S to the K

I need to replace the rear tires on the stock 18's on my 350. Does anyone know how much of an impact going with a lower profile tire size of 255/35/18 tires will increase the miles I put on my car at faster pace versus going with the stock 255/40/18?

Is it that much of a difference?

I also have the F-Sport Springs. I imagine the gap will increase as well with a lower profile tire, correct?

Also, as F-Sport spring owners know, the front gap is much larger than the rear. Is there a recommended size that will fill it out some without rubbing? (something a bit meatier without looking too 4x4 ish)

Maybe 225/45/18? Is that okay and will that rub?

Any suggestions? I appreciate any feedback.

edgeucated

iTrader: (4)

you can google any tire calculator and put in the measurements. it'll tell you exactly how much. i use http://autorepair.about.com/gi/o.htm.../tirecalc.html

its a miata website, but a calculator is a calculator

lobuxracer

iTrader: (2)

^^Sort of. The skid control ECM takes the wheel speed input from all four wheels and averages them to produce speed. So the impact of one end of the car being a little off is going to be less than a simple calculator could figure.

S to the K

Do you think going with 255/35/18 will make a negligible difference in the rate of accruing mileage on my car versus going with stock 255/40/18?

lobuxracer

iTrader: (2)

Hard to say. The only way to know for sure is to test it. I did this with my Supra and found with the OEM sizes the odometer showed 98 miles for every 100 I traveled (using Interstate mile markers on a very long trip.)

S to the K

Thanks for the response. Is mileage calculated by the rear AND front tires, or just the rear?

Also, with stock 18's and Fsport springs, I want to fill out the larger front gap to even it out with the rear. I know it will look meatier. but do you think 225/45/18's would be okay instead of the stock 225/40/18?

With a larger diameter tire in the front, do you think it will offset changing the rear tires to a lower profile 255/35/18 as it pertains to mileage accumulation?

dappy

iTrader: (13)

You can use the tire calculator on 1010tires.com to determine the speedometer difference. I actuallly did the work for you below:



As you can see, the speedometer reading will be 4.0% faster than actual and your rolling diameter difference will 3.89%. It's recommended that you stay within 3%. Otherwise, you risk brake failure. I would recommend staying with the OEM 40 series profile tires for 18" wheels. Unless, you switch to 19s then 35 series would be more suitable.

S to the K

Thanks for the info. Looks like I'll stay with the stock sizes.

lobuxracer

iTrader: (2)

1010tires is assuming only the rear wheels are used for measuring speed. That's not the case with any 2IS. All four wheels are used, so the error will likely be smaller than what you see here.

Spagolli94

My 330 has 255/35/18 in the rear. This way, the profile looks the same as the front, which is 225/40/18. When I was shopping for the IS, I thought it looked odd that the back tire had a higher profile than the front. I'm not a fan of the ultra low profile look and the rim damage potential that goes with the territory. With the IS, I'd almost be inclined to leave the rear as-is, and up the front to 225/45/18. Then again, if that made the front profile look taller than the rear, that would look bad. I guess the goal should be to have an even profile. The sizes on my 330 certainly looked equal to the eye, even if they were technically off by a few mm.