Super compact crank for the LHT

Shimano "STX" crankset. 42X32 chainwheels.

I'm a big fan of compact cranks, the cranks with the 110mm BCD, (bolt circle diameter). This is a very useful size for road riding and gives you the ability to set up a pretty low low gear and still have a high gear approaching 100 inches. Lately I've been interested in the super compact cranks, like the old TA Cyclotourists and now Velo Orange has introduced it's Gran Cru with a 50.4 BCD that uses the same pattern as the old TA cranks. I'll probably have to pick up one of those some day.

VO's GRAN CRU

Anyway, I was mulling over these cranks when I remembered an old mountain bike crank I had bought years ago from Nashbar. It was a clearance sale, naturally, so I got this crank for a song. The Shimano STX 5 pin crankset. These super compacts were the standard for mountain bikes in the mid 90s, but as the style in mtn cranks shifted to 4 pin, these became passe. Added to this was the fact that these were 170mm  arms which are not as popular as longer arms. 

Anyway, I got these a long time ago and have never really used them. Tried to use them on an occasional mtn bike build but I always suspected the the InterGlide (IG) sprockets wouldn't work well with non IG chains. At any rate, they sat in my parts bin for a long time. But after considering the possibilities offered by this small BCD, I decided to investigate the compatability. Finally found a reference to the IG from Sheldon Brown,(who else?), which stated that the IG would work fine with SRAM chains. 

So what the heck? I decided to make a super compact double, by removing the inner granny gear. An unusual feature of the STX is that this sprocket is bolted to the middle cog, not to the spider. 

I tried a couple of different bottom brackets, finally settling on a 110mm UN54. There is ample clearance for both the crank arms and the sprockets on my Surly LHT. But no more room for the spider on the BB spindle!

Lot's of room for sprockets and crankarms, but the inner face of the spider is getting close to the BB!

If you had a bottom bracket you could slide around a bit, like a Phil Wood, I bet you could get away with a 108mm. With the stock 32 and 42 chainwheels, there is no threat of scrapping the chainstays. I'm sure a 46 could fit, and I have ordered one. I thought I would have a problem with the front derailleur, I could not lower it enough to get it within the 2mm's I would usually set it at, the tail of the derailleur hits the chainstay! I got it as low as I could. Testing on the stand seemed to show no trouble shifting or loosing the chain.

Note the large distance between big chainwheel and derailluer.

Took the LHT out on a little jaunt to Lincoln and back to test out the new crank. It is working very well! I have to say that I really enjoyed the 42 tooth big ring. I could easily go over Sierra College hill in it, of course, back in the day, a 42 was my small ring on my Nouvo Record equipped bikes! Shifting was excellent, so much nicer than with a triple, especially if you're a retro-grouch friction shifter like me. With a 32 in the back, this actually gives me a double with a 27 inch low. If you need anything lower than a 27 inch gear, you should be walking anyway.  

Also, the IG teeth have not become a factor at all. The SRAM 8-spd chain I use works fine.

I have a 46 tooth chainwheel on order to fit this crank, so I will have some higher gears, and the gap between the front changer and sprocket should not be an issue any more. But it will probably be a while before I put it on, I could get used to a 42 for my big ring!