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Running a sq taper Middleburn RS7 with 22 32 42 set up. UN73 bb, 68 x 113mm. Getting too much chain suck, esp when mud/grit gathers on the granny.
Not sure if related, but the granny ring is very close (and closer than my old XT set up) to the chain stay ... I'd guess at a couple of mm? Pic here
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Ideally I'd like a 24T granny but think it'll rub the stay. A 20T granny causes less chain suck, and is further than the chain stay but is a little small for my rides.
Is the normal? I've tried a temporary spacer to push the chainset out 1-2mm which helped the granny issue, but threw out the big ring. I'd like to switch to 2x9 (24T and 34T) but not sure how feasible.
Any thoughts?
Ta
that is close - what chainline is it? should be 50mm from middle ring to centre of seatube / centerline if it's a recent 9-speed shimano rear. looks closer, 45-47mm or so, if that's a 22 inner?
if you use a double, the distance from halfway between the 2 rings and the centreline should be about 47-50mm - so you'll have more room for bigger rings.
What BB are you running? I'd say there should be a 2.5mm spacer or two in the driver side.
Are there any spacers on the non-drive side?
Chainsuck in combination with a frame with little chainring/chainstay clearance is always going to be risky. Chainsuck is not caused by the size of chainring though clearly reducing the clearance to the frame will make the effect on the frame worse when it does happen.
I'd go for a wider BB - a 68x118 should do the job nicely and should allow for decent clearance even with a 24. I'd always advocate a 2x9 over 3x9 too unless you do a lot of road riding as well as mtbing. I'm running 24/36 and 11-34 which I find spot on but there are plenty of other threads on here discussing which ratios are best.
thanks all ...
- it's a 68x113mm axle, as recommended by Middleburn I think
- it's a Shimano UN72 sq taper bottom bracket
- keen to go for the 2x9 set up
- will look into a 118mm altho, when I temporarily bodged a spacer in to shift the drive side outwards, it did seem to force the chain to severe angles on granny and outer?
What frame is it (can't see the pic).
Some frames unfortunately will always be more affected by chainsuck than others because they have wide chainstays and you may have to compromise on chainline to get more clearance.
It's a Dekerf Elysium ... not sure it has esp wide chainstays.
Just back from a spin and the gearing / chainline all looks reasonable with a 113mm axle ... just damn close to the stay. Will order a 118mm bb and have a go at 2x9
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