Ok guys so long story short, I picked up a set of tires for the front of my car from a buddy and he threw in a rear used pair basically for free that still has some meat on them.. so of course I accepted them!!

Now my issues comes in because my old rear set of Falken 452s (275-40-19) are done and I decided to replace them today with this used set of Potenza S-04 pole positions (285-30-19).. well on the way home when I throw it into 3rd gear my slip light comes on and slows my car down

I did some research and figured out that its because rears are 285-30 and above the diameter difference by +3.57% from original (aka spin faster) and thats where the issue is correct? So I'm wondering if anyone has found a way to "trick" or readjust the VDC computer to not give me the slip light all the time or if I will be stuck riding with traction control off until I replace the tires for some 285-35's?

Also I'm curious because the previous tires on the volks where 275-40's which according to the tire calculator are also above the 3% for proper VDC reads but I never had this issue then?? is it just because they were actually spinning slower so they wouldnt lead to this issue or what?

Thanks for the help!! Also to be complete I have 245-35-19's in the front currently and will be switching to 255-35-19's which are basically brand new

 

Turn the VDC off.

 

The 3% rule is basically a difference between front and rear tires sizes, not from OEM. The 285/30 will work great with the proper front tire, 265/30 would be the front you want.

 

Exactly what terrasmak said. However, if you already have the 255/35/19 fronts then you'll want to buy the 285/35/19 rear.

 

I ran 245/35 & 255/35 with a 285/35 without problems for years. Currently running a 265/30 w/ 305/30.

 

Yeah this is what I was thinking.. since I already got a set of basically brand new 255/35/19's for the front, the rears that are 285/30/19's only have about 50% treadlife.. so I guess for now my best bet is to just take em to a track/auto x day and run them with VDC off till they wear out.. or go drifting haha

but so to repeat this question again.. there is no way to readjust the way the VDC computer reads the tire spin speed so that I can just get it in the mean time to not give me the slip light all the time??

 

Yes... Turn it off.

Seriously though... No VDC cannot be adjusted. It takes reading from a yaw monitor mounted under your center column near your parking brake. TCS (which is integrated into your VDC) takes reading from your speed sensors on all four corners. When it detects one wheel spinning faster than another it activates your VDC for traction control. Only way to avoid all this is to turn VDC off.

 

well thanks for you input.. although I got it fixed and don't have the slip light coming on anymore and I can still keep VDC on.. So guess there might be other ways to avoid it then just giving up..

it may be magic but my assumption is that after a reset it just noticed that the difference between the front and new rear set are still within the 3% range it needed to be and poofffff the slip light was gone!!!

 

It's not from the OEM tire sizes individually, but rather it's based on the relationship of the OEM tires, right? My understanding is that with stock tires, the rear is 2.73% bigger than the front. This is the number that needs to be matched as closely as possible, and you have a window to go up 3% from the 2.73 number or down 3% from the 2.73 number. That's what i gathered from the sticky thread. Is my interpretation correct?

 

No. The 3% difference is from front to rear. It's not giving you a 3% margin from the stock difference. So you can't go up to a 5.73% difference or down to a -.27% difference. Make sense?

No matter what tire size you run in the front you need a taller tire in the rear UP TO 3% taller to avoid throwing off the computer.

 

I don't believe all this 3% non-sense. I ran a 245/35 and a 285/35, 19 w/o any problems with my VDC. I'm now on a 265/30 and 305/30-19 and no issues.

 

Either you're mistaken or the sticky thread needs to be revised. It suggests that you can have your front:rear difference anywhere in that -.27 to 5.73 range (in the post its simplified to just be 0%-6%).

Seems like you're saying the front to rear difference just has to be less than 3% and with a largerrear tire than front. I don't see how this can be true though as there are many setups that violate this and work fine, including my own
(255/35/19 and 285/35/19).

In my head I want to say the tolerance described in the sticky seems to make more sense

 

That doesn't disprove the 3% rule defined by the sticky thread. Neither of those setups violate the rule (They are both within the range of what the computer will tolerate).

 

Your right and thats why he didn't have any issues, although from my own experience I believe its just dependent on the diameter difference from the front and rear currently that need to be within the 3% range, which is why my current setup ended up working without issues

I don't know that the stock setup comes into play I believe in the sticky it was used more as a reference, but correct me if i'm wrong

 

You're right in that the only thing the computer cares about is the rear relative to the front. The purpose of the stock numbers coming into play is because that front/rear relationship can be thought of as the ideal ratio to keep the computer happy. The closer you can get your aftermarket ratio to match the stock ratio (2.73%), the less likely you are to have issues. The 3% rule comes from the fact that your aftermarket front/rear relationship can differ from stock (so it doesn't have to be exactly 2.73%), but can only go as high as 2.73 +3% or as low as 2.73 -3%.

Now I think it can be assumed that 3% is not an absolutely verified number since 2.73-3 puts you in the negative range (taller front tire). So it can be though of as more of a rough guideline. Your setup shouldn't approach the upper or lower end of that +/- 3 spectrum anyway, as you should ideally keep the front/rear relationship as close to the stock relationship as possible.

 

Fix everything by turning the damn nanny off!

 

having the option is always nice. Also ABS kinda also reads wheel speed and is programmed for the difference in tire height.

 

Even though you can ignore vds by turning it off or simply getting a model without vds, does it really make sense to run a tire setup (talking diameters here) with such a big deviation from the factory set up? Vds will tolerate a pretty big range of sizes, there's really no reason to have a setup outside of what it will allow, at least from a functional standpoint. Giant drag slicks would be the exception I guess.

 

ABS and TCS works off of the vehicles speed sensors. Therefore it's not tire height but circumference. VDC reads the speed sensor and a yaw module in your center console.

 

Tire diameter and tire circumference are linearly proportional to each other so regardless of what is actually being read by the sensor both work the exact same way for determining front:rear ratios (ie The front:rear diameter ratio is equal to the front:rear circumference ratio).