# Thread: Tire height vs. rim width

1. If bike tires were belted circumferentially, then rim width would not affect the outside diameter. However, most tires (ok, the ones I have) have two belts 90 degrees to each other and 45 degrees to the equator. With this belting pattern, an individual patch of tire is "area conserving", but can stretch in one direction and shrink in another (e.g. an X that gets taller / skinnier, or shorter / fatter), or it can shear. So I think the overall outside diameter, and thus wheel height, can change.

Also, my slide rule is longer than yours.

2. Originally Posted by kapusta
The center strip of the tire is a certain length. Once inflated, the diameter (height) of the tire is that length / pi. Yes, tire pressure could stretch that length slightly, but that is a separate issue from rim width.

If two identical tires at identical pressure on rims of different width were to have different diameters (height), that would mean that some force is stretching the tire material along the center strip more in the taller one. I can't think of anything that would explain that, which is why I agree with what Derby is saying.

I think that the problem with the diagrams above is that they assume the cross section of the tire retains a perfect arc shape as you change the rim width. this would be true for a straight tube, but not for one in a ring like a tire.
(Edited, based on measurements, facts. See measured evidence: Tire height vs. rim width - Page 3)

This is long..... Maybe I should simply stand by my claim that by changing rim width, the tire's profile is changed, but the tire height does not change.... However, due to tire construction, not by geometry, there could be minimal height difference from structural casing tension changes, but in practice the height does not change when the rim width is changed.

Yes, without changing a rim width, a the tire circumference can stretch or shrink very slightly with higher or lower air pressure tension with the “bias-ply”, 45 degree to bead, crossing thread directional cloth in mountain tire casings.

I guess the question then becomes would a wider rim (up to a width the beads can't reach) reduce the spread of the thread spacing near the circumference and allow the tire to grow higher with the same air pressure?

The casing on either side of the tread center which is the line of circumference, is also limiting growth in height of this near tread center area.

I think the sidewall closer to the bead is relaxed in structural thread tension with a wider rim. So more structural thread tension is transferred towards the tread area. The area near the corner knobs then supports more of the resistance to the same air pressure, stretches and stands up the corner knobs taller.

1. Does the added tension taken by the corner knob area of the casing then relax thread tension along the tread center area of the casing? Would the center tread then shrink shorter in height? (Edit added: the answer is yes, see measured evidence: Tire height vs. rim width - Page 3)

2. Or the taller corner knob area of casing maintain center tread height? (Edit: Maybe, the measured difference is minimal, less than 0.0005 % smaller circumference with a wider rim).

Then the same air pressure could stretch the relaxed casing threads in the center tread area, and raise the center height as much as the edge knob height is raised. (Edit added: No, wrong, this does not happen using the same tire pressure with a wider rim. The fact is that a good quality mountain bike tire does not increase in height or circumference when going to a wider rim)

I suspect the more stretched edge knob cloth area profile angle does not raise in height much, and the center of the tread could not be raised in height further than the edge casing is raised. And visually we always see the tread become more square, the edge knobs are raised more than the center knobs.

Generally we lower tire pressures when going to a wider rim to maintain consistent tire suspension bump feel. And the lower pressure would negate any minimal tread center height stretch gained by relaxed center tread structural resistance to the air pressure.

Edit added: Measuring the same tire and rim with pressure dropped from 30psi to 20psi, may have shortened the rollout circumference, by 0.5mm, less than 0.00025%. In conclusion lower or higher practical use air pressures do not significantly stretch a good quality mountain bike tire.

3. Originally Posted by derby
Maybe I should simply stand by my claim that by changing rim width, the tire's profile is changed, but the tire height does not change....
By definition, if you change the profile of the tire, then the length of various (virtual) circumferential bands along that profile must change length / diameter also. So what makes the top / outermost band special?

4. Originally Posted by derby
This is long..... Maybe I should simply stand by my claim that by changing rim width, the tire's profile is changed, but the tire height does not change.... However, due to tire construction, not by geometry, there could be minimal height difference from structural casing tension changes, but in practice the height does not change when the rim width is changed.
And this would be incorrect. Not just in theory, but in practice.

5. Originally Posted by kapusta
The center strip of the tire is a certain length. Once inflated, the diameter (height) of the tire is that length / pi. Yes, tire pressure could stretch that length slightly, but that is a separate issue from rim width.

