Traction control and 245/40/18 tires
 

I had to get some unplanned (flat, emergency) tires the other day, and the store only had some 245/40/18 tires, and said they wouldn't be an issue. Anyway, they installed two in the rear and do an alignment...and now the traction control keeps activating at highway speeds?!?!?!? Do you guys think this is due to the tires being slightly shorter, or something else? All was working well before the new rear tires and alignment. :mad:

what size tires do you have in the front?

put both tire sizes into this website

http://1010tires.com/TireSizeCalculator.asp

it'll tell you how far off they are.

The fronts are 245/45/18. I know that they're "off" just trying to confirm that it's what's causing my traction control issue.

Yes, that will cause it. With the rears being a smaller diameter, and therefore making more revolutions per mile than the front, the Traction Control interprets this as wheelspin...

Just for curiosity sake, swap your wheels front to rear. What does the traction control think if the rears are moving slower than the front?

Bump to what Dave Mcdonold said.

But it also seems weird cause guys run staggerd tires and wheel setups and dont have any issues.

I wonder if the tire place you went to accidently uncliped a sensor or pinched a wire ( always a possibility)

Staggered is fine... it's the diameter of the wheels that can cause issue... not width. (My CCW setup is "staggered" with the rears being 2" wider than the front... but the diameter of the tires is correct.) If the overall diameter of the rear wheel/tire combination is too much shorter than that of the front, it will cause problems.

ya i mean staggerd tires not just rims, theres guys that run 255/45 in front and 275/40 in the rear.
Which is close but not exact.


and I see guys run 245/45 in front and 255-265/45 rear and they have no issues either..

i dont think our traction control is that sensitive unless his new tires are just wayyy off..

Remember though... the second number represents a percentage, not a MM measurement like the first. So a 255/45 front and 275/40 rear are only about a tenth of an inch difference in overall height, so it works.

Now, the difference in diameter between a 245/45/18 and a 245/40/18 is almost an inch. That makes a big difference in revolutions per mile. 780 per mile for the 245/45. like 810 for the 245/40. That's a lot of difference... and it will cause issues.

I don't know enough about the TCS to know what happens if the rears are larger than the fronts, but suspect it's like C5s... where it shouldn't cause issues, at least not as easily.

at 80mph your ~3mph off....dunno if thats enough to set off traction control.

Thanks guys. I kinda figured that the shorter tires had to be the issue.

I'm going to try that and see what happens.

^^

I'd check the sensor connections.

I got a flat about 10 days ago. I run 275/35's on all corners. My spare is an old 245/45. I've been running 3 and 1, and haven't had any issues.

I also ran 275/35 out back 245/45 up front for a few thousand miles when I got some spare rims.

Both of these combos looked retarded, but I never had any TC problems.

-Chris

im pretty sure it wi.ll fix the problem. the good news is that if the tire shop is a reputable business, they will have no problems ordering the tires you wanted in the first place and letting you pay the difference if there is one, since their "advice" was wrong on it not being an issue.:engarde:

Im gonna say the tire size is the issue. I'm not sure how sensitive the sensors are on these cars, but my old Audi hated any minute difference. Even different tire manufactures had different sizes. Like a 245/40 in a Bridgestone would be slightly different than a 245/40 in a Michelin. I always had to run the same tires on all 4 corners or it would cause problems.

I used to run 245/40/18 in front and 245/45/18 in the rear and had no issues. Reversing the tires may be the answer. If not, have your mechanic check the code to see which wheel is throwing it. Then check the hub sensor and wiring.

That would probably set off a ABS code or episode?