Bicycle Mechanics - Double to a triple?
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If I wanted to transform my road triple that has RSX STI shifters, RX 100 components, and a 7 or 8 speed cassette from a double crank to a triple crank, would I need any more than a new triple crank and front derailer? Can the left hand sti shifter be set for a triple without replacing it? I appologize for my ignorance and appreciate your intelligence. Thanks
Your front derailleur will most likely work fine for a triple; it's the rear derailleur that will most likely need to be replaced. A double crank rear derailleur has a short cage but the rear derailleur for a triple needs a long cage due to the fact that it needs to take up more chain slack. Rear derailleurs are rated by how many teeth they can compensate for. A typical long cage derailleur can compensate for a 30-tooth difference between differing sizes of sprockets.
You will need an STI shifter for a triple crank; your present double STI shifter is not going to work. If you had down tube shifters you would be fine as there is no detent for the middle chain ring and you just use the stops for the big and little chain rings. An STI shifter has detents for all three.
09-17-06, 04:41 PM
A more practical conversion would be going with a compact double instead. Pretty straight forward install.....no other components to replace, in most cases.
09-18-06, 01:20 AM
There apparently was once a device that would allow you to do it. I think that it had an extra lever to shift to the third gear. It was made by Glenn Erickson, and was called a "triple adapter". Unfortunately, I don't think that it was ever widely available.
Sheldon Brown used to have a bike with such an adapter (in fact, the only references I can find are on his site), but he sold it on eBay.
Barring one of these, your options are to either buy a new front shifter, derailleur, chainring, and bottom bracket, or you could go with a compact double. The Stronglight Impact compact double will fit on a square taper bottom bracket, so it might be a pretty easy swap (I just picked one up for about 120 shipped).
Thank you for all your help. It sounds like a compact maybe the way to go in order to get a lower gear when cassette is maxed out.
Triple crankset, triple bottom bracket, both derailleurs.
I agree with Al1943, check the spindle length requirements of the triple crank you intend to buy and I'd suspect you'll need to by a new bb bracet with a longer spindle.
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