Valve stem mod
 

I've got a Park Tools floor stand pump that works great, except on smooth road tire valve stems, which tend to pop out of the clasp when you approach 100 psi. This doesn't happen on the threaded stems. The guy at the LBS where I bought the pump suggested holding the clamp in place while pumping, but as much as I hate to admit it in a public forum, I'm not strong enough to pump to 100 psi with only one arm. Well, I can do it, but it ain't pretty.

Anyway, I found that by scuffing up the valve stems with a piece of coarse sandpaper, it creates enough rough surface area to hold the pump clamp in place.

If that violates some rule of biking etiquette then I apologize in advance. It doesn't look bad--more like brushed stainless or aluminum than anything else. Goes with the brushed aluminum finish on my Giant.

Get a presta to shrader adapter. They have plenty of thread for the pump to grip.

You could also make up a nylon strap with a velcro strip to "clamp" the hose in place and free up both hands.

Well, I guess if you wanted to do it the easy way.......

I tried the strap. Not bad, but it's easier to score the valve stem.

I'll have to try the adapter. What you're saying is to put the adapter on the valve stem and then use the shrader side of the pump, right?

Your pump is defective. Smooth stem or not, the park pump can at least get it up to 135psi.

I've only got one tube with a non threaded Presta stem... at least that's what I'm assuming you mean by "smooth road tire valve stems". In a fit of pump love I once lubed the rubber inserts with some automotive rubber protectorant that was more slippery than snot. This made putting the chuck on and off the threaded stems better but on that one smooth stem the chuck would fire itself off just as you're saying. Well it only took a few times on the other stems to wear away most of the protectorant and from then on it stuck to the smooth stem with no issues. So you may just need to use the pump more often to weat away whatever production wax or coating it has on it.

In the meantime roughing up the stems is a bright bit of inspiration.

Pretty common issue over 100psi when pumping up my disc wheel. Just hold it on there and you'll be ok.