Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

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.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 01-15-12, 05:51 PM   #1
bellweatherman
Senior Member
Thread Starter
 
bellweatherman's Avatar
 
Join Date: Aug 2005
Location: Austin
Bikes: Too many to count
Posts: 2,103
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Post-mount disc brakes: changing from 160mm to 140mm?

Is it possible to change from 160mm to 140mm disc brakes and rotors if your frame has post-mount (not ISO) disc tabs? Do frames welded with post-mount tabs allow adjustability when changing to different rotor diameters?
bellweatherman is offline   Reply With Quote
Old 01-15-12, 06:42 PM   #2
mechBgon
Senior Member
 
mechBgon's Avatar
 
Join Date: Jul 2002
Bikes:
Posts: 6,957
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Interesting question. As you probably noticed, post-mount rear disc setups aren't common. If your caliper jives with a 160 when not using an adapter, then it's safe to say 160 is your effective minimum size. If your caliper lines up to a 160 with an adapter, then a 140 may work with the adapter left out. Consult the frame manufacturer if it's unclear whether it'll work or not.
mechBgon is offline   Reply With Quote
Old 01-15-12, 07:19 PM   #3
bellweatherman
Senior Member
Thread Starter
 
bellweatherman's Avatar
 
Join Date: Aug 2005
Location: Austin
Bikes: Too many to count
Posts: 2,103
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by mechBgon View Post
Interesting question. As you probably noticed, post-mount rear disc setups aren't common. If your caliper jives with a 160 when not using an adapter, then it's safe to say 160 is your effective minimum size. If your caliper lines up to a 160 with an adapter, then a 140 may work with the adapter left out. Consult the frame manufacturer if it's unclear whether it'll work or not.


This is specifically why I posed the original question as there is no manufacturer that i am aware of that even offers a manual about the braze-ons and other fittings on a frame.

Plus, AFAIK, there is no such thing as an adapter for changing to different diameter disc brakes and rotor size.
bellweatherman is offline   Reply With Quote
Old 01-15-12, 07:30 PM   #4
AEO
Senior Member
 
AEO's Avatar
 
Join Date: Jun 2007
Location: A Coffin Called Earth. or Toronto, ON
Bikes: Bianchi, Miyata, Dahon, Rossin
Posts: 12,258
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I thought there were ISO to post mount adapters to change disc sizes?
I've never seen a post to post mount adapter that allows different sizes, however.
__________________
Food for thought: if you aren't dead by 2050, you and your entire family will be within a few years from starvation. Now that is a cruel gift to leave for your offspring. ;)
http://sanfrancisco.ibtimes.com/arti...ger-photos.htm
AEO is offline   Reply With Quote
Old 01-15-12, 07:32 PM   #5
reptilezs
Senior Member
 
Join Date: Sep 2004
Location: boston, ma
Bikes:
Posts: 2,852
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
you can upsize but not downsize unless an adapter is already on. most specialized mtb with post mount will fit a 140. my crux disc is 140 rear with no frame clearance for bigger rotors.
reptilezs is offline   Reply With Quote
Old 01-15-12, 07:58 PM   #6
bellweatherman
Senior Member
Thread Starter
 
bellweatherman's Avatar
 
Join Date: Aug 2005
Location: Austin
Bikes: Too many to count
Posts: 2,103
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
The original poster (i.e., me) stated that the frame in question has post-mount disc tabs, not ISO. Sorry, that was not clear.

Anybody ever seen a post-mount adapter? I don't believe they exist.
bellweatherman is offline   Reply With Quote
Old 01-15-12, 08:08 PM   #7
reptilezs
Senior Member
 
Join Date: Sep 2004
Location: boston, ma
Bikes:
Posts: 2,852
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
+20 and +40 adapters are readily available http://www.artscyclery.com/descpage-AVAPA185.html
reptilezs is offline   Reply With Quote
Old 01-15-12, 08:19 PM   #8
jimc101
Senior Member
 
Join Date: Oct 2007
Location: West Yorkshire, United Kingdom
Bikes:
Posts: 4,883
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 53 Post(s)
It's much easier to go larger than smaller, if the frame / forks have a post mount, you are most likely limited to 160mm smallest, 203mm largest via Post to Post adaptor.

Post mount is becoming the standard mount, it already is for forks, and is slowly going that way for frames, all disc calipers are now post mount, and use adaptors to go IS.

What is the need for going down to 140mm? this is almost a dead size, Shimano only ever did it in XTR, and Avid still persist with the BB series, but road disc when they come out will most likly be F180mm/R160 for modulation, killing 140mm forever.
jimc101 is offline   Reply With Quote
Old 01-15-12, 08:45 PM   #9
reptilezs
Senior Member
 
Join Date: Sep 2004
Location: boston, ma
Bikes:
Posts: 2,852
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by jimc101 View Post
It's much easier to go larger than smaller, if the frame / forks have a post mount, you are most likely limited to 160mm smallest, 203mm largest via Post to Post adaptor.

Post mount is becoming the standard mount, it already is for forks, and is slowly going that way for frames, all disc calipers are now post mount, and use adaptors to go IS.

What is the need for going down to 140mm? this is almost a dead size, Shimano only ever did it in XTR, and Avid still persist with the BB series, but road disc when they come out will most likly be F180mm/R160 for modulation, killing 140mm forever.
i just got my crux with 140mm rotor on the rear the other day. already dislike it. not enough power combined with the long full length housing run. frame has no clearance for 160mm. the front 160mm is fine for road duty. i like my brakes powerful with low hand effort
reptilezs is offline   Reply With Quote
Old 01-16-12, 02:15 AM   #10
mechBgon
Senior Member
 
mechBgon's Avatar
 
Join Date: Jul 2002
Bikes:
Posts: 6,957
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by bellweatherman View Post
Anybody ever seen a post-mount adapter? I don't believe they exist.
Yeah, they're commonplace actually.
mechBgon is offline   Reply With Quote
Old 01-17-12, 06:05 PM   #11
bellweatherman
Senior Member
Thread Starter
 
bellweatherman's Avatar
 
Join Date: Aug 2005
Location: Austin
Bikes: Too many to count
Posts: 2,103
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by mechBgon View Post
Yeah, they're commonplace actually.


Link?
bellweatherman is offline   Reply With Quote
Old 01-17-12, 06:44 PM   #12
jimc101
Senior Member
 
Join Date: Oct 2007
Location: West Yorkshire, United Kingdom
Bikes:
Posts: 4,883
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 53 Post(s)
Try Googling! there are lots available, here are a couple for you to start with

http://techdocs.shimano.com/media/te...9830667774.PDF

http://www.chainreactioncycles.com/M...?ModelID=13729
jimc101 is offline   Reply With Quote
Old 01-17-12, 06:52 PM   #13
Bomccorkle
Senior Member
 
Join Date: Oct 2011
Bikes:
Posts: 76
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Why smaller?? If I may ask. I've always liked my brakes as big as possible....
Bomccorkle is offline   Reply With Quote
Old 01-17-12, 06:59 PM   #14
mechBgon
Senior Member
 
mechBgon's Avatar
 
Join Date: Jul 2002
Bikes:
Posts: 6,957
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by bellweatherman View Post
Link?
Well, I could walk up and down my showroom and point some out on Trek Fuel EX's, they're stock equipment. Anywhere you can buy a disc adapter, there should be post-mount models for rotor size changes.

Quote:
Why smaller?? If I may ask. I've always liked my brakes as big as possible....
Weight. Big rotors are heavy, and how much brake power do you actually need on a rear brake (barring tandems)?
mechBgon is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

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



All times are GMT -6. The time now is 08:12 PM.