Any good oval track suspension guys?

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rick7343
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Any good oval track suspension guys?

Post by rick7343 » Wed Sep 19, 2012 3:25 pm

Looking for roll center discussion- asphalt..

TEROL
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Re: Any good oval track suspension guys?

Post by TEROL » Fri Sep 21, 2012 4:11 pm

Look for anything by Bob Bolles on Circle Track magazine's website.

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Re: Any good oval track suspension guys?

Post by rick7343 » Sat Sep 22, 2012 12:21 am

Ya, I've been thru most of his stuff, even emailed him...

It is about roll center location... Most of his articles say to run the roll center right of center, but now he says left, which is more inline with what I'm hearing... Just looking for details-how far left, how high,and what else is needed to make it work on a mid banked asphalt 1/4 mile track...

Seems even without bump stops the trend is to move it left and hopefully keep the left front tire doing more work... just can't really get my head around it...

Thanx!

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Re: Any good oval track suspension guys?

Post by ZIGGY » Sat Sep 22, 2012 9:13 am

I'm not a pavement racer and my view of Bolles is mixed. Try this. http://www.racingsoftware.com/newpage1.htm

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Re: Any good oval track suspension guys?

Post by rick7343 » Sat Sep 22, 2012 5:35 pm

Thanx ziggy... I've read most everything I could find on the net...The newest trend is to move the RC left... I think it transfers weight down onto the RF without lifting the LF as bad ... hard to visualize...

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Re: Any good oval track suspension guys?

Post by RCJ » Tue Sep 25, 2012 12:49 pm

I'm begining to think the virtual swing arm of the r/f is more important.When measuring the r/c the l/f has as much importance as the r/f ,but on the track the r/f is doing a higher precentage of work.
When the r/f is loaded some wieght is transfered thru the a-arms and some thru the springs.The r/c height has an effect on this balance but what balance should we be trying for?
If you are looking for a good starting piont I think the best you can do is set the lower r/f arm close to level then work with one of the programs to get a spindle height that the r/c doesn't move alot in dive and roll and a upper a-arm length and angle that gives the camber curve you need.Or just slam it down on the bumpstop then most of this stuff doesn't matter.

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Re: Any good oval track suspension guys?

Post by rick7343 » Wed Sep 26, 2012 1:14 pm

I get all that... but there seems to be something about moving it left... seems to plant weight on the right without lifting the left as much... 4 wheeled race cars are faster..

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Re: Any good oval track suspension guys?

Post by Warpspeed » Fri Oct 05, 2012 7:38 pm

Roll centre height does nothing to transfer any more or any less total lateral weight.

Track width and CG height only, effect TOTAL lateral weight transfer, and nothing you can do to the suspension design or suspension tuning can ever alter that.
Think about it................

Roll centre height mainly effects roll couple and the amount of body roll for a given roll stiffness.

The interesting thing about this, is that the lateral weight transfer through the suspension links is virtually instantaneous. And lateral weight transfer through the bars and springs is applied more slowly, only as body roll develops during a sudden change of direction. Until the body actually rolls, roll bars can do zero.

Although you can do absolutely nothing about total final lateral weight transfer, you have two tuning tools.
Front and rear relative roll stiffness effect steady state understeer/oversteer.

Roll axis inclination effects how fast the relative lateral load is applied at each end during sudden changes in direction.

Roll axis height (both ends together) determines total body roll and sensitivity to tuning the bars and springs.

High roll centres create jacking, horrible camber curves, tire scrub, and generally make the suspension untunable.

Low roll centres create massive body roll which needs very high spring and bar rates which can then cause very sudden changes to tire loadings over small bumps, reduce traction and road holding. It will slide all over the place and have less grip.

What to do ?

The whole thing is a giant compromise, and you need to do some testing to develop your own package.
But basically first get it neutral on a skid pad by adjusting the front/rear roll bar relative stiffness.
Do this at a high constant speed, the steering wheel angle will tell you what is happening as you gradually increase speed.

Try some slalom turns, first left, then right, and see how it behaves.
Tilting the roll axis forward will give you best transient response with good turn in.
Tilting the roll axis too much forward will cause transient oversteer, it will feel lively, loose, and twitchy.
Not enough roll axis forward tilt will cause transient understeer, it will not turn in well and feel unresponsive.

Yeah, I know you guys only turn one way, but to test to get this right you need to make repeated very sudden changes in direction, much easier to do it with repeated slalom turns first one way then the other.

Overall roll centre height is a compromise between handling and road holding.
High roll centres at both ends with soft springing will stick like glue, but it will just fall over in a turn. It may even get up on two wheels or even roll over. Great roadholding, crappy handling, just like a soft 1960's factory road barge.

Low roll centres at both ends with very stiff springing and stiff bars will handle really well, but it will slide all over the place. It will be diabolical on loose dirt, in the wet, or over bumps. And it will be SLOW because you will always be going sideways and fighting for control.

