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-   -   Ultegra SL Crank (https://www.bikeforums.net/touring/746510-ultegra-sl-crank.html)

sheller73 06-25-11 08:36 AM

Ultegra SL Crank
 
I am currently running an SL road triple with a 12-27 in the rear. I recently just purchased a 11-32 Sram PG1070 cassette to replace the 12-27. I am looking to replace the SL's chain rings with a 48/36/26 set-up and was curious what problems I may run in to. I got some good info from friends but just doing more research before I attempt this.

Will I need a new FD? I read up on Peter White's site and came across his explanation as follows...

Lowering the gearing with a ten speed Ultegra crank is not really viable. The reason is the design of the front derailleur. The inner plate of the 6600 series triple FD is lower than the 9 speed version, to accommodate the 39 tooth middle ring on the ten speed crank vs the 42 tooth ring on the 9 speed crank. For the FD to properly control the movement of the chain from ring to ring, the sizes of the two outer rings must match the derailleur's shape. The relative size of the inner ring on a triple is less critical than the relative sizes of the middle and outer rings. So you could reduce the 52 - 39 - 30 to 51 - 38 - 29 and everything would work, but that's a bit silly. It's not enough of a change to warrant the expense of changing.

So, with that being said, do I need to replace my SL FD with a Deore XT M770 10-Speed Front Derailleur if I change out the chainrings from the 52/39/30 to a 48/36/26?? I am using a 9spd XTR RD btw

Any opinions, thoughs, recommendations would sure be appreciated!

Thanks!!

sstorkel 06-25-11 09:29 AM

You don't say what type of shifters you're using, but be aware that the Deore XT FD requires different cable pull than the Ultegra FD. Which means that it won't work with Ultegra STI shifters.

I have Ultegra STI shifters and an Ultegra triple FD on my touring bike, combined with a 9-speed 48/36/26 Deore trekking crank. Had to remove one of the spacers from the drive-side of the bottom bracket to get the chainline to work. With a little adjustment, shifting is fine. Perhaps not as smooth or quick as with the original Ultegra triple crank, but I have no complaints. There was another recent thread where a rider complained that lowering the Ultegra FD to accommodate a 48-tooth chain ring meant that the derailleur cage was hitting the chainstay. That wasn't a problem for my frame+derailleur, though I probably had the FD set a bit higher than normal due to having to avoid a water bottle boss.

No idea what happens if you simply replace the chainrings on the Ultegra crank, unfortunately.

sheller73 06-25-11 09:38 AM

Ah yes... I apologize... I am using Ultegra STI shifters.... I forgot the obvious! lol Thanks! Maybe just lowering the 30 to a 26 would work... that's where I would really need it the most after all

GeoKrpan 06-25-11 09:55 AM

Try riding the crank as is with the new 11-32 cassette. There will only be a miniscule difference in the lowest gear. With a 700x32 tire the 30/32 combination nets 25.3 GI, the 26/32 21.9 GI, only about 3 GI difference.
A 34 tooth cog on the rear would have netted you 23.8 GI, a 36 tooth 22.5. Or, just replace the inner chainring with a 26 tooth.

sheller73 06-25-11 12:23 PM

Geo... that's what we were just talking about a lil bit ago.... the inner ring swap with a steel 26tooth and leave the rest as is. I think that is probably the best and cheapest solution!

oldride 06-25-11 02:10 PM

I don't think your Ultegra crank will accomodate a 26t inner ring. You need to check and compare the BCD of the crankset and the 26t ring.

sheller73 06-25-11 02:23 PM

2 Attachment(s)
Will do Old!! Thanks for your input!http://bikeforums.net/attachment.php...hmentid=208011http://bikeforums.net/attachment.php...hmentid=208012

desertdork 06-25-11 07:27 PM

The smallest middle ring you can fit on the Ultegra triple crank is 38t, regardless.

Andiroo99 06-25-11 09:25 PM

xx


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