Road Bike, Cycling Forums banner
1 - 8 of 8 Posts

· Registered
Joined
·
176 Posts
Discussion Starter · #1 ·
I was wondering if there is a compact crankset that is able to be used with the DA 7800 shimano BB. I know i can use the ultegra level compact, but are there any others out there? I want the compact for certian hill climb and will only use it once in a while.
Also comment on setup/swapping the shimano compact w/ the regular DA double.
It looks to me like it would be as easy as changing a cassette..
 

· Steaming piles of opinion
Joined
·
10,520 Posts
b987654 said:
I was wondering if there is a compact crankset that is able to be used with the DA 7800 shimano BB. I know i can use the ultegra level compact, but are there any others out there? I want the compact for certian hill climb and will only use it once in a while.
Also comment on setup/swapping the shimano compact w/ the regular DA double.
It looks to me like it would be as easy as changing a cassette..
The external bearing Shimano's are the same as the FSA Mega-Exo's, so those would be interchangeable as well. My bike currently has FSA cranks running in Ultegra bearings. I've not had my hands on the new shimano crank, but as they're all pretty much the same I can say yes, it's not that hard to change.. But....

Swapping them back and forth isn't as easy as a cassette. Sure, swapping the crank is that easy, maybe even easier. But to get better shifting performance, you'll want to lower the front derrailleur for use with the compact, which then necessitates a cable adjustment, and so on. With cassette swaps, I rarely need more than a twist or two of a barrel adjuster.

I don't want to oversell the trouble. If you work on your own bike, it's a half-hour at worst to swap and adjust the cranks. I spent an hour at it the first time, but only because I installed all four possible combinations (really, three plus the one I started with) of bearings and cranks to see if the parts were truly compatible.
 

· Registered
Joined
·
180 Posts
I agree. Shimano's compact crankset is designed to work with their standard double front derailleur. That said, in order to switch between a double and a compact crankset, you'll likely need to modify your chainlength as well as adjusting the front derailleur. I live in the mountains, so a compact with an 11-25 has been pretty nice for me. As I get stronger, I'd imagine I will eventually move to a standard road double. Avoid the triple's like the plague - the chainline on them sucks and even the high end versions shift like poo.
 

· Registered
Joined
·
274 Posts
Largets number of teeth...

Can anyone tell me the largest number of teeth a DA 7800 rear derailleur would be able to handle without haveing to lengthen the chain or make any other major adjustments. Currently riding a 12-25 cassette, is a 12-27 the largest? Is that also the largest available? Thanks
 

· Steaming piles of opinion
Joined
·
10,520 Posts
ifcjti said:
Can anyone tell me the largest number of teeth a DA 7800 rear derailleur would be able to handle without haveing to lengthen the chain or make any other major adjustments. Currently riding a 12-25 cassette, is a 12-27 the largest? Is that also the largest available? Thanks
Depends on how long your chain is now. Shouldn't need a change, unless it's already closer than normal to the limits. 2 teeth on a cog is worth approx. half a link of chain length, so normally it wouldn't matter. And if you're changing to a compact at the same time, you are effectively getting that half link back, so it nets to zero.

The DA 7800 specs are as follows:
Max. Front Difference 16T
Total Capacity 29T
Max. Rear Sprocket 27T
Min. Rear Sprocket 11T

Part of your question doesn't strictly relate to chain length.
27 is the largest rear cog the 7800 will take, so it's OK in that regard.

However, (50-34) + (27-12) = 31, so running a 12-27 and a "standard" compact is over the 29 tooth capacity by 2 teeth. Shimano's numbers are known to be conservative, and it's not a problem unless you ride in the extreme crosses, which you shouldn't do in any case. There are those who say they've run this combo without troubles, and based on what I've seen I have no reason to doubt it.
 

· Registered
Joined
·
72 Posts
I have a DA7800 setup on one of my bikes and swap the DA crankset back and forward with a new Shimano Compact. Takes less than 10 minutes. I've marked the seat tube with the relative positions for the front der so that's no big deal to adjust either. No change to chain length (don't even need to break the chain) or any other fiddling. Easy!
 

· Registered
Joined
·
5,358 Posts
danl1 said:
However, (50-34) + (27-12) = 31, so running a 12-27 and a "standard" compact is over the 29 tooth capacity by 2 teeth. Shimano's numbers are known to be conservative, and it's not a problem unless you ride in the extreme crosses, which you shouldn't do in any case. There are those who say they've run this combo without troubles, and based on what I've seen I have no reason to doubt it.
I run that combo. The chain length needs to be just right but it works fine. I can just shift into the big/big combo (in case I make a mistake while shifting). If you can find one, you can use a GS rear derailleur instead of an SS. The GS has a longer cage so it can handle more chain wrap. It weighs about 10g more. Then chain length will not have to be quite as exact.
 
1 - 8 of 8 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top