During my last autocross, I had a LOT of trouble keeping the rear end in check on a wet coarse (intermitant light rain, some small puddling). I originally attributed it to driver inputs, but the instructor who rode with me all day (8 runs) seemed to think it was more than that. Even very delicate rolling onto the throttle at apexes would cause the car to break loose, and often spin out. Having never spun before, spinning 4 times in 3 runs was very out of the ordinary for me. Trailing throttle oversteer seemed to come easier than I am used to as well. I began to get hesitant to input any throttle if the steering wheel was turned at all. After riding in a similarly setup car (same suspension, but stiffer sways and 245/40/17 shaved Kuhmo's all around) with the same coarse under the same conditions, I believe something is awry.

Here is the setup on the car.

TC Kline coilovers with SA Koni's 400F/500R
rebound settings: F 2 turns off full stiff/R 1 turn off full stiff
TCK camber plates
new front control arms and bushings (stock 96+)
new tie rods
1 yr old rear lower control arms (stock, not boxed)
1 yr old RTABs (stock 96+ w/ GC shims)
staggered stock wheels w/ 15k mile Yokohama AVS Sports
stock sways front and rear

alignment specs:
f camber -3.1
caster 7.1
toe 0.06" OUT per side
r camber -1.8 (max)
toe 0.06" IN per side

tire pressures were 40F/34R (cold). Wear was not over onto the sidewall as much as I'd like (front or rear), even after going down to 35F/30R (semi-hot). Ambient temp was 55*F.

My initial thoughts were that the tires just aren't great wet tires. The wear is no more than ~50% to the wear bars, so they should be ok, but having a staggered setup, I was very surprised to get more of a loose rear end than push.

Another thing that crossed my mind was that I may have introduced some preload on the front sway when I put it back on as I didn't attach the endlinks under load. I'm not sure that would affect handling this drastically though.

Any input for things to check would be appreciated.

only thing i can think of is that your rear toe more positive than you think.. and on a side note, how do you like the AVS sports? comparable to anything in the same category?

Are you getting into the rear bumpstops? Whats your rear ride height?

Thanks for the replies guys.

only thing i can think of is that your rear toe more positive than you think.. and on a side note, how do you like the AVS sports? comparable to anything in the same category?

I think the alignment specs are accurate. I had it done at the shop that does Turner's alignments and I was sitting in the driver's seat while they set it my specs. I <I>thought</I> I liked the AVS sports, but after this experience, <B>IF</B> it turns out to be the tires, I'd have to say they are not comparable in the wet to even Kuhmo's, which for me are slightly cheaper. I liked them in the dry although there are stickier options (S-03's, PS2's) at ~$30 more per corner.

Are you getting into the rear bumpstops? Whats your rear ride height?

Sean,
My ride height is fairly conservative at 13.25"F/12.5"R measuring from the center of the wheel to the fender lip. The car is not (yet) cornerbalanced. Isn't their a zip-tie trick to find out if I'm getting into the bump stops?

Another question: With only rebound adjustablility (external all around), should I just be setting and forgetting or is their a reason to stiffen up for events and soften up for street driving (double duty car)?

After riding in a similarly setup car (same suspension, but stiffer sways and 245/40/17 shaved Kuhmo's all around) with the same coarse under the same conditions, I believe something is awry.

You may want to consider adjustable sway bars - a simple upgrade, but one that makes a big difference.

mebe try -2.5 rear camber?

You may want to consider adjustable sway bars - a simple upgrade, but one that makes a big difference.
You are probably right that they would make a big difference, however, if there is something "wrong" currently, I don't want to cover it up. From what I've read and heard, sway bars should be used to fine tune your suspension... I want to fix it first!

mebe try -2.5 rear camber?

I am max'ed out at -1.8 on one side and I'm not really sure why. The lower control arms are fairly new and not visibly bent, but small bends can be subtle. Regardless, I don't think -0.7 camber difference is causing this much instability - but I'll keep that in mind as things move forward.

A few things to check:

Re-check the rear toe-in to make sure its still 1/16 per side. Rolling on to the throttle with not enough toe-in will do what you say. If its correct (and equal on both sides) then maybe consider 1/8" toe-in per side, although for autox people tend to run a bit less to rotate the car easily.

