how does rebound affect handling?

[Gforce]

I posted this on the SRT list but I figured some of the smart people may not be monitoring this one so I tied you guys as well.

Can anyone help me understand how "too much" or "too little" rebound affects the handling? i have a set of adjustable motons for my SRT and I want to be able to dial in the best settings.

Any advice is appreciated.

cheers -

j

 

[Irid]

Nuts I just posted war and peace over on that thread. Go look there ;-)

 

[Gforce]

Thanks Irid. When I saw your post over on the other group, I wondered if you were a regular over here. I figured I'd come over here and let people know that I found what I was looking for but you beat me to it

What a great explaination you had in the SRT group!! I am still trying to absorb it all but your examples and patience is very much appreciated!!

BTW - left a couple of quesitons over there just to see if I understood enough of the science to accurately apply it.

thanks again.

j

 

[GTS Dean]

Too much rebound can lead to "packing down" of the dampers over short frequency bumps. Packing down is when the piston and shaft do not extend back to their curb setting after a full stroke cycle. This progressively lessens the available bump travel. Stiffer springs can overcome this problem, but the best fix is the right valving for the correct spring.

Handling wise, too much rebound can make the car prone to snap oversteer under hard braking and cornering. It can also hurt power-down over medium length heaves in the road surface.

 

[Gforce]

Thanks GTS DEan. Skip White and others have built you up as quite the suspenstion expert so your advice means a lot.

Problem I had last time was really with the "S" curves. Any particular corner where the car settled before the next one was fine. Transition before settling wa pretty scary. I had +6 from soft on the bump and +1 from soft on the rebound.

I almost think the transition problems were due to one side being weighted (from the 1st turn) and then having that side unweight (from the 2nd turn) faster than the oposite side could compress. Based on Irid's post last week, this seemed to make sense.

I ran into Rick (Bob Woodhouse's mechanic) this weekend at ALMS in portland. He and Bob run +3 on the bump and +6 on the rebound for Portland International. That was for a comp coupe but I assume/hope it would work for SRT as well.

I was thinking about trying this for the corvette day next week and seing how it went.

I know its impossible to diagnose a patient over the web but do the above settings seem like a sane place to start? In case it helps, my spring rates are 500/700, Bob's were 500/850.

 

[GTS Dean]

You need to set aside some laps for real testing. Set one end in the middle of the adjustment range, then go from zero to full on each adjustment at the test end. Do a lap or two on each setting to get a gross range feel for braking, corner entry, track-out and bump response. Make notes in a book that stays with the car.

 

[Gforce]

Great idea. Given that I am an engineer, you'd think I would have thought that one through.

Wonder if I will even notice 1 click or not? I guess probably only if I am pushing the limits but then again, with new settings, I'll be a bit shy pushing the limits.

In any case, you are spot on. I'll just spend the morning playing with it and seeing how it drives. Did that last time with the rebound at +1 from soft and ended up with the bump dialed out to +6 from soft.

Thanks again -

j

 

[GTS Dean]

I don't recommend going through the range click by click. It'll take too long and you probably won't feel any major difference. Make major swings - all or none - or zero, middle, max; and define the limits of adjustability. Then, tune to suit with minor adjustments.

 

[Gforce]

I wanted to thank those of you who helped so much on this board with my motons (special thanks to Irid and GTS Dean).

My last track day RULED. I had the fronts set at +4 on bump, +3 on rebound. I had the backs set to +3 on bump and +4 on rebound. Idea here was to get the weight on the rear wheels and keep it there. I might even try a +5 on the rear rebound next time just to see if it helps.

Between the brakes and the Motons, my SRT/10 a blast to drive. Lacked a little "oomph" on the straights compared to my GTS (540hp, 620 lb/ft).

Anyhow, just wanted you guys to know that neophites like myself really appreciate the help.

cheers -

j