Compact Drive Question

[Road Toad]

I currently have Dura Ace triple, 9 spd., on my bike. I am considering switching to compact drive. Aside from the crank, what will need to be switched out? Will the long cage rear derailer and triple specific front derailer be optimal for this set up? Your advice will be greatly appreciated.

 

[shannons dad]

I currently have Dura Ace triple, 9 spd., on my bike. I am considering switching to compact drive. Aside from the crank, what will need to be switched out? Will the long cage rear derailer and triple specific front derailer be optimal for this set up? Your advice will be greatly appreciated.

You don't need to change anything. All triple chainsets need a long cage rear mech. I can't remember why, but there is a reason! Your front mech shouldn't need to be changed either. Why do you want to change anyway?

 

[Road Toad]

"All triple chainsets need a long cage rear mech"

But do compact cranks also use the long stuff?

 

[John M]

I currently have Dura Ace triple, 9 spd., on my bike. I am considering switching to compact drive. Aside from the crank, what will need to be switched out? Will the long cage rear derailer and triple specific front derailer be optimal for this set up? Your advice will be greatly appreciated.

For starters, switching the crank and selecting the appropriate length BB should be fine. Your triple shifters and FD will work with the compact as will the long cage RD. You may get slightly snappier rear shifting with a shorter cage RD, but will be limited as to how large a rear cog you can use (and thus negate some of the benefit of going compact in the first place).

My question is why change from triple to compact? The weight savings is realtively small and the triple can allow you smaller steps between gears for the same overall range of gear ratios. I would suggest that you think about which gear ratios you use most now, and what you would gain (or lose) by switching to compact.

 

[shannons dad]

"All triple chainsets need a long cage rear mech"

But do compact cranks also use the long stuff?

Yup. They sure do.

 

[tanggoman]

I currently have Dura Ace triple, 9 spd., on my bike. I am considering switching to compact drive. Aside from the crank, what will need to be switched out? Will the long cage rear derailer and triple specific front derailer be optimal for this set up? Your advice will be greatly appreciated.

First off, why would you want to change? If its weight you're after, there's not much difference. You can definitely get the same gear combo from a triple and in the compact.

 

[Road Toad]

I appreciate y'alls advice. I spent a few years off the bike (I was a racer until I was 21, am now 32) so I bought the triple thinking that it will take a long time to get my legs back. I quickly shed 20 lbs and can now easily climb anything around here. That is why I was going to change.

 

[tanggoman]

I appreciate y'alls advice. I spent a few years off the bike (I was a racer until I was 21, am now 32) so I bought the triple thinking that it will take a long time to get my legs back. I quickly shed 20 lbs and can now easily climb anything around here. That is why I was going to change.

Now I see! You can change it but I dont know if there would be issues on the length of the triple BB and the FD. What I tried and there were no issues whatsoever was changing a standard double cranks to a compact drive. BB and FD was a sure fit. I just have to lower the location of the FD.

 

[shannons dad]

I appreciate y'alls advice. I spent a few years off the bike (I was a racer until I was 21, am now 32) so I bought the triple thinking that it will take a long time to get my legs back. I quickly shed 20 lbs and can now easily climb anything around here. That is why I was going to change.

Ah well, in that case, don't change anything. There WILL come a day, when you'll greatly appreciate that extra ring.

 

[boudreaux]

You don't need to change anything. All triple chainsets need a long cage rear mech. I can't remember why, but there is a reason!

Well, actually they don't.AFWIW, if you don't know about wrap and cage length wy bother posting drivel?

 

[boudreaux]

You may get slightly snappier rear shifting with a shorter cage RD, but will be limited as to how large a rear cog you can use (and thus negate some of the benefit of going compact in the first place).

That's nonsense..Cage length is about wrap caspacity.not big cog ability.

 

[boudreaux]

Yup. They sure do.

They can,but don't have to.

 

[boudreaux]

You can definitely get the same gear combo from a triple and in the compact.

Don't know how you do that with a minimum chainring of 33 on a compact and a standard 30 on a triple but you can go as small as a 24....

 

[shannons dad]

Well, actually they don't.AFWIW, if you don't know about wrap and cage length wy bother posting drivel?

Here we go again..................
OK, I will admit I made one TINY little mistake. But, he doesn't need to change it. OK with you?

 

[boudreaux]

Now I see! You can change it but I dont know if there would be issues on the length of the triple BB ....

He'll need a shrter BB spindle length.

 

[shannons dad]

That's nonsense..Cage length is about wrap caspacity.not big cog ability.

I'm amazed at how unbelievably rude you are.

 

[boudreaux]

There WILL come a day, when you'll greatly appreciate that extra ring.

Sheot.....boudreaux has 32 years on him and doesn't need a rocker, and warm lap dog.

 

[John M]

That's nonsense..Cage length is about wrap caspacity.not big cog ability.

But I think you would have to agree that since the wrap capacity required is directly dependent on the number of teeth in the largest rear cog and largest chainring, for any given large chainring size the limitation between two rear derailleurs of differing cage lengths to handle the shifting is dependent on the size the largest rear cog. After all, a smaller rear cog will allow a shorter chain, and therefore a shorter cage rear derailleur.

I would then reiterate that for a given setup the limiting factor on whether a short cage rear derailleur can be used is likely to be size of the largest rear cog. That is unless you compensate for the larger rear cog by using a lesser toothed large front chainring-but I doubt that the original poster here wants to go with a 46 or 48T large front chainring.

 

[boudreaux]

But I think you would have to agree that since the wrap capacity required is directly dependent on the number of teeth in the largest rear cog and largest chainring, for any given large chainring size the limitation between two rear derailleurs of differing cage lengths to handle the shifting is dependent on the size the largest rear cog. After all, a smaller rear cog will allow a shorter chain, and therefore a shorter cage rear derailleur.

I would then reiterate that for a given setup the limiting factor on whether a short cage rear derailleur can be used is likely to be size of the largest rear cog. That is unless you compensate for the larger rear cog by using a lesser toothed large front chainring-but I doubt that the original poster here wants to go with a 46 or 48T large front chainring.

A long cage utegra RD has the same big cog spec as the short cage. Cage length is about wrap capacity.Big cog is in the paralleogram. If he uses a 50/34 front and 12x27 rear he is 2 teeth over wrap spec for the short cage. Shimano spec is conservative,and one shouldn't be in the the small cogs anyway...You don't even have to have a long cage with a triple, if you just use the granny as a bailout as it should be and stay out of the small cogs when in the granny.None of my road triples have. a long cage.

 

[Insight Driver]

A long cage utegra RD has the same big cog spec as the short cage. Cage length is about wrap capacity.Big cog is in the paralleogram. If he uses a 50/34 front and 12x27 rear he is 2 teeth over wrap spec for the short cage. Shimano spec is conservative,and one shouldn't be in the the small cogs anyway...You don't even have to have a long cage with a triple, if you just use the granny as a bailout as it should be and stay out of the small cogs when in the granny.None of my road triples have. a long cage.

Here is a good factual answer. Boudreaux knows what he is talking about, folks. Amazing thing is, this is an internet board and there are great sites online, easy to find, often recommended, that talk about the facts and yet you find people who post an answer that means almost nothing other than it shows the lack of knowledge they have. You can get derailur specs on the Shimano site. Sheldon Brown's sites explain the details of gear capacity and cage length.

Now the one thing that does favor a compact over a triple is that you have a crisper-shifting front DR. It's only a slightly better shift, but noticeable.