Shocks play a very important role in transitional handling. Is the rear getting loose while entering or exiting a corner in particular ? What are your rebound setting front and back ? On a slippery track there isn't enough weight transfer so if your front rebound is not firm enough you'll get a quick weight transfer to the back and with less traction the rear would get loose.

You can disconnect the rear sway bar to get more grip at that end. However, you may get more tire roll-over with -1.8 camber so do this one just for giggles...

Hope some of this helps.

Shocks play a very important role in transitional handling. Is the rear getting loose while entering or exiting a corner in particular ? What are your rebound setting front and back ? On a slippery track there isn't enough weight transfer so if your front rebound is not firm enough you'll get a quick weight transfer to the back and with less traction the rear would get loose.


This was particularly prevalent on exiting the corner, usually just as I was inputting throttle at the apex. The only cases where the rear got lose entering a corner was from trailing throttle oversteer and/or over-trailbraking. I think you may be onto something here. The one thing that I am <I>certain</I> changed from the previous autox to this one was my rebound settings. Both days were semi-rainy but this time I softened everything up and with my front softer than the rear anyway, I might have overdone it. Rebound settings: Front 2 turns off full stiff/Rear 1 turn off full stiff. That is easy enough to test out, but I'll double check the rear toe as well.

This brings me back to a previous question:


With only rebound adjustablility (external all around), should I just be setting and forgetting or is their a reason to stiffen up for events and soften up for street driving (double duty car)?

You are probably right that they would make a big difference, however, if there is something "wrong" currently, I don't want to cover it up. From what I've read and heard, sway bars should be used to fine tune your suspension... I want to fix it first!.


Good point - I'd suggest two things. You might want to lower your ride height. I'm running Koni SEA CO's with Eibach race springs and my heights are set at 12.6 front and 10.2 rear. The lower CG reduces roll, which may help. The other suggestion is to give Pete at TCK a call - he was invaluable in helping me on more than one occasion to get my suspension settings dialed in right. Good luck.

Good point - I'd suggest two things. You might want to lower your ride height. I'm running Koni SEA CO's with Eibach race springs and my heights are set at 12.6 front and 10.2 rear. The lower CG reduces roll, which may help. The other suggestion is to give Pete at TCK a call - he was invaluable in helping me on more than one occasion to get my suspension settings dialed in right. Good luck.

Those ride heights are way too low for my double duty machine, but I do agree with your about Pete though (he's got mail :D ).

Those ride heights are way too low for my double duty machine, but I do agree with your about Pete though (he's got mail :D ).


LSD worn out?

LSD worn out?

I would think that would make the car less prone to jumping in to oversteer. Of course it would be even more pronounced when it's dry out.

Those ride heights are way too low for my double duty machine, but I do agree with your about Pete though (he's got mail :D ).

I'm in the same boat with a double duty car, but that's the great thing about CO's. For the street, I raise my front 1 1/2" 's, set my shocks at full soft and set my front camber at -2.0, which makes the commute bearable. As far as alignment - I have it set for my track settings and deal with the consequences for the street.

I'm in the same boat with a double duty car, but that's the great thing about CO's. For the street, I raise my front 1 1/2" 's, set my shocks at full soft and set my front camber at -2.0, which makes the commute bearable. As far as alignment - I have it set for my track settings and deal with the consequences for the street.
You do know that your front toe is going to change when you adjust your ride height and/or camber, right?

You do know that your front toe is going to change when you adjust your ride height and/or camber, right?

Like I said, I deal with the consequences for the street. For me, it's more important to have the alignment set for the track.

I usually set everything to full soft in the rain. You will be running at 6/10 maybe and full soft will be fine. You will notice it in how the car reacts but it slows things down a bit and helps with not upsetting the car.

I agree with most all of the comments. The forum guys are on the right
track for sure. Here is exactly what I would have tried:

Disable rear sway.
Install 400 lb rears.
Set front rebound full soft + 1/4 turn.
Set rear rebound full soft + 1/2 turn.
Add weight to the front area of the spare tire well in the rear
45-65lbs. Use a spare wheel & tir if you have to. You want a lot of body
roll in the wet to transfer weight the outside tires.

Note: We set the rake of the car at 1/2- 3/4" higher in the rear. We
always measure from the rocker panel to the ground at a common point
close to the rear of the front tire and in front of the rear tire. The
front should measure near 5- 5 1/2".

Feel free to publish this info.

Pete


I should have noted that I DID have the spare in the trunk during every run.

