Tubeless rims are usually cast wheels with a lip or ridge (below) to help locate and seal the tyre bead securely on the rim. This lip is also considered a safety feature which stops the tyre coming off the rim should the tyre deflate on the move. In my experience, it works. You will feel the softened tubeless tyre long before it comes off the rim and can keep riding slowly without it coming off the rim.
I’ve discovered lately that spoked rims with the safety lip suited to TL tyres are designated MT as opposed to WM. Even for bikes running inner tubes. The two rims left are from the back of an Africa Twin and an Excel 21 (see below).
However, according to ADS’ comment below, his 2005 KTM’s Behr rim is stamped MT but has no lips, so as he says: … while it may be true that safety-lip wheels have the MT code, it doesn’t appear to be true that all MT-code wheels have the safety lip.
This lip also makes removing and mounting the tyre difficult by the roadside if you need to repair a tube. It varies from bike to bike and tyre to tyre, but usually, with tubeless you only need to remove a tyre to replace it when it is worn out, not to fix endless punctures. And unlike punctures, fitting a new tyre is usually done at a time of your choosing and in a tyre shop which has the know-how and tools, including a powerful compressor and lube to force the new tyre over the lips and into the rim’s groove with a nice ‘pop’.
Oddly, for years and years bikes running tubes also have this safety lip. Old Yamaha XTs like the one above had it on the rear wheel. Out of interest, this disproves another tubeless urban myth: you can only stick a tube in a TL rim to ‘get you home’ because it will eventually rub on the lip and explode with terrible consequences. Well, clearly not on a stock tubed ’86 Tenere with a lipped DID rim (above). I know because I remember putting that bike on a crate with the rear tyre removed, sticking it in gear and ‘hand-lathing’ off that safety lip with a chisel so that I’d not get stuck in the desert trying to break the bead to fix a flat. And as importantly, remounting it with – back then – just a bicycle pump. All this faffing is why we like tubeless.
But to convert spoked tube rims to tubeless, this lip is actually a good thing and my 2008 Tenere (above) also had them on the back wheel. The front rim was normal which is a risk when converting to tubeless. But can it be any worse than a tubed tyre puncturing? Tubed tyres deflate faster and therefore more dangerously than tubeless tyres, so even without the safety lips or humps on the front, with tubeless you’re already ahead. But, as I found, you can get slow leakage along the seal.
Pictured left: the top WM rim has no sealing lip; the lower MT rim does. Note also the angle of the tyre bead–rim interface; the lower rim with the lip is flat which helps make a better seal. The upper lipless rim slopes into the well making it easier to change by hand, but it won’t hold or seal a tubeless tyre half as well. I think my 2008 Tenere front-wheel sealing problems were because the rear wheel was like the lower rim – good for tubeless. The 21-inch front was like the upper rim; less good seal.
21-inch spoke rims with safety lips
I spent weeks online tracking down a 21-inch alloy rim with the safety lip suited to converting to tubeless. They were rare, but not anymore it seems.
Taiwan-based Giant (or GLM) is the biggest bicycle and motorcycle rim manufacturer in the world. They make such a rim in ‘big bike’ 2.15 width with 36 holes (bigger BMWs have 40; lighter trials bikes have 32). In the UK Central Wheel Components sell them for £111 (2.15kg) + 24 quid to anodise. It may be branded SM Pro (see bottom of the page).
Rally Raid use this rim on their own wheelsets with BARTubeless conversions for Africa Twins (left) at a staggering £1500 a pair.
A quote to build that rim onto my Himalayan hub and seal it with BARTubeless (done in Italy) came in at £420. A quote to do the same for my AT: new 2.15 GLM rim £135; S/S spoke set and wheel build £105; Airtight TL band £120; post £21 (£381). Some find the GLM a bit soft.
More research unearthed Japanese Excel Takasago TL rims in 21-inch, but only a 1.60 size (left; p/n ICK408, and below) which is OK for dirt bikes but not adv twins. Talon in the UK import them at £165; I bought a pair in Italy for a lot less and have kept one for a rainy day. This rim has an unusually deep well which should make for easy tyre mounting, even after you’ve sealed it whichever way.
In 2018 there was talk of Excel making a wider 21 x 2.15 suited to bigger bikes and in 2019 it was produced, apparently.
And in 2021 a mate bought a 2.15 x 21 SM PRO Platinum from Central Wheel for £135, as mentioned above. So these rims are out there now in black or gold.