Karate Monkey Two-Speeding With My Friend Melvin

All the perils of single-speeding coupled with all the issues of a front derailleur! And how!


I was sitting around at the shop, minding my own business, when I decided to check out Paul’s stuff on QBP. It was innocuous, a chance meeting, a coincidence… what’s that old saying? A flap of a butterfly’s wings can start a hurricane. That’s where I first saw the Paul Melvin Chain Tensioner.


Pretty, isn’t he?

The Paul Melvin lets bikes without sliding dropouts run a single-speed drivetrain. My Surly Karate Monkey has sliding dropouts, so I shouldn’t need a Melvin at all, but there’s one other nifty little feature on the Melvin; two floating pulleys and a little bit of give in the spring mechanism allow you to run two or even three chainrings up front, with a maximum tooth difference of 20. You can run a 32/46 CX double, or a 24/32/44 triple if you’re feeling ambitious.

I had a vision! I had always admired single-speed mountain biking and dreamed of doing it myself, but the difficulty of pushing a fully loaded bikepacking rig up hills AND spinning out on long stretches of dirt road didn’t appeal. I was a bikepacker first and a mountain biker second.

Could the two-speed drivetrain be the answer to my prayers?

This little tensioner offers so many interesting drivetrain combos, I knew I had to have it. I ordered a Paul Melvin,  a Surly Spacer Kit for my Shimano XT hub, and a Surly Single Cog, 17T. I had stars in my eyes, apples in my cheeks, and all the innocence of youth.


That innocence was quickly shattered during the build process.

First off, I had to figure out my chainline. Since I figured the jump from the small ring up to the big ring would be the harder feat for the derailleur, I spaced the rear cog to favor the right just slightly. The Melvin has spacers at the derailleur mount that offer a little flexibility, but the Surly spacers were the ones small enough for fine-tuning. It was a funny sort of dance; remove four spacers, add back three, place the cog, space the rest of cassette body out to the lockring, over and over until I got to just the right combination.

Ok! Let’s roll! Slap a 9-speed chain on there, and test run!

Skip, Skip, Skip, Skip

I put the bike back in the stand to try and diagnose the skip. It wasn’t chain tension, since I had the Melvin at maximum tension in the big ring. It was possibly the 9-speed chain. I broke down an 8-speed chain to the proper length and tried again.

Skip, Skip, Skip, Skip

Well, that didn’t work. I flipped the Surly cog around to the other direction, hoping that it might’ve been slightly ramped on one side.

Skip, Skip, Skip, Skip

It’s probably a chainline issue. I’ll just adjust it a bit more to the left…

Skip, Skip, Skip, Skip

Back to the right…

Skip, Skip, Skip, Skip

Maybe space the Melvin a hair left?

Skip, Skip, Skip, Skip

Well, shit. Is the Melvin even the problem?! After five hours in the stand, I had had enough.

I sent an email to Paul Components asking if they had any advice. To my surprise, I got an email back pretty quickly, from Paul Price himself. He got me sorted out. I needed a new cog, one with a different tooth profile from the Surly one I was using.

So, new cog and chain. Bummer. That’s exactly what Steven at Laughing Dog diagnosed, too. There was something fishy causing that skip, and the only solution was to go total war on my drivetrain. Steven had the genius idea of throwing a cassette cog in the back… and that did it! The skip was dead! Turns out the chain had been catching on the square profile of the Surly cog’s teeth, causing a skip.


Call me a purist, though; I couldn’t live with a skinny little casette cog in my drivetrain. We had diagnosed the Surly cog as the issue (to no fault of Surly, my front rings demanded an incompatible chain), so I set about replacing that cog with another.

Steven let me know that my front chainrings were also shot, so I was looking at a full drivetrain swap. I went back on the shop computer and browsed for new chainrings for my X9 crank. Funny… 120 BCD seemed like an odd bolt pattern. Turns out, it’s proprietary to the SRAM crank… and the chainrings are mega-expensive to replace. When the Great Bike Mechanics Revolt happens, it’ll be based around proprietary component fittings. I mean, it’s just infuriating.

I went back to the web for advice, posting in a few mechanic forums and asking for recommendations. My first idea was a replacement crankset with a normal 104 BCD bolt pattern spider, which was also mega expensive… but wait!


