Go Back  Bike Forums > Bike Forums > General Cycling Discussion
Reload this Page >

Cracked road bike rim

General Cycling Discussion Have a cycling related question or comment that doesn't fit in one of the other specialty forums? Drop on in and post in here! When possible, please select the forum above that most fits your post!

Cracked road bike rim

Old 04-21-24, 11:25 PM
Senior Member
79pmooney's Avatar
Join Date: Oct 2014
Location: Portland, OR
Posts: 13,033

Bikes: (2) ti TiCycles, 2007 w/ triple and 2011 fixed, 1979 Peter Mooney, ~1983 Trek 420 now fixed and ~1973 Raleigh Carlton Competition gravel grinder

Mentioned: 131 Post(s)
Tagged: 0 Thread(s)
Quoted: 4895 Post(s)
Liked 4,067 Times in 2,636 Posts
Originally Posted by Duragrouch
It's a confluence of bad: Aluminum has a high coefficient of thermal expansion, small diameter rim (20"), so less heat sink, and short spokes, so less elasticity. In my case, also add only using rear brake on that descent, because front rim sidewalls were more worn and I was trying to baby that. A particular small wheel bike company hypes their 20" wheels as "stronger"; Sort of. Stronger rim "hoop strength", so less likely to dent from impact. Short spokes are more rigid, but you don't want that, you want longer and more elastic, that is the driver for double-butted spokes, thinner diameter in the middle, away from bending loads on ends.
Thanks. I like learning stuff.
79pmooney is offline  
Old 04-24-24, 01:25 PM
Crawlin' up, flyin' down
bikingshearer's Avatar
Join Date: Jan 2006
Location: Democratic Peoples' Republic of Berkeley
Posts: 5,739

Bikes: 1967 Paramount; 1982-ish Ron Cooper; 1978 Eisentraut "A"; two mid-1960s Cinelli Speciale Corsas; and others in various stages of non-rideability.

Mentioned: 42 Post(s)
Tagged: 0 Thread(s)
Quoted: 1069 Post(s)
Liked 2,651 Times in 1,107 Posts
ADAM31: If you are going to stay with your current LBS, I strongly suggest that you educate your self about bike repair, expected component lifespans, sings of trouble, etc. In my estimation, you should not have had to ask us about that rim - it needed to be replaced, period. (Yes, it was safe enough to get you home, but not for going out on another ride. I'm glad your LBS has arranged the appropriate warranty replacement.) Expanding your bike-mechanic knowledge increases you ability to be your own "reality check" when you get advice that sounds sketchy. BF is a great place to learn such things.
"I'm in shape -- round is a shape." Andy Rooney
bikingshearer is offline  
Old 05-11-24, 08:42 AM
Thread Starter
Join Date: Jul 2017
Location: Off the grid
Posts: 33

Bikes: 2013 felt

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 30 Post(s)
Liked 3 Times in 3 Posts
Update I got a new rim and I am going to try riding with lower tire pressure as the lbs belies that this may be the cause of cracking my rims as this is the second time in last year I have cracked my rim
ADAM31 is offline  
Old 05-12-24, 07:10 PM
Senior Member
Join Date: Apr 2017
Posts: 2,356
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 1078 Post(s)
Liked 573 Times in 462 Posts
Originally Posted by ADAM31
Update I got a new rim and I am going to try riding with lower tire pressure as the lbs belies that this may be the cause of cracking my rims as this is the second time in last year I have cracked my rim
My usual disclaimer applies, "I could be wrong". And always good to try different things. However, in my mind, I'm not seeing air pressure as the stressor; That is a double-wall rim, so the inner "pointed" wall where the spoke nipple seats, and an outer radiused wall where the tube rests on, and that has somewhat large access holes to be able to access the spoke nipples. The air pressure in the tube exerts force in all directions; Circumferentially, radially outward to support the tire, radially inward against the outer rim wall, and laterally (sideways) outward on each rim sidewall. That last force is the critical one, pushing both sidewalls apart, and it stresses the outer radiused wall in lateral tension, and fatigue cracks happen mostly in tension, sometimes in torsion or shear or bending, almost never in compression. And yes, no cracks in the outer radiused wall. That same lateral outward force that pushes the sidewalls out and tension in the outer radiused wall, puts the inner pointed wall in lateral compression, which normally would not cause a fatigue failure. Only if the lateral compression force were so great as to try to increase the tightness of that pointed bend in the rim (bending is both compression on one side, in this case the inside of that bend, and tension, the outside of that bend where you see the crack), would there likely be fatigue. It's a possibility. But I think that tension from the spokes is a greater factor, although those forces can and do combine. I'll be interested if lower pressure results in longer rim life. I can't recall if the rim is radially spoked, that can require higher spoke tension and thus fatiguing rims quicker. Oh, you said disc wheel, so probably not radially spoked, though I have seen some that are crossed on the drive side and radial on the non drive side, though usually not with discs I think.
Duragrouch is offline  
Old 05-13-24, 07:52 AM
Senior Member
Join Date: Jan 2013
Posts: 2,732

