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Tuesday 4 August 2020

Lessons learnt fitting bike tyres

I don't have to fit bike tyres very often so I am not an expert. Each time I do, I have to remember what I did last time. Years apart for some tasks!

This time I was fitting some 29" Schwalbe Hans Dampf Supergravity tyres to a couple of different rims. Fitting them did not go to plan, so I have learnt a few things:

1. Tyre leavers are for getting tyres off not usually for putting on

I've fitted other makes of tyre and was able to force the tyre on the rim with just a bit of effort. The Schwalbe's, I've just fitted, were more difficult.
One side goes on reasonably easily, with a bit of effort, but despite positioning in the hollow, as best I could, I just could not get the other tyre bead over the lip. I resorted to tyre levers but they just scratched the rim and I felt like it was only going to work if I had three hands.

The solution I eventually worked out was that if I manoeuvred the rim to the corner of my bench and forced down on the tyre I was able to get it most of the way on. I then just needed to use a single plastic tyre lever, in the centre of the remaining short length, while pulling the tyre down with the other hand to hold it on the wheel. The single tyre lever in the middle was then enough to  flip it over the edge. Still tough but worked.

I have since managed to fit them without the tyre lever. Which is how I would expect to fit tyres. [Update: I have decided that it depends on the weather. In the warmer months tyres are easier to fit!] To fit the troublesome tyres, I had to get it setup just right, to be able to put pressure using both hands to pull the whole tyre down so the bead popped over.

[Update: I now use bead sealant. Brush that on before fitting and it is much easier to slip the bead over the rim] 

I bought the Supergravity variant of the Schwalbe, Hans Dampf, tyre because it has the toughest sidewalls. I guess that has a disadvantage when trying to fit them!

2. Put the tubeless tyre sealant in AFTER the tyre has been fitted
It was a lot harder struggling to get the Supergravity tyres on the rims whilst also trying to prevent all the sealant pouring out.
I gave up on that idea, emptied out the sealant before fitting the tyre.

Once fitted and inflated to pop the bead on, I used a large syringe to inject the sealant through the valve tube.
This also has the advantage that it is possible to check that the tyres hold pressure without the sealant masking poorly fitted tyres. If I have time I like to leave the tyre inflated for an hour or so, without sealant, to see how well it holds pressure.
The tyre sealant, in my opinion, is primarily for punctures although, in most cases, it is necessary to help the tyre stay inflated for longer.

3. It's better to replace rather than repair tubeless rim tape
Changing the tyre was the result of a 3" nail. It also punctured the rim tape through to a spoke nipple and nearly punched a hole in the inner trough. I thought it would be simple enough to patch a section of rim tape over the existing. After one ride the tyre had deflated!
Very disappointing. After the struggle to get the tyre on the wheel, I had to do it all again. This time I stripped off the old rim tape. It came off very easily, so I should have done that the first time.
This time, with a completely fresh install of rim tape, the tyre has stayed fully inflated.

4. The tubeless rim tape needs to stick, a little
I used Stans No Tires Tubeless Rim Tape on the first wheel I did. That stuck well. I did exactly the same from, the same roll, on another rim and it would not stick at all, even after carefully cleaning with isopropyl alcohol. I'm guessing it's something about the material used to coat the inside surface of the rim.

On my first few attempts with this wheel, I managed to keep it down just enough to get the run round the rim. I then fitted the tyres and inflated them. As the tape was a seal from bead to bead, it inflated. It lasted a few rides but after a while it would deflate overnight, despite the sealant.

I've now had another rim which was similarly difficult to stick to and would leak air through a spoke nipple. I eventually had to sand down the inside of that particular rim. It was the only way to get the rim tape to stick at all. I have found that for a long term seal, the tape has to stick round each spoke hole in the rim.

I think the rim tape, being the correct width for the tyre, minimises leakage and in many cases, I have found, that is all that is needed, stick or not. The typical recommendation of about 1mm or better 2mm greater than the internal width of the rim, works best for most wheels that I have worked on.

As a result of the troublesome wheels, I have tried lots of different rim tape. They all work to some degree but my favourite, because it conforms fairly easily to the inside shape, is from Muc-Off. [Edit: I have been told, using a good hair dryer or carefully with a lower power heat gun, that other tape can be made to conform.]

By writing these notes down, hopefully I will remember them for next time.


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