Go Back  Bike Forums > Bike Forums > Framebuilders
Reload this Page >

Bolt size question

Notices
Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

Bolt size question

Old 05-25-21, 01:50 PM
  #1  
Tandem Tom
Senior Member
Thread Starter
 
Join Date: Dec 2011
Location: NE Ohio
Posts: 2,289

Bikes: 1992 Serotta Colorado II,Co-Motion Speedster, Giant Escape Hybrid, 1977 Schwinn Super Le Tour

Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 337 Post(s)
Likes: 0
Liked 47 Times in 40 Posts
Bolt size question

I was listening to a podcast about bike touring and the fellow,a bike mechanic, said he changed the holes in the rear drop out to M6 vs. M5 as this is a common weak point.

Thoughts?
Tandem Tom is offline  
Old 05-25-21, 02:42 PM
  #2  
JohnDThompson 
Old fart
 
JohnDThompson's Avatar
 
Join Date: Nov 2004
Location: Appleton WI
Posts: 22,662

Bikes: Several, mostly not name brands.

Mentioned: 133 Post(s)
Tagged: 0 Thread(s)
Quoted: 2629 Post(s)
Liked 1,281 Times in 801 Posts
Which holes are you referring to, the eyelets for rack and mudguard mounting? Some dropouts have M6 eyelets out of the box.
JohnDThompson is online now  
Old 05-25-21, 03:29 PM
  #3  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 15,036

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2966 Post(s)
Liked 1,250 Times in 878 Posts
The typical reason why rack bolts fail is from fatigue. A rack flexes with pedal strokes and road surface shocks. If the rack isn't well braced (and many would be surprised at the number of racks with no lateral triangulation) this flex will be worse. If the rack bolts are doing double duty, like fender brace attachment too, then again the bolt's flexing will be worse. If the bolt is allowed to become loose the flex will be greater. And in time the paper clip breaks, so to speak. Increasing the bolt's diameter by about 20% sure extends the life span of poorly dealt with bolts. Note that last bit "poorly dealt with". because for most people's touring a well engineered rack using M5 bolts that are kept tight and don't do any other job are quite strong enough.

it's when the tour is over lot's of unimproved/unpaved roads and the pack loads are really high (think 75+ lbs) and the consequence of a broken rack/bolt is possible unhealthy (think third/forth world countries, deserts and such) that going to a M6 bolt is really a smart idea.

In my shop experience (and of course my personal touring which last time had a bike and load weight of over 110 lbs) the number of broken rack bolts has been less then the number of eyes damaged by loose bolts, by over tightening or by using a miss matched bolt/screw (like dry wall screws ). I even have heard of eyelets breaking off the drop outs from too much flex and stress. On my first Scotland tour the Eclipse front low rider rack strut broke, after it had seen thousands of loaded miles over the 15+ years of it's being in use. But bolt breakage is not too common IME.

Still were I to make a third world touring bike I would strongly consider going with M6 bolts and their bigger eyes and bosses. But those dreams are in my past so M5s are fine for me. Andy (who for his touring bikes followed the one bolt does one job policy)
__________________
AndrewRStewart
Andrew R Stewart is offline  
Likes For Andrew R Stewart:
Old 05-25-21, 05:09 PM
  #4  
unterhausen
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 21,607
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 1,329 Times in 963 Posts
As long as the bolts are tight, 5mm is more than enough. I imagine if you have them cantilevered out to hold up fenders as well as a rack and let them get a little loose 5mm might not be enough. I recommend not letting them get loose.

When I had a rack and fenders on the same eyelet, I ran the bolt from the inside, put the rack on first, used a nut, then a washer then the fenders, then a washer and then another nut. Seemed to work well and there was much less chance the bolt would loosen up and get hammered by the rack.
unterhausen is offline  
Likes For unterhausen:
Old 05-25-21, 05:32 PM
  #5  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 15,036

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2966 Post(s)
Liked 1,250 Times in 878 Posts
I agree with Eric. We see quite a number of rack and fender equipped bikes at the shop and many that have only one eyelet per side to use. Most have the fender braces inside the rack's. Most of these also have no large (yes, a "fender" washer) washer on both sides of the common "V" bent fender brace. So not only does the single bolt see the rack's vertical loads far from the eye (thus a bending instead of a shear stress) but the fender brace can open up and cause the bolt to not snug the rack up as much. I believe this is done because of a few reasons. First critical thinking and basic mechanical concepts are not well taught any longer in school. Second most can't or won't figure out how to bend the fender brace so it wraps around the rack brace on it's way to the top of the rear fender. And third is that bike accessory companies rarely work together to make more then their product fit well in many situations. A simple solution would be if rack manufactures included a fender eye behind and to the rear of their rear most brace. That Eclipse low rider rack I mentioned included this (yes on a front rack) way back in the late 1970s. But I suppose some rack brand's liability lawyer would not like this... Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Likes For Andrew R Stewart:
Old 05-26-21, 06:28 AM
  #6  
Tandem Tom
Senior Member
Thread Starter
 
