Effect of Rim Width on Tyre Clearance

[madmacca]

I am considering an upgrade to my stock wheels.

I currently run 28mm Conti GP 4000's (which I love) on rims with a 15mm internal width. Frame clearances are tight, but workable - a couple of mm on the sides, and 3 mm at the top.

I was looking at Pro-lite's in particular. The Bracciano's have an internal width of 13mm, and I have seen comments in several places that this is too narrow for a 28mm tyre. The Bortola's have an internal width of 17mm - is this going to increase the width of the tyre and cause problems with already tight clearances? Or should I look at some alternatives wheels that retain the 15mm internal width?

[biker jk]

A 28mm Conti GP 4K on a 17C internal rim width will measure 31mm wide at 100psi.

http://www.bicyclerollingresistance.com ... i-23-25-28

[madmacca]

A 28mm Conti GP 4K on a 17C internal rim width will measure 31mm wide at 100psi.

http://www.bicyclerollingresistance.com ... i-23-25-28

Who the heck runs 28mm tyres at 100 psi?

[Nobody]

Who the heck runs 28mm tyres at 100 psi?

Heavy people. Tandems.

Don't go to 17mm inner rims if it's marginal at 15mm.

I use Durano 23mm tyres and have 17mm rims front and 19mm rear. That way I can move the tyre from front to back and it changes from about 24mm to 25mm.

[find_bruce]

One bit that people seem to miss is the combination of tyre & rim in creating the width.

Basic maths tells you that diameter= circumference/π If you increase the circumference by 2mm, the diameter will increase by 0.64 mm

Sure tyres are more complex shapes than simple circles, but you get the idea.

As biker jk says pressure also affects it

[panosk]

Here is a picture of how different tyres, inflated at different pressures, actually measure when mounted on different rims

[madmacca]

One bit that people seem to miss is the combination of tyre & rim in creating the width.

Basic maths tells you that diameter= circumference/π If you increase the circumference by 2mm, the diameter will increase by 0.64 mm

Sure tyres are more complex shapes than simple circles, but you get the idea.

As biker jk says pressure also affects it

Yeah, the basic maths had me concerned, but the more complex shape had me wondering, as I do have a little more height to play with than width.

[find_bruce]

Here is a picture of how different tyres, inflated at different pressures, actually measure when mounted on different rims

Excellent pic panosk - while I am younger than the introduction of the metric system, I still look at pressure in PSI 6 bar=87 psi, 7 bar=100 psi, 8 bar=116 psi.

Unless you are one of the aforementioned tandems, I would be using 6 bar as the benchmark. The pic demonstrates the wisdom of Nobody's advice not to go 17mm inner rims if it's marginal at 15mm - you are looking at ~1.5mm increase in width, which means your clearance is getting very marginal.

[madmacca]

Here is a picture of how different tyres, inflated at different pressures, actually measure when mounted on different rims

Thanks Panosk. That is good info and seems to answer my question (need to stick with 15mm internal width rims). Not relying so much on the absolute measuments (as GP 4000s have a reputation as running wider than the label), but more the relative shift with each increase in rim size.

Source?

[panosk]

Source?

https://silca.cc/blogs/journal/part-5-t ... rodynamics

I almost paid the price of my ignorance (or failure of those who promote wider rims to alert people about the changes in tyre width),
and my 25mm tyre on my 17mm rim rubbed on the seat stay of my bike on very tight turns.
Thankfully i noticed a noise and checked the bike and saw it has scratched the paint.

[elfoam]

My GP 4000s 28c (Tyre of Gods right now) Measures 28mm on a skinny rim and 31mm on a 21mm rim. That's at 60-70 psi Which is the most pressure I ever run them at, 45 psi on dirt/sand. Very few of my bikes can take a tyre that width which is unfortunate because riding that fast, that comfortably over any surface is revelationary.
.