I have some Mavic Open Pro rims and the braking surfaces are getting quite concave: Any ideas of when they should be replaced?

Hi mikey. About 500 miles ago! Apart from your brake blocks wearing uneven giving poor braking. There is a chance a section of the rim could blow-off! Your tyre pressure is 110psi pushing on the rim!!!

This one went when I was pumping the tyre up:

Difficult to condemn rims without seeing them but they sound bad- get a shop to look at them before you consider riding on them any more – they could be very dangerous.
If they fail on the road it will most likely be when braking downhill-the heat generated and consequent pressure increase is usually the final straw.Could be a quick route to A&E.

This one went when I was pumping the tyre up:

had one do that but the braking suface was broken (unlike photo) the sharp end brushed across my face a few mm from my eye!! might be mental but i know where safety glasses when i pump up road wheels.

Hard to judge, even if you can inspect them (is there no wear indicator?) but if you are concerned then do it.

How many miles do you guys get out of them?

Depends, rims on my commuter were trashed (well beyond what I’d consider safe even at 60psi) in about 2000 miles, lots of winter grit, grime, water and general mud, combinded with stop/start riding in traffic.

On the road bike I’ve done 10k on the same wheels and they still look as new. Mainly dry miles with a small % of the braking.

Couldn’t say, depends on conditions etc – I remember getting through a Velocity rims in a year (say 5,000-6,000 miles?) but according to clubber and various other southern softies I was dragging my brakes 🙄

I only use rim brakes on my summer bike now.

Most newish rims have wear markers. Keep an eye on those. If they are older than that, once they start to look concave, either change them (sensible) or pump them up to 180 psi every so often to see if they give way (stupid)

BTW do the pumping outside. When a rim lets go in a concrete garage it is very loud.