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Discussion Starter #1
In all of the inch to metric tire sizing charts I can find it shows a 90/90 to be the equivalent to a 2.75/3.00 tire. BUT, the first 90 in 90/90 is supposed to be the width in millimeters, and the second the aspect ratio. Well, to get inches, divide millimeters by 25.4 so a 90/90 should be 90 divided by 25.4, or 3.54 inches. How in the world does this even come close to a 2.75/3.00 size? A 3.00 inch tire in my thinking should be 76.2 millimeters. What gives?
 

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We live in an imperfect world. Throw in the wide variation in actual widths of tires branded the same size from different manufacturers, and it's a crap shoot.
 

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Discussion Starter #4
Brent, that figure of 3.3 would be the height not the width. In a 90/90 tire the first 90 is width, the second 90 is height as a percentage of width.
 

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If true to size, a 90/90 tire is 90mm wide with an 81mm sidewall height. That equates to approximately 3.54 inches wide with a 3.18 inch sidewall height. Inch-sized tires are 100% aspect ratio, so a 3.5" wide tire has a 3.5" sidewall height.
 

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I can't answer your question, but on another bike, I've has both a 90/90-19 Dunlop and a 3.50-19 Avon Speedmaster and the widths were practically identical at 3.5". I also had a 3.25-19 Continental on the same bike and it was closer to 3.75" wide - almost rubbed the fender brackets.

If you have a specific tire size/brand in mind, start a new thread and ask if anyone with your model bike has used one and if there were any issues (after you've done a search on the subject).
 

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I can't answer your question, but on another bike, I've has both a 90/90-19 Dunlop and a 3.50-19 Avon Speedmaster and the widths were practically identical at 3.5". I also had a 3.25-19 Continental on the same bike and it was closer to 3.75" wide - almost rubbed the fender brackets.

If you have a specific tire size/brand in mind, start a new thread and ask if anyone with your model bike has used one and if there were any issues (after you've done a search on the subject).
Well now I'm totally confused.
 

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Well now I'm totally confused.
Brent, the bottom line is, the width printed on the sidewall of a tire is basically an approximation of how wide a tire really is. Depending on the company making the tires and the specific model of tire, the width of any given tire size can (and will) vary. It would be nice if all 3.25 tires were really 3.25 inches wide (or all 90/90 tires were really 90mm wide), but in reality, they aren't.
 

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Yeah, I bought a matching pair of tires for my CL350. The rear tire, a 3.50-18, measured 3.5" wide. The front tire, a 3.25-19, measured 4" wide. I sent the front one back and exchanged it for a different style, and it was true to size. All from the same manufacturer...
 
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