If two identical tires at identical pressure on rims of different width were to have different diameters (height), that would mean that some force is stretching the tire material along the center strip more in the taller one. I can't think of anything that would explain that, which is why I agree with what Derby is saying.

I think that the problem with the diagrams above is that they assume the cross section of the tire retains a perfect arc shape as you change the rim width. this would be true for a straight tube, but not for one in a ring like a tire.
Center strip? Do you mean breaker? A breaker is not a belt. It is not intended to alter the profile of the tire. It's purpose is to increase the puncture resistance of the tire in the tread area, not alter the profile of the tire. When I worked at Maxxis / CST we commonly added or removed breakers from tires, and it had no effect on the tire's profile.

FWIW, I now design and develop ATV and UTV tires for Carlisle / ITP. These are bias and radial, belted and non-belted tires. Even in belted radial ATV tires there is a change in O.D. with a change in rim width. Granted, these are 2 ply high angle nylon belts (not steel), but belts nonetheless.

6. Originally Posted by bholwell
And this would be incorrect. Not just in theory, but in practice.
I see derby's point being dismissed without really addressing it. Even if the tire can stretch enough to allow it to get taller (I'll take your word that it does) surely that resistance to stretching will result in a profile different that what those diagrams indicate.

I'm thinking I need to see some actual evidence that the diagrams used in this thread work out in reality to believe it. Because at this point I am doubtful.

7. Originally Posted by kapusta
I see derby's point being dismissed without really addressing it. Even if the tire can stretch enough to allow it to get taller (I'll take your word that it does) surely that resistance to stretching will result in a profile different that what those diagrams indicate.

I'm thinking I need to see some actual evidence that the diagrams used in this thread work out in reality to believe it. Because at this point I am doubtful.
Ok. Nylon fabric is elastic in the direction of the threads, and has almost no strength in the direction perpendicular to the threads. This is why two plies are needed at opposing angles (all mountain bike tires are of bias construction).

Yes the hoop tension at the outermost circumference of the tire will increase as the tire O.D. attempts to increase, and will restrict it to some degree. In my first graph, the section height changes, what, 1mm when going from a 17mm rim to a 27mm rim? Or less than a 3mm change MAX? I would venture to guess that in practice, the section height would change 80-90% of the theoretical.

8. ## Tire height vs. rim width

Originally Posted by kapusta
I see derby's point being dismissed without really addressing it. Even if the tire can stretch enough to allow it to get taller (I'll take your word that it does) surely that resistance to stretching will result in a profile different that what those diagrams indicate.

I'm thinking I need to see some actual evidence that the diagrams used in this thread work out in reality to believe it. Because at this point I am doubtful.
He just proclaimed that tire height doesn't change and followed that with a 500-word post that I can't really make any sense of. He also states as fact things that are demonstrably untrue, so it's hard to take him seriously.
If you need to see some evidence and you don't believe a tire development engineer telling you then bust out some measuring equipment.

9. Originally Posted by meltingfeather
He just proclaimed that tire height doesn't change and followed that with a 500-word post that I can't really make any sense of.
If you need to see some evidence and you don't believe a tire development engineer telling you then bust out some measuring equipment.
You missed my point. Luckily, the tire developer you refer to did not

10. ## Tire height vs. rim width

Originally Posted by kapusta
You missed my point. Luckily, the tire developer you refer to did not
I didn't think I missed it, but I'm always glad when Bryan jumps in anyway.
derby essentially proclaimed that tire casings do not stretch. He said "in practice" as if he has some working knowledge of the fact that they do not, which he can't, since they do. A few minutes and a measuring tape will demonstrate it.

11. Originally Posted by bholwell
Ok. Nylon fabric is elastic in the direction of the threads, and has almost no strength in the direction perpendicular to the threads. This is why two plies are needed at opposing angles (all mountain bike tires are of bias construction).

Yes the hoop tension at the outermost circumference of the tire will increase as the tire O.D. attempts to increase, and will restrict it to some degree. In my first graph, the section height changes, what, 1mm when going from a 17mm rim to a 27mm rim? Or less than a 3mm change MAX? I would venture to guess that in practice, the section height would change 80-90% of the theoretical.
I realize we are splitting hairs, since we are talking about very small height differences for typical rims and tires. I figured this discussion was more more one of concept rather than practical application.

