Bicycle Mechanics - Chainrings in un-approved combinations

On the off-chance that somebody else out-there is thinking of trying alternative chainring combos on an FSA crankset...

My CX bike came with an FSA Energy Compact crankset with 36/46T chainrings. The only other "approved" combination for this crankset is 34/50T, but I thought I'd like to run with 34/46T. Not an earth-shattering change, but helpful for climbing long Alpine passes.

Swapping the rings is easy and doesn't entail removing the cranks, and doesn't seem to have any negative effect on the gear-shifting. The only hiccup is that the chain rubs when on the 34T and the smaller sprockets:

https://lh6.googleusercontent.com/_D_t58WugL_s/TaHaDpwGmTI/AAAAAAAAGVM/xZPiFhUhJVs/s800/chainring-rub.jpg

I thought this was odd for such a modest alteration, but comparing the 34T and 36T rings the reason is clear. The new 34T ring has a milled area around the fixing bolts, moving it 0.6mm outwards and closer to the large chainring:

https://lh6.googleusercontent.com/_D_t58WugL_s/TaHZ_3TlnhI/AAAAAAAAGVI/NwiKPEK3DfU/s800/chainring-milled.jpg

So the fix is easy: just add five 0.6mm thick spacing washers between the spider and the chainring. :thumb:

Looks like a milling modification for the (too many cogs) 10 and 11 speed narrow chains,
to keep from dropping the chain between the 2 chainrings,
You could have just flipped the chainring over and used that as the inside face,
or bought a chainring from another company , not FSA,
that was not milled down to work with 10~11 speed chains. too ..

Looks like a milling modification for the (too many cogs) 10 and 11 speed narrow chains,
to keep from dropping the chain between the 2 chainrings,

The 36/46T combo is also 10-speed compatible. It must be that on the 34/50T crankset the rings are both positioned further outwards than on the 36/46T set, though I don't know why they would be designed this way.


You could have just flipped the chainring over and used that as the inside face,

Unfortunately the chainrings aren't left-right symmetrical, and flipping the 34T would make the ring-spacing much too large.


or bought a chainring from another company , not FSA, that was not milled down to work with 10~11 speed chains. too ..

Well it needs to be 10-speed compatible, because that's what the bike has. With another brand I risk exactly the same spacing issues, plus other incompatibilities.

I wasn't too surprised that a non-recommended chainring caused problems, but was happy to discover that the incompatibility was so easily solved.