On a 20mm road rim?

They are fairly narrow road rims, dunno the dimension, however.

Presta valves suck.

Pff. They sh|t on the alternatives.

What could possibly be your beef with em?

I use the caps since there is really no reason not to, and it might keep dirt out of the core. When it comes to the ring, I keep one on the bike to use when I have to inflate from flat. Its keeps the stem in place when starting to inflate. BUT while I usually use a inflaters, if you use a mini pump I loosen the ring so the stem is not so rigid. I have broken off stems with the ring tight when using the mini pump.

BTW as far as im concerned mini pumps suck. Two have failed or broke when flatted on the trail. Then as above I broke a stem when using. I do carry one, but use inflators normally.

I'm also not a fan of mini pumps, but not because of valve breakage. It's just too slow to get decent inflation with one, and I carry a full length frame fit pump on my road and commuter bikes. I consider CO2 inflators too expensive and enviromentally unfriendly. (it's not the gas, which is either volcanic in origin or distilled from the air, it's the cartridge and entire process)

Any pump use shouldn't lead to valve breakage, so here's a few hints. Most of the folks I see breaking valves do so because they are not effectively bracing the business end of the pump as they work the other end.

First, even though the thumb lock makes it unnecessary, grip the pump head and tire together in one hand, so the pump is braced (through your hand) to the wheel, and doesn't stress the valve with each stroke. This takes a bit of practice, but comes naturally to those who've used push-on heads without thumb locks. Also do not brace the bike too rigidly, leave room for the wheel to move or actually support the bike by the wheel while pumping. With a bit of practice you'll never break a valve again while pumping, even if you use a hand pump daily.