The difference between WM type and MT type of the rims.


P10103061.85 47mm

Image A WM type rim

Image B MT type rim

The WM type is in the shape shown in image A, and the MT type is in the shape shown in image B, the so-called normal tubeless wheel with a hump.


In general, the role of a hump is to restrain the tire bead part in order to avoid bead drop when air leaves the tire, but as seen in the image below, if the air pressure is such that normal driving is possible, the bead part does not directly touch the hump, meaning that in the end the tire and wheel are joined together due to air pressure.



The weight of the bike + the body weight of the rider + the traction while driving cause the internal pressure of the tire to increase, and the beads become less likely to drop the more the tire is pressed against the road surface and flattened.

As you can see in the image below, during cornering the wheel is weighted by centrifugal force on the outside, maintaining the tire's grip, meaning that the rim is pressing the bead part of the tire in the direction of the white arrow.

The rim is pulling the side wall, and the side wall does not stretch, so the outside bead part is not burdened due to the deformation of the tire tread shape.

This driving image is from the Tsukuba Circuit, and the tire incorporates an OUTEX tubeless kit.

The air pressure at this time is set at 1.2kPa (17psi) cold, and the results of the race were a win and the establishment of a course record.

We have also seen results where the WM type rims on employees' super-cabs and Z-1s have been made tubeless and driven more than 50 kilo meters round trip every day to work for years with no problem, SR400 normal rims (WM types) have run for test in circuit, and DRZ50s and CRF50s with WM type rims made tubeless have won in mini-bike races.

When switching to tubeless rims, most riders say that the handling is improved while driving.
This is largely due to the fact that the bead part adheres solidly, making the wheel and tire join together, even more than the reduced unsprung weight caused by the lack of a tube.
With tubed tires, there are places where the bead part of the tire and the bead part of the rim do not adhere to one another, making it difficult to feel the sense of contact with the road surface, and also causing the tire to rotate if there is no bead stopper (rim lock) when driving off-road.

Whether tubed or tubeless, the causes of WM type rims experiencing bead drop are the air pressure being extremely near zero or something causing the tire to leak air when the bike is parked.

Considering punctures, when a tubed tire is pierced by a nail, etc., starting a sudden leak of air, the handling suddenly changes, leading to a falling down in the worst case.

With tubeless tires, in most cases you can keep driving as it is even if pierced by a nail, etc.
In other words, the speed at which air leaks is slower with tubeless tires, making their safety factor exceptionally higher.

In rare cases air may gradually leak even with tubeless tires, but as the air pressure drops the handlebar will become harder to move and you will be unable to keep riding, so you could notice the problem immediately.

Due to the above facts, if you maintain regulation air pressure, we think it is safe to say that there will be no difference between WM and MT types as well as no fear of bead drop. However, when the bead part has become rough it is necessary to repair it to a clean state, and it cannot be said to be safe with all rims, so some workmanship is required.

The reason OUTEX tubeless kits have spread not only across Japan but also overseas is that they work with no problem with WM type rims as well as long as they are installed properly.

Incidentally, this kit has been on sale for 9 years now and there has not been a rim that couldn't be installed on.