Bikes: too many sparkly Italians, some sweet Americans and a couple interesting Japanese

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 575 Post(s)
Liked 619 Times in 427 Posts
What pressures do you run? I suspect your LBS is not your friend.
easyupbug is offline  
Likes For easyupbug:
Old 05-13-24, 08:19 AM
Senior Member
Join Date: Dec 2020
Location: Wake Forest, NC
Posts: 6,045

Bikes: 1989 Cinelli Supercorsa

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 3663 Post(s)
Liked 3,100 Times in 1,868 Posts
Originally Posted by ADAM31
Update I got a new rim and I am going to try riding with lower tire pressure as the lbs belies that this may be the cause of cracking my rims as this is the second time in last year I have cracked my rim
How come my rims haven't cracked? I suspect I run my tires at a significantly higher pressure than you do.
smd4 is offline  
Old 05-13-24, 10:52 AM
Senior Member
bboy314's Avatar
Join Date: Dec 2008
Location: Pioneer Valley
Posts: 1,353
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 447 Post(s)
Liked 1,044 Times in 534 Posts
Do you know if those rims spec a maximum rated pressure?
bboy314 is offline  
Old 05-13-24, 12:02 PM
Senior Member
phughes's Avatar
Join Date: Mar 2011
Posts: 3,178
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 1088 Post(s)
Liked 1,358 Times in 780 Posts
I still say the spokes were most likely improperly tensioned. I find it difficult to believe it was a result of too high pressure. I do understand the theory though, I just don't buy it. You would have to be bashing into curbs and that type of thing for pressure to make a difference, and it would have to be awfully high for it to crack at a spoke. Near impossible due to pressure. The crack would have been on the tire side of the rim, not at the spoke.
phughes is offline  
Likes For phughes:
Old 05-13-24, 12:57 PM
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 24,508
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 3,802 Times in 2,593 Posts
I don't think that's where a rim cracks due to high pressure. There is a max pressure for many rims though.

When the LBS owner said it was safe, he was thinking, "for me." Granted, it's probably not going to cause injury, but it might cause a long walk.
unterhausen is offline  
Likes For unterhausen:
Old 05-13-24, 10:26 PM
OM boy
cyclezen's Avatar
Join Date: Jul 2005
Location: Goleta CA
Posts: 4,482

Bikes: a bunch

Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 564 Post(s)
Liked 723 Times in 484 Posts
Originally Posted by ADAM31
Update I got a new rim and I am going to try riding with lower tire pressure as the lbs belies that this may be the cause of cracking my rims as this is the second time in last year I have cracked my rim
Alu rims come in a variety of quality, and wheels in a variety of build care. This and a poorly balanced wheel build, add in some hard roads hits, and a spoke carrying much more load than the ones surrounding it, will pull thru.
If your rim is of decent quality, and you replace instead of buying a new wheel, then make sure you have a wheel builder who really knows how to build a wheel.
Putting the wheel together in some fashion is quite easy, but building that wheel to it's optimum strength and service is a very real skill, a craft... ANd a good builder will know if the rim and hub are worth the effort, expense and service quality.
Wheels and tires are THE contact points with the riding surface, the only contact points... good wheels mean everything, and often they need not be the most expensive...
Ride On
cyclezen 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread

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

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.