Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

Hollowtech 2 68/73 BB: OK on a road bike?

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

Hollowtech 2 68/73 BB: OK on a road bike?

Old 05-30-19, 10:46 AM
  #1  
mfcity
Senior Member
Thread Starter
 
Join Date: Feb 2015
Location: Cheltenham
Posts: 130
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 39 Post(s)
Liked 0 Times in 0 Posts
Hollowtech 2 68/73 BB: OK on a road bike?

I'm looking to change the chainset on my Genesis Day1 Alfine, and currently leaning towards an Alfine 39T one to replace the stock chainset and square-taper BB. It looks as if 39T in front paired with a 22T sprocket will fix the gearing ratios, judging by Sheldon Brown's online calculator for the 11-speed hub.

There are some decent quality Shimano Holowtech2 MTB bottom brackets for sale that claim to be 68/77mm compatible, so I'm wondering if these will work in terms of the shell size, but also the spindle length on my bike. I've also heard people mention needing to chase/face the shell when changing to a new bottom bracket type. Is is better to stick with a road bottom bracket? Would appreciate any insights here -- thank you.
mfcity is offline  
Old 05-30-19, 11:04 AM
  #2  
sch
Senior Member
 
Join Date: May 2003
Location: Mountain Brook. AL
Posts: 3,787
Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 244 Post(s)
Likes: 0
Liked 55 Times in 45 Posts
Without doing any research, I suspect the BB you mention is 73mm and comes with a few spacers for
use in 68mm BB shells. This is generally acceptable but the sensitive may notice the slightly wider
Q. Most of us would not or would acclimate rapidly. Chasing the shell is not necessary.
sch is offline  
Old 05-30-19, 11:18 AM
  #3  
base2 
Random Internet Person.
 
base2's Avatar
 
Join Date: Jun 2015
Location: Pacific Northwest
Posts: 1,348

Bikes: 5 good ones, and the occasional project.

Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 691 Post(s)
Liked 267 Times in 164 Posts
Yep. 73mm mountain crankset will work fine in a 68mm shell. The mountain bottom bracket usually comes with 3, 2.5mm aluminum spacers. Place one on each side between the cup/bearing and the shell. I have had several bikes configured that way at various times.

Concerning the 3rd spacer: It may/may not be needed if you are using road bottom bracket in road shell with mountain crank. The hollow tube inside might need to be mix-n'-matched though. At least that has been my experience.
base2 is offline  
Old 05-30-19, 03:08 PM
  #4  
mfcity
Senior Member
Thread Starter
 
Join Date: Feb 2015
Location: Cheltenham
Posts: 130
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 39 Post(s)
Liked 0 Times in 0 Posts
Originally Posted by sch View Post
Without doing any research, I suspect the BB you mention is 73mm and comes with a few spacers for
use in 68mm BB shells. This is generally acceptable but the sensitive may notice the slightly wider
Q. Most of us would not or would acclimate rapidly. Chasing the shell is not necessary.
Sounds right about those spacers, but isn't Q factor set by the crank spindle rather than the bottom bracket?
mfcity is offline  
Old 05-30-19, 03:11 PM
  #5  
mfcity
Senior Member
Thread Starter
 
Join Date: Feb 2015
Location: Cheltenham
Posts: 130
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 39 Post(s)
Liked 0 Times in 0 Posts
Originally Posted by base2 View Post
Yep. 73mm mountain crankset will work fine in a 68mm shell. The mountain bottom bracket usually comes with 3, 2.5mm aluminum spacers. Place one on each side between the cup/bearing and the shell. I have had several bikes configured that way at various times.

Concerning the 3rd spacer: It may/may not be needed if you are using road bottom bracket in road shell with mountain crank. The hollow tube inside might need to be mix-n'-matched though. At least that has been my experience.
I was looking at some XT/XTR BBs initially, but I've found Ultegra (BBR60) road BBs are very reasonably priced, and since I've used one on another bike and found it works well, I'll probably go with that one.
mfcity is offline  
Old 05-30-19, 03:12 PM
  #6  
Metaluna
Senior Member
 
Join Date: Aug 2005
Location: New Hampshire
Posts: 1,221

Bikes: Niner RLT 9 RDO, Gunnar Sport, Soma Saga, Workswell WCBR-146

Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 114 Post(s)
Liked 18 Times in 18 Posts
Originally Posted by mfcity View Post
I'm looking to change the chainset on my Genesis Day1 Alfine, and currently leaning towards an Alfine 39T one to replace the stock chainset and square-taper BB. It looks as if 39T in front paired with a 22T sprocket will fix the gearing ratios, judging by Sheldon Brown's online calculator for the 11-speed hub.

There are some decent quality Shimano Holowtech2 MTB bottom brackets for sale that claim to be 68/77mm compatible, so I'm wondering if these will work in terms of the shell size, but also the spindle length on my bike. I've also heard people mention needing to chase/face the shell when changing to a new bottom bracket type. Is is better to stick with a road bottom bracket? Would appreciate any insights here -- thank you.
So if I understand this correctly, you want to use an Alfine Hollowtech II crank (FC-S501?). That component is designed for a 68mm bottom bracket shell.

(See the following link, scroll down to "Product Specifications" then click on the down arrow to expand the table. The BB width is a ways down).

https://bike.shimano.com/en-EU/produ...0/FC-S501.html


An MTB bottom bracket can work with a 68mm shell, but it does so by effectively expanding the shell width to 73mm via spacers. The BB will be too wide for the spindle on the Alfine chainset, I fear. A road BB should work fine though.
Metaluna is offline  
Likes For Metaluna:
Old 05-30-19, 03:16 PM
  #7  
mfcity
Senior Member
Thread Starter
 
Join Date: Feb 2015
Location: Cheltenham
Posts: 130
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 39 Post(s)
Liked 0 Times in 0 Posts
Originally Posted by Metaluna View Post
So if I understand this correctly, you want to use an Alfine Hollowtech II crank (FC-S501?). That component is designed for a 68mm bottom bracket shell.

(See the following link, scroll down to "Product Specifications" then click on the down arrow to expand the table. The BB width is a ways down).

https://bike.shimano.com/en-EU/produ...0/FC-S501.html


An MTB bottom bracket can work with a 68mm shell, but it does so by effectively expanding the shell width to 73mm via spacers. The BB will be too wide for the spindle on the Alfine chainset, I fear. A road BB should work fine though.
Thanks, very helpful info. It also turns out there's probably no savings in an MTB BB, since the BBR66 is widely available and I've found it trustworthy so far.
mfcity is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
HooKooDooKu
Bicycle Mechanics
11
08-14-13 08:54 PM
Oldsport
Bicycle Mechanics
9
05-01-11 04:32 PM
surfer
Bicycle Mechanics
2
08-07-10 10:47 AM
ru-tang
Bicycle Mechanics
3
06-08-10 08:11 PM
mickey85
Bicycle Mechanics
11
02-02-10 07:53 PM

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