rim width effect on tire height
11-17-19, 05:02 PM
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rim width effect on tire height
Would a wider rim lower the height of a given tire? If so, how much? I'd love to get a wider rim and simultaneously widen the tire and lower its height too. Maybe even enough to move up from the 31mm model to the 33mm model? That would be amazing. Anyone have experience with this?
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2014 Cannondale SuperSix EVO 2
2019 Salsa Warbird
2014 Cannondale SuperSix EVO 2
2019 Salsa Warbird
11-17-19, 05:28 PM
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Would a wider rim lower the height of a given tire? If so, how much? I'd love to get a wider rim and simultaneously widen the tire and lower its height too. Maybe even enough to move up from the 31mm model to the 33mm model? That would be amazing. Anyone have experience with this?
A (simplistic) way to visualize what's going on is to imagine that you've got a tire that always inflates to a perfectly round profile. Suppose you've got a rim with an internal width of zero, squeezing the tire's beads together. This causes the tire to form a complete circle:
Now imagine a second rim, where the internal width is equal to twice the diameter that the tire has on the zero-width rim. Now we have this:
The tire is now half of a circle with twice the diameter than before; the circumference has doubled, but the tire only exists across half of the new circle's circumference. The radius is the same as the old circle's diameter, so the inflated height is equal.
In practice, the height doesn't stay the same across the range of rim widths, but it also doesn't just trade height for width.
//============================================
But I also don't understand your objective. Insofar as tires serve as a suspension system, the main value to using a bigger tire is that it achieves more suspension travel by inflating taller. In order to avoid bad behaviors like bottom-outs, it seems like a wide-and-short tire would need to be pumped just as stiff as a narrow-and-short tire.
Last edited by HTupolev; 11-17-19 at 09:49 PM.
11-17-19, 09:43 PM
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I have a set of GK slicks that are 39.1mm wide and 35.2mm tall on Kinlin TL-23 rims with 23mm IW. Same tires at the same sag on OEM HED Tomcat 17.5mm IW are 38.3mm wide and 37.4mm tall. If I use the same pressure on both rims, the sag decreases on the Kinlin and the height goes to 36.6mm with the width the same. Tire height is much more affected by pressure than width.
Wide rims are also seriously prone to pinch flats, IMO a rim wide enough to drop the height of a 33mm tire is also going to greatly shrink the fast/comfortable/traction pressure window for that tire.
Wide rims are also seriously prone to pinch flats, IMO a rim wide enough to drop the height of a 33mm tire is also going to greatly shrink the fast/comfortable/traction pressure window for that tire.
11-18-19, 08:44 AM
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The effects of rim width on tire height can be a bit complicated, but no: within the reasonable scope of rim widths, the impact of rim width on height is less dramatic than you might expect, and a wider rim will often result in the tire inflating both wider and taller.
A (simplistic) way to visualize what's going on is to imagine that you've got a tire that always inflates to a perfectly round profile. Suppose you've got a rim with an internal width of zero, squeezing the tire's beads together. This causes the tire to form a complete circle:
Now imagine a second rim, where the internal width is equal to twice the diameter that the tire has on the zero-width rim. Now we have this:
The tire is now half of a circle with twice the diameter than before; the circumference has doubled, but the tire only exists across half of the new circle's circumference. The radius is the same as the old circle's diameter, so the inflated height is equal.
In practice, the height doesn't stay the same across the range of rim widths, but it also doesn't just trade height for width.
//============================================
But I also don't understand your objective. Insofar as tires serve as a suspension system, the main value to using a bigger tire is that it achieves more suspension travel by inflating taller. In order to avoid bad behaviors like bottom-outs, it seems like a wide-and-short tire would need to be pumped just as stiff as a narrow-and-short tire.
A (simplistic) way to visualize what's going on is to imagine that you've got a tire that always inflates to a perfectly round profile. Suppose you've got a rim with an internal width of zero, squeezing the tire's beads together. This causes the tire to form a complete circle:
Now imagine a second rim, where the internal width is equal to twice the diameter that the tire has on the zero-width rim. Now we have this:
The tire is now half of a circle with twice the diameter than before; the circumference has doubled, but the tire only exists across half of the new circle's circumference. The radius is the same as the old circle's diameter, so the inflated height is equal.
In practice, the height doesn't stay the same across the range of rim widths, but it also doesn't just trade height for width.
//============================================
But I also don't understand your objective. Insofar as tires serve as a suspension system, the main value to using a bigger tire is that it achieves more suspension travel by inflating taller. In order to avoid bad behaviors like bottom-outs, it seems like a wide-and-short tire would need to be pumped just as stiff as a narrow-and-short tire.
I have a set of GK slicks that are 39.1mm wide and 35.2mm tall on Kinlin TL-23 rims with 23mm IW. Same tires at the same sag on OEM HED Tomcat 17.5mm IW are 38.3mm wide and 37.4mm tall. If I use the same pressure on both rims, the sag decreases on the Kinlin and the height goes to 36.6mm with the width the same. Tire height is much more affected by pressure than width.
Wide rims are also seriously prone to pinch flats, IMO a rim wide enough to drop the height of a 33mm tire is also going to greatly shrink the fast/comfortable/traction pressure window for that tire.
Wide rims are also seriously prone to pinch flats, IMO a rim wide enough to drop the height of a 33mm tire is also going to greatly shrink the fast/comfortable/traction pressure window for that tire.
__________________
2014 Cannondale SuperSix EVO 2
2019 Salsa Warbird
2014 Cannondale SuperSix EVO 2
2019 Salsa Warbird
