measurement of a 35" mtr

[BLU-125]

Actually, Matt, my point is that the diameter (height) is fixed by substantial steel, and other belts which are under the tread of your tyres. If the tread belts were elastic, the the diameter could change, but normally steel, kevlar, even rayon aren't going to stretch to allow a diameter change to take place. If they do, you should remove the tyre immediately from the vehicle, as lives are at stake!

The reason that a range of rim widths are given for a given tyre size is that anything outside the given range may cause a bead angle that may make the containment of air to be compromised!

[sir_camel]

When you put a wide tyre on a narrow rim the tyres 'crown' though dont they? As in the centre is raised a bit (ie bigger) leading to greater diameter. So you put the same tyre on a wide rim and doesnt the opposite effect of 'crowning' happen? Thus creating a slightly smaller diameter. We are talking at road preasure here.

[Magnus_yj]

Originally Posted by blu125

Actually, Matt, my point is that the diameter (height) is fixed by substantial steel, and other belts which are under the tread of your tyres. If the tread belts were elastic, the the diameter could change, but normally steel, kevlar, even rayon aren't going to stretch to allow a diameter change to take place. If they do, you should remove the tyre immediately from the vehicle, as lives are at stake!

So by bringing the beads closer together (narrower rim), it won't change how the tread contacts the pavement? Because, like you said, the belts won't stretch.
I believe that if you bring the beads in, you'll pull up on those sidewalls and hence the outer part of your tread will be higher than the center. Afterall, the sidewalls aren't hinged where they meet the tread. This would be particularly apparent if you're comparing at the same PSI. I'm not talking about a 1" or more difference in height based on rim width, just a slight difference......maybe a few tenths.
My tires would seem to be a pretty good example, with a 10" wide rim and a 33x12.5" GY MT/R. They're speced to 32.4" diameter, and mine were only 32" diameter new..........and after 2 years, no safety issues to report.

[Magnus_yj]

Originally Posted by sir_camel

When you put a wide tyre on a narrow rim the tyres 'crown' though dont they? As in the centre is raised a bit (ie bigger) leading to greater diameter. So you put the same tyre on a wide rim and doesnt the opposite effect of 'crowning' happen? Thus creating a slightly smaller diameter. We are talking at road preasure here.

I didn't read your post before I did mine....

We basically said the same thing.

[BLU-125]

Tyre Rack are a major tyre retailer in the US. The following link is a good place to learn to understand tyre descriptions.

http://www.tirerack.com/tires/tiretech/tirespecskey.jsp

Rim Width Range

Because tires have flexible sidewalls, a single tire size will fit on a variety of rim widths. A tire's rim width range identifies the narrowest to the widest rim widths that the tire is designed to fit. The width of the rim will influence the width of the tire. A tire mounted on a narrow rim would be "narrower" than if the same size tire was mounted on a wide rim. NOTE: Because the overall diameter of a steel belted radial is determined by the steel belts, there is little, if any, change to the overall diameter of the tire due to differences in rim width.