What is a good trail fixie?

Tracklotrail, tracklocross, fixed off road, trail fixie. Is there any difference compared to a single speed?

There are a few characteristics with fixed trail riding to think of, when designing a frame and when building a bike from it.

And no experience or riding condition is universal. So we write this from a Nordic, often wet, always rooty, rocky and rolling terrain point of view.

Our key idea is agility. When riding fixed, you will not need the usual stable high speed properties or leverage force in the bars. You will need ultra light and fast response, agile body, your firmest deathgrip of the bars and a riding presence sharp as a razor.

Those fast moves call for a fast handlebar. No bus driver 80 cm thing. Narrow bars, in the size of your shoulder width, and comfort for your hands.

Skidding? Strongly discouraged on the trails. That should be avoided, is not cool and is not necessary but it messes up these trails if you do it, so don't. Keep your pace planned, meditative and consistent instead. But you need to keep the wheels light just in case. Rotating weight is a powerful force. And a low, short and steep bike turns and moves ultra fast just like you need when you have no suspension or brakes to save you.

So, the way to build up the Heroux Tao fixie we have found to be a narrow bar (680?), a mid-long stem (75?), the widest grips you can find (145+), light strong rims (20-25 mm inner) and fat, light, low-treaded tires (e.g. XR2 3.0) for summer or rugged grippy like Vigilante 2.8 in the offseason.

This build makes it flickable, light, fast to respond.

Tech build details

You should not have to buy a bunch of fancy stuff when you get a new frame - so rear spacing on our fixed frame is 135 mm, BB is 73 mm threaded, and ZS HS with 1 ⅛” straight steerer (or a tapered, should you find a short fork with it).

Just get an old MTB 29" wheelset, pull the discs off, QR, cogs and tires off. Flip the rear over and bolt a cog on the disc mounts, get a pair of massive tires, get the strongest bolt-in axle and a tensioner, a nice old steel 26” fork, a stripped classic 3-speed crankset which gives a perfect 54 mm chainline. Cheap yet good stuff all of it, get it from your friend’s bin of “not fancy enough” parts and build something awesome!

  • Cog: the key to the fixie. Velosolo, Gusset and a few more make cogs boltable to regular 6-bolt disc mounts. That is great! Because it gives around 53 mm chainline, just like a classic MTB single speed rear hub. And it beats threaded track cogs by far in reliability and ease of use.
  • Rear hub: So, get a 6-bolt cog like above, and any 135 mm rear disc hub, flip the wheel over and bolt the cog to the disc mount and you are done. A geared hub works fine, but a single speed one of course looks a lot better.
  • Spacing: 135 mm, classic MTB/QR, is what enables the above with track fork ends. So this is not quite like track parts. Modern TA like 142/12 and sliding dropouts (as the Zen SS frame) allows the disc-mounted fixed 53 mm-ish drivetrain too, but not 148/12. So we don't build with 148 mm since it has implications on choice of both SS hubs, fixed setups and crank/chainring options.
  • Chain, halflink, tension, tensioner: BMX/single speed/track chains of full 1/8" width look nice, are strong. Half links allow you to fine tune the length of the chain and thus also the effective chain stay length.
    For track ends a chain tensioner for BMX/track is recommended. We have found the MKS CA-MX 10 a very clean, strong and reliable option but anything for 10 mm axle and at least 6 mm dropout thickness works.
  • Chainring: narrow-wide works, is easiest to get hold of, and it actually works with 1/8" chains and half links (although not ideal), but not with narrower chains and half links since it gets out of sync. So all-wide 1/8" is preferrable, however track and fixie parts typically do not go as low as trail gearing needs (around 30-34T).
    We have also learned that modern direct mount chainring splines tend to develop play rather fast with the changing direction of force on a fixie drivetrain, so classic bolted rings are best. Velosolo, again, have a nice assortment and we are working on our own too!
  • Chainline and more on drivetrain: there is probably no better place to learn all about this both simple and complicated topic than the Velosolo FAQ, or the dead but archived and wonderful 63XC site! Recommended reading!
  • Fork: 445 mm forks with 41 mm rake. This is the lowest non-suspension fork that safely fits a 29x3.0 without relying on custom forks. 445/41 mm is available as nice steel forks for the 26" aftermarket. We use Identiti XC 445 on the demo builds, have also tried the old Planet-X (440 mm) and if you find the discontinued Salsa CroMoto 445 it is a great option!
    45 mm rake, if you find a 445 mm fork with it, will give a lower trail number and an even more quick and well-behaved bike. This is what we will have on our own forks when available.
  • Headset: the frames are designed for "zero stack" 44 mm headsets (4 mm lower build height). That gives the geo in the geo chart, combined with a 445 mm fork with 41 mm rake. However the 44 mm head tube allows you to use an external lower cup and a tapered steerer if you need to, although it obviously slightly tweaks the numbers to a few mm more stack (like 6-8 mm) and BB height (less than 5), and a fractionally slacker head angle (around 0.5 deg). If you are sensitive to these subtleties, you can do some magic here.
  • Seatpost: 27.2 mm. Classic. Re-use that old Thomson you invested in many years ago, before the dropper post craze!
  • Brakes or not: of course adding a front brake is the only sensible thing to do. You should really have one. And try not to use it.