UPDATE:Page2 - Alignment Issues - Can Toe-In Significantly Affect Rain Perf?

I've been struggling with an issue for the longest time now! My car is terrible in the rain on the highway. The rear end "wiggles" even at moderate speeds (even below 55mph) on the interstate in the rain. I run PS2 street tires - when brand new, it's hardly noticeable, but with even 1/2 tread remaining it's disturbing at best, downright scary at worst. I finally started to consider if it was toe settings, duh... and I'm convinced this could be the culprit. The toe was set at about 0.06-0.08 (degrees in) toe in the rear. I've recently had it changed and it's now about 0.18 (degrees in) in the rear for each wheel. 0.37 total I'm hoping this will do the trick. For the past 2 years, my garage has used the old "Those tires suck in rain and your car is set up for the track" and I just can't buy that a world-class german sportscar handles THAT badly in the rain. Any thoughts? Interested more in concrete experience than conjecture if you don't mind.

What's your front toe setting? In general, toe settings do affect straight line stability. FWIW, I drove through horrendous downpours near Philadelphia yesterday, in PS2s that have been around the block, so to speak... maybe 50% good in the rear and 25% good in the front, and I had absolutely no problem in the rain. Eventually I did slow down to about 55 MPH, but only because of a lack of vision - not a lack of stability.

You mentioned that half the tread is remaining, where are you measuring it? Toe-in can cause the inside edge of the tires to wear more quickly than the center. The fact that this behavior isn't present with new tires suggests that it's a wear issue, not just the setting itself. I had exactly this issue with exactly the result you have in my previous car.

I have an aggressive setup with over 2 degrees negative camber in the rear and about -1.6 or so in the front. Not certain, but I'll check front toe. I get pretty even tire wear, generally - I live in the mountains and I drive my car mainly for pleasure or track - not much interstate. I think that's why the tires still wear pretty well. I guess I'm wondering if anyone else has experienced this kind of "looseness" in the rear end at speed - it feels just plain unstable with a bit of a wiggle to the right, then a bit of a wag to the left, and so on... It almost feels like one tire is getting traction over the other and pushing the rear to one side, then they swap. These are absolutely minimal movements mainly on interstate - even without much water - noticeable, but very fine. On the track, even in the rain, the car has always felt stable and has great grip, but I'm on the gas or brakes almost the entire time, and I'm guessing this is mitigating the effect.

Perhaps you are experiencing this... and it's just more noticeable in the wet? Tramlining: Coping with the Ruts in the Road You might also double check your air pressure.

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Funny - I've had cars that weren't properly set up with wicked tramlining in the front-end. And it's interesting because I guess that's the same kind of "feeling" I'm getting in the rear end of my C2. Tire Pressure - tires, etc - all doubtful - I've had this for almost 2 years. Different tires, even running my Toyo R888's between autocross or track days on the interstate. I still want to think it's just a simple toe adjustment, but the rain keeps on missing me this week - haha.

Getting current alignment specs would be a good start. Where it WAS set may not be where it is now. For these cars you want neutral toe in the front and a touch of positive toe (toe-in) in the rear. The positive tow in rear creates a better straight line stability. If you deviate from that at all you can exibit what you are experiencing. If you toe in the front gets knocked to positive from neutral you will have more understeer but still no instability problems. Get negative toe and you will have great turn-in but straight line could be a touch floaty (like it's tracking randomly). If the toe in the rear gets knocked out and goes back to neutral, or even worse, negative toe, then you are going to be all over the place and it will be a really ALIVE rear end. Hello solid barriers I'd get your alignment checked before anything. Then you can make some decisions. ***sounds after reading everything that your toe in the rear got knocked out to a negative setting***

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Thanks Dell - Have the pre and post settings - just not sure exactly what the front toe is set at. Camber -1.6 front, -2.0 rear Rear toe was 0.08 (toe-in) on either side now it's set at 0.18 (toe-in) on each side. ps - Dell, will I see you at VIR in a few weeks?

Are you talking about the Mon/Tues event on July 12/13 with Carolinas?

Yep - I was running in front of you at the last VIR event w/Carolinas while you were driving someone's white 997S - then I was running behind you after a few laps I couldn't keep up with you with your great line and late braking at the end of the back straight. Need to get a ride along if you're open to it next time you're at VIR.

Ah, that was Scott's C4S that i was driving. Heavy pig It's nice to be able to push a students car a little more than average to show them some of the capabilities of the car. Now he has a GT3 and I really enjoy helping him in that car I'm not going to be at the July DE since I can't cancel class during the summer as easiliy as the fall/spring but I am going to try and make it up for a day (Monday) to see how everything is going and saw hi to everybody. I'd be happy to have you in my car or ride along in your car and offer what I can.

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Your toe settings are in degrees? fyi, 0.08 degrees = 4.8 minutes Way too low. 0.18 degrees = 10.8 minutes About as low as you'd want to go. It should feel a lot more stable. Cheers,

I ran 2mm toe-in for the rear and .5mm toe-out for the front (the front setting was for track application). Remember, toe setting is different (for conversion between minutes, degrees, mm) based on wheel size.

