As usual the internet has plenty of links to people who have done it before, I ended up trying 2 methods.
For my first attempt I went down the taped tubeless and foam route but couldn’t get the tyre bead to seat nicely on the duct tape (my first mistake was to run it up the rim wall) so when it was pumped up there was way too much leakage from the rim and bead. Frustration, nightfall and a ride scheduled for the following day caused me to abandon this attempt.
Attempt 2, a month later:
Given the challenge of getting fatbike tubes in my current location I didn’t much fancy hacking up the original tubes so I went hunting for suitable tubes from other vehicles: local tyre shop TyreMax had some Maxxis dirt bike tubes, allegedly 20″ but they slipped onto the 26″ Surlys with surprising ease. Bonus is that the valve stem is fully threaded and comes with washer and locknuts (had to drill out the Presta holes to receive Schrader valves). Not being a weight-weeny I haven’t bothered weighing the parts, the bike has a NuVinci hub gear: another 200g is hardly noticeable!
Stanley knife around the centre seam has it nicely opened up and on with the tyre (stock Dillingers): easy-peasy. Hook up the compressor and jiggle a bit until the bead seats and whoosh: up to 15psi. Surprise: no leaks! Not even a hiss.
Since the primary reason for going tubeless is puncture prevention I then deflated, removed the valve core and injected about 250ml of Stan’s Sealant, aired-up again and on to the second wheel.
One hassle that comes up a lot when people are talking about ghetto tubeless is getting the tyre to seat, and the time taken for the compressor to get enough air in fast enough to seat the tyre as above suggests that if the tyre burps on the trail or is holed so badly that a plug is needed then it would be insert-a-tube time.
So for wheel 2 I slipped in a layer of closed-cell builder’s foam: 10mm thick trimmed to fit the “trough” of the rim: 45° angle on the sides made it a nice snug fit, and a layer of duct tape to hold it in place. On with the tube, aplit the tube and then… sweat. Filling up the rim trough made the bead seriously tight: had to use tyre levers and serious thumb action to prise the tyre bead over the rim.
The fit is tight enough that a hand-pump can be used, but you’d better be ready for a fight if you have to get the tyre off again! And have good stamina: fatbikes take a lot of air.
In with the sealant, up to 15psi and off round the garden. Job’s a good ‘un.
Went for a spin round the village with Miss G, left the bike to stand and it was still holding air after 48hrs.
I’m now 560km away and only going home in a week’s time so I’ll take it out to the thornland and update the post then.
150km in the last two weeks, time for a progress report:
Ghetto tubeless fat tyres rock.
Had a couple of occasions where I had to top up with air, but in general the system works well. No apparent difference between the wheel with foam-cell and the one without.
The rear tyre did start losing pressure and I topped up with branded Slime (the green one – P650 for 5 litres from Riley’s Garage in Maun, substantially cheaper than the alternatives). I thought the depressurising might have broken the seal between tyre and ghetto rim liner as it was not holding pressure. I managed to trace this to a stubborn hole which I plugged with a normal tubeless plug.
I had to top up once on the trail today, after about 10km, but it has survived the rest of the day with no further pumping.
The Stan’s Sealant in the front tyre is still doing its thing: when a thorn drops out or remains attached to the branch I ride over it sprays out for anything up to a couple of minutes before finally plugging. Might be time to top up though, as it has started taking longer to seal when moving at speed.
Riding has been a mix of dry river bed (sandy, debris from dead thorn bush), dry river bank (dead, dry, thorn bush and other spiky debris) and cattle trails (thorn bush, thorny grasses and endless Tribulus terrestris).