My tubeless mod

[Target]

After twelve years on 24", I wanted to try a new wheel size. To make things more interesting and challenging, I decided to implement an idea I had been thinking about for a long time - going tubeless.

Tubeless setup

Getting punctures and snake bites is a pretty common thing in trials.  I can recall some gaps and drops with sharp edges that I avoided doing because of the risk of a pinch flat.

Meanwhile, a lot of mountain bikers ride tubeless setups with a sealant that repairs any punctures by itself, sounds like magic. There is also a cool thing called tyre inserts that is used in downhill and enduro to protect the rim and the tire when hitting some rocks, and to prevent the tire from ripping off the rim.

Inspired by Ali C videos with tubeless setup on a street trials bike, I've decided to give it a try myself.

Usually, an MTB rim is sealed for tubeless setup with an adhesive tape: Gorilla, Stans, Tyvek, etc. I've made several attempts to use Gorilla tape, watched a lot of manuals, all seemed nice and sealed, but all attempts failed: the air was leaking in different points around the rim cutouts. 

After reading mtb forums and especially fat bike forums, I found out that a lot of fat bikers have troubles with adhesive tape for tubeless setups too. Either it didn't work for them just after installing, or the setup failed after some period of time. 
Fatbike rims are very similar to trials rims: wide, single-layered, large cutouts for saving weight. It looks like adhesive tape doesn't stick well to them because of the cutouts: sealant and air sooner or later find their way between the tape and the rim, the leakage starts, and it doesn't seal by the sealant afterwards and only gets worse.

It turned out there is only one reliable way to seal a non-tubeless ready rim with cutouts: so-called "ghetto tubeless" when a tube is cut around and stretched over the rim, so that all the rim cutouts are sealed, and then the excess material is cut after the tire sits in place. Also, there is a modern variation of this method - a latex strip and a tubeless valve are used instead of a cut tube (the "Fatty Stripper" solution).

So, in order to seal the rim, I've used a TPE (similar to latex) strip about 0.5 mm thick on top of normal rim tape, and it worked perfectly: the setup sealed instantly. As for the valves, I've used some Presta valves cut from old Schwalbe tubes.

There’s one really cool thing that became popular in recent years in the mountain biking world: tyre inserts. It gives a lot of benefits with practically no drawbacks:
- Protects the tyre so the rim cannot cut through the tyre when the wheel hits some sharp edge
- Protects the rim from impacts 
- Prevents the tire to be blown off from the rim
- Makes pumping a tubeless tyre and sitting it to the bead much easier even with a small pump
The only disadvantages I can think of are:
- Additional weight
- Inserts may be difficult to install

As one can imagine, there are not so many tyre inserts available for wide 20" rims. So I've used a DIY solution that seems to be popular, more or less reliable and customizable for any rim size - backer rods. It's a cord made of closed cell polyethylene foam. It feels dense, much more dense than a pipe insulation or a yoga mat, but less dense than some heavy duty tyre inserts like Cushcore.

A nice thing about tubeless is that punctures are fixed with the sealant from the tire, so you have nothing to worry about and might not even notice that you had a puncture. I've used around 60 ml of Stans sealant for each wheel.

The weight of my tubeless setup is basically the same as with the tubes. For example, for the front wheel: the latex strip is 25 g, the tyre insert is 30, a valve is 7, and a reasonable amount of sealant could vary from 30 to 80 g. That sums up to 90-140 g for tubeless setup, while 20" tubes weigh 100-150 g. 

The only advantage of the tubeless setup for trials supposed to be forgetting about snake bites. So I'm going to test it properly on different kinds of obstacles and see if it really works.

 

Some photos of the process

A rim with a normal rim tape that is necessary to protect the latex strip

Heat bonding the TPE strip edges

 

Stretching TPE strip over the rim, making a nice sealed surface

Tire insert is made of a backer rod cut in half. This is how it supposed to seat over the rim to hold tyre beads and to prevent tyre/rim damaging

One bead of the tyre is installed, it's time to install the insert. The insert diameter is smaller than the wheel diameter, so that the insert sits tight and holds the tire.

