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Discussion Starter · #1 ·
All,
I'm shopping for a new set of wheels and have somewhat of a tight clearance between the tire and the frame where the seat post is. its a tri bike with the frame cutout to make room for the tire.

So if i'm currently running a 23mm tire on what i believe is a 21mm hub, if i increase the width of the rum to 23-24, will that make the tire balloon up more at the top or will it spread out and create more space? when i brought my bike into the shop for some tune up and repairs last night, the tech said that i cant run a bigger tire, but a bigger rim will be fine. just want to solicit some feedback before i buy new wheels.

Thanks!
Greg
 

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It will make the tire wider like the rim but not as tall as it is now.

Because it isn't as tall, you'll have to be more careful about pinch flats and may have to run a higher pressure to avoid them.

I recently switched from very wide rims to ultra wide rims and I love it. To me they're faster and more stable, especially during high speed cornering.
 

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Discussion Starter · #3 ·
It will make the tire wider like the rim but not as tall as it is now.

Because it isn't as tall, you'll have to be more careful about pinch flats and may have to run a higher pressure to avoid them.

I recently switched from very wide rims to ultra wide rims and I love it. To me they're faster and more stable, especially during high speed cornering.
Thanks! maybe i'm wrong but i heard that with a wider wheel you can ride at a lower PSI? but for me, i'll do whatever it takes to avoid flats. probably going to get a conti gatorskin for them.
 

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The most operative rim dimension that effects changes in the geometry of an inflated tire is the inside dimension so make sure you are comparing that when looking at various rims. I suspect that outside widths are most frequently reported in specifications because folks use that information to infer the aerodynamics of the setup. Just guessing. None the less in my experience picking up additional inside width of the rim has added width to my tires. I run Continental tires (Gatorskin, Gator Hardshell, GP4000) and I imagine different brands/models will have their own unique changes. Since moving to wider rims I have dropped considerable PSI, again how much you can get away with will probably vary with tire make/model/size.

I have not measured inflated tire OD changes (how "tall" the inflated tire is) so I cannot remark on that. I have the capability so perhaps I could run a study and report on it for folks but quite frankly I have better things to do.
 

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It will make the tire wider like the rim but not as tall as it is now.

Because it isn't as tall, you'll have to be more careful about pinch flats and may have to run a higher pressure to avoid them.

I recently switched from very wide rims to ultra wide rims and I love it. To me they're faster and more stable, especially during high speed cornering.
With all due respect, a few things you said here are incorrect. A wider rim will make the tire slight wider AND taller because the bead isn't being squeezed in as much.

AND, they will actually be less likely to pinch flat because there will be less of a "light bulb" effect.

As Craiger_NY already stated, it is the inside dimension of the rim you need to be concerned with. When I went from a 15mm to a 17.5mm rim, my 28mm tires expanded to around 29mm. Stability and cornering are also better. But where the wider rims really shine is if I go onto dirt/hardpack, there is no squirmy feeling like there used to be.
 

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Discussion Starter · #6 ·
With all due respect, a few things you said here are incorrect. A wider rim will make the tire slight wider AND taller because the bead isn't being squeezed in as much.

AND, they will actually be less likely to pinch flat because there will be less of a "light bulb" effect.

As Craiger_NY already stated, it is the inside dimension of the rim you need to be concerned with. When I went from a 15mm to a 17.5mm rim, my 28mm tires expanded to around 29mm. Stability and cornering are also better. But where the wider rims really shine is if I go onto dirt/hardpack, there is no squirmy feeling like there used to be.
i thought there would be less likely to be a pinch flat also... but now i'm a bit concerned that if i put a 23 mm tire on a 23/24mm wide rim (assuming the internal measurements increase by roughly the same amount vs my current 21mm rim, is there a stronger likelihood that the tire will rub against the frame? the "cutout" from under the seatpost?
 

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Hed released a great image a while ago that showed different sized tires on different width rims.

