Tyre height (frame clearance)

mpie

Short question:
Does putting the same tyre on a wider rim increase the tyre height?

Longer question:
I'm currently running 25mm GP4000s (80/90psi) on aging RS10s and have only just enough clearance to the downtube on my SuperSix. Looking at new wide rimmed wheel as a replacement, but concerned that above tyres on wider rim may reduce clearance to an unacceptable degree.

Opinions?

rafletcher

Short answer - no, the reverse.

arlowood

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19688992#p19688992]mpie[/url] wrote:

Short question:
Does putting the same tyre on a wider rim increase the tyre height?

Longer question:
I'm currently running 25mm GP4000s (80/90psi) on aging RS10s and have only just enough clearance to the downtube on my SuperSix. Looking at new wide rimmed wheel as a replacement, but concerned that above tyres on wider rim may reduce clearance to an unacceptable degree.

Opinions?

Short Question - Just have a think about it. The bead to bead circumference of your tyre is fixed so if you seat it in a narrow rim this will push the tyre contact point to a certain height above the rim defined by the width of the rim. If you seat the tyre on a wider rim this will effectively reduce the height of the contact point so you will gain more "breathing space" on your frame if it is already tight using the narrow rimmed wheels.

Longer Question:- refer to answer above

mpie

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19689217#p19689217]arlowood[/url] wrote:

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19688992#p19688992]mpie[/url] wrote:

Short question:
Does putting the same tyre on a wider rim increase the tyre height?

Longer question:
I'm currently running 25mm GP4000s (80/90psi) on aging RS10s and have only just enough clearance to the downtube on my SuperSix. Looking at new wide rimmed wheel as a replacement, but concerned that above tyres on wider rim may reduce clearance to an unacceptable degree.

Opinions?

Short Question - Just have a think about it. The bead to bead circumference of your tyre is fixed so if you seat it in a narrow rim this will push the tyre contact point to a certain height above the rim defined by the width of the rim. If you seat the tyre on a wider rim this will effectively reduce the height of the contact point so you will gain more "breathing space" on your frame if it is already tight using the narrow rimmed wheels.

Longer Question:- refer to answer above

Not that simple, at least in theory. Tyre height is a non-linear function of the bead width. If you imagine a variable bead width such that the tyre goes from a circle to a semicircle (extreme, I know), the tyre height initially increases to a max and the falls. Here are a couple of picture which show the effect...

http://www.google.co.uk/imgres?imgurl=http://www.slowtwitch.com/articles/images/3/86683-largest_1_SlowtwitchTire-Comparison_small.jpg&imgrefurl=http://road.cc/content/review/149583-continental-grand-prix-4000s-ii-28mm-tyres&h=548&w=620&tbnid=gWNeXraBw_qrRM:&docid=zE07BFO0iEwtsM&ei=_hbfVfvuNIrB0gS-mrjYCQ&tbm=isch&ved=0CCsQMygLMAtqFQoTCPvliaW1yccCFYqglAodPg0Omw

http://www.google.co.uk/imgres?imgurl=http://fcdn.roadbikereview.com/attachments/wheels-tires/305177d1428906077-19mm-vs-23mm-rims-659645d1323878159-tire-height-vs-rim-width-tireheights.jpg&imgrefurl=http://forums.roadbikereview.com/wheels-tires/19mm-vs-23mm-rims-327980-2.html&h=480&w=800&tbnid=uXuJBMraec6CaM:&docid=EVSYvKvhQcxixM&ei=_hbfVfvuNIrB0gS-mrjYCQ&tbm=isch&ved=0CC8QMygPMA9qFQoTCPvliaW1yccCFYqglAodPg0Omw

So it appears that the answer to my question is non-trivial (it depends on the size/type of the tyre and the precise bead spacing) - hence the search for some real practical evidence rather than theory/speculation. I really don't want to buy some nice new wheels just to find I have to go back to 23mm tyres!