So your design roll centre heights depend on tires, type of surface, and you need to compromise between grip and handling with the spring rates allowable suspension travel, and ride height that are practical.

Start off with it as a symmetrical vehicle.
When it is as good as you can possibly make it, THEN you can start experimenting with some of the the oval track tricks.
If the basic vehicle handling, roadholding and balance is totally screwed up, messing with tire stagger, weight jacking, funny diffs, and weird Ackerman will only confuse things further.
Cheers, Tony.

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Re: Any good oval track suspension guys?

Post by rick7343 » Sun Oct 07, 2012 9:22 am

So with latteral location,does moving the roll center to the left allow vertical loading of the RF without taking as much weight off the lf?

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Re: Any good oval track suspension guys?

Post by rce4csh » Sun Oct 07, 2012 12:11 pm

Within reason the answer is yes!

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Re: Any good oval track suspension guys?

Post by Warpspeed » Sun Oct 07, 2012 6:03 pm

rick7343 wrote:So with latteral location,does moving the roll center to the left allow vertical loading of the RF without taking as much weight off the lf?
Any extra loading on the RF must come off the RR.
Total lateral load transfer cannot be changed, only moved from one end of the car to the other.
Cheers, Tony.

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Re: Any good oval track suspension guys?

Post by rick7343 » Sun Oct 07, 2012 7:41 pm

Our class doesn't use bumpstops or coil bind, but they ( cars form the most successful shop) tell me for the last 5 years the rc has been moved to the left side... I have not been racing for quite a few years, so I'm trying to catch up...

The bumpstop guys say they have their rc outside the car to the left..

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Re: Any good oval track suspension guys?

Post by RCJ » Mon Oct 08, 2012 12:53 pm

If you use the theory that the car pivots around the r/c, if the r/c is in the center for every inch the r/f compresses the l/f will lift the same amount.Moving the r/c to the left will change this ratio,for every 1.5 inches the r/f compresses the l/f might only lift .5'' as an example.The nose of the car will be lower in this example and the extra grip could be from aero downforce.You would also have more camber at the r/f and less camber loss at the l/f.

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Re: Any good oval track suspension guys?

Post by rick7343 » Tue Oct 09, 2012 12:37 pm

OK.. so do have any known starting points? What else needs to be done to make it work?

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Re: Any good oval track suspension guys?

Post by raceman14 » Mon Nov 05, 2012 3:56 pm

To really get a handle on this it would be real helpful to spend some time on a 7 post shaker rig or at least a chassis pull down rig.

Warpspeed is pretty up on his info.

I think the driver feels the dynamic loading of the chassis and application at the tire more than the changing around of roll centers and their location left right or middle.
I do have a couple areas where I may be different than most only because I have run Karts and Suspended race cars, and I feel that dynamic suspension loading for pavement cars is diagonal corner to corner.

In my own personal designed chassis, I designed the suspensions for maximum travel ( high dive ) and maximum caster and camber gain under travel with minimal amounts of static caster and camber. I also worked for minimum scrub radius and maximum ackerman while using rear steer to compliment the ackerman. The closer you can get your wheels and tires to a F-1 / Indy car configuration the better your tires will work ( ball joints inside the wheel ) or at least get your KPI to as close as you can to the center of the tire contact patch thru suspension travel. This will work on cars that turn right or left and once you master that you can make them turn left even better.

You ever drive a forklift??? or a Ladder Truck? Rear wheel steering is about 100 times more effective than front wheel steering, at least it feels that way when you are going fast...and that is what counts.

What this will result in is a car that can drive anywhere on the track an if applied properly it will use the tires up in 100 laps, while getting faster later in the run. You can change the feeling and grip level of the car greatly with bump stops but there is a trade of in getting wicked loose when grip level drops. I am kinda old school and run higher chassis heights and more suspension travel than most, still using mid to soft springs and medium sway bars.

What kind of car are you running? Stock suspension Coil spring or Coil Over tube frame car?

They both have their own character and are very different in how you hook them up. My description above is more for a Coil Over Car and not a Big Coil / A-arm car as you have to get the motion ratio considered with the Big Coil car.

I have built them both from a pile of tube and plate and still have all the jigs for a-arms, truck arms, front clips and rear clips for both PortCity and Big Coil H&P, Hopkins, Hess, Hendrick and Gibbs clips. Still got 3-4 Gibbs and Hendrick cars I will probably build back and sell to a Historic or Vintage racer. I think some of my stuff is almost 10 years old now.

A lot of this stuff is vague generalities and to really get specific you need to get a car built or have some idea of the existing chassis configuration you are trying to improve on as well as the tires you are using, as the tires are the most critical component of the dynamic race vehicle.

When I build a car from scratch, the first thing I do is contact the tire manufactured to get some engineering specs on the tire. Believe it or not there are engineers at Goodyear, Hoosier, General, Yokahama, Pirelli & Michelin that love to have you pick their brain.
More is always better!!! Most of the time.

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