Is the second generation Active Handling / traction control sensitive to tire size changes where the stagger is eliminated and all tire sizes are the same? I'm investigating going to 18 X 10.5s all around, and using a single tire size while I'm at it. This is probably the last question I have before pulling the trigger.

Thanks in advance

Pat

 

From what I have read, you need at least 1/2" taller rear tire with a max difference of one and 1/2". If it were me, before I spent a lot of $$ on wheels and tires I would test it on my car. Borrow another set of fronts the same size as yours and put them on the back of your car and drive it. Another way would be to buy a cheap set of used or new tires to match diameter of 2 you have now, install and drive. You should know quickly if it's going to be a problem.

 

My 04 Z works fine with the same size tires at all 4 corners. Traction control might be a little more intrusive than normal (I'm not really sure, I tend to use my right foot as traction control rather than just mashing the pedal and letting the computer sort it out) but it definitely works and active handling appears to be completely unaffected. I tried throwing the car sideways a few times just to verify that it was working and it does indeed work just fine.

 

Curious where you learned there were 2 generations of AH/TC. I know it was first an option and then became standard in 2001 if I remember correctly. Would like to read.

 

Thanks for the responses. I'm not sure whether to have hopes or not. Thanks for responding to Daderoo, 8vette7. Worst case, I could run M-PSSs, 275/35 front and 295/35 rear on the oem Z06 18x10.5s. That'd give me a .55 diameter differential, I believe. Anyone have a photo of a 275/35 on a 10.5 rim? In particular a M-PSS?

I can try my wife's '99 Mags on the front as well, just to test the TC issue, but right now I'm Jonesing for a new pair of OEM rear Speedlines. I think the extra diameter (even with 275s) up front will help with driveway clearance issues and the width will handle the wider 275s with a little more stability. I found a great deal on the Speedlines, and don't want to miss out on that.

 

Don't have a 275 photo, but here's a 265/35/18 PSS on an OEM 18x10.5 Z06 wheel:



It's a bit of a stretch but not too terrible.

 

Thanks for the pic Troy. Do you find the rim protector to remain effective?

 

I can't say that I ever actually tested it to be honest, but I doubt it would be very effective. I just try to stay far away from curbs and tilt the right side mirror down when parking to be sure I'm nowhere near it (I've only actually had occasion to do this maybe twice since I've owned the car - it's extremely rare that I ever have to parallel park any vehicle).

 

My car had 285/35/18s all the way around when I bought it in May, and replaced all 4 with the same size later in the summer. Most of the time it doesn't seem to be an issue. However I did have a problem once on a freeway on-ramp where the TC was wanting to kick in when it shouldn't have. Also I have found it is 2-for-2 activating AH momentarily at 110 mph at WOT. It nudges the car to the right as if you just hit a strong cross-wind gust. The last time after it happened I turned around, turned AH/TC off, ran the car up to 120 WOT - no problems. I'm thinking 295/35/18s in the rear ...

 

THAT must be a little unnerving at 110 mph! The 295/35/18 will give you about a .5 inch difference. This is the minimum required for most C5's to be happy. Stock is closer to 1 inch.

 

It was somewhat unnerving. The first time it happened was the first time I had hooked up my G-Tech in the car and was looking for its 1/4 mile time and speed. I decided to give it a go on New Years Day, figuring about all of the cops had been on duty the night before and were now at home getting a well deserved break.

It was a clear day, temp around 40, but had been below freezing the night before. I wondered if I might have hit a small patch of ice but the road seemed dry and ice free. I lifted off of the throttle shortly after feeling the quick pull to the right. G-Tech showed me decelerating at the end of the 1/4 mile at 109. HPTuners scan showed a negative voltage spike just before I lifted off of the throttle making me wonder if that was due to Active Handling activating. I had not looked at the cluster at the time - my attention was fully on the road.

So I decided to see if this was repeatable and sure enough it was. Right around 110 again, although this time I didn't start from a dead stop but got on it from a roll around 50 or so. Same stretch of road, although may have been a 1/4 mile or so farther down the road. This time I was expecting it and looked down at the cluster and sure enough the Active Handling message popped up on the cluster.

 

Equal diameters will usually be accepted from a traction control standpoint. I can't say for sure since I only had one car with two different EBCMs installed. Neither one had any problems running 25.3 in diameter tires front and rear. Speeds were as high as 150 with no issues.

AH doesn't activate based on wheel speeds so equal diameter tires will not cause it to activate any different than if they are stock diameters. AH is activated by the EBCM comparing your steering input, the yaw rate of the car and the lateral Gs being pulled. When the EBCM isn't turning properly to meet your steering input it will decide to apply one brake to change the yaw rate. That is when wheel speed could affect AH since the EBCM only knows the stock calibration and will apply the brake based on what it thinks it knows.

If somebody is getting an AH activation while driving straight down the road the problem isn't due to the tire diameter. It is due to a steering, yaw rate or lateral G sensor issue.

Bill

 

What you are saying sounds very logical and ordinarily I would think it to be spot on but something seems to be consistently triggering AH at 110 going perfectly straight. Either that or by coincidence I've experienced side wind gusts each of the two times I've hit 110 with AH on and didn't experience side wind gust the one time I've hit 110 with AH off (which was within 5 minutes of the last AH on going opposite direction). Seems quite strange to me and that motivated me to post this to see if anyone else had experienced something similar.

Car is an auto with the 3:15 rear. 2-3 shift transient is settled out by 110. Just steady state straight-line WOT acceleration when this is happening. Car's been dynoed at 383 rwhp - I don't believe I'm loosing traction at 110. (Probably doing better than 383 in the cold weather versus July dyno day but not that much better.)

 

AH isnt triggered by wheel speed but i am fairly sure traction control is. If comp mode fixes the issue then its very possibly traction control not AH. In which case its possibly an issue with tire size. is it nudging the car or possibly jsut firing the rear brakes and deceling the car. at 110 i imagine rear brakes could be sketchy directionally?

 

It is definitely nudging the car to the right. When I looked at the cluster the last time it showed AH being activated, not TC.

 

I want to point something out to the folks that are have their car being "nudged" to one side or the other and blaming AH/TC. That nudging you feel is a "classic" symptom of the Steering Wheel Position Sensor starting to go bad (intermittent). It may not be your tire sizes setting off the AH/TC.

Just my $0.02 YMMV

 

Thanks for the info. Still curious though as to why I'm only seeing this at 110...

 

The "technology" in the steering wheel position sensor is the same brass contact sliding over a rheostat wheel that you find in a slot car. It may be that at 110 MPH the road vibration is able to cause the contact momentarily bounce off of that rheostat wheel. That can cause the AH/TC to engage.

Just a guess though.

 

it's not even on the same planet. the 01+ cars have a completely different system

everything was redesigned and improved

like most of the rest of the car 2001 marked the biggest change of the production.

and another reason why 97-00 is so much less desirable

 

If the SWPS is gong bad then he can blame AH. It is one of the 3 inputs to AH.