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


Upgrading from downtube to modern shifters
#1
I have a 1987 Cannondale SR500 which I am considering upgrading to a more modern drive train. I am leaning towards collecting Shimano 105 parts from eBay with a triple chain ring. I have various things I need to figure out. For the moment I want to understand how to route the cables beyond the down tube on up to the combination shifter/brake levers on the bars.
Any ideas?

  Reply
#2
There are very standard cable stops that replace the downtube shifters. The cable housing runs from the "brifters" to the downtube.

A bigger issue is the rear spacing. Is your bike a 6 or 7 speed? Either way, it probably has 126mm spacing in the back. 8 speed and above uses 130mm spacing. It's only 4mm difference, but it's generally not recommended to flex an aluminum frame. Ideally you'd find some old 7 speed parts in good shape, but they're getting rarer.
There's ways to play around and fit the 8-9-10 speed hubs in there, but then you're also buying a wheel or at least a hub.
Triple crank might require a longer BB spindle.
  Reply
#3
How do you measure this spacing? What is on the bike is a 6 speed SunTour with a Maillard 400CX sealed mechanism 36 hole hub. When I measured the spacing between the inside of the frame drop outs I only get about 107 mm. Since that is so much less than what you suggest, I suspect I am not measuring the right thing.

  Reply
#4
Actually I found a good picture at http://sheldonbrown.com/frame-spacing.html that shows how to measure. I will try that and see what I get.

  Reply
#5
I don't know why I got such a small number before. I clearly get 126 mm. So I can look for a 7 speed freewheel but I imagine I need a threaded one.

  Reply
#6
Yes, you would need a freewheel and not a cassette. If you get a shimano or "shimano-compatible" freewheel, it will work with shimano 7 spd shifters. You might be able to use an 8 speed shifter with one click locked out. But I'd do a little checking on compatibility between 8 and 7 speed stuff. I can't remember what all works with what.

  Reply


Possibly Related Threads...

Forum Jump:

[-]
10 Latest Posts
New Travel Battery
Today 04:31 AM
Bike lines @San Diego
Yesterday 10:05 AM
The great thing about trikes
Yesterday 09:58 AM
Pros and cons of hydraulic brakes
Yesterday 05:18 AM
Pros & Cons of presta valve vs schrader ...
Yesterday 01:19 AM
Peak Power - how to calculate
07-20-2025 12:39 PM
Biking with helmet laws
07-20-2025 09:56 AM
Velotric Nomad battery - does anyone els...
07-19-2025 04:57 AM
New rider — happy to be here
07-17-2025 10:47 PM
Best bike for tall and big rider
07-17-2025 09:43 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. GirishH
30 posts
no avatar 2. Flowrider
19 posts
no avatar 3. meamoantonio
16 posts
no avatar 4. rydabent
16 posts
no avatar 5. enkei
15 posts