Old 10-20-20, 07:04 PM
Andrew R Stewart 
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Originally Posted by Richard1964 View Post
Having read an earlier thread here ( 410453-double-triple-outer-chainring-differences)
I have a similar question. Taking the advice in that thread I *think* Id be OK with the following, but wanted to ask here for a consensus opinion.

i have a homemade bike (not mine) equipped with a worn 9speed Shimano Deore Double chainset (44/32j. Im not 100% sure that is the original setup, it may have one time come from a triple, or been transplanted to this bike. Whatever, it works.

When Im shopping for replacement rings, I find seemingly compatible rings (correct BCD=104mm, also 44/32 teeth, even also Deore (or Alivio) ) but they explicitly say This Outer Chainring can only be used with Shimano Deore FC-M591 9spd Triple Chainsets with a 44-32-22T set up. I enquired why that constraint is given, and the retailer responded "Because it's a specific offset fitting for use with the FC-M591 crankset. Hence it will not fit anything else other than this

Can anyone offer their expert view on this. My own view is that Im not changing the bottom bracket, the cranks or the 4arm spider mount. Assuming all 9speed chainrings are the same width, these should mount correctly on the existing BCD mountings, and therefore why wouldnt these fit and work in practice.

FYI Im in the UK. Im too new to post URLs yet, but am considering Deore M530 or M510 rings. there are also cheaper Alivio ones in the same category which seem as though theyd work.

thanks in advance, Richard
This is a big assumption. More to the point the face of the ring, that mates to the crank arm's tab face, dimension from the teeth's center plane can be different from brand or model to brand or model. This is one of the draw backs to an indexed front system. The, often, overlooked dimensional relationships can have an impact of shifting and chain rub. Andy
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