The Karate Monkey That Shares a Drivetrain

Manufacturer

Surly

Model

Karate Monkey

Frame material

Steel

Wheel size

27.5+

Gear ratio

32:20

Fork

Marzocchi Bomber Z2 E-Opt, 140mm

Brakes

Hope M4

Wheels

Hunt Trail-Wide V2

Tires

27.5x2.8

Chainring

32t

Cog

20t

Owner

Blake Cannon

Build purpose

Trail riding, commuting

There's a version of this story where the second bike was a deliberate plan. That is not this story. The truth is closer to: I was already building up a Krampus, had a spare 32-tooth chainring and a 20-tooth cog sitting on the bench for it, and then a Karate Monkey frame turned up on Facebook Marketplace for a price that didn't leave much room for saying no. The chain that came off the Krampus's donor drivetrain happened to be almost exactly the right length for the new frame. One measurement, one missing link removed, and suddenly two bikes were running on borrowed parts from the same lineage.

It is not an elegant story. It is a single-speed story.

One measurement, one missing link removed.

Why 27.5+

The single-speed part was never really the question. That was already decided. The question was wheel size. I'd just finished SSUSA Richfield on the Krampus, which is a 29+ bike, big and stable and not exactly quick to change direction. It's a great way to cover ground, but after a few hundred miles of it I wanted the opposite for a while: something lighter, snappier, more willing to change its mind mid-turn. 27.5+ instead of 29+.

The Karate Monkey frame showing up on Facebook Marketplace right around then wasn't really a coincidence so much as a want looking for an excuse. It found one.

The $199 Fork Question

The fork that ended up on this bike is a Marzocchi Bomber Z2 E-Opt, 27.5", 140mm, and it was $199, which is a genuinely strange price for a fork that isn't broken. The catch is the "E-Opt" part: it's spec'd for ebikes, built a little heavier and a little differently than the non-E version, and apparently nobody wants one for a normal bike at full price.

I figured: screw it, how bad can it be. It went on the Karate Monkey instead of an ebike, which is not what it was designed for, and it has been completely fine.

The real worry going in wasn't the ebike spec at all. It was tire clearance. E-Opt forks are not always generous inside the arch, and I was running a 27.5x2.8 tire, which is not a small tire. I fully expected to unbox it, mount a wheel, and immediately need a different plan.

It fit. Clearance is not enormous, but it's real clearance, with room for mud and not just an optimistic reading of the spec sheet.

Tire clearance was not the last surprise. Marzocchi publishes a chart that tells you what PSI to run for correct sag based on rider weight, which is a nice, confident, official-looking chart. I aired the fork up to the number it gave me, set sag, and the sag was wrong: not "round to the nearest five PSI" wrong, but "this chart and this fork have never met" wrong. Getting actual, correct sag took meaningfully less air than the chart suggested.

I don't know why. I don't care why. What I do know is that riding around at the chart's suggested pressure would have turned the front end into a pogo stick, and not the fun kind you rode as a kid, the kind that makes you question every decision that led to this moment on this trail.

The chart is a starting guess, not a setting. Pull out a shock pump and a tape measure, set sag by what the fork is actually doing under you, and treat the printed number as a rumor.

Wheels, and a Freehub Lesson

The wheels are Hunt Trail-Wide V2s, and they're running that same 27.5x2.8 tire, a width Hunt doesn't officially suggest for this rim. Their recommended range tops out narrower than what's actually mounted. It has been fine anyway. The tire seats, holds pressure, and hasn't done anything alarming on the trail. Recommended ranges are a starting point, not a hard limit, and this is one of those cases where ignoring the fine print worked out.

Getting to "fine anyway" took one detour first. I opened the box, pulled the rear wheel out to admire it the way you do with new parts, and then realized I'd made a genuinely dumb mistake: I'd ordered the wrong freehub driver. I chose HG when I actually needed Microspline, because the Krampus (which shares this bike's drivetrain) runs a 12-speed cassette on the geared side, and 12-speed on that bike means Microspline, not HG.

I eMailed Hunt expecting an argument. Instead they told me I was not the first rider to make that mistake, and probably wouldn't be the last (it's an easy one to make), and sent out the correct Microspline freewheel with no fuss. Genuinely good customer service for a completely self-inflicted problem.

The Turner 5.Spot Parts Bin

A fair amount of this bike didn't come from a bike shop at all. It came from a box.

My old 26" Turner 5.Spot (RIP, full-suspension, long since retired) had been sitting disassembled at my brother-in-law's place, and he was kind enough to box up a pile of parts and mail them to me rather than let them keep taking up space. The stem and bars on the Karate Monkey are straight off that bike. So are the brakes: Hope M4s, which are ancient at this point and still work perfectly. Hope brakes never die.

None of it was bought for this build. All of it just happened to fit, which is most of what a parts-bin bike actually is.

The Number That Actually Mattered

After all of it (steel frame, ebike-spec fork, wide tires on wheels that weren't quite rated for them, a box of hand-me-down parts from a bike that no longer exists), the finished build weighed in at 27.8 lb on a cheap Amazon luggage scale.

That's not a light bike by any serious standard, and the scale is not exactly lab equipment. But any time I build a bike out of whatever parts happened to be lying around, ending up under 30 lb feels like a win.

• mountain-bike
• single-speed
• steel
• hardtail
• surly