But back to the topic, a 1mm increase in tire height is a roughly 6.3mm increase in the outermost circumference. Is that amount of stretching achieved (or 80-90% of that) at mtb tire pressures?

12. Originally Posted by kapusta
But back to the topic, a 1mm increase in tire height is a roughly 6.3mm increase in the outermost circumference. Is that amount of stretching achieved (or 80-90% of that) at mtb tire pressures?

Yes, easily.

Circumference of a 26x2.0 mtb tire = approx 2074.71mm

Add 2mm to diameter = circumference of 2080.99mm

So that's an increase in circumference of 6.28mm (like you said), or an increase of 0.3 percent.

Keep in mind that the threads of the casing fabric do not run parallel to the direction of travel, but are at an angle. Inflation pressure easily spreads the threads apart (so if the tire was an unbelted radial, there would be little to no resistance to OD growth), but since the tire is a bias construction the threads pantograph a bit with inflation.

13. Originally Posted by bholwell
Yes, easily.

Circumference of a 26x2.0 mtb tire = approx 2074.71mm

Add 2mm to diameter = circumference of 2080.99mm

So that's an increase in circumference of 6.28mm (like you said), or an increase of 0.3 percent.

Keep in mind that the threads of the casing fabric do not run parallel to the direction of travel, but are at an angle. Inflation pressure easily spreads the threads apart (so if the tire was an unbelted radial, there would be little to no resistance to OD growth), but since the tire is a bias construction the threads pantograph a bit with inflation.
Right. Thanks!

14. ## measured: no difference, if anything shorter with a wider rim

Measured three times with each rim, the same new unused tire on the same brand rims, Velocity 28mm Blunt and 35mm P35, inflated carefully to 30 psi with the same pump. Measured carefully at 1" mark on tape for accuracy, square to the corner edge of the closest outer knob with valve aligned plumb with axle.

In fact the wider rim rolled out the same tire with same air pressure on a 7mm wider rim almost 1/16th inch shorter, so I'll round to 1mm shorter rollout. Virtually the same circumference, certainly not larger.

I don't have a narrower rim to measure with a greater difference.

I don't think it matters except bigger wheels would show more difference if there is any.... the rim and tire were 584 size bead-seat, VeeRubber Trail Taker 2.4, 88 1/8 inch rollout with 28mm wide rim, 88 1/16 inch rollout with 35mm wide rim.

BTW, the trail Taker is still very round in profile on a 35mm rim, looks like it would require a 60mm wide rim to square the edge knobs up slightly.

I'll go edit my 500 word essay and correct it to explain why wider rims in fact slightly shorten a tire circumference and height!

15. ## Tire height vs. rim width

Originally Posted by derby
Measured three times with each rim, the same new unused tire on the same brand rims, Velocity 28mm Blunt and 35mm P35, inflated carefully to 30 psi with the same pump. Measured carefully at 1" mark on tape for accuracy, square to the corner edge of the closest outer knob with valve aligned plumb with axle.

In fact the wider rim rolled out the same tire with same air pressure on a 7mm wider rim almost 1/16th inch shorter, so I'll round to 1mm shorter rollout. Virtually the same circumference, certainly not larger.

I don't have a narrower rim to measure with a greater difference.

I don't think it matters except bigger wheels would show more difference if there is any.... the rim and tire were 584 size bead-seat, VeeRubber Trail Taker 2.4, 88 1/8 inch rollout with 28mm wide rim, 88 1/16 inch rollout with 35mm wide rim.

BTW, the trail Taker is still very round in profile on a 35mm rim, looks like it would require a 60mm wide rim to square the edge knobs up slightly.

I'll go edit my 500 word essay and correct it to explain why wider rims in fact slightly shorten a tire circumference and height!

How many times did you measure the rollout?

I usually do two revolutions, three times and average. Normal to have a 10mm range in the double rollout distances.

16. Originally Posted by shiggy
How many times did you measure the rollout?

I usually do two revolutions, three times and average. Normal to have a 10mm range in the double rollout distances.
5 times the first time, there was a 1/8 inch, about 3-4mm, difference from the first to the next 4 virtually identical rollouts after I got the alignment with the tape squared consistently. The second set of runs of the same tire with the wider rim, same high traction rug surface, 3 rollouts all measured within less than 1/32 inch, virtually identical, well within a margin of error.