Question for the masses: Is your rake set for the car to be higher in the rear or the front?

Thought I'd bump this thread up with some more data and a couple more questions.

<B>Adjustments made and results</B>:
At an autocross after the one at the beginning of this thread (this time nice, sunny, warm (88F), and dry) I stiffened up the front rebound damping (to 1 turn off full stiff) based on Sarwat's suggestion and slid the rear bumpstops down ~1 inch from the tops to check for bottoming out (thanks Sean). The rest of my settings, tire pressures, etc were the same.

In general, the car felt much better... but not perfect. I was getting a little understeer on corner entry as I would have expected based on my tire widths (225F/245R) which wasn't happening before. However, after 4 runs, I checked my rear bump stops and they were pushed all the way up to the top again (ie I am getting into the bumpstops).

<b>Questions</b>
I know I need to check the fronts for bottoming out (couldn't easily reach the bumpstops under the dust shields inside the springs), but what is the order of operations for solving my running-out-of-travel issues in the rear?

1) Soften up the rear rebound a little to make sure it isn't overpowering the springs
2) Cut the rear bumpstops down a bit (currently what is supplied by TCK which are ~2" in length)
3) Re-adjust my ride height (I assume a last resort as I'd need another alignment). Current ride height is: 13.25"F/12.5"R measuring from the center of the wheel to the fender lip OR ~5.25"F/6"R measuing from the ground to the rocker panels 6" back from the front wheels and 6" in front of the rear wheels.

bumpity bump for some opinions.

eat more fiber??? (sorry, couldn't resist)

Update: Finally fixed the problem!!!
...And the winner was...... SG_M3! After checking and re-checking alignment settings, rake, rebound settings, etc - I finally hacked about 3/4" off my rear bump stops. All I can say is WOW! It feels like I have a new suspension all over again! I am almost thinking it is going to be hard to get the car to rotate vs. it's previous pseudo drift-mobile status on the auto-x course. Thanks again Sean.

Update: Finally fixed the problem!!!
...And the winner was...... SG_M3! After checking and re-checking alignment settings, rake, rebound settings, etc - I finally hacked about 3/4" off my rear bump stops. All I can say is WOW! It feels like I have a new suspension all over again! I am almost thinking it is going to be hard to get the car to rotate vs. it's previous pseudo drift-mobile status on the auto-x course. Thanks again Sean.

:alright

Mark Donahue might suggest not rolling into the throttle at the apex, but waiting until you are pointing straight then mash it.

Glad you found teh problem though.



During my last autocross, I had a LOT of trouble keeping the rear end in check on a wet coarse (intermitant light rain, some small puddling). I originally attributed it to driver inputs, but the instructor who rode with me all day (8 runs) seemed to think it was more than that. Even very delicate rolling onto the throttle at apexes would cause the car to break loose, and often spin out. Having never spun before, spinning 4 times in 3 runs was very out of the ordinary for me. Trailing throttle oversteer seemed to come easier than I am used to as well. I began to get hesitant to input any throttle if the steering wheel was turned at all. After riding in a similarly setup car (same suspension, but stiffer sways and 245/40/17 shaved Kuhmo's all around) with the same coarse under the same conditions, I believe something is awry.
Here is the setup on the car.
TC Kline coilovers with SA Koni's 400F/500R
rebound settings: F 2 turns off full stiff/R 1 turn off full stiff
TCK camber plates
new front control arms and bushings (stock 96+)
new tie rods
1 yr old rear lower control arms (stock, not boxed)
1 yr old RTABs (stock 96+ w/ GC shims)
staggered stock wheels w/ 15k mile Yokohama AVS Sports
stock sways front and rear
alignment specs:
f camber -3.1
caster 7.1
toe 0.06" OUT per side
r camber -1.8 (max)
toe 0.06" IN per side
tire pressures were 40F/34R (cold). Wear was not over onto the sidewall as much as I'd like (front or rear), even after going down to 35F/30R (semi-hot). Ambient temp was 55*F.
My initial thoughts were that the tires just aren't great wet tires. The wear is no more than ~50% to the wear bars, so they should be ok, but having a staggered setup, I was very surprised to get more of a loose rear end than push.
Another thing that crossed my mind was that I may have introduced some preload on the front sway when I put it back on as I didn't attach the endlinks under load. I'm not sure that would affect handling this drastically though.
Any input for things to check would be appreciated.