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How come there is a difference in the allowed (recommended?) chainring sizes between Shimano's 610 and 820 1x grx chainsets, when the BCD, chain offset and q factors are all the same.
610 - 38 or 40t - https://bike.shimano.com/en-SG/products/components/pdp.P-FC-RX610-1.html
820 - 40 or 42t - https://bike.shimano.com/en-NZ/products/components/pdp.P-FC-RX820-1.html
FYI I am currently on the 610, 40t with a 165mm and looking for an equivalent upgrade.
Is it “allowed” or “sold with”?
To be fair, I'm not seeing anything about 'allowed' or 'recommended', the wording is that 38T & 40T and 40T & 42T chainrings are 'available'. Since both groupsets use the same rear mech. I can't see a problem swapping in an 810 for a 610 (you might need to tweak chain length).
Shimano seem to assume that better cyclists buy better groupsets and therefore can turn bigger rings (back in the olden days Deore triples had a 42T big ring whilst XT & XTR had 44T). Similarly 610 doubles are 46/30 whilst 810s are 48/31.
Think you may be correct PJay. I went 610 for the shorter cranks.
I've been looking at hope and garberuk cranks but there is a difference in q-factor and chain line.