cgfen

Hello
Can you suggest either;
1. a good book describing how bounce / rebound adjustments influence a cars handling that discusses what adjustment to make to see specific changes.
or
2. conventional wisdom rules of thumb that describes the same.

I understand the bump adjust - effect part pretty well, but rebound adjust - effect
is a new variable for me.

thanks

Craig

jscott82

To get the conversation started... I’ll tell everything I know...
1) Adjust bump for turn-in
2) Adjust sways for mid corner/steady state
3) Adjust rebound for corner exit

There you have it... the extent of my knowledge...

cgfen

yeah, but you have a pretty car...................

jscott82

A wise man once said "either go fast or look good". For some reason the former escapes me.... but thanks

Van

In general, softening the suspension, sways, springs or shock settings, will give that part of the car more grip.

Compression and rebound are going to give you dual control over weight transfer when you're transitioning from braking to turning, and so on.

I believe that stiffer compression in the front will reduce the weight transfer to the front under braking, which will reduce the traction at the front. This means you can fine tune the car's balance at turn in.

I'd think that rebound plays a role in how fast the tire comes back down to meet the surface (to keep a constant contact patch) and you can adjust it to give the most grip mid corner (like sway bars).

3 and 4 way shocks have high speed compression and low speed compression to further adjust between weight transfer compression and simple bump compression.

Bill Verburg

Bilstein has some good info

JClark

Smith's Engineer to Win and Puhn's How to Make Your Car Handle are two of my favorites but for the love of God be careful who you listen to....like....well...this thread.

Figure out exactly what the handling problem is and exactly where it happens (type of corner and WHERE in the corner). If you can do that and really understand exactly what the car is doing wrong, you'll know what to adjust.

jscott82

+1 on the how to make your car handle book... The book was written in the 70's, and while it’s still relevant, the pictures are hilarious (gotta love plaid pants and dress boots).

chris walrod

The dampers you are installing, I assume they offer high speed bump/rebound only?

With low speed adjustments you can play around roll control, kinda like artificial roll bar adjustments.

Larry Herman

IMHO you need to have a good mental grasp of exactly what the shock is doing, and then apply that understanding to what you want the car to do. It is difficult to grasp because the shock is not anchored to a fixed point. It floats between a suspension member that operates at a high frequency, and a body that operates at a low frequency. The point is that they BOTH move, and you have to account for that in your understanding.

As you raise the "bump", the suspension will compress less. This is good because it helps to keep the tire on the track when you go over bumps. As you continue to stiffen it, you can get to the point where you start moving the body too much and then you once again can lose grip, for longer periods of time (because the body is slower to recover - remember, low frequency). BUT, as you stiffen the bump, the body will lean less in the turns

As you raise the rebound, you slowly reduce the suspensions ability to expand, and that is bad because as it unloads (through a bump or body lean) you reduce the grip of the tire on the track. HOWEVER, as you raise the rebound it helps to reduce the body "floating" over the suspension, giving your car that locked-down feel.

They work together in that if you are running higher compression, you can run higher rebound because the suspension will not compress as much over bumps (or when the body leans) an so it will not have to expand as much to recover. There is such a thing, though, as running the shocks too stiff, and your settings have to be with-in the operating range of the springs.

Now here's where your head explodes. The shock operates over time in that it's effect is immediate as the suspension moves, but diminishes as the suspension settles. So accomplishing things like dialing in a little more "turn-in" has to be done with consideration of what the body and suspension are doing at that moment.

For me, this way of looking at what shocks do explains what all of the adjustments do, and why they produce the effects that they do. Of course, YMMV.

85Gold

Rebound has always been my nemisis. At Homestead last weekend we were finally getting the GT2 to handle with the new rear sway bar. Back felt planted but the front was pushing badly on turn in. (no bite) Took a click of front rebound (moton 3 way) out it and it was worse, (reasoning for lowering rebound was let the front settle faster on picking up power) boy were we wrong. Cranked in more front rebound and suddenly the front was gripping (our reasoning for the improvement was slowing down weight transfer to the rear on power application) Shock tuning is fun but it can also be very frustrating at times.

Peter

cgfen

LOL understood

I'll try to get it close then ask someone more knowledgeable to drive and comment

Agreed, i just re-read through chapters 2 and 3 last night. I love the goodyear photo showing the tire selection, everything from Art Arfons Green Monster to midget car options.

Thanks Larry, this makes good sense to me and aligns with my current understanding which is.
1. springs basically exist to insert additional compliance into the system.
2. shocks exist to control / damp the oscillations caused by the springs.
and both work toward the goal of maintaining maximum contact patch (grip) while minimizing any unsettling of the chassis.

I"m still reading / asking / learning.
Much of it is a moot point since i am not currently a big track kind of guy, just an over-analyzing kind of guy.

Don't get me started on my trying to understand where the spring shock combo = good enough set point is where a person then begiins to consider ARB tweaking to fine tune the system

cheers.

Craig

ninjabones

I'm definitely a novice in the suspension tuning stuff (actually just installed my new suspension and have my first event in two weeks at NJMP).

However, if you're pushing at turn in, wouldn't logic dictate taking rebound out of the rears (not fronts). For turn-in issues, shouldn't we be thinking about weight transfer under braking (not power application). If you're trail-braking, softening rear rebound should theoretically increase the speed of forward weight transfer, and thus increase grip of the front tires at turn-in. Same principle should apply at track out.. if you're pushing, stiffening front rebound should slow down weight transfer to the rear tires and allow more front tire grip at track out.

Again, I'm just starting to learn about suspension tuning. I'd appreciate some feedback from the rennlist "elders" on this line of reasoning.

claykos

This is a decent article by an IRL or CART engineer.

http://www.smithees-racetech.com.au/...hocktune1.html

I have always found increasing front rebound to be a very effective way to limit corner exit push.

Larry Herman

That article does a good job explaining why that works.