Strengthening the valve hole of a rim during manufacturing

Question

Various technologies(sleeved, soldered, pinned) exist to reinforce the place where the rim makes full circle. A major argument against Schrader valve is it's large diameter weakens the rim. I, however, enjoy that valve and was wondering the following. Are there rims* with AV and proper strengthening around the air hole? Just like seat tube reinforcement.

_{* - let's say intended purpose is enduro riding style (drops up to 1m), mid-level budget(300EUR for wheelset); but any technologies are of interest!}

Answer 1

The question is a misnomer. In the earlier days of mountain biking, Schrader was the more common and the rims were much wider. The size of the hole is a real issue for narrow road rims and the narrow XC rims that became more common into the late 90s.

I have a set of the very first Mavic CrossMax wheels which were very very light XC race wheels and these are drilled for schrader without apparent reinforcement, and profided with a small plastic shim for presta valves. The strength of the rim around the valve hole was never an issue for this incredibly light rim. You may find reports of its other weaknesses though, when used for too heavy an application.

Modern MTB rims are again wide, very wide, and you shouldn't be concerned about the size of the valve hole in these. where the manufacturer allows a schrader. It's personal choice (&risk) if you decide to drill a presta hole to take a schrader valve, of course, but that's not in the scope of your question.

Answer 2

I think this is a non-issue these days.

Early rims were made of steel, and had a consistent thickness which was pressed into a U shape, and then rolled into a long coil. The only parts of the rim which were thicker were the bead seat, where the tyre hooks on, and the folded corners which would thicken up some during folding.

Modern rims are made of aluminium - there are few-to-no steel rims sold these days for bicycles.

These are made from extusions of aluminium which is coiled while formed. The cross section is part of the design, and there are thicker parts where needed, and voids where it helps to save weight.

A steel rim would be like the left-most image, but without the two holes.

So there is additional support in aluminium rims that steel tended to lack.

Additionally, the valve stem itself is part of the support material. It is a small tube of brass mostly, which will resist crushing forces, and (as long as its not a sloppy fit in the hole) will perform a similar function to a reinforcing grommit.

Carbon Fibre rims are more "designed" and will have sufficient extra material in the rim at the valve hole. They are generally a lot deeper, which by-itself adds support.

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So why are grommited spoke holes desirable still, where a grommited/reinforced valve hole isn't common? I suspect that the nipple in the hole still has a lot of room to move, to allow for hubs of different sized and widths.

Additionally the spokes and nipples hold your weight under a continuously-varying level of tension and less-tension, whereas the valve only has to resist the fairly-consistent pressure from inside the tube/tyre.

Answer 3

Buy a rim wider than an old-style road rim and you'll be fine.

The valve hole being a weak point was really only a problem with 622-15C road rims, that are 15mm wide inside. Such narrow rims can only be used with 23mm-32mm tires, anything wider would be a hazard. Today even road bikes can use 622-19C rims that can use tires starting from 28mm. The trend towards wider tires and rims has accelerated by the introduction of disc brakes on road bikes that no longer require little tire clearance if the brake is to be made lightweight and stiff because the brake is no longer around the tire.

Mountain bikes may have used 15C rims only during the introduction of the first MTBs that had to use non-MTB components. I'd say even 19mm wide rim today would be quite narrow on a mountain bike. So there's plenty of material around the Schrader valve hole.

It's still true that the valve hole is the weakest point of the rim. However, "weakest" does not equal "too weak".