Have questions or want to discuss cycling? Join Now or Sign In to participate in the BikeRide community.

New: Take Part in the June Giveaway to Win the Kazam Buddi 20" Aluminum Trailer Bike


Help with compact dbl
#1
I have a 53/39 standard double. I want to get a 50/34 compact double, and need help identifying which parts are compatible. I have a TruVatia Elita, Isis drive, with a Shimano 105 front derailer. The center of the crank arm has "68/108 BB Only" on it. I've seen some compact dbls with the bottom bkt. Should I get one of those. My bike is a 2004 Cannondale R700.
  Reply
#2
Is your front derailleur a clamp on or braze on ? if it is braze on that may impede your crank selection. Your crank would determine your BB spindle length. so if your spline type and length differ from Isis/108 replace it. just make sure you get one for your 68mm shell width
I think you have to have a clamp-on style front derailleur if you cannot move it down the tube. check the specs of the FD to make sure it can handle the 16t difference also
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
  Reply
#3
You might also need a new chain due to the length changes with any gear changes.
  Reply
#4
(01-22-2012, 11:12 PM)AndrewB Wrote:  You might also need a new chain due to the length changes with any gear changes.
at most you would shorten the chain you have for this mod. if your chain is good leave it and shorten to proper length.
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
  Reply
#5
(01-22-2012, 08:48 PM)painkiller Wrote:  Is your front derailleur a clamp on or braze on ? if it is braze on that may impede your crank selection. Your crank would determine your BB spindle length. so if your spline type and length differ from Isis/108 replace it. just make sure you get one for your 68mm shell width
I think you have to have a clamp-on style front derailleur if you cannot move it down the tube. check the specs of the FD to make sure it can handle the 16t difference also

So the 68 is the diameter of the bottom bracket and the 108 is the length from side to side? How do I calc the 16t difference and how do I ck it.
Tx- Jeff
  Reply
#6
(01-23-2012, 12:15 PM)Jeff5 Wrote:  
(01-22-2012, 08:48 PM)painkiller Wrote:  Is your front derailleur a clamp on or braze on ? if it is braze on that may impede your crank selection. Your crank would determine your BB spindle length. so if your spline type and length differ from Isis/108 replace it. just make sure you get one for your 68mm shell width
I think you have to have a clamp-on style front derailleur if you cannot move it down the tube. check the specs of the FD to make sure it can handle the 16t difference also

So the 68 is the diameter of the bottom bracket and the 108 is the length from side to side? OK-I got it (50-34=16) How do I ck if my FD will be OK with the 16t diff.
Tx- Jeff
  Reply
#7
(01-23-2012, 12:15 PM)Jeff5 Wrote:  ......

So the 68 is the diameter of the bottom bracket and the 108 is the length from side to side? How do I calc the 16t difference and how do I ck it.
Tx- Jeff

Yes 68mm is diameter of the BB, and 108mm is the length.

16T difference - is the difference between the largest and smallest cogs on the chain ring: 50-34=16, vs 53-19=14. Front derailleurs are rated for this difference in number of teeth. Should not be an issue. You can check the tech docs that Shimano has on the web.
Nigel
  Reply


Possibly Related Threads...
Thread
Author
Replies
Views
Last Post

Forum Jump:

[-]
10 Latest Posts
1994 Trek 730
Today 11:44 PM
Freehub pawls or ratchet : Grease or oil...
Today 11:39 PM
Would you use WD-40 for cleaning and/or ...
Today 11:30 PM
Anybody watch on YouTube Global Mountain...
Today 05:03 PM
Bianchi Oltre Pro Garmin Mount
Today 10:57 AM
How to keep your bicycle safe?
Yesterday 03:20 PM
1998 Cannondale H300 Hybrid
Yesterday 03:16 PM
Community Discussion Cycling Myths
Yesterday 03:01 PM
Sora, shift gear cable stuck (wrongly in...
Yesterday 12:12 PM
Man on e-bicycle, Fire, pregnant woman!
Yesterday 09:15 AM

[-]
Join BikeRide on Strava
Feel free to join if you are on Strava: www.strava.com/clubs/bikeridecom

[-]
Top 5 Posters This Month
no avatar 1. Jesper
33 posts
no avatar 2. Flowrider
24 posts
no avatar 3. meamoantonio
21 posts
no avatar 4. GirishH
18 posts
no avatar 5. enkei
18 posts