Need some Tire/Wheel advice for Plus sizing

[martinelles]

Ok, so I have the stock 17 inch wheels that came with 235/45R17 conti’s on my 2012 Sport. I would like to upgrade to the 18 inch polished interlagos (super awesome) and increase the sidewall height to get a bit more rubber for a smoother ride. Now I know that will change the overall circumference of the tire, but on the MFD there is a setting to adjust/calibrate the car for "winter" tires. Keeping that the vehicle actually runs about 3mph slower than indicated (tested with two different gps units and at various speeds), If I were to put the new wheel/tire combination on (say 235/55R18) that would put the actual indicated speed roughly 8 mph too slow (by calculation). Add that to the original 3mph deficit that makes roughly 5 mph too fast (actual speed) which the "winter tire" adjustment can correct. Or am I missing something?

[snobrdrdan]

Do not get 235/55/18....that'll look ridiculous

If you want a little more sidewall....just go to the next size...235/45/18

[martinelles]

Do not get 235/55/18....that'll look ridiculous

If you want a little more sidewall....just go to the next size...235/45/18

I would love to but, the tire i want to get does not come in that size! and i dont know if i can correct the speed ireqularities with a 45 aspect tire on 18s

[old guy2]

I really would not recommend doing that. The 235/55/18 would be almost 3" larger in diameter than the OEM optional size of 235/40/18. My guess is that you would have rubbing somewhere. Either on the suspension components, inner fender well or both.

[doctrsnoop]

Just stick with the 235 40 18. Don't worry about the speedometer. The ride is fine if you choose the right tire. Don't make your car look ridiculous for the sake of an accurate speedo.

[lipprandt35]

This should help ya.

http://www.1010tires.com/tiresizecal...cde-gen-by-svr

[snobrdrdan]

I would love to but, the tire i want to get does not come in that size! and i dont know if i can correct the speed ireqularities with a 45 aspect tire on 18s

And going with a larger tire is the better idea?
3.5% vs 11% change

That's the closest you're going to get (in a 235 tire). If you go 245/40/18...that's even worse.

Regardless...going to a bigger tire will only make the speedometer read slower...it's not gonna hurt anything.
If you were downsizing a lot...okay, that would be a problem....you'd be accumulating more miles than you're actually driving.
Bigger tire will accumulate less miles on the odometer though, and set the speedo for 75 on the highway....you won't get busted for speeding, lol

235/40/18 or 235/45/18 is gonna be your best bet.
Either that or change your tire selection

[martinelles]

Thanks guys for all the info. Its precisely what i was looking for. I'll just stick with the 245 40 18's