Wider inner rim width, lower tire height?

[cyan]

Is the inner rim width (for clinchers) and mounted tire height inversely related? So the same tire mounted on a rim with narrower inner width will be taller than on a rim with wider width? Or is the difference negligible? Also does the outer width play any role here?

And does the same principle apply to tubular as well where there is only the outer width?

[yinzerniner]

Originally Posted by cyan

Is the inner rim width (for clinchers) and mounted tire height inversely related? So the same tire mounted on a rim with narrower inner width will be taller than on a rim with wider width? Or is the difference negligible? Also does the outer width play any role here?

And does the same principle apply to tubular as well where there is only the outer width?

Don't know about tubbies, but with clinchers the tire height also increases when the inner width increases. How much is tire and rim dependent, and he height increase only increases up to a point past safe installation, but see post here for clarification:
https://www.slowtwitch.com/Products/...view_4056.html
http://forums.mtbr.com/wheels-tires/...th-756818.html

[Davist]

yes, you're adding to the circumference, so width and height grow. I just got 28mm (outside) rims and my Conti GP4kSii 28c measure 34mm wide by my eyeballs.. wow! decreased pressure to about 75 for my 190lb carcass, but what a ride!

[weiwentg]

Originally Posted by Davist

yes, you're adding to the circumference, so width and height grow. I just got 28mm (outside) rims and my Conti GP4kSii 28c measure 34mm wide by my eyeballs.. wow! decreased pressure to about 75 for my 190lb carcass, but what a ride!

I don't mean to be that guy, but is this possible? If we are talking about the same tire, e.g. a 28c Conti GP4KS2, mounted on a 18mm versus a 20mm internal diameter rim, then the total arc length (or whatever it's called) of the tire is fixed. You're adding 2mm to the circumference because of the rim, but the tire shouldn't stretch. I don't see how it is that the same tire would be higher. Is the Hed diagram correct?

[muz]

Originally Posted by weiwentg

I don't mean to be that guy, but is this possible? If we are talking about the same tire, e.g. a 28c Conti GP4KS2, mounted on a 18mm versus a 20mm internal diameter rim, then the total arc length (or whatever it's called) of the tire is fixed. You're adding 2mm to the circumference because of the rim, but the tire shouldn't stretch. I don't see how it is that the same tire would be higher. Is the Hed diagram correct?

I did the following thought experiment: consider the case where the width is zero, causing the tire to make a full circle (in cross section). Also consider the case where the rim is so wide that the profile is a half circle. The diameter of the first circle is the radius of the second circle (they have the same arc length). Therefore, the height is the same.

Based on this reasoning, I would guess that the effective tire height is largely unchanged with the rim width.

[Black Dog]

Originally Posted by muz

I did the following thought experiment: consider the case where the width is zero, causing the tire to make a full circle (in cross section). Also consider the case where the rim is so wide that the profile is a half circle. The diameter of the first circle is the radius of the second circle (they have the same arc length). Therefore, the height is the same.

Based on this reasoning, I would guess that the effective tire height is largely unchanged with the rim width.

Nope. Lean a stick against a wall at any angle. Now move the base of the stick towards the wall and watch the top of the stick move upwards along the wall. The bottom half of the side walls of the tire are like the stick. On narrow rim they are angled towards the rim. As you widen the rim the side walls become more vertical, this increasing the hight of the tire. If you keep increasing the width past the point of the sidewalls being vertical they will start to angle away from the rim and and the tire hight drops.

[Davist]

Originally Posted by Black Dog

Nope. Lean a stick against a wall at any angle. Now move the base of the stick towards the wall and watch the top of the stick move upwards along the wall. The bottom half of the side walls of the tire are like the stick. On narrow rim they are angled towards the rim. As you widen the rim the side walls become more vertical, this increasing the hight of the tire. If you keep increasing the width past the point of the sidewalls being vertical they will start to angle away from the rim and and the tire hight drops.

This makes sense, perhaps it's only width.. I'd say that the beads stretch as well, we've all seen this, and it's not a matter of width it's a larger circumference, so not entirely impossible that the height grows

[muz]

No matter what, something is wrong with the HED drawing. The cross section length of a tire should be constant, no matter the rim width, unlike in that picture.

[yinzerniner]

Originally Posted by muz

No matter what, something is wrong with the HED drawing. The cross section length of a tire should be constant, no matter the rim width, unlike in that picture.

Did you look at the picture clearly? They're showing two different tires on three different inner width rims. The "length," aka measurement of the tire when laid flat, of the GP4000s stay constant no matter what the rim width, but the shape differs on different rims.



As you can see white, light blue and red are 25mm, and the width gets wider as the rim does, but the height actually decreases from the 17mm to 20mm ID rims.

Grey, dark blue and maroon is the 23mm, and the shape measurements look to alter in a similar manner with the increasing rim sizes.

The answer to the OP's questions is... it depends on the tire and rim. But generally going from skinny to wider adds width and height, but the height figure goes down after a certain point.

[ultraman6970]

Cyan I use tubulars and IME wider rim did not change the height of the tubular, I havent measure it but what happenes in tubulars is that the tubbie will sit lower depending on the rim profile, im talking about where the tubular sits, tubular sits deeper the tubular height changes. So pretty much depends a lot of the rim and the tubular combination.

Some tubulars tend to be taller than other ones eventhought they are rated the same wide.

With clincher well.. that i do not know, but i have to believe what the manufacturers say.

[mhespenheide]

In any normal circumstance for bicycle tires, the rim width is less than the diameter that would come from a semi-circular arc of (clincher) tire. In that case, you're effectively adding to the circumference of the space enclosed by the tire, and the tire height will increase.

From practical experience, I've found the same thing. Going from a 12-14mm interior rim width to an 18-19mm interior rim width will increase the "height" of the tire. Seems to be 1-2mm increase in height for the tires I've checked.

[muz]

Originally Posted by yinzerniner

Did you look at the picture clearly? They're showing two different tires on three different inner width rims. The "length," aka measurement of the tire when laid flat, of the GP4000s stay constant no matter what the rim width, but the shape differs on different rims.



As you can see white, light blue and red are 25mm, and the width gets wider as the rim does, but the height actually decreases from the 17mm to 20mm ID rims.

Grey, dark blue and maroon is the 23mm, and the shape measurements look to alter in a similar manner with the increasing rim sizes.

Yes, but I still don't see it. White curve is 25mm on 13mm ID rim, and bright red is the same tire on 20mm ID. Bright red is the tallest, and white is in the shortest group. How is it possible that these two lengths are equal?

[bitpuddle]

Originally Posted by Davist

yes, you're adding to the circumference, so width and height grow. I just got 28mm (outside) rims and my Conti GP4kSii 28c measure 34mm wide by my eyeballs.. wow! decreased pressure to about 75 for my 190lb carcass, but what a ride!

I don’t think so. Wider rims change the shape of the tire, from elliptical to more round. The same tire gets a little shorter with wider rims.

[dddd]

Originally Posted by bitpuddle

I don’t think so. Wider rims change the shape of the tire, from elliptical to more round. The same tire gets a little shorter with wider rims.

I measured tire height on different rims about ten years ago, and the tire height definitely increased with increased rim width.
It challenged what I had read in a certain bike newsletter at the time, and which I thought needed some investigation.

[Black Dog]

Originally Posted by bitpuddle

I don’t think so. Wider rims change the shape of the tire, from elliptical to more round. The same tire gets a little shorter with wider rims.

Look at the diagrams above. Tires will get taller then shorter as rim width increases.