 

Second bead is installed. It's better to use some soapy water when doing this. 

Adding some sealant through the valve

Pumping the wheel. Sealant starts to seal the leaks. 

After some period of time, all the leaks are sealed. Now it's time to cut the excess strip.

Bike

The idea was to get a functional and lightweight 20" bike for cheap, in order to try this wheel size. Also, I wanted to be able to get a truly top-spec mod in the future by changing a few components in case I stuck to 20" size. That's why here you can see a weird combination of a heavily used frame with a rewelded disc mount, chainstays grinded because of failed sidehops, and lots of dents, cheap heavy spokes, used alu fork, and in the meantime expensive handlebar, brakes, and a front hub.

 

Spec

Frame and fork
- Frame: Born Sun, painted black, bashguard mount removed
- Fork: Echo SL

Front wheel
- Rim: Hashtagg
- Tyre: Jitsie Reverz
- Hub: Jitsie Race Disc
- Spokes: Sapim Leader
- Nipples: Sapim 14 mm alu

Rear wheel
- Rim: Hashtagg
- Tyre: Clean Koala
- Hub: Echo SL 116
- Spokes: Sapim Leader
- Nipples: Sapim 14 mm alu

Brakes
- Brakes: Hope Trial Zone
- Pads: Jitsie
- Rotors: Hope V2 160 mm

Drivetrain
- Cranks: Echo TR
- Freewheel: Jitsie 108.9
- Bashring: Trialtech Sport Lite
- Chain: KMC X9-73
- Rear Sprocket: Echo splined steel 12T
- Pedals: Trialtech Jack Carthy
- Bottom bracket: Trialtech Sport Lite
- BB bolts: Ti M15

Steering
- Stem: WAW Ultimate 155 mm, painted black, re-anodized bar clamp and top cap, ti bolts
- Grips: Pro bar tape
- Handlebar: Clean Carbon K1.2 690 mm
- Headset: Born
 

Weight: 7.26 kg
 
Geometry:
Wheelbase: 1008 mm
Chainstay length: 350 mm
BB rise: 85 mm

Edited January 15, 2021 by Target

[Petrum]

wow! And really nice job on the brakeless mod!

[cwtrials]

That's a really good looking bike!

[Pít]

Beautyful and unique! And lighter than my Crewkerz with light spokes and carbon fork 

[kovacstrialHUN]

Beautiful as always. Make some more  

[onzatpro09]

Definitely keen to see how it works with pure trials applications at low pressures. On my street bike the lowest I can go without burping is just under 40psi, but that's on narrower rims. Definitely a fan of the perseverance! 

[David Michie]

Well done! That's a Beautiful looking bike! Loads of effort gone into that!!! 

[Maintenance Justice]

It's a good looking bike and I applaud the effort and thought gone into converting it to tubeless. I'm glad someone out there has the drive to try these things so we can read about it! I'm very tempted to try and source a lefty fork from a Cannondale Hooligan just because...

[Target]

I guess it's time for a little update.
The tubeless experiment went surprisingly well! I didn't have any issues at all with the tubeless setup. No burping, no suddenly lost pressure, no snake bites. I've broken 2 frames and a fork since December, so I guess you can't say that I was too careful with the bike.

I wasn't happy about presta valves cut from the tubes. It was tricky to install them properly on the rim. They area between the valve and the rim was the weakest place in the setup, and tended to leak air if the valve installed not ideally and its nut not tighten up really hard.

So I bought and installed tubeless aluminium schrader valves. They hold in the rim valve hole much better, and the setup feels really reliable now. They needed some modification though since they originally designed for using with high double-wall rims. Some rubber and plastic washers have made it work on the single wall rim.