kasarap

iTrader: (1)

I have an AWD IS350 and i decided to replace the rear tires with 255/40r18 instead of 255/35r18. I really wanted taller tires to protect my rims because i live the NE and potholes are everywhere.
Once installed i got the "Check AWD System" message. I know they are about an inch taller than the fronts but i didnt think it would be that big of an issue other than the speedo being inaccurate.

Should i replace the front tires with 225/45r18? I know the speedo will be wrong but the tire heights will be the same again. Would i run into the CEL message again?

arentz07

Paging @ShrinkDoc

I believe they have the same setup with taller sidewalls. Ideally you'd want the tire diameter F/R to be as close to identical as possible.

Maxxxx

An inch in difference is really a lot for an AWD system...(Think of tire manufacturers recommending replacing all 4 tires if the tread difference is greater than 4/32"), and it may damage the system in a long run. If you don't mind the speedo inaccuracy...I would recommend replacing the front tires with a taller sidewall as well....(Pothole usually gets the front tires anyways. I popped 2 front tires in a year here at NYC...back tires are totally fine, then I ended up replacing all 4 because the tread life is bad for the original tires).

VisualEcho

Yes, immediately. You're basically confusing your AWD system. As mentioned before, you should shoot for the exact same OD front and rear. Stock is .1" taller in the front than the rear, but you get the idea.

kasarap

iTrader: (1)

Just ordered 225/45r18 hopefully the .1" difference in stock tires front to back doesn't make a difference.

TonyN

iTrader: (1)

ShrinkDoc

Arentz is correct!! I think you overtaxed your AWD system, and over time you will likely destroy the transfer case, if not also do damage to your tranny. I ran with this setup:

• 255/45/18 (fronts
• 225/50/18 (rears)

It works perfectly. For now, I wouldn't drive over a few miles on your car. There are certain tolerances that the transfer case can work with; however, if you lock up your AWD to drive in the snow or in a slippery area, my suspicion is that you will damage the AWD system to the tune of $2000-3500. I recommend that you make the change ASAP (yesterday) to avoid severe damage to your drivetrain.

arentz07

This might be obvious, but thought I would mention that I think you accidentally swapped the front and rear sizes, lol. 225-width is typically the size on the front, 255's in the rear.

ShrinkDoc

Oops, yes, got them mixed up. But yes, the 255's are on the rear and 225's on the front.

BTW, OP, you cannot get a taller tire on either the front and rear w/o rubbing.