So you want to get some new cranks on your bike but you’re unsure if you need BOOST compatible spacing on your cranks. Getting the correct crank spacing is especially important now-a-days with two piece systems that you have almost no way to adjust the chain ring distance in or out. The front chain ring must align with the median chain position of the rear cog-set to keep the chain-line within optimal angle so not to affect the Q-factor… it just makes for a better ride if the chain-line matches up.
The first clue that you have a BOOST compatible bike and rear hub is if your bike has some kind of marking or sticker saying it is “148 BOOST” – usually on the chain stay. The second clue would be if it came with a 148mm x 12mm thru-axle.Â To make sure, follow the flowchart below to find out.
O.L.D. = Over Lock-nut Distance
FTF = Flange To Flange
DONT just assume you have a boost compatible bike and hub because you have a 148 x 12 thru-axle, the axle insertion depth into the frame may be fudged to fit a narrower hub into the frame.
There are EXCEPTIONS. You will encounter bikes with GNOT-BOOST from Surly or future-proofed thread attachments from Raleigh. These bikes have a non-standard 145mm frame width in the rear and accommodates a Â±3mm margin by simply having some flex in the frame.
Raleigh even provides a thru-axel that is technically too long for the old 142mm standard and can actually support a 148mm hub (although it’s labeled 142 O.L.D. x 12mm). A thread attachment that is independent from the frame sits on the outside of the frame loosely to compensate for the change in torque angle when the frame flexes.
Now that SRAM has announced its NX Eagle 12 speed cassette, you can go ALL SRAM on your old bike without searching for a XD driver for your hub. Previously, the only route to do this was to use a SunRace 12 speed cassette, but now SRAM is sramming (sic) the door on the Taiwanese manufacturer.
A quick note for those looking to retrofit a 12 speed cassette onto their 8/9/10 Shimano freehub body/driver. Other than the 29 grams in weight, the difference between the SRAM NX Eagle and the SunRace MZ90 is in the 6th & 7th gear â€“ there is Â a slight difference in the teeth count.
SRAM NX Eagle PG1230 (Easier/Slower mid-range) 615g
SunRace CSMZ90 (Harder/Faster mid-range) 586g
Maybe the SRAM is smoother than the SunRace? Maybe the SunRace is closer to the XD hub ratio? Until somebody puts both cassettes on exact same bikes and rides them for a 100 miles side by side, we wouldn’t know the difference in performance.
But the BIGGEST DIFFERENCE is that the SunRace CSMZ90 is AVAILABLE NOW and the SRAM NX Eagle PG-1230 won’t be in anybody’s inventory until September – That’s the end of the season for a lot of us in the midwest. Coincidentally, the new Shimano M9100 will not get to local dealers until September either.