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22 May

Tubeless tyre and rim compatibility how to fit them and make it work.

Posted by Bold Apps

Why tubeless, well lower pressures, more grip the possibility of self sealing punctures are all reason to use them. More space in your back pocket for important stuff like good is another. Gone are the days were I head out with 4 tubes in my back pocket. I am that unluckily.

Tubeless tyres have been around for a long time. Airliners landing gear have tubeless tyre at over 200psi so it not like tubeless tyres can't hold high pressures. While low pressure MTB tyres are more forgiving on the rims that can be used, the higher pressures in road tyres and the smaller air volume necessitates tighter tolerances. This is what this page is about. This is a generic tubeless tyre guide which is not brand specific or bike type specific. Tubeless tyres when done right are not faff. The faff starts when your setup is not really tubeless compatible.
What is tubeless compatibility?
Well think of a car wheel. When a car tyre punctures and flats, the tyre does not unseat from the rim. This is important because tubeless means tubeless all the time not done of the time.
A tubeless tyre that has flat but remains seated can be fixed externally most of the time permanently. This is alot easier if your not having to try to get the tyre seated at the side of the road.
A tubeless compatible retains the tyre well enough that it can be ridden flat or with very little air (5 to 10 psi) . Having done this for 10 miles then reinflating the tyre after fixing it, it certainly is a useful get out of puncture jail free card.
So what is about some rims that retains tyres while other let the tyre unseat with no pressure. Well let's start with a rim cross section.
The two images are of a Kinlin rim and a Mavic UST rim. Both are very tubeless compatible. All tubeless rim have the centre channel so when the tyre is mounted it sits in here. When you initially inflate the tyre is forced up to the larger diameter shelf. Now if the tyre is mounted to the Kinlin rim the bead moves under the bead hook and cannot unseat because the shelf is not flat. A Mavic UST rim use a bump next to the channel to ensure the tyre cannot unseat.

Mavic UST 

 

 

BORG/Kinlin XR22T/26T/31T

I hope you see what is in common. The rounded well sized bead hook that does not cut into the tyre and the uplifted inside edge of the bead hook is also an important characteristic. 

Sadly not every rim conforms. Here is a rim without these features. The tyre maybe retained but only by friction. This means if you have to plug the tyre it might unseat on you. Personally this sort of rim is not one I would define a tubeless compatible. You can run them tubeless of course but I am picky. The bead hook on this rim is also a bit small.

So the guide covers both types of rims. Those that retain the tyre and those that don't. Of course it is assumed you are using a tubeless compatible tyre. If your not and get faff well that was your choice.
Making your tyres tubeless ready. If you have a tubeless compatible rim that has spoke holes you will need to fit tubeless tape. Two complete layers is required normally. Some rims can be a bit undersized and need more layers. More layer will normally insure the tyre retaining features do your back to friction alone holding the tyre in place. The tape should be pulled tight when fitting and pressed in place ( I use my thumb) do that the tape is bubble free and conforms to the rim.
On rims with deep channels this is harder to achieve than on rims with shallower channels. Of course a deeper channel can make tyre fitting easier. Next make a small hole with a sharp point coming up from the valve hole. Then using the closed presets valve push it through the tape and use a rubber mallet to tap the valve in place. Thread the collar tight and bingo the rim is sealed. The tape should be 2 to 4mm wider than the internal width depending on the depth of the channel.
How to mount a tyre and what to expect.
A tubeless tyre on a tubeless compatible rim should be fairly tight. As a rule of thumb if it can be mounted by handed it's probably too easy. First Make up a bottle of dilute soapy water and dribble over the rim. This is essential as it get everywhere. Mount the tyre and chase the slack before using tyre levers. Fitting the tyre dry is a mistake as if it tight you can damage the bead and end up with the join between the bead and the tyre carcass failing and separation. The tighter the tyre fit is the more secure it will be. This is a good thing.
Once the tyre is mounted, inflate. If a floor pump does not get the tyre up, try compressed air. A CO2 cartridge will also work. The tyre should seat and seal. Not all tyre Tim combination pop and ping when this is achieved. Inflate to a pressure where there are no low spots in the tyre. Let the air out. Then remove the valve core and inject 40ml if sealant for a 25ml tyre. Bigger tyres can use more. Then inflate again. If the rim retains the tyre this will be clean. If the rim dies not retain the tyre s tight fitting tyre means you won't have to use compressed air to reinflate and that less messy and better for the sealant.
Which sealant I hear you ask. There are three kinds.
1) latex free sealant
2) natural latex sealants.
3) artificial latex sealants.
My own experience tells me for road use the artificial latex sealants seal the best at higher pressures. Examples include, Effetto Mariposa, Orange Seal, MaXalami MaXSeal. These simply seal the best at higher pressures.
Now you should not be relying on the sealant. Its not going to seal everything. You also may find one day, as I have that the sealant had dried up and then you puncture and the tyre leave you feeling flat.
Now if your tyre is not retained by the rim or weakly retained, your best of packing a tube, a portable set of pliers ( to get the valve collar undone) and levers.
If your rim retains the tyre and if it is hard to push of by hand, don't bother packing a tube as you may find very hard to get it in anyway. Instead carry tyre plugs.
These tacky butyl rubber fibrious strips can repair a tyre permanently or fix a big slice well enough to limp home. Carry what I do, 1.5mm and 3.5mm thick plugs. Most punctures can be fixed permanently with these. If the plugs wants to push out use a lower pressure to get home. often the sealant will glue the plug so after 24hrs it can be more firmly held to allow normal pressures. If you get a 1cm sidewall slice then don't fret. A big plug or two can seal the hole and inflate to a low pressure and get home if somewhere safe. You'd be surprised how far you can go on 20 psi with plugs sticking out of the side. I carry a blade to cut the fat worms down before inserting. The MaXalami tubeless repair kit Had the two thickness of tacky plugs. You may think that the fat plugs are for MTB tyres and that's what the manufacturers say but I have found otherwise.
Through the life of a road tubeless tyre I generally end up with plugs shoved in the sidewall through the tread and they are in there for a few thousand km. I should really stop riding road tyres off road and down filthy lanes in winter but really where the fun in being sensible.
My tyre is deflating or loosing air over night? 
First of all check the simple stuff. Remove the valve core and seal up the the seal and reinsert. Check the collar is tight. If this is the case and the tyre is not holed you can do one of two things.
1) if your confident your taping is good add fresh sealant. This can seal up small holes in tyres.
2) leaks can be caused by poor taping. Time to do again.
One final thing. Leave a tubeless tyre in place. It takes very little bead stretch for it be difficult to refit so remove only if you really have to.
Tubeless tyres are not to be feared and if you do encounter faff it's probably user error. This guide has been written because I have learnt the hard way so you have an easier time.
Read this blog post on how to fix tubeless tyres at the road side. 

 


1 Comments

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Posted by M Ellis on April 04, 2019

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