I was concerned with the first 4mm variance in a single revolution from all the others being within 1mm, I threw out that first measurement due to error in my technique.

I may do another test with two wheel revolutions for each measured rollout. I thought of that during the second rim test. But the measurements were consistent and virtually identical after correcting my alignment method.

The small reduction in circumference measured with the wider rim, could be better verified with doing two revolution rollouts many times and averaging. Right now I've proved to myself that good quality mountain tires don't stretch longer in circumference or height when going to a larger rim.

BTW, after the tests at 30 psi in the same tire with both rims, I lowered pressure to 20 psi more appropriate while on the wider rim, but the tire still measure nearly the same in circumference, possibly 1mm shorter at most, insignificant, IMO. However, I imagine race car bias-ply tires, much fatter higher volume smaller rim and light weight, would stretch and shrink far more significantly from air pressure variation, and those tires are designed to do so for tuning.

17. Originally Posted by derby
... Right now I've proved to myself that good quality mountain tires don't stretch longer in circumference or height when going to a larger rim.
...
I'm glad that you've proved your own preconceived notions, but that doesn't make them any less incorrect.

A crude rollout measurement is likely not accurate enough to measure the subtle increase in tire circumference.

18. ## My little experiment

To back up my claims, and to satisfy my curiosity, I performed the following experiment:

I mounted a used, 29x2.2 Ikon eXC onto a road rim (13.04mm internal width) and inflated the tire to 40 psi. After 72 hours, I used a calibrated Pi tape to measured the circumference. I then deflated to 25 psi and measured the circumference. Two more measurements were taken at each inflation pressure, and the results were averaged.

I then made a SolidWorks sketch of a tire profile on the narrow road rim, and adjusted the casing arc length so that the diameter matched what was measured. I then adjusted the internal rim width to generate diameter data. This data is plotted in the graph below.

I then mounted the tire onto a Flow rim (22.85mm internal width) and inflated to 40 psi. After 48 hours, diameter measurements were again taken and averaged using a calibrated Pi tape. These measurements can also be seen in the graph below.

At 25 psi, the measured diameter grew to 82.78% of the theoretical growth.

At 40 psi, the measured diameter grew to 68.74% of the theoretical growth.

This difference makes sense, because at higher pressures the casing has less ability to expand at the outer circumference as the rim grows in width. I would expect to also see a smaller percentage of growth with 60 tpi or 27 tpi casings, a heavier UST construction, etc.

Bottom line, even though the growth in O.D. is minor, a bicycle tire will still grow taller when mounted on a wider rim.

19. Originally Posted by derby
5 times the first time, there was a 1/18 inch, about 3-4mm.
Maybe part of your problem is that you can't accurately convert between inches and mm.

Your claim of measurement accuracy of < 1/32" for a rollout test is silly.

20. ## Tire height vs. rim width

Originally Posted by bholwell
To back up my claims, and to satisfy my curiosity, I performed the following experiment:

I mounted a used, 29x2.2 Ikon eXC onto a road rim (13.04mm internal width) and inflated the tire to 40 psi. After 72 hours, I used a calibrated Pi tape to measured the circumference. I then deflated to 25 psi and measured the circumference. Two more measurements were taken at each inflation pressure, and the results were averaged.

I then made a SolidWorks sketch of a tire profile on the narrow road rim, and adjusted the casing arc length so that the diameter matched what was measured. I then adjusted the internal rim width to generate diameter data. This data is plotted in the graph below.

I then mounted the tire onto a Flow rim (22.85mm internal width) and inflated to 40 psi. After 48 hours, diameter measurements were again taken and averaged using a calibrated Pi tape. These measurements can also be seen in the graph below.

At 25 psi, the measured diameter grew to 82.78% of the theoretical growth.

At 40 psi, the measured diameter grew to 68.74% of the theoretical growth.

This difference makes sense, because at higher pressures the casing has less ability to expand at the outer circumference as the rim grows in width. I would expect to also see a smaller percentage of growth with 60 tpi or 27 tpi casings, a heavier UST construction, etc.

