I’m happily running an old 3×9 XT drive chain with 44,32, 22 rings. The outer ring probably needs replacing and I’ve found some good deals on older Blackspire chainrings. My front mech is designed for a 44 tooth ring but I was wondering whether I could get away with a 46 tooth one; this would make the middle – outer tooth difference 14 teeth.

It’s probably not worth the saving if it mucks up the shifting.

Sorry, I have an additional question but my edit ability has timed out. Does anyone know the arm/spider with of Blackspire chainrings (I have emailed Blackspire); ideally I’d be looking for 18mm.

Bump for the morning crowd.

You would need to find out the max capacity of the front mech, and it’s more about the difference between outer and inner rings. The ones I’ve had in the past IIRC were 22 teeth, so 46-22 would be over that.

Does the 46 tooth ring have the correct PCD for the XT chainset?

The chainring does have the correct BCD for the chainset (104). My current XT mech. is meant to handle no more that a 44 tooth outer ring but I can get a cheap 9 speed Deore mech. that’ll handle a 48, 36, 26 touring chainset (although this is still only 22 teeth and I can’t find the total capacity figure anywhere); there’s even a review stating that anything less that a 12 tooth gap between the middle and outer rings will cause shifting issues. I can’t be sure that whether it’d manage with 46, 32, 22 (the 14 tooth difference between middle and outer).

The chainwrap capacity of the rear mech is 45 so should handle the 46 tooth ring as long as I keep my 11-32 cassette and don’t increase to 11-34.

Can you see how high the mech has to sit with the new ring and then if that will work Ok with the wee ring in clearance terms? This is the issue I’d have thought.

It’s bound to shift, mayb just not brilliantly.

It may well not be worth all the hassle of mucking about; a cheap Deore 44 tooth outer ring will almost certainly do the job. I imagine that the whole drivetrain (it’s not just 3×9 it’s 3×9 and Octalink too!) will need replacing at some point.