This is attributed to an email from Michelin, on an Ariel forum:
The conical washer sits over the inner tube valve stem and should follow the contour of the valve so that the convex side sits against the wheel rim when fitting.
Once fitted to the wheel the two lock nuts sit on the valve cap side of the wheel rim. After fitment and inflation to the correct pressure, the two nuts should be backed up towards the valve cap, and locked against each other.
This is not usually an issue on correctly inflated road going tyres, but should there be any slippage of tyre on the rim, during heavy braking or acceleration for example, the inner tube could be pulled around slightly with the tyre and if the inner tube is bolted to the rim the valve can be ripped out. If the lock nuts are raised towards the valve cap then inner tube has some leeway to move before this happens. Any movement is thus obvious as the valve stem will no longer be straight and pointing at the centre of the hub, but will be pulled round at an angle.
Does anyone really believe that that little nut on the valve stem is going to 'hold the tube in place' if the tire slips on the rim? Some folks just have to learn the hard way.
The only thing a nut is needed for is for preventing the stem from slipping inside the tire when mounting the tire on the rim and when pushing the stem inwards to allow the tire to properly seat on the rim.
Speedway bikes have an elegant solution: the stem protrudes not from the rim, but from the tire sidewall and has a 90° bend in it (at least they did the last time I went to a speedway race).
When people who should have known better cautioned me about the dangers of motorcycle racing, I always told them that a fear of death is nothing more than a fear of life in disguise.
Good grief ! That explains it all. Needles has thrown his nuts away !! Seriously, in this day and age would tyre manufacturers cling to hangovers from pushbike days ! Those nuts are obviously still supplied for a reason ! I agree with RF as to the placement of those nuts.
Well, TT, I've been fitting tubes to my bikes the way I was shown all those years ago.And, thus far, haven't had any problem. When I was operating, I only did service work and some engine rebuilds on motorcycles. Although I change my own tyres I stayed away from that aspect re customers.Actually,the bulk of my work was with stationary engines. No call for tyre changing there ! But, one things for sure, I'll be having a bit of a think now !
I fit mine as shown on the Ariel note above, I used to lock both against the rim until my off roading pal told me that the valve could rip out before I even know the tube had shifted, and that if i lock the nuts by the cap I could quickly inspect the valve and see if the tube has moved or not.
One nut against the sealing washer on the inside of the rim. One nut on the outside of the rim.
I recognize you as the expert, but are you really sure about that?
What could possibly be the function of a nut inside the rim?
Why is the dished washer on the tube a really good fit for the rim, but is awkward and grossly out of place against a hex nut?
Why isn't the inside nut a "stress point" for the tube?
I always considered the stem as a separate piece from the tube, and that the washer and first nut were a mechanical backup system in case the bonding between the 2 parts was faulty.
The described stack-up was what I was shown during my professional training in 1966. Every customer and personal tire I've changed since then (which must by now number in the thousands) has been fitted that way with no known failures.
I will point out that the outside nut is left loose (just spun on), because if the tire does slip on the rim, the angle of the valve stem will be the first indicator of trouble, well before the stem is ripped away from the tube. This is important because punctures can be repaired on the road side, but once the stem is ripped free of the tube, replacement is mandatory.
However, being an old dog that's still able to learn new tricks, I'm rethinking the stack-up based on the Michelin memo. You're never too old to learn !