Bottom line, even though the growth in O.D. is minor, a bicycle tire will still grow taller when mounted on a wider rim.

What about the differences in the above rims' sidewall height? The interior depth of Notubes rims is less than ISO rims.

21. Originally Posted by shiggy
What about the differences in the above rims' sidewall height? The interior depth of Notubes rims is less than ISO rims.
Very good question. Yes, the bead hook height of the NoTubes rims are lower than a typical rim.

I asked Mike B. (lead engineer at NoTubes) about this a couple years ago. His response was that the bead hook height is only lower because the bead seat diameter of the rim is raised. The actual overall diameter of the rim is the same as a typical rim. Measure them yourself if you have a ZTR rim- you'll see that it's true.

The overall diameter of the rim was my critical dimension in my SolidWorks sketch, since this is where the casing bends and takes on its rounded shape. So my 'casing arc length' that was constrained was the arc distance from bead hook to bead hook.

If you like, I can go back and measure the O.D. of both rims.

22. ## Tire height vs. rim width

Originally Posted by bholwell
Very good question. Yes, the bead hook height of the NoTubes rims are lower than a typical rim.

I asked Mike B. (lead engineer at NoTubes) about this a couple years ago. His response was that the bead hook height is only lower because the bead seat diameter of the rim is raised. The actual overall diameter of the rim is the same as a typical rim. Measure them yourself if you have a ZTR rim- you'll see that it's true.

The overall diameter of the rim was my critical dimension in my SolidWorks sketch, since this is where the casing bends and takes on its rounded shape. So my 'casing arc length' that was constrained was the arc distance from bead hook to bead hook.

If you like, I can go back and measure the O.D. of both rims.
Notubes talks about the shorter rim sidewall giving the tire greater volume.

I have measured the interior depth to the bead seat of Notubes Crest rims and they are ~2mm shallower than UST and standard ISO rims

23. Originally Posted by shiggy
I have measured the interior depth to the bead seat of Notubes Crest rims and they are ~2mm shallower than UST and standard ISO rims
1.8mm is what I have measured.

Originally Posted by shiggy
Notubes talks about the shorter rim sidewall giving the tire greater volume.
This might be true, but only if the tire's beads are stretched beyond what they normally would be on a UST rim.

Going from a UST rim profile, if NoTubes rims just lowered their bead hook height, then yes, the tire would gain volume. (This would also drastically increase the likelihood of blow-offs.) But what they've done instead is left the bead hook location the same, and they've raised the bead seat shelf. So the only way the tire can gain volume is if the bead seat shelf is forcing the beads up and away from center.

Aramid beads are elastic, and this is not outside the realm of possibility. In fact, if my rim was a Flow EX instead, I wouldn't have used it to perform the experiment. The Flow EX has an even larger bead seat shelf diameter. But the beads of the tire in my experiment (used Ikon, regular clincher) seated on the Flows at less than 15 psi, meaning at 25 and 40 psi there is not much, if any, bead elongation occurring.

24. ## Tire height vs. rim width

Originally Posted by bholwell
1.8mm is what I have measured.

This might be true, but only if the tire's beads are stretched beyond what they normally would be on a UST rim.

Going from a UST rim profile, if NoTubes rims just lowered their bead hook height, then yes, the tire would gain volume. (This would also drastically increase the likelihood of blow-offs.) But what they've done instead is left the bead hook location the same, and they've raised the bead seat shelf. So the only way the tire can gain volume is if the bead seat shelf is forcing the beads up and away from center.

Aramid beads are elastic, and this is not outside the realm of possibility. In fact, if my rim was a Flow EX instead, I wouldn't have used it to perform the experiment. The Flow EX has an even larger bead seat shelf diameter. But the beads of the tire in my experiment (used Ikon, regular clincher) seated on the Flows at less than 15 psi, meaning at 25 and 40 psi there is not much, if any, bead elongation occurring.
That would make the Notubes BSD 3.6mm larger than ISO BSD. I am not comfortable in stressing the tire bead in this manner.

25. Originally Posted by meltingfeather
Maybe part of your problem is that you can't accurately convert between inches and mm.

Your claim of measurement accuracy of < 1/32" for a rollout test is silly.
Thanks for finding the typo! Edited the post, corrected to 1/8 inch = 3.175mm.

