Bicycle Mechanics - Can I switch from Standard Double to Standard Triple Crankset?
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03-23-11, 07:04 AM
Will my Front Derailleur work if I switch from a standard 53/39T double crankset to a standard 53/39/30T triple crankset but remove the last 30T chainring and not use it? I want to have a shorter crank and may be able to get one but it is a triple instead of a double crank. Front Derailleur is a campy veloce.
I'm thinking the triple chainring spacing is a little different than the double... does that not work for the FD? Would I just need to adjust the derailleur?
Let me know. And thanks in advance.
03-23-11, 07:53 AM
The spacing between chainrings is the same. What differs is the length of the bottom bracket axle, a triple sticks out further. The pedals are going to stick out further with a triple bottom bracket. If both are using the same type of bottom bracket, you can just exchange cranks.
03-23-11, 10:09 AM
So if I used the same bottom bracket as the one for ultegra 53/39T double crank and changed it to an ultegra 53/39/30T triple crank, and removed the 30T ring... The crank will still stick out a little more than the double, no? Do I need to replace the front derail or can I just adjust the existing derailler?
Suggest you check it out before committing to a new crank.
Shimano makes two different FD in the Ultegra group. One for the double and another for their triple. The difference is the travel and reach of the FD. A double has a chainline of 43.5mm and a triple has a chainline of 45mm, but because of the way chainline is speced by Shimano - you`re really looking at a difference of 5mm in reach.
So since you aren`t using a Shimano but have a FD already installed - suggest you just back off the H stop screw on the FD and see if it`ll run out to cover another 5 to 6mm past the current outer chainring. If it will - you`re good to go. If it won`t better wait for a double that suits you or be prepared to buy a new FD.
03-23-11, 12:08 PM
If we were talking about older cranks/BB like square taper or Octalink, then you could get a shorter BB and get roughly the same chainline as you had before. With the newer Hollowtech II and integrated BB spindle, you're pretty much stuck with the chainline specified.
Chainrings are about 5mm center-to-center (EDIT: this is the spacing). A Triple has a chainline of 45mm, at the middle ring, which means the outer ring is at about 50mm. A double has a 43.5mm chainline, measured halfway between the two chainrings, so the outer ringsits at about 46mm.
If your FD can swing another 4mm out from where it currently is (with the H-limit screw backed out), it'll be able to get out to the triple's outer chainring.
03-23-11, 03:18 PM
Ok... this is good info. Thank you again for the help. I appreciate it.
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