FWD snap loose problem

[ATOYOTA]

anyone have experiance with this problem and possible solutions? We're fighting this since day one of the season. Thrown about everything at it from one extreme to another. The only handling characteristic that changes with any chassis change is push off the corner. car always turns in fine but breaks loose bad mid corner. this is asphalt track.

to try and reduce this sudden and immediate spin, I've tried spring rates on the rear from 200# to 600# no difference, front spring rates from 300# to 550# no change removed front sway bar to running it with a lot of preload, no difference for snap loose but with load on bar, it pushes out so bad, I couldn't get on the gas at all. I've added 100# weight to the back of the car. with weight on LR car would still snap around and then push off. with the weight on the RR car snapped around and actually pulled hard right down the straights. Put 50
# on left front behind back bumper and no improvement on the snap loose but it did have better pull off the corner.

I verified there is nothing binding in the suspension nor any loose parts or worn bushings.


i searched for days on the net and all I find is a bunch of forums where guys talk smack about all driver error.

Any ideas on snap loose issues/resolution

[boportt]

tow in rears and wats ur caster #s?

[Egoracing]

Something to keep in mind is a RWD car drives off of the LR and RF, an FWD car drives off of the LF and RR.

[boportt]

ya so hows that spose to help the man?

[ATOYOTA]

increased caster and put some toe-in on the rear. still loose but much better, no sudden unpredictable snap anymore.

[Egoracing]

ya so hows that spose to help the man?

A stiffer spring in the RR may make it worse if the car is overloading the RR already. Also adjustments for the problem that would help a car driving off of the LR could compound the problem of a car that is already on the RR.

[ATOYOTA]

I had a spring as soft as 200# in the rr to 600# and there was no change what so ever. today I ran 60+ laps in practice and got it turning really nice and was 1/2 sec faster. All I did was took out 225#lr spring and put a 275# then I put a 280# rr. I increased RF caster 1° and toed in the LR wheel to 1/2" and toed out RR to 3/8" netting 1/8" toe in on the rear. after all those laps no unpredictable twitch, car rotated very nice in the corner to just a touch loose. But the watch showed over 1/2 second faster than it's ever been. I'll live with the slight loose for that kind of gain, especially since my times were .3 - .4 faster than this years fast times. I've been timing in 3rd - 6th all year. Now I should be on track for fast time.

ego, your input didn't really add to what I already did (which I started with changing springs all over on the rear). I think the alignment angles did more to help the problem. I found some SCCA road race guys that basically said what boport relayed with rear toe in and more positive caster.

[Egoracing]

I had a spring as soft as 200# in the rr to 600# and there was no change what so ever. today I ran 60+ laps in practice and got it turning really nice and was 1/2 sec faster. All I did was took out 225#lr spring and put a 275# then I put a 280# rr. I increased RF caster 1° and toed in the LR wheel to 1/2" and toed out RR to 3/8" netting 1/8" toe in on the rear. after all those laps no unpredictable twitch, car rotated very nice in the corner to just a touch loose. But the watch showed over 1/2 second faster than it's ever been. I'll live with the slight loose for that kind of gain, especially since my times were .3 - .4 faster than this years fast times. I've been timing in 3rd - 6th all year. Now I should be on track for fast time.

ego, your input didn't really add to what I already did (which I started with changing springs all over on the rear). I think the alignment angles did more to help the problem. I found some SCCA road race guys that basically said what boport relayed with rear toe in and more positive caster.

Glad you found it, I was just posting something basic that Might help, you would be surprised at how many people do not understand that an FWD operates differently than a RWD.

[Dentman]

What kind of car is it? What are the front spring rates and alignment settings? Are you sure that you don't have a broken bushing or some other damage causing this issue? Is the track banked or flat? What tires are you running and are they all the same size?
On a FWD, the rear follows the front end out of the turn, instead of pushing the front end out like a RWD. For a FWD car to snap oversteer, the car must lift and rotate around the RF coming out of the turn. If the RF is toed way out or a control arm/tie rod is moving backward/broken, this may cause the back to want to pass the front for a split second. Otherwise, hard acceleration should just pull it along.
We have FWD cars running with bump stops for rear springs and they still turn where the front wheels are pointed as long as they are properly aligned.
On left turning pavement, I suggest you use an alignment rack to set both front wheels at zero toe and +2.5 degrees caster, with the RF wheel at 3 degrees negative camber and the LF at +1. Toe in each rear wheel by .1 degree and set the rear thrust angle to zero if it's not. Set both rear springs at the same rate and see what happens.
Hope this helps.
Dentman