26. Perhaps 650b behaves differently?

The irony is that the original purpose of the thread was to show that height is relatively insensitive to rim width which ran contrary to common lore. The claim has been that wider rims support lower pressures and that is, at its most generous, an oversimplification. Tire pressures can't be lowered when rim strikes are a threat. For some people rim strikes are never a threat and those people are, no doubt, connoisseurs of tire performance here.

Feel free to deny this despite common sense, readily observable fact, and the experience of an actual tire designer. Funny that it is commonly accepted that tires need to be given days to stretch before measuring their final size yet stretching is rejected here for not suiting the argument. MTBR is place where objective truth is simply not valued. It's more important to win than to learn.

If a bicycle tire stretches when new, which I think everyone accepts as true, then you have to wonder how its construction allows that while preventing growth in overall circumference.

It's comforting to know that drag racing slicks don't change diameter because they are belted.

27. Originally Posted by shiggy
That would make the Notubes BSD 3.6mm larger than ISO BSD. I am not comfortable in stressing the tire bead in this manner.
Whether it's mechanical stress from the rim, or stress from the inflation pressure of the tire, the beads must be strong enough to withstand all situations plus a factor of safety. Responsible tire manufacturers know this and utilize QC checks like hydrostatic burst testing to ensure the construction of the tire is adequately strong. For example, at Maxxis the spec is that the tire must withstand twice the max inflation pressure before it bursts. And many times, the tire's carcass would fail before the beads. And now, Bontrager has released tubeless ready ROAD tires that utilize aramid beads. Have you seen these? But I don't fault you for not trusting the NoTubes rim design; there are certain tires I would not use tubeless on Stan's rims. Even Schwalbe's first tubeless ready tires' beads were of inadequate strength.

That's why I'm all for standardization. The UST standard isn't flawless, but it at least gives tire manufacturers a target to aim at. But you must realize that for a tubeless setup to perform adequately (without burps), there MUST be an interference fit between the beads and the rim. And of course this will induce additional mechanical stress on the beads. No getting around it.

28. ## Tire height vs. rim width

Originally Posted by bholwell
Whether it's mechanical stress from the rim, or stress from the inflation pressure of the tire, the beads must be strong enough to withstand all situations plus a factor of safety. Responsible tire manufacturers know this and utilize QC checks like hydrostatic burst testing to ensure the construction of the tire is adequately strong. For example, at Maxxis the spec is that the tire must withstand twice the max inflation pressure before it bursts. And many times, the tire's carcass would fail before the beads. And now, Bontrager has released tubeless ready ROAD tires that utilize aramid beads. Have you seen these? But I don't fault you for not trusting the NoTubes rim design; there are certain tires I would not use tubeless on Stan's rims. Even Schwalbe's first tubeless ready tires' beads were of inadequate strength.

That's why I'm all for standardization. The UST standard isn't flawless, but it at least gives tire manufacturers a target to aim at. But you must realize that for a tubeless setup to perform adequately (without burps), there MUST be an interference fit between the beads and the rim. And of course this will induce additional mechanical stress on the beads. No getting around it.
I would rather not have the stress of mechanically (over) stretching the tire beads before adding the normal stress of inflation pressures. That the conversion "tubeless" setups are limited to much lower pressures than UST and tubed systems tells me that a pushing hard at the safety margins.

29. Originally Posted by derby
I don't think it matters except bigger wheels would show more difference if there is any.... the rim and tire were 584 size bead-seat, VeeRubber Trail Taker 2.4, 88 1/8 inch rollout with 28mm wide rim, 88 1/16 inch rollout with 35mm wide rim.
Digging up an old thread here, but I hope to have some more numbers for a Vee Trail Taker 2.4 soon.

Originally Posted by derby
BTW, the trail Taker is still very round in profile on a 35mm rim, looks like it would require a 60mm wide rim to square the edge knobs up slightly.
I'll be mounting a 650b 2.4 TT on a WTB Scraper i45 rim. Curious to see if this rim is wide enough to finally to get the TT's side knobs to have a profile similar to something like an HR2.

I'm reading 2.4 TT's on Blunt 35's measures to 27.75" tall. Curious to see what it comes out to on a super wide i45 rim.

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