I was so impressed by the smooth and silent shifting that Shimano’s new ‘composite’ chainrings give me on my SLX chainset, that I bought an extra composite middle ring to put on my other bike which has a M542 Deore chainset.

Tried it today and although the chainring bolts are in the same place, it seems the spider arms on the deore are longer than the SLX so the thing won’t fit!

Anyone else had this issue, and found a solution? I’m considering filing down the ‘lugs’ on the chainring to make it fit, as this would seem easier than the alternative of trying to make the spider arms shorter somehow.

yep I always recommend deore rings to m8’s, though I’ve bought some SLX to try myself next time. You just file down the extra metal on the chainrings, have done it many-many times and the chainring hasn’t been compromised (well none have failed due to it)

Thanks Z1ppy – guess it’s time to get the file out!

Just been doing a bit of digging on the interweb, and seems like this is a general incompatibility between any Shimano crankset with composite middle ring (like M660, M770, M590 10sp), versus ones with all metal ring (like M665, M410, M590 9sp). Even though the BCD is the same, the composite middle ring requires a shorter spider, so if you try and fit it to cranks designed for a metal ring it won’t fit without filing either the ring or the spider!

You have been warned….

There are 2 issues.

1. The newer (composite friendly) cranks dont have the inner ‘shoulder’ (or shorter spider as you call it) so the inside diameter of the rings is smaller, meaning you have to attack them with a file to fit to older ‘shouldered’ shimano cranks.

2. The offset of the middle rings on the new cranks, and hence the chainring too, is different by 0.6mm (apparently). This means if you do get a new ring to fit an old crank the teeth will be 0.6mm closer to the big ring. Not life ending but could cause some shift inconsistency.

Hi Stato. With you on No. 1, but thought the 0.6mm difference in spacing was between 9sp and 10 sp. chainrings, not composite vs metal?

This would be a moot point if all 9sp were metal and all 10sp composite, but there are a few 9 speed composite middle CRs out there (like the SLX M660 9sp).