Tire Measurement when Changing Rim Width, Diameter, Offset or Tire Size

[JJ 911SC]

I'm going from 7.5" rims to 7" and wanted to know the impact on the tire measurement.

Came across this site, very useful; Custom rims, wheel tire packages for your ride - RIMSnTIRES.com

Enjoy

[Dublinoh]

Seems like it would be more useful for diameter changes, cool site

[Bill Verburg]

Originally Posted by JJ 911SC

I'm going from 7.5" rims to 7" and wanted to know the impact on the tire measurement.

Came across this site, very useful; Custom rims, wheel tire packages for your ride - RIMSnTIRES.com

Enjoy

a wider wheel will do two things to a tire
1) stretch the overall width by ~.2" per additional .5" of wheel width note that the tread width is not altered by a change in wheel width
2) reduce the unloaded overall diameter of the tire by ~ .1" per additional .5" of wheel width.

So for your change from a 7 to a 7.5" wheel w/ a nominal 205/50 x17 tire expect the following change. I chose a BS RE-11 tire as typical

base measurements for this tire are on a 6.5" wheel
section width = 8.4"
overall diameter = 25.1"
the tire is distorted into a 213/48 x17

this tire mounted on a 7" wheel can be expected to measure
section width = 8.6"
overall diameter = 25.0"
the tire is distorted into a 218/47 x17

on a 7.5" wheel
section width = 8.8"
overall diameter = 24.9"
the tire is distorted into a 223/46 x17

[JJ 911SC]

Hi Bill

My second time typing this so hopefully...

I'm going the other way, 7.5" --> 7"

Before I found this one, I was on the Tire Rack site and understand the rule of thumb about a change of .2" in section width for every .5" in rim width change. They also mentioned 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.

So logically if the tire is squeeze in by .2", the displacement got to go somewhere but not in the overall diameter dimension due to the steel belts. Probably due to this small variation, the program in the link below does not record any significant changes.

So when everything is said an calculated, is this change OK without changing the tire. If not, which way in width/ratio should I go as the present set up is at the limit before rubbing (on full turn at low speed)?

Cheers

JJ

[Joe Bob]

Also depends on the tire.....a 205 can vary from brand to brand.

[JJ 911SC]

Originally Posted by Joe Bob

Also depends on the tire.....a 205 can vary from brand to brand.

And so does the Tire Pressure one use.

Unless Bill say no... I'm going with this set-up

I tough that the link can be useful. I played with just changing the Offset input to actually see the difference it makes.