[335ai]

i am on 397 wheels and planning to change to 245/45/18. i also want to keep the speed as accurate to the speedo when on 225/45/18.

is it better on the 245/40 or 245/45 ?

http://www.agcoauto.com/content/plug...peed/calc.html

i tried 245/45 and it shows up as it being slower by about 3mph. but on 245/40, it is faster by 1mph

[alohasurftoad]

Originally Posted by 335ai

i am on 397 wheels and planning to change to 245/45/18. i also want to keep the speed as accurate to the speedo when on 225/45/18.

is it better on the 245/40 or 245/45 ?

i tried 245/45 and it shows up as it being slower by about 3mph. but on 245/40, it is faster by 1mph

split the difference with 235/45/18, 26.3" diameter. here's a thread with them on oem 18x8 400m, same spec as 397.

https://f30.bimmerpost.com/forums/sh...45%2F18&page=2

[Onizukachan]

Checking yours is even close now. mines about 3 mph fast compared to gps at 75 indicated on stock 225s and 400m, so having a tire that is 3 mph faster on the chart would actually make it right.

[kilogram]

Isn't there a speedo correction factor somewhere in the coding stuff? I switched to 245/45/18 square on mine and the speedo seems spot on, where my GPS had it 3mph fast on the OEM tires.

[johnung]

Originally Posted by 335ai

i am on 397 wheels and planning to change to 245/45/18. i also want to keep the speed as accurate to the speedo when on 225/45/18.

is it better on the 245/40 or 245/45 ?

http://www.agcoauto.com/content/plug...peed/calc.html

i tried 245/45 and it shows up as it being slower by about 3mph. but on 245/40, it is faster by 1mph

I don't suggest choosing tire sizes by speedometer readings. You know that BMW doesn't set speedometers accurately anyway. If you really want to know your exact speed then get a Uniden R7 which has a GPS speedometer on it. Most of the time it tells me that I'm actually going 1-2mph less than the BMW speedometer says that I am.

I've got Michelin Pilot Sport 4S in 245/40-18. The handling is incredible and they soak up rough roads and potholes much better then the old wagon wheel runflats.

If you want good handling and even more comfort then go with 245/45-18. The slightly higher sidewalls give the appearance that the car has been lowered since they take up more of the tire/fender gap.