Matching Tires And Wheels:

[LennyLexus]

Full article can be read here

Summary:

Widest tyre for rim width: Best ride comfort, worst grip

Narrowest tyre for rim width: Best Grip, worst ride comfort

It seems this is formula for working out the best tire WIDTH for the Yokohomas recommended setting for performance handling and good ride comfort, this 90% of tread width should cover the rim.

Tyre Width (e.g 7.5)

x 100/90

x 25.4

Then round up or down to the nearest five.

e.g for my TTE Chicanes it should be

7.50 x100/90=8.33 --> x 25.4 = 212 round to 215.

For the profile, a tyre calc can be used.

Input the originals (IS Mk1 215/45 R 17) and your new ones.

Stock Tire - 215/45R17

Tire 1 - 225/40R18 (My Current Setup, experiencing a bit of rubbing on the front inner arches at full lock, with 50ET and a drop of 35mm

Speedometer Difference: 1.905% too slow

Diameter Difference: 1.88%

Tire 2 - 215/40R18 (Ideal speed up for keeping the speedo correct, but i may still experience rubbing)

Speedometer Difference: 0.643% too slow

Diameter Difference: 0.65%

Tire 3 - 215/35R18 (would look brilliant, and should most likely stop my inner arch rubbing, but would put the speedo and odo out. It should recover itsself tho as I have been understating my mileage for 2/3 years. The difference is minute 360 miles a over over stated on 12k at 3% too fast.)

2.887% too fast

Diameter Difference: 2.81% (smaller)

Hope this is of some help to people when deciding on new tyres, and if any information is incorrect please do say and leave general comments. I bought my last set of tyres on Lexus recommendations (i.e OEM styling kit tyres) and under the idea the widest rubber available is the best for grip, it seems the opposite is true.