Go Back  Bike Forums > Bike Forums > Cyclocross and Gravelbiking (Recreational)
Reload this Page >

rim width effect on tire height

Notices
Cyclocross and Gravelbiking (Recreational) This has to be the most physically intense sport ever invented. It's high speed bicycle racing on a short off road course or riding the off pavement rides on gravel like :The Dirty Kanza". We also have a dedicated Racing forum for the Cyclocross Hard Core Racers.

rim width effect on tire height

Old 11-17-19, 05:02 PM
  #1  
shoota 
Senior Member
Thread Starter
 
shoota's Avatar
 
Join Date: Jun 2012
Location: not sure
Posts: 6,574
Mentioned: 19 Post(s)
Tagged: 0 Thread(s)
Quoted: 1115 Post(s)
Liked 71 Times in 57 Posts
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?
__________________
2014 Cannondale SuperSix EVO 2
2015 Cannondale SuperX Hi-Mod
shoota is offline  
Old 11-17-19, 05:28 PM
  #2  
HTupolev
Senior Member
 
Join Date: Apr 2015
Location: Seattle
Posts: 2,987
Mentioned: 36 Post(s)
Tagged: 0 Thread(s)
Quoted: 1324 Post(s)
Liked 132 Times in 87 Posts
Originally Posted by shoota View Post
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?
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.

Last edited by HTupolev; 11-17-19 at 09:49 PM.
HTupolev is online now  
Old 11-17-19, 09:43 PM
  #3  
Spoonrobot 
Senior Member
 
Spoonrobot's Avatar
 
Join Date: Jul 2006
Posts: 3,420
Mentioned: 63 Post(s)
Tagged: 0 Thread(s)
Quoted: 1143 Post(s)
Liked 102 Times in 72 Posts
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.
Spoonrobot is offline  
Old 11-18-19, 08:44 AM
  #4  
shoota 
Senior Member
Thread Starter
 
shoota's Avatar
 
Join Date: Jun 2012
Location: not sure
Posts: 6,574
Mentioned: 19 Post(s)
Tagged: 0 Thread(s)
Quoted: 1115 Post(s)
Liked 71 Times in 57 Posts
Originally Posted by HTupolev View Post
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.
Originally Posted by Spoonrobot View Post
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.
Very interesting. Thanks guys. Spoonbot, what PSI are you running those (38mm?) GKs at?
__________________
2014 Cannondale SuperSix EVO 2
2015 Cannondale SuperX Hi-Mod
shoota is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.