O Canada, our home and native land! The Canucks at North Shore Billet were machining a 64/104bcd 2×10 Spider for the X9 crank with a very agreeable bolt pattern, and room for a bash guard. A few torque screws later, and my X9 crankset was as flexible and cross-compatible as any.

I went with 36/22 gearing in the front, figuring to go lower than I need in the low gear and higher than I need in the high gear. I also grabbed a 17T Wolf Tooth Single Speed Cog for my rear, and mashed it all together. Truth be told, I just guessed on the gear ratios, and I got pretty close; I’ll swap the 17T cog for a 19T cog and call it good to go!

So, how does it ride?


First off, the spring in the Melvin is burly. Everything feels super tight and durable, and my chain rarely slaps. It’s almost as good as a clutch derailleur. Additionally, the pulley wheels themselves are gorgeous! They roll super smooth, and there doesn’t feel like an ounce of drag in the system.


Up front, the X9 derailleur handles all my shifting needs. It’s a clean, precise shift back and forth between the big ring and the small ring, with plenty of distance in tooth capacity to keep the tension on the melvin wound tight. I’m using an 8-speed chain, and that seems to interface perfectly with everything.


It doesn’t skip, doesn’t drop chains, doesn’t rub, can’t cross-chain, can’t really suffer from a rock hit since the Melvin is a lot burlier than a derailleur, and I lose a ton of weight from losing my cassette. That’s a lot of pros! The only cons are the relative durability of a front derailleur when compared to a singlespeed setup; this is slightly more complicated and therefore, I can’t really boast “simplicity” all that much. Still, it’s better than a full drivetrain if you can swing the gear ratios all the time.


James and I hit up Earl’s Trails just past Hampshire College in Amherst and tore it up for a couple of hours. I was geared really high for how much insane climbing we did. It was a good indication to add a couple teeth in the back, but good lord, was it fun!

I feel like I “get” singlespeeding now, at least more than I did. I can focus all of my attention on my front and rear tire, my brakes, and the trail ahead. There’s no other use of brainpower dedicated to thinking about gears, preparing to shift, or worrying about rock hits to my derailleur (since the Melvin is so burly). I just hammer the pedals and keep my momentum. It’s positively… zen.


I also dig the clean aesthetic on the handlebars with one less shifter. 1×10 riders can relate. Part of me wants to ditch the pretense of that front derailleur and go full-on singlespeed, but I’m enjoying myself now and I need to do a little bikepacking before I commit to losing the range this setup affords me.


And there you have it. A two-speed Karate Monkey for ripping and shredding your way across the country. If you’ve played around with a Melvin or a Dinglespeed setup, let me know how it went!

Believe it or not, I have two big upgrades coming for this bike over the next few weeks, so stay tuned to watch the evolution continue…

And keep riding!

12 thoughts on “Karate Monkey Two-Speeding With My Friend Melvin

  1. What’s the weight of that tensioner?
    Have you calculated what the same range would weight with a RD?
    It’s a fun little setup, but other than moving weight to the center of the frame (which is good) I cannot see any other benefits.

    Oli in Denmark (from Iceland)

  2. I’ve set up a dingle-speed on my EBB equipped Niner frame. Running 32 up front with a 19 and a 22 in the rear. Takes about 3 minutes with a 5mm and a 6mm allen key to switch gears, so not as convenient as a derailleur, but much simpler and no chain tensioner required.

  3. Hi, interesting read, thanks, so what actually fixed the skipping, was it that you shortened the chain, or changed the sprocket (or both). Looks like the teeth on those Wolf sprockets are quite ‘square’ and similar to the Surly one.

  4. Thanks for your post Dilthey!

    I built up a Fuji Monterey with a melvin, surly spacer kit and 18t cog. It has skipped since day one. Thus i haven’t rode the bike out of the drive way. I’ve been really frustrated with the set up. It all makes sense now.

    Skip, Skip, Skip

    That surly cog is one fat larry.

    I needed this article.

    Be easy Amigo!

    1. Stache! You found my blog! I can’t believe the issue I had was replicated elsewhere, with all the variables in chains, cogs, spacing, component wear, etc. But, I’m stoked I helped you get to the bottom of the issue.

      It’s been too long since we’ve been in the woods together. Let’s make some plans!

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