I just got this email from Michelin about their Commander 2 line, I bolded the most important part:

In regards to the email you sent stating:
---------------------------------------------------------------------
So the 200/55r17 tire is actually 219 mm? 8.66" = 219 mm.
That seems too wide to still be listed as a 200 series tire?
Mike
---------------------------------------------------------------------

Thank you for your interest in Michelin motorcycle tires, Mike.

Actually 8.66" (220 mm) is the overall width of the tire when in use.
When you are riding your motorcycle, the tires become a little bit wider and there is an increase in the width and diameter.

The mounted overall width of the Commander II 200/55R17, is 7.87" or 200 mm


We appreciate your business and thank you for choosing Michelin, Mike.

Am I crazy or do tires really expand by 10% of their width while in use?

 

Interesting. If anybody knows the answer to this, should be the the manufacturer R&D guys.

 

Sounds like some shenanigans. I've never heard of a tire getting wider at speed, only taller. Actually as speeds increase and the tire gets taller it gets narrower. Watch a top fuel car burnout for an exaggeration.

 

I am calling shenanigans too. The point of my call into Mich was to find out if this tire would be too wide for my rear fender once mounted, then they told me 219 mm, to which I replied that cannot be correct, but thats the info they had, 219 mm while in use....?

 

http://www.avonmoto.com/download/Tir...rConsumers.pdf

See section 4 on page 5 of this pdf from Avon. Actually the whole thing is worth a read but tire expansion is what has been asked... Hope this helps. I learned new stuff... tp

 

How on earth could you or anyone verify the validity of that statement??? Just think about it.

 

The air in the tire does heat up and expand. There will be an increase in dia. and width. But it is relative to the situation!
But basically the cold dimension of the tire is less then the hot. Air expands and it has to go somewhere. So unless you release the pressure it will change the dimensions. But the size increase from the manufactures specs. will vary depending on the starting pressure.

These days companies fill the tires with Nitrogen because it is less prone to expansion. Make for a more consistent tire, and ride.

So the amount of increase in size from expansion is dependent on many factors. Best you can get is a ball park idea of what that is, and that it does occur.
And really it's nothing that the "average joe" needs to be concerned with. If your tire clearance is that close?? Just making turns will make your tire rub. Because the tires leans and distorts as directional forces are applied.