Join Date: Dec 2011
Location: NE Ohio
Posts: 2,289

Bikes: 1992 Serotta Colorado II,Co-Motion Speedster, Giant Escape Hybrid, 1977 Schwinn Super Le Tour

Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 337 Post(s)
Likes: 0
Liked 47 Times in 40 Posts
Thanks for your replies!
I like the idea of running the bolt from the inside. Going to take a look at our racks before our next tour from Wyoming back to Ohio.
Tandem Tom is offline  
Old 05-26-21, 09:50 AM
  #7  
unterhausen
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 21,607
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 1,329 Times in 963 Posts
Wouldn't hurt to use some blue threadlocker
unterhausen is offline  
Likes For unterhausen:
Old 05-26-21, 03:06 PM
  #8  
Tandem Tom
Senior Member
Thread Starter
 
Join Date: Dec 2011
Location: NE Ohio
Posts: 2,289

Bikes: 1992 Serotta Colorado II,Co-Motion Speedster, Giant Escape Hybrid, 1977 Schwinn Super Le Tour

Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 337 Post(s)
Likes: 0
Liked 47 Times in 40 Posts
Blue will clash with my frame. I have to find another color!😁😁
Tandem Tom is offline  
Old 05-27-21, 10:07 AM
  #9  
unterhausen
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 21,607
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 1,329 Times in 963 Posts
You aren't supposed to see the threadlocker.

Red will probably work fine in this application
unterhausen is offline  
Old 05-31-21, 11:30 AM
  #10  
headwind15
Bikeable
 
headwind15's Avatar
 
Join Date: Jan 2011
Posts: 182
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 96 Post(s)
Likes: 0
Liked 47 Times in 33 Posts
Wow, one of my favorite issues. Another reason rack bolts fail is when tourists ride off road and the jolting when you hit bumps can shear water bottle cage bolts right off. When the bolts shear off you are faced with what could be a difficult task (out in the field), of removing the broken piece in the eyelet. My solution is to mount the bolts from the drop out inside and attach nuts from outside the rack, so when they should shear off you just need to unthread them with the still intact allen head, and replace. You may need to use a button head type of bolt on the right side, so the chain avoids jamming in the small cog.
headwind15 is offline  
Old 05-31-21, 07:44 PM
  #11  
unterhausen
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 21,607
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 1,329 Times in 963 Posts
The load limit in shear of a 5mm bolt is over 1000 pounds. The fatigue life of a bolt is reduced markedly if the bolt is improperly preloaded, i.e. it's loose.
unterhausen is offline  
Old 06-10-21, 06:32 AM
  #12  
Doug Fattic 
framebuilder
 
Join Date: Dec 2009
Location: Niles, Michigan
Posts: 867
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 305 Post(s)
Liked 635 Times in 259 Posts
Originally Posted by unterhausen View Post
When I had a rack and fenders on the same eyelet, I ran the bolt from the inside, put the rack on first, used a nut, then a washer then the fenders, then a washer and then another nut. Seemed to work well and there was much less chance the bolt would loosen up and get hammered by the rack.
I just did this on a transportation bicycle I'm putting back together for when my daughter visits. I hadn't thought of doing it this way before. My brain was just programmed to screw in the bolt from the outside. I did exactly as Eric said, I screwed the bolt in the dropout with the head on the inside. After I put the rack on, I tightened it up with a nut, then washers on both sides of the fender struts and finally a nylon insert lock nut on the outside. An added bonus was that it was easier to assemble the various units with the head on the inside. I could put the struts on the end of the bolts already sticking out instead of putting the bolt through the struts 1st and then trying to locate the threaded hole with the interference of the weight of the accessories. I am sure it is much less likely to come loose doing it this way.

This transportation frame has had an interesting history. I made it as an example of the kind of frame we wanted the XB3 bicycle company in Kharkov, Ukraine (near the Russian border) to make for our charity bicycle project. They used to make the majority of bicycles for the former USSR. It then spent time in the city of Cherkassy, Ukraine at the home of one of the owners of the laser cutting company that makes our main triangle fixtures. Eventually I brought it back to the States with me where it was stolen one rainy night when I hadn't brought it back inside. One of my framebuilding class students spotted riding by while he was waiting at a red light. Eventually the guy was arrested and I got it back. I repaired the repainted the damaged paint and now I am putting it back together again with the bolts in the dropout eyelets pointing out instead of in.
Doug Fattic is offline  
Old 06-10-21, 09:33 AM
  #13  
unterhausen
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 21,607
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 1,329 Times in 963 Posts
It's great you got your bike back.

The other bonus of doing it inside out is that you don't have to trim the bolt so carefully, it's not going to run into anything like it will if it's a little too long and the head is on the outside.
unterhausen is offline  
Likes For unterhausen:
Old 06-11-21, 01:35 AM
  #14  
guy153
Senior Member
 
Join Date: Dec 2019
Posts: 574
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 206 Post(s)
Liked 116 Times in 94 Posts
The other bonus is that if for whatever reason you lose the threads cut into the frame (I'm always nervous about threads cut into permanent fixtures) you can just throw a nut on the outside.
guy153 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 - Do Not Sell My Personal Information -

Copyright 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.