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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



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.


235 mm

Optimal for sedate sedan comfort where sporty or emergency driving is not expected. All season tires.


206 mm

Sporty street use with some comfort retained


183 mm

Emphasis on street performance not comfort.


165 mm

Near race, my stock 78 Trans/Am.


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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