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Hi all,
One for the properly tech savvy of you out there.
Right so, I was under the impression Sram cranks are the same chainline whether boost or not and it's just the chainline made different by either a 6mm (old) or 3mm (boost) direct mount chain ring.
I've got an Evil offering frame and because it's got an integrated chain guide the chain line needs to be mm perfect!
I did have a GX eagle boost chainset in there, and the chainline seemed right (3mm chain ring).
However I've bought a set of x0 carbon cranks, when I fit the 3mm offset chain ring off the GX cranks, it appears to move the chain ring in board a fraction on the x0 ones, maybe 1mm or so compared to the GX ones. This is with the same 3mm offset chainring.
Does anyone know, is this just manufacturing tolerances between the two sets of cranks or is there an actual difference between where the chain ring sits on the crank itself between the two cranks in question?
Does anyone sell a 1.5mm offset chainring?
Thanks in advance
Xx1 and x01 Cranks came in 2 sizes to accomodate different BB30 sizes. Not sure if you're on a BB30 but if you are you might want to check it out.
Cheers. No it's gxp on a 73mm shell.
I've got no spacers on the bb. That's correct isn't it?
no you should have a 2.5mm one drive side
I don't think SRAM gxp uses any spacers on 73mm shells (unlike Shimano). The chainline is set at the nds bearing, so spacing the ds shell won't change that anyhow.
Is the integrated chain guide not adjustable at all? Have you shaved the paint off the nds bb shell end?
The DS spacer on a shimano HTII BB was to allow fitting of a 2.5mm thick backplate for either a front derailleur or chain guide.
Not sure why SRAM wouldn't also make their threaded external BBs compatible with chainguide backplates.
but fair enough if you're sure.
shouldn't be difficult to find a tech doc online to find out if not.
Yeh sram is no spacers for 73mm.
Greyspoke... good shout on facing the nds. That might buy me 0.5mm, I'll do that tonorrow.
Thanks.
Pretty sure it's just slight tolerance differences between the GX and x0 cranks, as opposed to a manufactures difference.
It's amounted to about a 1mm shift and it's less than perfect.
GXP means the NDS determines the chainline, and you could move the chainring further inboard by adding spacers to the NDS but you can't move the c/ring outboard (f you currently don't run any NDS spacers).
Seems a tad odd. As said. you could trim the NDS BB shell, or the NDS GXP cup, or both, to gain the extra mm. Or file the chainguide mount a bit?
If you use a HTII cup and 24mm id bearing on the nds with the conversion reducing shim things, you could then fit a 24mm id shim washer under the inboard shim thing. My gxp cranks run on a Hope bb with those things, and I can't see how half a mm of spacing would affect how it works.
ETA these are the reducing things I am talking about. I suppose you could just stick a 22mm shim washer inside the bearing cup before pressing the bearing in, but it would be a bit of a faff to fit.
https://www.chainreactioncycles.com/hope-bottom-bracket-truvativ-gxp-converter/rp-prod26899
ETA2, actually, as it is such a close thing, maybe a change of bb would be enough to give you the space you need.
Cheers gents. I rode it today and it rides fine. It's not perfectly central but I think this is one of those times when you have to just say "that'll do".
It's a bit close for comfort on the swing arm, but there's no rub happened today. I'll keep an eye on it.
Appreciate the input.