Compact chainrings

Ian00

Hi all,

First time post ...
Just had a question around whether it's possible to get compact chainrings to fit a '07 Ultegra standard 53/39 crankset ?
I see Shimano are bringing these out for the new Ultegra groupset in 2008.

My knees don't seem to stand up to grinding a big gear these days, so I am toying with the idea of getting some FSA compact cranks (only brand I've seen advertised much) or fitting smaller chainwheels to my existing cranks.

Is this possible & would I need to change my front (Ultegra) derailleur or bottom bracket ?

Thoughts/comments would be appreciated

Cheers,
Ian

nerdag

No. Compact and standard rings have a different bolt circle diameter (130mm vs. 110mm).

A good alternative are the Shimano R700, R600, or R4550 cranksets.

R700 is Ultegra grade - hollowtech II and everyhting else with smaller rings. R600 has solid crankarms, so its a bit heavier, but the same 10sp rings as the R700.

All of these sets use the same external BB as the ultegra you currently have now.

If you're on a budget, then consider the R4550 Compact - specified/marketed as a 9sp, but works fine with 10sp if you use a 10s chain and FD (yes, I have tried it and it works well). Cell bikes have these for a pretty decent price if you are looking for a local dealer.

n

Ian00

Cool thanks ! - well there you go didn't know they used different bolt sizes.
Thanks for the info on mdel numbers - found this too for anyone else interested
http://sheldonbrown.com/harris/cran...act-double.html

So I guess the FSA's would need a different bottom bracket too ?

nerdag

IIRC, FSA and Shimano external BBs are interchangable.

n

alfeng

You can put a 38t 130BCD chainring on your current crank ...

I think IRD has 12-30t cassette ... BUT, if that was the gearing you wanted, then you would just need a 30t cog & the desire to restack your rear cassette (NOT difficult ... you just need to decide which of the intermediate cogs you want to remove ... e.g., 15t). It's probably cheaper to cannibalize a 9-speed LX cassette for the cog than to buy a separate cog through your LBS.

If you substitute the 11t UPPER pulley wheel with a 10t, you should be able to use a 32t cog on the back with your current rear derailleur (a 39t chainring & a 32t cog is a slightly lower ratio than a 34t chainring & 27t cog) ... you might have to make an adjustment to the B-screw (at the rear of the derailler -- it adjusts the angle of the parallelogram ... it is BETTER to make this adjustment when the derailleur is NOT on the bike).

If you eventually decide that you want a 34t cog in the back with your 39t inner chainring (close to, but not quite as low, a gear as having a 34 chainring & 30t cog), then you will want to get an LX/XT/XTR rear derailleur and use the hubbub.com alternate rear derailleur cable anchor position to make it index with a 10-speed STI shifter & 10-speed Shimano cassette. Now, if you happened to go the re-stacking route with a cannibalized 11-34 9-speed Shimano LX cassette, you would have the 34t cog (but, not the rear derailleur unless you have a MTB that you want to cannibalize, too!) if you wanted an even lower gear.

The Shimano rear derailleurs are capable of an 8t (possibly, greater) "jump" between rear cogs.

Of course, there is an aesthetic trade-off with having a really LARGE cog on the back which some die-hard roadies won't want to make ...

alfeng

I can confirm that they are interchangeable.

caferacerwanabe

the new Ultegra SL compact cranks are pretty sweet.

Ian00

thanks & also to n

Ian00

Can you pls explain y it's better to adjust the B screw when the derailleur is off the bike ? B screw is used to make sure the pulley doesn't touch the smallest sprocket right ?

LeDomestique

[QUOTE=alfeng]

The Shimano rear derailleurs are capable of an 8t (possibly, greater) "jump" between rear cogs.

QUOTE]

Lots of info in your post, thanks

Do you know if you can use a 30T cog with the standard cage DA derraileur (10 speed)?

thanks again

alfeng

Yes, the B-screw is used to adjust the upper pulley wheel's offset from the cogs.

I find it easier to do when the derailleur is not attached to the frame because of the resistance encountered by "pushing" the screw against the tab on the derailleur hanger when the derailleur is attached to the frame vs. when it is off the frame.

Of course, if you want to make the adjustment when the derailleur is attached, you will quickly see what I mean ... it may not bother you ... but, minimally, on the downside of making the adjustment when the derailleur is attached is that you are grinding the B-screw into the forementioned tab.

So, "easier" is a term which you may choose to discount BECAUSE it is less convenient to remove the derailleur & then re-install it ...