on the front springs, lower the car a little and pick up maybe a second quicker lap time. Go for it.
- #1,190
Vintageracer13
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Its only .550 so I can't load it too much. I just want to be able to tighten the car on exit if needed.
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