The_Mickstar

I'm building up an All City Nature Boy as a SS gravel race bike. It has a 68mm English threaded bottom bracket.

I'd like to use 180mm cranks (since I'm fairly tall and like the extra leverage for SS riding), but I'm having a lot of trouble finding 180mm road cranks that aren't crazy expensive. For example, to get 180mm road cranks from Shimano, you have to step up to Dura Ace. However, it's fairly easy to find reasonably-priced 180mm MTB cranks (Shimano XT, for example). I realize the Q-factor will be a little wider, but is it possible to use MTB cranks in a 68mm shell? If so, how? Any downsides?

If anyone knows of a moderately priced road crankset that is available in 180mm, I'm all ears. Something that's actually designed for 1x use would be a bonus, but not a necessity.

Thanks.

HillRider

MTB cranks for English threaded bottom bracket shells are typically designed to be used with 73 mm bottom bracket shells but commonly come with spacers so they can be used with a 68 mm wide shell. That should make them compatible with your bike.

Andrew R Stewart 

Since we don't yet know the hoped for crank's BB spec we can't really answer your question. There are modern cranks which won't have threaded 68mm wide shell Bb's compatibility. But assuming the crank/BB isn't a problem then the next factor might be the chain line of the crank not playing happy with that of the road bike rest. Then there's the ring/frame clearance thing if you're running a large ring. Lots of maybes. Andy

FBinNY 

Assuming you get one with BSC threaded cups, you're close. Getting the cigar depends on the right BB width to match your frame, and spindle length so the arms and chainrings clear the chainstay.

Note, you might get a 73mm BB to work by using spacers between cup and BB shell, depending on specific design elements. But you also have to keep chainline in mind.

All told, the odds favor you, as long as you're attentive to details.

well biked

Since you mentioned XT cranks, it sounds like you are considering Hollowtech II cranks. If so, as Hillrider says, you'll simply use spacers to make up the 5mm difference in shell width when you install the Hollowtech II bb cups. As for chainline, assuming you are using a cassette hub/singlespeed cog with spacers (Nature Boy with rim brakes has 130mm rear dropout spacing, the NB Disc has 135) achieving an ideal chainline with pretty much any crank you use is super easy by playing around with the spacers as you position the cog on the freehub body.

FrontRanger

The XT's q-factor is a lot wider than a typical road crank. If you can live with 177.5mm arms, SRAM has road 1x cranks that would probably work better with the AC's spacing.

The_Mickstar

Thanks, guys. I'm looking at the Nature Boy 853 which has 135mm rear spacing and plan to use a Chris King SS rear hub, so getting the chainline right shouldn't be too big of an issue. At this point, I think the best choice is probably to go with a Sram Rival 1 crankset in 117.5mm. It's not a perfect solution, but I do really like the removable spider options so I can replace the spider with a Wolftooth Oval ring when the stock ring wears out. Finding big enough oval rings for MTB BCD is a pain (or not even possible), too.

FrontRanger

I ran an absoluteBLACK 40t DM ring on SRAM Force 1 cranks, and it worked really well (frame had 135mm rear spacing).

Eric S.

180mm SRAM Apex road cranks are readily available on eBay for just over $100 new.

Mr IGH

All the Shimano MTB cranks I've installed have spacers to make the bb work with either 68mm or 73mm. Since the frame is set with 135mm spacing the chain line issue is moot (with mtb cranks).

Dan Burkhart 

73mm is not universal on MTBs. I see lots of them with 68. You are correct that outboard bearing type MTB BBs will come with spacers to adapt either way, cartridge type must be ordered for the specific width.