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Thanks - yep, important to note degrees, minutes, or mm. I was talking in decimal degrees - so standardizing on minutes where 60 minutes = 1 degree: I pulled out the Streather "bible" last night (forgot it was sitting on my shelf!) and the specs on rear toe are 10' +/- 5' - translating to +5' to +15'. It was previously set at the lowest setting but still "in spec", about 5' - now it's at the middle of the spec, 10' - if this makes an improvement, which I suspect it will, I'll post the results. Unfortunately, the rain is hiding from me this week!

Yes

I went out in a storm today - 60-70mph - no standing water - going in a straight line, it felt like I was going to go into a spin at any time - feels more like an amusement park ride.... thrilling. Not. I'll run by the shop and get exact specs on my current alignment and post them.

Doug, how sensitive is your tactile sense differentiating between front and rear of the car when driving? Reason I ask is if you can describe what you are feeling and where exactly it is coming from we could probably figure this out......and obviously to be confirmed by alignment check. Were you feeling the spin coming from your fingers and feet or your butt?

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I think you could be right Dell - I'd like to think I'm "that good" but perhaps my judgment is off. I think it's coming from the rear because it's my "butt sense" but then again, felt like the front was also squirmy today. Wonder if it could be both - and I don't honestly know the front toe settings so awaiting an email reply from my shop now on the specs. Will post when I get all the details.

Could be their machine is out of whack.

Front toe out can make the car darty and then you might be feeling the rear moving to catch up, causing your uneasy feeling.

As Allan points out, their equipment could need calibration. Regardless, make sure they get you BEFORE and AFTER readings.

eDoug - sorry to be late to the party. Toe in tends to make the car more stable - quite the opposite of what you are feeling. I like 2 mins of toe-in at the front to make the car a little more stable in a straight line. In back you want something like 14 minutes of toe in per side. Less than that and the car becomes unstable under hard braking. As to what you are feeling in the rain, wide tires, worn roads with ruts worn into them and NEGATIVE CAMBER will cause your car to be darty. My RS suffers from this. High performance tires put rain grooves in the middle of the tread. Having the tires at an angle to the surface (i.e., neg. camber) reduces their ability to evacuate water. Worse, roads with ruts worn in them collect water in said ruts and the car can be a handful. Ask me how I know If you don't track the car enough to need to negative camber, get your alignment corrected to a compromise setting. As others have suggested, it is possible your alignment is out of whack. The rear toe setting on our cars is fragile unless you have toe links installed. A couple of good bumps and rear toe is out of spec and that can make your handling very odd.

Thanks for all the comments - finally got the car into another reputable shop. They checked the alignment on their Hunter machine and it shows the following: (In Degrees) Front: Camber: -1.5L -1.2R Caster: 8.5L 7.8R (car pulls slightly to the right - and dealer indicated replacing control arms because of this???) Toe: -0.02L +0.07R Rear: Camber: -2.2L -1.9R Toe: +0.45L -0.01R (WTF????) So I'm NOT crazy - and my shop's Beissbarth alignment system is CLEARLY out of whack. I'm heading down to a dealership in Hickory NC tomorrow to have it aligned on their equipment - checking before and after to verify this. And to think, I've been dealing with this issue to varying degrees for the last 2 years. I just about want to strangle him for giving me the runaround for the past 2 years making me feel like an idiot. Recommendations on a good track alignment? I don't think I can get much more negative camber in the front - and I drive my car about as much on the track as I do on the road - which is to say I'd rather lean towards a good track alignment. Running Toyo R888 R-comp DOT legal on the track. Looking forward to any comments.

Okay - went to dealer, took 3 hours for the alignment - mechanic said the rear left wheel was frozen after taking out the adjustment bolt on the rear left. AThe bushing was lodged sideways in the track and he had to use a nylon strap and a come-along to free up the wheel to adjust the toe. I figured best to start reasonably neutral and had him set it up to GT3 stock specs as follows (degrees): Front: -1.5 Camber both sides 0.07 Toe-in Rear: -1.8 Camber both sides (I can get over -2.2, but figured it's probably better to leave it closer to the front camber as I've had a bit of understeer on the track in the past) 0.2 toe-in (in spec but more toe than I'd like) Plan to be at VIR on Monday/Tuesday and it already feels better and tracks dead straight on the interstate. Hit some rain today (light) and didn't notice any wiggle, even at 95mph. Wondering whether to even bring it up to my (probably now former) local mechanic. Thanks for the comments.

Wow, looking at your original alignment settings- they were more toe steering than toe settings front end steering to the right and the rear end steering to the left Sure must be better now, unless you always wanted to drive in tight right hand circles

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These setting are probably good for your driving. The toe in at the rear should help quite a bit with stability. Especially under braking. It's so important to calibrate these machines! On another note, what did they say about the difference between left and right caster? That's usually a sign of a problem or using the wrong adjuster if you have gt3 control arms.

Okay, steering angle sensor off by 5 degrees... PSM was apparently kicking in when driving in a straight line... How about that??? Finally after about 2 years...

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wow, glad to hear you finally have that resolved!