supa_89

I am looking to change my 17" for some 18" aftermarket wheels. I see everyone upgrading to 19's and 20's but thats not me. I was told if I wanted a smoother ride I should get a different size tire so instead of 225/45/17 on my IS 250AWD I should get 225/50/17 or 215/55/17. My question is, Can I fit 215/50/18 or 215/55/18 on my IS 250AWD without touching or rubbing?

Please Advise me...

FiveOhNine

I think tires that tall would look off on the IS, regardless of wheel diameter. Higher profile tires do tend to give you a bit better ride, but they sacrifice performance. Even if you aren't into performance, I would think twice about compromising your ability to avoid obstacles. Your steering response, turn-in and a number of other aspects will suffer.

Is your standard setup that bad?

What tire pressures are you using?

Namir

larger sidewalls won't necessarily affect performance, Nascar Indy Forumla 1 all have considerably larger sidewalls than road cars.
They will reduce road noise and give you a slightly smoother ride.
I do agree with 509 that it would look quite weird on an IS. rather than looking for tall tires you can look for ones that are less aggressive tread patterns/compounds. Tirerack gives reviews on road and noise comfort

supa_89

Thanks guys really appreciate the feedback, but honestly my concern is just about the ride, I dont care how it looks and am not one to be speeding thats why I bought the 250, so would I be able to fit 215/50/18 on my IS 250AWD without touching or rubbing?

FiveOhNine

Ok, let me rephrase:

Tire A and Tire B, both same composition, weight, and indistinguishable apart from the difference in profile.

The higher profile tire will decrease performance in cornering and acceleration due to decrease in the lateral and torsional rigidity respectively.

Edit: My guess is that high performance racing tires, as in those you mentioned are set up so as to decrease rotational diameter under high torsional rigidity situations (i.e. rapid acceleration) which 'spreads out' the rubber horizontally to increase the contact patch.

BounceNY

iTrader: (9)

with the tire sizes u posted, the odometer will be affected. Check out some online tire size calculators which will help u decide on the correct size for the car. (1010 tire website has good calculators).

Bichon

If your main concern is ride quality, why are you changing to an 18" wheel?

is4fsr

The 215/50/18 should not be a problem as long as you have the correct offset. But if you want to improve ride quality keep the 17" and go for a larger sidewall but it may affect your speedo. you can have your speedo recalibrated then. With regards to going to 18" you will end up w/ smaller sidewall to maintain OD. Smaller sidewall means less tire play thus stiffer = bad ride quality.

with your current set up 225/45/17, your tire sidewall is 4 in, OD 25 in
with 215/50/18, the sidewall will be 4.25 in, OD 26.5 in
so w/ bigger OD you have to recalibrate your speedo.
if you don't mind having your speedo recalibrated and also improve the ride quality, keep the 17" and go for larger sidewall.
current set up 225/45/17 sidewall = 3.99, OD = 24.97
comparison 215/55/17 sidewall = 4.66, OD = 26.31
215/50/18 sidewall = 4.23, OD = 26.46
215/55/17 and 215/50/18 almost the same OD but look at the side wall
4.66 in vs 4.23 in

lobuxracer

iTrader: (2)

1. Your speedo cannot be recalibrated. It isn't possible without a software change in the skid control computer or an intercept device in the speed signal generated by the skid control computer. However, this also affect the ECM's decisions about shift points, so it may have seriously painful unintended consequences. If you change to anything you've listed, you will be going faster than indicated and showing less mileage than actually traveled.

2. If you want better ride quality by adding sidewall, stick with the 17s and go narrower on the stock rims. 205/50/17 would add sidewall but not affect your speedometer/odometer.

3. Going to 18" wheels makes everything worse, not better.

supa_89

Thanks alot guys..definitely learnt something here..

is4fsr

I did not know our ISs speedo can not be recalibrated. Thank for the info, Lobux.