Bicycle Mechanics - Simple Ultegra triple to double conversion question.

I feel kinda silly asking because I've worked in shops for a while, I just kinda specialized in high end MTB stuff and didn't pay too much attention to road tech.
Is there a fundamental difference between 9sp triple and double cranks other than the extra drilling for the granny?
I ride a double 9sp ultegra setup right now. Can I buy a used triple crankset, remove the granny, and use it as a double with a 109.5mm octalink? I'm trying to experiment with arm length. Thanks.

Should be close enough for testing purposes. Might require minor readjustments in FD throw in or out.
Steve

Well yea, I figured that FD adjustment was a given, I just wanted to make sure the crank castings didn't have insanely different Q-factor dimensions or spider offsets that would prevent me from using a triple crank as a double.

I just looked at my 9-speed Ultegra triple crank and the bosses that the granny ring bolt on stick inboard a little (2- 3 mm I estimate) from the plane of the middle ring so using a 109.5 mm spindle may let the bosses hit the chainstay. It will probably work but try it carefully at first. The recommended bb is 118.5 mm so the difference is appreciable.

what about the other way around? Can you just take the granny gear chaniring off of a triple and adjust the stops to make it a double?

what about the other way around? Can you just take the granny gear chaniring off of a triple and adjust the stops to make it a double?
That's what we're talking about, spanky. And no, it doesn't work that way depending on your BB and shifter.


Thanks for the observation hillrider. My double has 7-6mm of clearance between the chainstay and the middle ring, so the bosses will clear, especially since they're closer to the BB as the stays come in.

So as long as everything clears, you should be okay? I think I may be reading this wrong... Its been a long day.

If you ride a triple gruppo now, and just want to have two rings, I suppose you could unbolt the granny and adjust the stops, but you would have extra indents in your shifter which would be annoying (personally at least), and it seems like you havent' done much except delete a gear. Unless you absolutely never use the granny, then I would just keep it as is.

I'm trying to use a triple crank on a double setup with a short 109.5mm bottom bracket and double shifters.

I'm trying to use a triple crank on a double setup with a short 109.5mm bottom bracket and double shifters.

Well, 9-speed Ultegra and 105 shifters (not Dura Ace) are both double and triple compatable. There are no specific double shifters. If you use them with a double, you get an extra trim click.

I have a friction FD with downtube shifters. so the extra indents

You have a friction shifter with indents? If it has indexes, wouldn't that mean it isn't friction? Did you just mean downtube shifter?

-Paul

I forgot to finish the sentance. I meant to say I have a friction from D, so I will not have a problem with extra indexes.

Any tech heads want to chime in here with some numbers? Otherwise I'm gonna pick up a set of Ultegra triples tomorrow and gonna swap the rings over and toss it on. I'll let you know how it goes, and how the swithch to 165 works out.