Triple RD compatible with Compact?

[Podore]

When I convert from Ultegra 10 speed triple to compact crank, will the rear derailleur need to be changed? I have received two different opinions from bike shops. Thanks for the help.

[Ray]

When I convert from Ultegra 10 speed triple to compact crank, will the rear derailleur need to be changed? I have received two different opinions from bike shops. Thanks for the help.
No. If you were going the other way, and introducing a larger spread between big/big and small/small, you might. But going in the direction you're going, you don't need to. You probably COULD go to a shorter cage rear der if you WANT to, but you absolutely don't need to. Some people think the short cage derailures shift more precisely, but I use a long cage mtb derailure on both of my road bikes and I've never lost a race because of it. Of course, I don't race, so ymmv.

-Ray

[stevep]

nope

[Pete Serotta]

nope, you will be fine....Ultegra is good stuff and will handle the chain wrap.


Triple vs non triple rear der - has to do with the amount of chain it will wrap (ie keep tension on the chain) when you go between the various chainrings in front (as well as large cogs in rear).

Long Cage (triple) dr is a little heavier than short cage (so what?)and some say shifts a little slower - it has never been a problem to me. (I am slow)

Pete

[Vancouverdave]

A triple rear derailleur is probably good to stay with because part of the function of a longer-cage derailleur is to absorb the slack chain created by the size difference between front chainrings. The usual front compact rings are 34/50. A sixteen-tooth chainring size difference means a lot of loose chain, especially if the chain is properly long for the large/large combination.
Yeah, I know, we never use it but when we do a long cage rear derailleur and a few links of chain beats a broken rear derailleur and dropout, doesn't it?
On almost any modern shifting system the rear shifts will be as clean and crisp with a long cage as with a shorter cage.

[handsomerob]

I think a side benefit is that long cage may enable you to switch back and forth from a compact to standard crankset without putting links in the chain. :beer:

[johnnymossville]

I have a question along the same lines. When going from a triple to a double on the crankset, is it necessary to change the bottom bracket and front derailleur?

Thanks.

[dave thompson]

I have a question along the same lines. When going from a triple to a double on the crankset, is it necessary to change the bottom bracket and front derailleur?

Thanks.
You will have to change the bottom bracket and only maybe change the dérailleur.

[Ray]

I have a question along the same lines. When going from a triple to a double on the crankset, is it necessary to change the bottom bracket and front derailleur?

Thanks.
Each crankset has a certain bottom bracket width it's designed to work with. In some cases, a double may work on the same width as the triple. In most cases, probably not. Also depends on the bb type - if its external bearings I'd guess that the cups are the same regardless and you'd be fine since the width is taken up with the axle attached to the crank? Assuming the same or compatible brands anyway. With octalink I'm sure there are generally different widths between doubles and triples. With square taper there are different lengths and possibly different tapers if you change the brand of crank you're using.

The triple front derailure may work with a double crank, but in my experience, its pretty finicky. You may need to get a double specific front derailure and, even if you don't absotely need to, you may want to.

-Ray

[palincss]

I have a question along the same lines. When going from a triple to a double on the crankset, is it necessary to change the bottom bracket and front derailleur?

Thanks.

You'd have an unnecessarily wide chain line if you didn't. I don't think anybody ever died of that condition, but it wouldn't be optimal (and people would point and stare at you and remark upon it, and you'd be an object of general ridicule). :p

Going from a double to a triple could cause damage if the chainrings hit the frame.

As for the front derailleur, I have a 105 triple on my commuter. The documentation insisted it wouldn't work with a 39/53 double. I'm friction-shifting it with bar-end shifters, and it shifts great. I have no idea how well it would fare with front indexing, since I don't use it.

[Grant McLean]

I don't think anybody ever died of that condition, but it wouldn't be optimal

That's the funniest thing i've read in a while!

:D

-g

[Podore]

Thanks to all for the input.