M730 & M550 chain rings ?

[Moto]

Can somebody confirm :

1) if the chainrings for deore LX M550 & Deore XT M730 are interchangeable. Photo's suggest they may be but I can't find any info either way.
2) what is the difference between XT chainring letters in front of the number (of teeth) to ID them. Some chainrings are stamped 46, others are stamped A46, B46 or C46. Again is it OK to mix letters on the same chainset?

Thx for any help

Moto

 

[hamster]

Yes, they are completely interchangeable. The M550 ones aren't as nice, having stamped teeth rather than the machined ones on M730. Regardless, they are both horribly soft and there are more durable (and better-finished) alternatives from TA and Stronglight.

 

[legrandefromage]

As above, they are the same size but the LX ones are thinner and you may need the little spacers that came with the 550 cranks.

The XT chainrings are more hard-wearing though.

TA or Stronglight make good alternatives

 

[Moto]

Re:

Thx for the info. Very helpful as I want a M730 chainset / crankset but am struggling to find one that suits. I have 3 NOS XT chainrings (46, 36 & 26) so happy to have one where the cranks are good but worn chainrings. However I would need the bolt sets and crank caps. This is proving less easy than I thought so when I saw a M550 chainset in near new condition for very little money, thought I may be able to fit my chainrings and Bob's your uncle.

Still curious why chainrings have different letters infront of the teeth no. Surely this must differentiate some aspect of the ring?

Moto

 

[Woz]

I'll chime in a bit. While BCD can be compatible, mixing chain rings and transplanting other series rings can sometimes be bothersome.

Chain ring thickness (usually accounts for chain width), contoured off-sets (accounts for chain line & shifting linearity), position of ramps, pins and gates (shifting precision) can play a part. Shimano have not been entirely consistent in the crank arm spider width either. For sure you will be able to ride, and they will probably work but not how the Big S intended. I mean Shimano would
go bonkers if you decided to have a Biopace oval middle ring and round outer ring!

My suggestion would be always buy a matched set for the middle and outer ring - but not necessarily the same as the
worn originals. The letters denote a series to help you match some of the characteristics mentioned above, and allow
within reason some flexibility in tooth count. It's the down side of Shimano aiming for shifting perfection.

 

[Moto]

Re:

Excellent explanation. All makes sense.

Thx

 

[Woz]

The precise answer to your question would involve trawling through Shimano tech docs for Compatibility and Interchangeable parts - it's a nightmare.

A more detailed explanation can be found here:
https://www.thetallcyclist.com/2013/01/ ... hainrings/

BITD you could mix and split sprockets of a cassette, but with teeth profiling it all went to hell. Sadly,
it's now pretty much the same with chain rings.