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BB for Crank Upgrade from RSX to Ultegra(10 posts)

BB for Crank Upgrade from RSX to UltegraTarzan
Sep 17, 2001 6:44 PM
Would I need to change my bottom bracket if I want to upgrade from RSX to Ultegra?

P.S. The reason I want to do this is that the crank arms are too long. They're 175mm and I'm 5'3 eith a 29" inseam.
re: BB for Crank Upgrade from RSX to Ultegranestorl
Sep 17, 2001 7:06 PM
Again, you are right 172s are too big...and don;t believe when people ask you to "see" how small is the 2.5mm... The force during an entire rotation makes the mm change significant. Read about it alot.
Now about the crankset. Ultegra has a splined system and the RSX most likely has an old squared system. They are not compatible. Get the ultegra BB for 29 at supergo. Although they do not have the 165s CSet...Performance does.
Once you get it be very very very careful about the splined style installation... you can destroy your cranks and the BB if you do not know what you are doing... read a lot a bout it, do not simply trust the shimano instructions (they are purposefully designed to be worthless), or take it to a good LBS. Hope this helps
re: More info on crank arm length & BB for RSX crankTarzan
Sep 17, 2001 11:47 PM
Thanks alot for your reply. Tell me where to read more about crank arm length.

How do I figure out if the BB for the RSX crank is splined or not?

Once I figure it out, I suspect I'll have my LBS install the BB. Thanks for the warning.
re: More info on crank arm length & BB for RSX cranknestorl
Sep 18, 2001 3:21 AM
If the cranks are splined then the bb is splines. If the cranks end up being self extracting then by default the bb is self slined, but if you need a crank extractor then it is squared. You will see the difference once you take the cranks out. Splined bb are holow and have a round shape with litlle serrations. Squared tapered are solid and simply have a square bolt that fits the square hole on the cranks.
re: RSX cranks......Rusty
Sep 18, 2001 6:03 AM
all used a tapered spindle. 9 speed ultegra cranks/spindle are splined. Pre 9 speed ultegra cranks used tapered spindle. Depends on what ultegra you are talking about.
Simple! It's splined!Tarzan
Sep 18, 2001 11:58 AM
Bottom brackets.nee Spoke Wrench
Sep 18, 2001 6:51 AM
Since the bottom bracket is the interface between the crankset and the frame, it obviously has to match both.

Most road frames today use 68mm wide bottom bracket shells and English threads.

When you buy a brand new crankset, all good suppliers will provide you with guidance regarding spindle length. It will usually say something like 111/115. Use a 111mm bottom bracket spindle with a 68mm bb shell and a 115mm spindle if you have a 73mm botom bracket shell. As a general rule, newer cranksets require shorter BB spindles than older cranksets.

You obviously can't mix and match splined cranksets and bottom brackets because the splines have to match. It's also better not to mix and match Shimano and Campy square tapered BB's because the cross sections are a little different. A Campy crankset won't pull far enough onto a Shimano compatable BB spindle.

In rare cases, all of this still isn't good enough. Bikes with big fat seat tubes, for example, sometimes need a little bit wider BB spindle. Occassionally you still have use a little trial and error guesswork.
re: Upgrade from RSX to UltegraChen2
Sep 18, 2001 7:30 AM
What size are your chain rings? Tooth count? RSX chain rings may be much smaller than the Ultegras. I'm asking this because if your RSX rings are smaller than the Ultegra rings you are going to realize a big change in gearing when you make the upgrade. This could be good or bad.
You might need to contact a bike shopAtombomber
Sep 18, 2001 7:34 PM
Shimano has a service manual that lists all component pieces of that certain model year. In it there is a compatibility chart which shows what cranks can go with what BB. I can't say if the RSX uses the same splines as Dura Ace, Ultegra or XTR or if the spline shape is that of XT/LX. I think that even 105 differs from the senior road versions. I'll try to find out some more, just to satisfy my curiosity, now that it has been piqued.
Further research on the net resulted in...Atombomber
Sep 18, 2001 7:44 PM
The RSX was available only in Square Taper. If you go to the older Ultegra, you should be able to use you current bottom bracket. When Ultegra went to 9 speed, they changed the crank and bottom bracket interface (as well as many other things) such that the system now has splines on a hollow tubed spindle. You will need a new BB if you get a current design Ultegra crank.