The Greatest Mystery of All Time - Where Do Valve Stem Nuts Go?

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Have you noticed that nowadays almost all tubes for tube type tyres are supplied with two nuts. But nobody tells you where to install the nuts. Booth outside the wheel? One under the other over the wheel? Tighten them down to the wheel or not? There are zealous proponents of pretty much every approach. I even asked ChatGPT what to do!

Recently I removed a used inner tube that I removed from a brand new Honda CRF300L, and from the factory, which is the indisputable temple of all knowledge and mechanical correctness installed it was installed like this: one nut bolted all the way down and inserted into the wheel like and then the other nut bolted onto the wheel to lock the valve stem to the wheel. Seeing as it came like this from the factory I assumed that is the correct way to do it so when I replaced the wheels that's how I put it back.

But more recently it was time to replace the tubes too and so I bought a brand new Michelin reinforced tube and when I was replacing the tires and tubes I proceeded to do the usual one nut inside one nut outside. But it simply wouldn't work. I couldn't get the bead to seat no matter what I did and then I looked on the box of my brand new Michelin inner tube. And there, black on white, in beautiful clear as-day monochrome an image was proudly displayed. On that image both nuts were installed outside, seemingly locked to each other. No nuts inside to disturb the relationship between the valve stem and the hole in the rim. The valve stem can now go all the way in.

So Michelin disagrees with Honda! Two temples of indisputable mechanical knowledge disagree with each other. But then I took my other box in which the inner tube for my rear wheel came and there I found a picture suggesting Honda's approach. So one of the temples of indisputable mechanical knowledge disagrees with itself as well?

So I decided to dig and after digging and taking everything into account and employing common sense here is the resolution of the mystery: If you are riding on the street and you keep your tires inflated at the proper pressure than I agree with what is Michelin suggesting . Two nuts outside the wheel. The first nut is only finger-tight. That very important. Finger tight and nothing more. And then the second nut is used simply as a lock nut. You tighten them against each other which prevents either of them from becoming loose. This is the only purpose of the second nut. To make it possible to have a nut only finger tight on there. Without the second nut, the first nut would come loose.

However if you are riding offroad and you occasionally deflate the tires to below the recommended air pressure in order to improve your traction and handling in challenging terrarins then you should not tighten a nut, finger tight or otherwise, to the wheel.

Why? Because the tire and the wheel and the inner tube are not glued together. When you deflate the tire to a lower pressure you remove the force which is pushing against the tire and the wheel and keeping the tire, the wheel and the tube together. This means that the tire can shift or move on the wheel, it can rotate on the wheel, this is especially true if you have an engine capable of outputting high amounts of torque.

When the tire rotates on the wheel it will pull the tube with it. When this happens the valve stem will be ripped off if it is bolted down to the wheel. If we there is no upper nut then the valve stem is given some room to move and get pulled inside before it rips off. This saves you from a flat and gives you a quick visual cue telling you that your tire has slipped. It allows you save the tube by deflating, pulling the valve stem back into the proper position and inflating the tire again.
This is also why we put baby powder or corn starch inside the wheel during the installation of offroad tires. It reduces the friction between the tire and the tube and reduces the chance of the tire pulling the tube with it if it rotates.

I’d also like to say that, I don’t really think that the KTM approach with no nut at all on the stem is the best approach. If there is no nut at all then the valve stem can be pulled completely into the wheel. The plastic cap will not prevent this from happening. And if the stem is pulled all the way in then you have no way of getting it out again unless you remove the wheel and the tire and reset everything. I think that a nut right under the cap is the best idea because it gives the valve stem the most breathing room while at the same time preventing it from being pulled into the tire completely.

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#nuts #d4a