Yes PhGit, it is random and that's the worse part. I turned off my VDC and now I'm rippin' through those turns without any kind of problems. Although this does temporarily satisfy me, I don't really want to be rollin' around with the VDC turned off in the long run because it does come in handy sometime when you really are slippin'.

I've had these rims for a while and even had them on my friend's G and he never ran into this problem when everything was brand new. However, this is the first time the rear tires have been changed since the rims have been bought and the front tires are still the same ones.

So what I'm saying is, when everything was new, I didn't have a problem, the fronts were 245 and the rears were 275 (a significant difference already). Do you really think the brand new rears now (back to 275) with some worn down 245's in the front could have created a big enough difference to cause the car to be confused and slip when it never did before the tire change?

 

The width of the tire isn't as important as height when it comes to confusing the VDC.

Stock sizes on an '04 coupe with 18's are 225/45-18 front, and 245/45-18 rear. At these sizes, the fronts do 777 revs per mile and rears do 756 revs per mile. That means that whenever you get new wheels and rims, your front/rear revs per mile have to be close to the 756/777 ratio (97.3%). If you're too far off, the VDC gets hopelessly confused because it thinks something is slipping.

You said you're running 245/35/19 and 275/35/19. The front is 783 revs/mile, the rear is 759 revs per mile. (759/783 = 96.9%, not too far out of spec, but these rev/mile numbers are sometimes way different for different brands of tires). Let's say the fronts are a bit worn in my hypothetical tires and have lost an 1/8" of rubber. Their rev/mile then increase to 789 rev/mile, which gives a ratio of 96.2%, still not that much out of spec.

Did you maybe get tires with very different grip characteristics, or from a different manufacturer?

 

Yeah, the rear tires are Hancooks and the fronts are Toyo Proxes. Thanks for that insightful and indepth analysis of the rev ratio's.

So are you saying that this could be enough of a difference to confuse the VDC?

 

I don't know if that's enough to confuse the VDC, I'm not familiar with its settings. Hopefully someone else can chime in. Look up the revs/mile on your toyos and hankooks to get real numbers, the difference could potentially be greater, I just computed it for hypothetical tires, but those revs/mile are affected by tire construction too.

Given that your car handles ok with the VDC off, it's clearly getting confused. The sensors are working properly, if they weren't, it would go into error mode, so I really don't know what's up.

 

If you have a friend with a G or someone who would be willing. It might help to put on another similarly size pair of like new front tires and give it a try. Or if you can change all four to a stock setup and try it. I have always been under the impression that it's best to replace all four tires instead of just two. I'm sure that you know that shuddering is the VDC kicking in....it obviously thinks that your slidding alot more that you do. Since with the VDC off your fine looks like the VDC is functionally normally.

 

Hi. I thought I'd chime in...I am having similar intermittent problems on my '03. On a few broad, fairly flat, sweeping right-hand entrance ramps I have encountered slipping and VDC engagement while moderately accelerating. (I was well below 50MPH when this happened). At other times, I can take sharper ramps at 40-45 with no problems.

Everything is stock. I have 6-month-old Michelin Pilot Sports on the rear, and 4-year-old Goodrich Super Sports (cheap cheap!..previous owner) on the front. The odd thing is that the fronts have tons of tread left, almost to the the point of making me suspect that the rubber has hardened and is not providing enough traction. There is not non-uniform wear that would suggest alignment or camber problems. They were on the car when I bought it in 2008, and they still have plenty of tread.

I am wondering if there are diagnostics that could be run on the VDC or wheel speed sensors, or if I should just replace these suspect tires?

 

Honestly, I turn the VDC off as normal operating procedure now. Hit an autocross event or something to get a sense of your cars abilities without VDC and you will come to realize it's actually safer with it OFF. I can rely on the car to do what I expect. Before, when I would leave the VDC on, I could not rely on anything because sometimes the rear would get all slipy on hard acceleration, sometimes on just moderate acceleration with a some turning in the mix. Now the only time VDC is on is if the roads are wet. It's made the driving experience MUCH better under all conditions (except wet).

 

I have 245's in front and 265's in the back on stock 18" wheels....... this set up works perfectly fine for me...... no abnormal slips

 

I have having severe issues on stock 19" wheels with stock tire sizes. I've since moved to 18" wheels with 255/40 front and 275/40 rear. That actually does better than the stock 19" did, but I still turn off VDC as a rule.