Tire Width Primer

New 1/15/05

For a given size tire, (ex: 225/55 R16) the first number is tread width in mm. Divide that number by 25.4 to get tread width in inches. (ex: 225/25.4 ~ 8.85”.

Wider tires require wider rims. Tires that are too wide for the rim will shift over and the edge of the tire will lift, causing a sudden loss of traction. Point is you may never be able to use the small increase in grip of a 10mm wider tire, but that wider tire may give you abrupt breakaway in an emergency maneuver and get you killed.

This can be quantified by application. (for our 165 mm rims)

Rim/tread ratio	Tire width	Application
60%	275 mm	Perfect for trucks and SUVs in off road applications where ‘soft sidewalls’ are useful to adsorb rocky trails. Winter rims with snow tires. Use only with high profile, not low aspect tires.
70%	235 mm	Optimal for sedate sedan comfort where sporty or emergency driving is not expected. All season tires.
80%	206 mm	Sporty street use with some comfort retained
90%	183 mm	Emphasis on street performance not comfort.
100%	165 mm	Near race, my stock 78 Trans/Am.
110%	150 mm	Race use, no comfort.

You may think I am recommending narrower width tires for faster applications for a given rim width. I am not. I am recommending wider rims for sporty applications.

All of this neglects fitment issues and load ranges which are well covered on FAQ.

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