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Just building up my new Tarn frame and it's feeling a bit tight on the crank to chain stay clearances. NDS is the worst with 5mm at the pedals but only 3mm where the crank starts to narrow. Would you be happy with that or look at a different crank. Currently has a RaceFace affect fitted. There is no scope to alter the crank position using spacers. I'm wondering if I need a crank with a wider q factor (as this may mean a wider crank and more gap).
Ring - chainstay gap is also not great but hope I can sort that with a ring change.
This is the NDS.
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If it clears its probably fine depends on the flex from cranking on the pedals though - only riding it will tell.... If you ride it in alot of mud you might take the paint off so add some protection tape. Could you not adjust it if there's more room on the other side? You can shuffle the spacers on the Aeffect crank.
Chainring is very close on the DS and all the small spacers are already on the NDS unfortunately.
Fair enough. There's nothing wrong with a tiny gap - you'll obviously be more likely to get heel rub, and you might hit the chainstay if it flexes.
I'd give that a try, but I'd be more concerned about heel clearance.
I think I would try putting some tape or something on there and doing some sprints, steep technical climbs, etc that are likely to cause everything to flex then see if the tape gets scuffed.
I'll definitely be taping it. The frame is ti so want to avoid any impacts. I'm not normally a heel rubber but will be looking for marks.
I'd be looking at some new XT cranks or something with a wider Q-factor, that looks mighty close
New cranks time. If you are a bigger person you flex chainstays more than you think when hammering bmx style.
Surprised two people on this thread are presuming chainstays (a braced tubular structure) flex more than cranks (a cantilevered lightened unsupported beam).
Not quite as simple as that though, chainstay has a rather large rotating lever on the end too to aid deflection. If I was spending Ti money on a frame, I's also invest in new cranks as others have said.
You'll be surprised how much everything flexes, just look at the slow mo huck to flat vids from pinkbike, it's scary how much forks can bend.
I could probably make that crank touch by hand.
I could probably make that crank touch by hand.
Is that Geex come back with a new username?
I'll be trying to flex it by hand but don't think I'm that strong. Only 75kg as well.
Looking at other crank options if it is too tight (first ride hopefully later in the week) the SLX FC-M7120 looks like a reasonable choice. Wider Q factor (178mm vs 175mm) and ring spaced further out, 24mm BB so won't need to change that.
Tarn is a boosted frame isn't it? Is that a boost crank?
Yeap its a boosted frame. RF don't appear to make a boosted aeffect, can only find the 137mm axle versions. Their document at
RES.CLOUDINARY.COM suggests there is a longer axled version but I have not found one anywhere. Turbine is wider but do not really want a 30mm axle.
And this doc
suggests that the axle code I have is suiatable for 148mm. Think it may just be a bad combination. The 2020 steel tarn 20 appears to be running a SLX 1x12 crank.
Surprised two people on this thread are presuming chainstays (a braced tubular structure) flex more than cranks (a cantilevered lightened unsupported beam).
they're not braced very effectively in the correct direction though. up/down I'd completely agree, but side-side they flex loads. put a bike over on its side and push your foot on the cranks over the bottom bracket to see just how noodely almost any bike is. There's a huge amount more metal per cm (or whatever) in a crank than there is in a frame