Tyre and rim compatibility and pressures
The proliferation of tubeless ready tyre and rim designs has resulted in some significant compatibility issues where certain tyre and rim combinations don't work well together, or in some cases are dangerous. Actually these problems have existed since people started using tubeless tyres but it's got worse recently as different manufacturers come up with their own ideas for the perfect tubeless setup. This article is a brief summary of tubeless tyre/rim dos and don'ts.
DO NOT inflate a tubeless tyre above 40psi, ever, not even to seat the bead, and not even if it has higher pressures printed on the sidewall. Above 40psi most tyres show a tendency to pop off the rim. Stay below that and use good technique to seat the tyre - spread the bead out evenly around the rim - and it will be fine. Be sure your pressure gauge is accurate if you want to inflate near to 40psi. The only exception to the 40psi rule is Hutchinson road tubeless tyres.
Some new rim designs, such as those with Stan's NoTubes 2nd generation bead hook (Podium, Alpine, Crest, Arch EX, Flow EX for example) use a slightly larger bead seat diameter than the standard in order that the tyre sits more tightly on the rim. We have measured the difference in diameter at between 1mm and 1 3/4 mm depending on rim design. Doesn't sound a lot but it works out at over 5mm for the worst case. This is fine until a tubeless or tight-beaded tyre (such as some Schwalbe TL-ready and all UST tyres for example) meets a larger diameter rim.
The problems with these extremely tight tyre/rim combinations are:
1. You may struggle to get them on in the first place. It is possible to fit most of them in a tubeless setup, although it may be a battle and require pressure higher than 40psi (dangerous) to seat them. If you prefer tubes, or need to fit a tube on the trail you will find it hard or impossible.
2. The bead is sufficiently tight and non-stretchy that it lowers the spoke tensions dramatically leading to loosening. We have seen cases where the tension has dropped as much as 40% on the rear non-drive side and the wheel moves off-centre by up to 1mm when the bead is seated.
3. The bead may snap under the strain. We have had a few go off in the workshop and it's not a mistake you can keep quiet.
If you want to use "proper" tubeless tyres or Schwalbes, or any other really tight tyre, we recommend considering rims other than NoTubes. The NoTubes rims are great for running most standard tyres tubeless, where their bead socket design holds the trye securely without burping. However please also note that some tyre manufacturers such as Pacenti don't recommend their tyres for use on "non ETRTO standard rims". Often they will work fine but (according to the tyre manufacturers, anyway) the non-standard rims can cause tyre blow-offs.
Many cyclocross riders like to use pressures above 40psi. I wrote in the "general" section above that you shouldn't go above 40psi with tubeless but for some reason people seem to think a different rule applies to cyclocross tyres. It doesn't. Less than 40psi will work great for cyclo-cross so give it a go, but if you're not convinced and want to go higher you'll have to stick to tubes.
The only road tyres which can be used tubeless are Hutchinson's "road tubeless" tyres*. These use a special, very strong carbon bead to hold them in place at road pressures (90-100psi). They are the only type of tyre which can be used tubeless above 40psi.
*Other high pressure tubeless road tyres may be available but we haven't found or tried them.