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Can I use a triple derailer with a double crankset?(3 posts)

Can I use a triple derailer with a double crankset?Bruno S
Jun 18, 2001 9:59 AM
I have just changed a triple crank set for a double because I wanted to have longer cranks that only were offered in double (180mm)

I kept the STI ultegra derailer the bike had but its a triple. It is not working properly. With the triple I could use any of the 9 cogs with any two largest chain rings. When using the smallest I could not use the small cogs (high gears) but I never used that combination anyway. Now with the double, I can only use the 4-5 high gears with the big chain ring and 4-5 low gears with the small chain ring. Any other combination and the chain starts to rub against the cage. I have tried to adjust the limits but I haven't been able to make it work like it used to with the triple. I believe the LBS changed something in the STI shifters because it only has two positions now instead of three.

I guess another questions is: Does a properly adjusted triple derailer allow me to use any of the 9 nine gears with any of the two chain rings of a double crankset?
Absolutelygrz mnky
Jun 18, 2001 11:17 AM
You didn't make much distinction between front and rear der.s and component level, but if we're talking Shimano 105 or Ultegra it shouldn't really matter. The rear der. just has a longer cage while the front actually has some difference in the shape of the shifting plates for the higher chain deflection angle required by the triple. The STI shifters are the same regardless. You should confirm that the BB was swapped out - the triple uses a longer unit.

The crux of your problem is that your cable length is not set correctly. It sounds like you are indexing, but only through about half of the range.

First confirm that the limit screws are set wide enough that you can move the der.s through their full range. Next drop the rear into the smalest cog. Lightly grasp the rear der. cable along the seat stay and verify that the STI shifter is released all of the way. Now move the rear up ONE click (gear) and adjust the cable so that you are in the second to smallest cog. Now you should be in phase and able to hit each gear. The front der. is basically a repeat of the process, but focus on making things work on the large chain ring. Verify that you get all of the 1/2 shifts. There are 5 "detents" of positions available with the front STI lever.

Getting a copy of a set of Shimano instructions may be helpfful as well as the Park Tool website or Sheldon Brown (sheldonbrown.com). Setting up the gearing to work right is a bit subtle, but a roadie LBS should be able to do this correctly the first time - do they focus more on MTBs?
Its just a lousy LBS...Bruno S
Jun 18, 2001 8:41 PM
I went there because they had good prices but its not my regular bike shop. I could take the bike there and ask them to adjust it better but its far away from were I live. I'll give it one more try myself and if I am not succesful I will take it to the good LBS. Thanks for the reply.