It turns out that foot pumps

It turns out that foot pumps, like the vast majority of hand pumps, have a flap, either plastic or aluminum, whose function is to block the entrance of the air once the inflation nozzle has been inserted into the valve of the chamber . Up to that point everything is correct and easy. But as is normal, these pumps and other pumps are designed for standard size wheels, either road 700cc (28 "or" 29 ") or mtb 600cc (26") or even folding or bmx 20 "( Ertro 406) In all of them the radius crossing, or the angulation of these if not crossed, allows to perfectly unfold the locking flap, because there is enough distance to the hub. 3/8 (Ertro 349) can not be done easily, since if you manage to enter it, then it costs a lot to remove it without forcing it out because of the small size of wheel and short distance between the intersection of the spokes and the hub.