This will probably give you the info you need.

As you can see from the diagram, MMsRepBike and I were BOTH WRONG. Height doesn't appear to be affected at all.

So the question becomes, do you have enough clearance on the sides? Height will be a non-issue. If there is more than 3mm on each side of the seat stays and chainstays, you should be fine.
 

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Discussion Starter · #9 ·
Hed released a great image a while ago that showed different sized tires on different width rims.

This will probably give you the info you need.
Thanks so much! i'm glad you responded because i'm looking at getting the boyd altimount rims custom built (cheaper hubs so i can afford it) and looks like this should work.

THANKS!
 

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Okay, I'll just put my experience then:

23mm tires on small rims at 85psi rear = no issues
23mm tires on much wider rims at 85psi rear = pinch flats on bumps

Seeing how I'm unwilling to go higher on pressure I had to go up in tire size to 25mm on the wide rims to avoid pinch flats.
 

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It will make the tire wider like the rim but not as tall as it is now.

Because it isn't as tall, you'll have to be more careful about pinch flats and may have to run a higher pressure to avoid them.

I recently switched from very wide rims to ultra wide rims and I love it. To me they're faster and more stable, especially during high speed cornering.
Generally speaking the tire will NOT get shorter. It is likely to stay the same or get incrementally taller. I measured and found this to be true moving from an older Dura Ace wheelset to a set of HED Aredennes +. The tire width grew by 2mm+ and the height grew by about .2mm. Yes, a specific tire's layup could impact how it reacts to the increased width, but a bicycle tire's cross section acts more like a circle than, say, a car tire. Adding to rim width is similar to adding to the tire's cross sectional circumference. Tire does resist growing taller as the "top" of the tire is held in place by the circular structure in the perpendicular direction (the large 700c circle formed by the tire on the wheel)

Here is a chart developed by HED

 

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Discussion Starter · #12 ·
As you can see from the diagram, MMsRepBike and I were BOTH WRONG. Height doesn't appear to be affected at all.

So the question becomes, do you have enough clearance on the sides? Height will be a non-issue. If there is more than 3mm on each side of the seat stays and chainstays, you should be fine.
Thank you, i'm good on teh chainstays, i'll see better tongiht wehn i get the bike back and everything is evened and tuned up. but even so i think i had 3mm clearance. but will validate tonight
 

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As you can see from the diagram, MMsRepBike and I were BOTH WRONG. Height doesn't appear to be affected at all.
Look again and pay attention only to tires pumped to the same pressure. Both the 23 and 25mm tires pumped to 100psi got taller when moved to a wider rim. My experience has been some height growth, but not as much as shown in this chart, then again I was measuring a Hutchenson Fusion and not a Conti GP4000
 

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Discussion Starter · #14 ·
Look again and pay attention only to tires pumped to the same pressure. Both the 23 and 25mm tires pumped to 100psi got taller when moved to a wider rim. My experience has been some height growth, but not as much as shown in this chart, then again I was measuring a Hutchenson Fusion and not a Conti GP4000
pardon my ignorance, on this but whats the difference between the hutchinson fusion vs the conti gp4000 (which is hwat i currenly have)?

i'll ask the guy at the shop to measure the current wheels for me tonight so i can see for sure..
 

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pardon my ignorance, on this but whats the difference between the hutchinson fusion vs the conti gp4000 (which is hwat i currenly have)?
The point is that they are different brands and models. They likely have different casing materials (TPI), anti-puncture membranes, and rubber compounds and thicknesses. Any one of those could alter the way a tire's shape is impacted by widening the rim.
 

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Look again and pay attention only to tires pumped to the same pressure. Both the 23 and 25mm tires pumped to 100psi got taller when moved to a wider rim. My experience has been some height growth, but not as much as shown in this chart, then again I was measuring a Hutchenson Fusion and not a Conti GP4000
OK, I can see my eyes are going geriatric and were following the wrong curves. I stand corrected.
 
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