I’ve just fitted a new drivetrain. I’m using middleburn rings, PC991 chain and XT cassette. The cranks are RaceFace Turbine LP with an ISIS bottom bracket (that works very well) and offer adjustable chainlines.

My problem is, if I use a 47.5mm chainline (which is what the cranks were designed for) the shifting is clean and crisp but the bottom two sprocket on the cassette cause the chain to catch on the pick up pins of the big ring when in middle. If I move the bottom bracket across to stop this, the shifing is no longer clean and crisp.

So, would you just avoid the gears that don’t work but keep it sweet or have all the gears but not as crisp? I’m amazed how much the chainline can bugger up the front shifting.

Keep it crisp, and avoid the two smallest cogs. Should be in the big ring anyway 🙂

Maybe a double and bash would solve all my problems! I guess with 27, I can spare a few and keep it crisp. Still, this is STW, I’m just waiting for someone to come along and say the opposite.

Singlespeed.

I’m joking, just delivering the expected STW response to this.

I virtually never use those gears in middle ring. There’s no need for them really, since they’re duplicated on big ring. I’d go for better shifting/less gears.

cheers guys. Now, where did I leave that vernier?

I think that Middleburn rings are meant to run on a 50mm chainline. The website states that Middleburn rings should run on a 48mm chainline but after querying this I was told 50mm and that the website was wrong.

I’m running steel Deore inner and granny rings on an XT chainset and a 50mm chainline (118mm axle), when I fitted a Middleburn Hardcoat Slickshift outer ring to this set up I found that the chain caught on the shifting pins whilst in the Middle ring and the smallest cog, I don’t have this issue with a Shimano ring. I’ve queried this with Middleburn but not had a reply. It was suggested on here that I should avoid the middle ring/small cog combination but I tend to use it.

My Middleburn Hardcoat/Slickshif outer ring is noticibly wider than the Shimano equivalent (possibly down to the Harcoat coating which is supposedly 5x thicker than anodizing) and the shifting pins a fairly thick too. I was a bit annoyed actually.

Bear in mind that if you alter the chainline you’d need to tweak your front mech limit screws to accomodate the change otherwise I’d imagine that your shifting would suffer.

well, the bottom bracket is 113 but there’s no fixed up. If i centre everything up, I get a 47.5 chainline which is the best shifting I can find. If I shift it over for a 50mm chainline, I offset my legs 5mm from the centreline (not that I can feel it). It clears the big ring but the shift to granny is then hopeless. Think I’ll have to stick it out at 47.5mm The 8th sprocket clicks against the big ring in middle but is just about useable, the 9th if awful. However, Like everyone says, it’s not a gear you’re supposed to use anyway.

Thanks for the comments, I think you’re right PJ, the middleburn is a seriously chunky ring. Maybe something a little slimmer next time. I should have got an XT chainset but I’ve just not got the heart to bin a set of perfectly good Turbine cranks.

Did you tweak you mech though when you altered the chainline? My XTs should run on either a 47.5mm or 50mm chainline (but 47.5 is the prefered) although if your Racefaces are only meant to run on 47.5mm chainlines it might make a difference. I’ve got the same chainset and mech. on my old Inbred on a 47.5mm chainline but had to use a 50mm one on my current Inbred due to it’s extra wide chainstays. The shifting is just as good on both setups.

Oh yeah, I’ve reset the mech each time. It’s geting to be a real pain. Lost count of the number of time the cranks have been off today!