OneLargeToe

I'm real close to buying some new rims for my 08 GT. My current set is the stock 17" wheels with 235/50 17 tires.

I'm pretty certain I'll be going with 18x8.5 wheels. Now, I know from the pinned article in this forum that I could go as wide as 255/45 tires and this is the size that TireRack recommends...but I am wondering if it's the ideal size for 8.5" rims?

Looking up a tire diameter equation (link below for reference), I'm figuring my current set up comes to 26.25". The equation suggests that for an 18x8.5 wheel the ideal tire size would actualy be 245/45, which results in 26.68" vs 27.04" if I went with the 255s.

So I'm wondering why is TireRack recommending 255 tires when 245s seem to be the better fit?

Lastly, I'll be using my existing TPMS sensors and have them transferred to the new wheels. I realize I'll need new bands, but AmericanMuscle is also suggesting the purchase of a calibration tool. Is this still necessary even though the sensors are being re-used? I am assuming the tool is only needed for brand new sensors.

Thanks.

http://pepboysfleet.com/car_care_cor..._tire_diameter

Jazzer The Cat

So long as particular tire size is approved fit for a wheel width, "ideal" is really pretty subjective.

The needs of the driver come into play at this point and is my question to you. A 255 is gonna offer a bit better rim protection from curbs and deep pot-holes, where a 245 is gonna offer a bit better turn-in response (all else being equal). A 255 will fill the wheel well a bit more, as well as raise the car about 1/4" higher off the ground. Not a big deal, by any stretch, but just something to consider. Going larger/smaller diameter tire than OEM, will require a hand-held tuner to calibrate the speedo/ODO for accuracy, but would barely be noticeable between the sizes mentioned here. The ODO will be inaccurate over time and can be substantial if not calibrated after a lot of miles driven.

I cannot give you any info on the calibration tool, so hopefully Luke or another will chime in with some answers for you.

Jazzer

OneLargeToe

Thanks, Jazzer.

I've heard of Ford OEM 18x8.5" wheels coming stock with 235/50/18s. So I thought that 255s may be too wide. But, from your post, it sounds like they might be the better option after all.

Stoenr

Pep boys, there's the problem with the tire diameter tool, LOL


Ok
OE 16" tire 215/65/16 27.0"
OE 17" Tire 235/55/17 27.0"
OE 18" Tire 235/50/18 27.2"
Current Tire 255/50/17 27.0"

Recommended 255/45/18 27.05" (Mich Pilot Sport) Brands will vary

245/45/18 26.65" (Mich Pilot Sport) Brands will vary

All said and done, 255/45/18 Is the way to go.


255/45/18 on Ford 8.5" Wheel