albertchun

I am thinking to change my stock tires into a larger one with smaller offsets. After using the tire calculator, the diameter of the tires are larger than before. Since I am gonna use different tire offsets of tires between front and rear, I afraid that the traction control will wrongly sense that the front tire is skiding and wrongly function if the front tire circumfrance will be smaller... Would that happen? Nobody from tireshop can answer me that..

al503

If I understand you correctly, I think it all depends on how much you're going to be off.

I think the most important thing is to keep the stock stagger (difference in front and rear (larger) tire circumference), which is about 1". That should keep the electronic nannies happy. If you do this, you should be able to go a little larger or a little smaller than stock without any ill effects.

The manufacturers always allow for a little bit of room either way as cars with staggered set-ups don't allow for front to rear rotations. I see a lot of set-ups with what I think are questionable tires sizes and the people aren't complaining of any ill-effects (that I've seen.)

Gernby

iTrader: (1)

The difference in tire diameter is smaller if you have the stock 17s vs the factory 18s, so you know that you can get at least that close. I plan to do the same when my front or rears wear out, since I think there is WAY too much stagger. If my rears wear out 1st, then I'm going to replace the 255/40-18s with 245/40-18s. If the fronts wear out 1st, then I'm going to replace the 225/40-18s with 235/40-18s. That said, I imagine that you could probably get away with the same exact diameter at all 4 corners without any problems.

Pittdawg

Are the wheels all the same width? If so, when my factory tires wear out I would love to replace them w/ all the same size tires so as to be able to rotate, anyone no definitively if this possible?

al503

front's are 8" wide and the rears are 8.5" wide. Offsets are different also.

While I agree that you may not have any issues going with the same diameter front and rear, I think it's always prudent to get somewhere close to stock specs if at all possible.

Gernby

iTrader: (1)

You can definitely use the same size wheels on the front and back, and the car's VDIM, TCS, and ABS probably wouldn't give you any problem with running the same size tires front and back. However, the car might not handle the way you want at the limit due to oversteer. This wouldn't be a problem for "normal" driving though.

Gernby

iTrader: (1)

More specifically, you could use 8.5x18" wheels with 35-40 mm offsets with 235/40-18 tires on front and back. I just don't know how good it would look or handle.

albertchun

guys, thanks for your informative answers. i think i will go for 225/40/18" for front and 245/40/18" for rear. it sounds to be the safest choice. what i really afraid is fender rubbing while wide turning so i would choose a narrower front tires. the stock tires in HK are 205/50/16" which sucks and look ugly (mine is IS250. 350 isn't available in HK). feel unsafe while making quick turns or driving at high speed. gotta change it anyway!

some reference from another IS owner is using 235/40/18" for front and 265/35/18"... strange combination... i don't hear him complaining anything though.