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

43.5mm Chainline on a Hybrid? Large Chainrings on MTB Crankset?

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.

43.5mm Chainline on a Hybrid? Large Chainrings on MTB Crankset?

Old 06-10-21, 06:35 AM
  #1  
Moisture
Drip, Drip.
Thread Starter
 
Moisture's Avatar
 
Join Date: Oct 2020
Posts: 1,046
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 694 Post(s)
Liked 112 Times in 94 Posts
43.5mm Chainline on a Hybrid? Large Chainrings on MTB Crankset?

Hi all.. I've acquired a new bike last month..


Its a 2012 Trek FX 7.3, 22.5" frame. Its currently equipped with a Shimano Acera M361 mtb crankset, with three chainrings and a 50mm chainline. I just bought a new crankset with the same chainline designed for double chainrings.. -


The BCD is 104/64. I could've ordered it with 26/38t, but I'm planning to find and use 36/48t rings which should be more suitable for a hybrid bike. I heard that using a larger chainring such as 48 or 50t on a crankset with only 4 arms isn't a good idea. Will I be fine or should I buy a road crankset with the 43.5mm chainline and 110bcd?
Moisture is offline  
Old 06-10-21, 06:40 AM
  #2  
trailangel
Senior Member
 
trailangel's Avatar
 
Join Date: Feb 2014
Location: Pasadena, CA
Posts: 4,650

Bikes: Schwinn Varsity

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1783 Post(s)
Liked 549 Times in 324 Posts
trailangel is offline  
Old 06-10-21, 09:36 AM
  #3  
Moisture
Drip, Drip.
Thread Starter
 
Moisture's Avatar
 
Join Date: Oct 2020
Posts: 1,046
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 694 Post(s)
Liked 112 Times in 94 Posts
I read that the innermost cog on a 43.5mm chainline triple crankset may have trouble clearing the chainstay. Im upgrading to a double. I should still stick to the 50mm mtb crankset which this bike was designed around, correct?
Moisture is offline  
Old 06-10-21, 11:54 AM
  #4  
70sSanO
Senior Member
 
70sSanO's Avatar
 
Join Date: Feb 2015
Location: Mission Viejo
Posts: 3,569

Bikes: 1986 Cannondale SR400 (Flat bar commuter), 1988 Cannondale Criterium XTR, 1992 Serotta T-Max, 1995 Trek 970

Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 1027 Post(s)
Liked 833 Times in 554 Posts
The only way to really know is to measure your current chainline using the middle chainring.

You can always see how well it is centered on the cassette.

As for the new crank, I doubt there is an issue with a 48t on a 104bcd 4 arm. Shimano offers your original FC-M361 with a 48t and it is 104bcd.

Which does bring me to your current Shimano crank. From the tech docs I believe the BB for an M361 has a 123mm BB.

If you are that concerned about chainline, why not just get a 73x118 square taper BB, remove the inner ring, and use your Acera crank with the middle and outer positions? You may want to first take some measurements to ensure clearance, but you’ll get approx 50mm chainline as a double.

John
70sSanO is offline  
Old 06-10-21, 12:35 PM
  #5  
Moisture
Drip, Drip.
Thread Starter
 
Moisture's Avatar
 
Join Date: Oct 2020
Posts: 1,046
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 694 Post(s)
Liked 112 Times in 94 Posts
Originally Posted by 70sSanO View Post
The only way to really know is to measure your current chainline using the middle chainring.

You can always see how well it is centered on the cassette.

As for the new crank, I doubt there is an issue with a 48t on a 104bcd 4 arm. Shimano offers your original FC-M361 with a 48t and it is 104bcd.

Which does bring me to your current Shimano crank. From the tech docs I believe the BB for an M361 has a 123mm BB.

If you are that concerned about chainline, why not just get a 73x118 square taper BB, remove the inner ring, and use your Acera crank with the middle and outer positions? You may want to first take some measurements to ensure clearance, but you’ll get approx 50mm chainline as a double.

John
My new crankset has 190mm cranksets. Its about 1 or 2mm too long according to my inseam (21.7% of 87.5cm, but its the best i can do regarding the current situation with forging factories.

my new crankset will replace the square taper bottom bracket with outboard bearings and an integrated spindle. I should have measured the chainline firsthand...

I would have stuck with the 28/38/48 triple which I have now currently, but I prefer something between 185-188mm crankarms. I find myself cranking out the same cadence in lower gears when using the typical 170 or 175mm arms.

So would a road crankset work fine on this bike?
.
Moisture is offline  
Old 06-10-21, 12:39 PM
  #6  
alcjphil
Senior Member
 
alcjphil's Avatar
 
Join Date: Jun 2002
Location: Montreal, Quebec
Posts: 4,452
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 1157 Post(s)
Liked 561 Times in 369 Posts
Originally Posted by Moisture View Post
My new crankset has 190mm cranksets. Its about 1 or 2mm too long according to my inseam (21.7% of 87.5cm, but its the best i can do regarding the current situation with forging factories.

my new crankset will replace the square taper bottom bracket with outboard bearings and an integrated spindle. I should have measured the chainline firsthand...

I would have stuck with the 28/38/48 triple which I have now currently, but I prefer something between 185-188mm crankarms. I find myself cranking out the same cadence in lower gears when using the typical 170 or 175mm arms.

So would a road crankset work fine on this bike?
.
What is the width of the bottom bracket? If it is wider than 68 mm a road crank won't fit
alcjphil 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.