I have a 2015 Surly Long Haul Trucker with a Andel RSC6 crank and Shimano UN-55 bottom bracket. Is there a crankset I could replace that with that would be compatible with a single side power meter?

  • are you able to source a wheel-hub power meter? Or one of those handlebar ones?
    – Criggie
    Apr 26 at 19:37

Power meters for square taper BBs are hard to come by, and usually custom made and expensive.

However, fortunately the Surly LHT has an ordinary English threaded bottom bracket. Just swap out the UN-55 for any Hollowtech 2 compatible external BB, such as the Shimano Tiagra BB-RS500 or 105 SM-BBR60. Then, get any hollowtech 2 crank, replace the left side with a power meter, and you're good to go.

In fact, more recent models of the LHT use hollowtech-2-type crankset systems out of the factory.

I know Stages only sells power meters for 105 and above for road, so it might make sense to get a 105 BB and a 105 crankset, coupled with a 105 power meter such as the stages Gen 3 Power L, or 4iiii equivelant.

If you want more gearing range than a 105 crankset provides, you can mix and match with other cranksets that use the Hollowtech 2 interface, of which there are plenty.

  • I only recall one PM for a square taper BB: Power2Max offered a spider for the TA Carmina in its first generation of PMs. P2Max is now on at least generation 3. The Carmina takes either a 103mm or a 108mm JIS axle (documentation was poor and in French, but there are in fact two versions of the Carmina, and I can attest from experience), so the OP might need a BB change if they somehow found that P2M spider for sale, and in any case the Carmina crank is quite expensive and rare by itself.
    – Weiwen Ng
    Apr 26 at 18:11
  • @WeiwenNg, SRM made (makes?) a meter for square taper, but anything SRM is going to be $$$$ Apr 26 at 18:31
  • you're right, the SRM Science Road is for ST cranks.
    – Weiwen Ng
    Apr 26 at 18:40

While product recommendations are off-topic here due to their tendency to become obsolete, it's fair to say that what you're up against here is that touring triples (24-36-46 or thereabouts) of the type that LHTs come with are pretty far opposite from the type of cranks that get left-crank power meters.

But, what may exist is a 110/74 or 104/64 triple direct-mount spider for a crank of the milieu that get left power cranks made. Sometimes third party companies make such spiders. There are a lot of 104/64 double direct-mount spiders for such cranks, but I don't think there would be a way to hack them into running a triple without running into clearance problems with the crankarm and FD or the ring itself.

You can probably find an older native 104/64 crank with a power meter where you'd be able to replicate your chainring sizes, but the Q and chainline may not be right or at least may not be what you had.

Shimano has made various HT2 triple cranks with Euro trekking type chainring configurations. You could conceivably find a match between one of those and one of the XTR/XT/Saint/DXR power left cranks. HT2 mountain power crank interchangeability is kind of a maze and is again an area where things change, so it would be on you to figure that out. That would probably be the simplest off the shelf way to get something close to what you have. In other words, there are definitely 104/64 HT2 cranks that can take the same gearing as what you have and can also match with extant HT2 power cranks. I believe the stock LHT chainline might be in a bit from what you'd get if you did that though.

  • OPs problem isn't the gearing range, it's the BB interface. If OP had a 2020 LHT they'd have a HT2 50x39x30T crankset, and they'd be good to go with a simple replacement of the left side crank arm in 5 minutes. Apr 26 at 18:39
  • @whatsisname OP's problem is they presumably want to keep their 26/36/48 and want a power crank. Surly deciding to spec later versions with something other than proper loaded touring gearing is here nor there. It's right there in the post that they're open to buying a new crank. Apr 26 at 18:49
  • I don't read this as necessarily being about what the options are within square taper. Apr 26 at 18:54

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