Racing Damper Optimization 1

[yawpower]

Anyone here like to discuss their approach to damper setup for non/low downforce racing cars?

This is something no-one ever wants to talk about because they either haven't a clue, or they feel they have an advantage, and do not want to give it away.

I propose that discussion amongst race engineers will benefit everyone.

I will briefly describe my own approach, in hopes that some of you will add your own thoughts/experiences.

First off, all my experience is with sedans, either tube frame, or production tubs. Mostly solid rear axle.

I start by calculating critical damping of the sprung mass, and use a digressive piston with no preload to approximate a linear curve with the damping set at approximately 35% of critical.

Determining a starting point for the compression damping requires a bit more guesswork. So much guesswork that I am embarrased to describe it. The first thing I do is calculate the rebound force at the wheel for the front and rear. If there is a drastic difference between the two, I take that into account so that total damper force at the wheel is relatively equal at both ends of the car.

(By total damper forceI mean compression and rebound combined for each end of the car.)

I then use a digressive piston with very little preload, and set damping to approximately 50% of the rebound in the high speed range.

Once on the track, I start by varying the rebound damping until the driver feels that the car has "just enough" stability. Sometimes this results in gobs of rebound damping and the car starts to lose grip over rough surfaces. In this case I increase the preload to bring up the low speed damping, and then re shim to bring the high speed rebound back into a reasonable range.

Once this is done I try to make the car work over the curbs by varying the compression damping. In my experience, a softly sprung car will benefit from large amounts of high speed compression damping, while a very stiffly sprung car will normally need very little for best feel over the curbs.

Lastly, I look at tire wear/abuse during a long practice run, or a race. If the tires go off easily, reducing compression damping will usually make the tires much happier. The end result is normally a highly digressive curve.

Finally, once the driver is happy, I try to convince him to run less rebound. It is common for the driver to complain that the car is harder to drive, but the end result is better lap times unless the driver is relatively inexperienced,in which case he will drive the car harder with more rebound damping because the car feels more stable.

This is a very simplified description of my usual approach, and I would like to hear how the rest of you tackle initial damper setup.

I am sure I can learn something from all of you.

Paul Yaw

 

[yawpower]

Oops! I forget something. All the above assumes that the weight transfer due to springs, bars, roll centers, sprung mass results in a neutral car. (On paper at least!)

Paul Yaw

 

[pmwltd]

After reading your post I think it is the other way around, at least for me. I can learn from you. Have you had any experience with FWD cars. We have been trying to work with the shocks to control turn in under moderate to hard braking on a particular course. Using low speed bump to get the car to set quicker and not push on initial turn in. Raising bump and lowering rebound on the front. Have not had time for much test. The driver likes it but,have not seen anything definitive in lap times. Would be interested in your thoughts.

 

[yawpower]

I have no experience with FWD, or rally cars, still I assume that the same principles apply. To me, turn in under braking implies diagonal weight transfer. The outside front shock will be compressing, while the inside rear shock will be extending.

If this were a road race car, I would want to REDUCE the load on the outside front tire. I would do this by reducing front compression damping, or increasing rear rebound damping.

PY

 

[ecclestone]

I have only just picked up on this thread re FWD, You dont say wether you are running aN LSD or open diff.I have been involved with FWD race cars for some years. The main problem always seems to kill the understeer/push on corner exit. Now the driver is usually one of the biggest influences on push. Trail braking is a receipe for push. generally I run quite a bit of front rebound and rear bump stiffnes. I try to keep the platform flat on turn in. The rebound is to stop the front from tending to lift under acceleration after the transition from brake to accelerator..Spring rate and ride height are also critical . at least for a race car on race tires

 

[pmwltd]

Appreciate the comments on FWD. the car in question is a GT4/5 running in SCCA. Runs a Mugon LSD, is converted to SLA in front and a 4 link solid rear axle, with Mumforf link in the rear. Runs adjustable anti-roll bars front and rear. Tires are Goodyear cantilever slicks.

Won't increasing rebound stffness in front tend to unload the front tires under initial power on?

I have been trying to minimize forward pitch under braking by increasing front bump and rear rebound. This is to try and minimize camber gain under straight line braking, car does not have any anti-dive.

Tire temps and wear look pretty even. However at some tracks the inside edges of tires are working too hard. This appears to be mainly at a track where sustained hard straight line braking is required.

The camber gain is right at 1deg. per inch of bump travel. Any thoughts would be appreciated.

There are some pictures of the suspension in the gallery @

http://www.pmwltd.com

Dave

 

[joelbrown]

I've had fairly good luck finding a starting compression setting for the 2 IPS range on shocks by calculating the spring rate at the wheel and multiplying that by .4.

Rebound needs to be atleast twice the compression and depends a lot on the driver and how bumpy or smooth the track is.