I ran the 275/35R18 front and 305/30R19 (PS2's) combo on the track last weekend and at speeds above 90-100 mph the DIC would flash AH and TC messages. Looks to me that the differences in tire daimater between this combo and stock is off enough to confuse the computer (I was running Comp mode). Did a quick search and it appears that people have mixed results with this combo.

I think that the 265/35R18 front and 305/30R19 rear combo is a bit closer to the stock setup. Can somebody back me up that the 265/305 combo will be ok in Comp mode? The TC/AH message would only come on under hard acceleration above 90-100 mph.

Thanks for any help.

Sean

 

I ran a 245/305 combo on a road course and drag strip and never had issues...that should be almost identical to the 275/305 combo as far as height.

I've also run 265/35/18 front with 305/30/19 rear with no issues

I've also run 245/40/18 front with 275/40/17 rear

Now I'm running 265/40/18 front with 345/30/19 rear with no issues


Maybe my car just likes me, lol, because I've done it all

 

Floyd, I was kinda hoping you would chime in. I know that you have tried many tire brands and size combos over the years.

Looking at the tire size calculator, going from stock fronts to 275/35 is 0.5% smaller diameter. From stock rear to 305/30 is 2.4% smaller. To me, that means that the computer thinks the rears are spinning about 2% faster than they should be for a given speed. That could put the total difference between front and rear outside the max allowed 3%... If I swap to 265/35 fronts it will be 1.6% smaller than stock, but a little closer in the overall setup with 305/30 rears. Ideally, haveing both the front and rear wheels grow/shrink in diameter by the exact same percentage would create no issues with AH or TC. Unfortunately, the real world doesn't work that way, so we have to choose a combo that is as close as possible.

In addition to that, I have been having other wheel speed/sensor issues the past couple weeks with both the stock wheels and track wheel setup. Engine drag control has been kicking in every once in a whilewith both stock wheels and track wheels - can't explain that one. Got the Service AH/TC/ABS message during a weekend drive with stock wheels and 3 times on the track this past weekend with the track wheels on. I think I have a loose connection somewhere or I'm slowly losing a wheel sensor. I think those problems are unrelated at this point, but you can never be sure.

 

Well like I said these are diameters stock and for what I've personally run...all up to or over 130mph

25.7 front and 26.8 rear stock
25.7 front and 25.6 rear 245/ 275/40/17 (drag radial)
25.7 front and 26.3 rear 245/ 265/40/18 (drag radial)
25.7 front and 26.2 rear 245/ 305/30/19
25.3 front and 26.2 rear 265/ 305/30/19
25.3 front and 27.1 rear 265/ 345/30/19 (current)

I've never found, regardless of percent difference, tire heights to be a problem, and I've gone about as extreme as you can go currently haev a shorter than stock front and taller than stock rear

 

So why am I having trouble then? I just put the stock tire sizes. Ack on and will be checking to see of the problem repeats. If so, maybe it's related to the other wheel speed troubles ihave been having. This morning I took all wheel sensor connections apart and added dielectric grease. Found the RF wire came loose from its hold down in the frond cradle and the RR emergency cable was rubbing the speed sensor from coming loose from the rear cradle. Both have been fixed, hopefully that was the issue...

I will also take the car down to Autozone to see if they can read any ABS codes that may be stored.

 

I read somewhere on here that the rears need to be taller than the fronts or the car thinks that the rears are spinning.

Floy does have one example listed where the front is just "slightly" taller.

 

Grand, I tend to agree with your thoughts. That's why I'm leaning towards 265's on the front as it will help. Time will tell I guess.