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Conversion - Which deraileur should I buy?(3 posts)

Conversion - Which deraileur should I buy?c722061
Apr 10, 2003 12:49 PM
Hello All,
A friend of mine just bought a 7 speed cassette (12-30) to replace the cassette (12-23, i guess) on his 105 index 6 speed. By using his own shortcase Shimano 105 deraileur, he cann't use the 30 teeth ring due to chain rubbing. I advised him to replace with a MTB deraileur.

There are Shimano 8/9 speed, 7 speed and SRAM 6/7 speed available on mail orders, we just do not know which one to buy. If you have had experience with this type of change, please give us some pointers. Thanks,
re: Conversion - Which deraileur should I buy?Rusty Coggs
Apr 10, 2003 2:32 PM
first,make sure the chain is long enough to handle the big/big,just in case.Then try adjusting the B tension screw on the back of the derailer.I think spec on that derailer was 28 teeth for large cog ,and I have always been able to get them to handle more. Don't use a Sram ESP rear derailer with shimano indes.
LX is MTB equivlent to 105.Spoke Wrench
Apr 10, 2003 3:17 PM
Going from 23 to 30 teeth on the big cog is a fairly significant change. If he didn't install a new longer chain along with the new cassette, he definitely should.

A cassette with a 30 tooth big cog is kind of in between. It's on the big side to work with a road derailleur (although it might), and it's on the small side to need a mountain derailleur.

If it was my bike, the first thing I would do would be to dial the B tension screw on the existing 105 derailleur in all of the way to try to get the upper jockey pulley to miss the big cog. If that didn't work, I'd get an LX 8/9 speed rear derailleur.

A SRAM derailleur probably won't work on this bike.