Its not like i havnt been around cycling alot,but ive never seen this practice before. I was talking to a bike shop mech who tells me its common to not put plastic cap or the little knurled nut on presta tubes on bike. Ive never had troubles with using them although they can be a bit of a pain not to lose in dark with flat.
Is this a common practice to leave them off?
Is it ok. to not use them?

I use dust caps on schrader valves and presta valves and I always use the little knurled nut on presta stems (when threads are present).

All the little plastic cap does is act as a dust cap. You won't lose any air without it since the little nut on the stem itself is what keeps the air from escaping when tightened. If your ride is significantly muddy/gritty, then you would simply have to clean the valve before inflating. Otherwise, I wouldn't worry about not having one.

The dust caps are optional especially if you aren't riding in sloppy conditions. (I leave mine on but also ride through snow, mud etc) I've heard the threaded ring helps keep the tube in place and your more likely to suffer flats without it. I've been too chicken to try the experiment of leaving the ring off so I can't tell you if that's true.

The plastic cap on schrader valves is important to keep debris out of the valve stem opening that could interfere with the spring. Schrader valves keep air in by means of a spring actuated valve. Presta valves keep air in by means of the air pressure pushing the valve closed, then the knurled stem of the valve is screwed down as extra insurance. Given the difference in design there is little chance for debris affecting the presta valve. Some cyclists/mechanics omit the cap on presta as taking it off is just one more step that they have to perform before a punctured tube can be replaced. Some might consider using the cap as additional assurance that the stem of the presta valve won't unscrew or to give the wheel that extra "finished look". To answer your question directly, it is perfectly fine to leave them off if you so choose.

-j

I used to put the nut on the tubes of my 28-38 mm tires on my old road bike, since I had to deflate the tires every time I removed the wheels, and I did a lot of drive+bike+drive trips in a Toyota Corolla back then. The nut makes inflating a completely deflated tube a little easier.

Now that I hardly ever deflate tires, I don't put the nut or the cap on.

Thanks for answers,i thought possibly the mech was pulling my leg as hes prone to do.

The tube should only move around if you run fairly low pressures.

Yeah, I don't use either one. The Cap, just because the valve screws down and theres no place for dirt to get into them, and the ring, if you tighten them too much the valve comes out of the tube, I had it happen like 3x this last summer, the LBS mech said you don't even need them, so I don't use them to try to keep the tubes intact.

I don't use the caps, but I do use the knurled nut. It makes it easier to inflate, especially with a mini pump. I left it off once, and the valve would move around and make a ticking noise with every rotation. Put the nut back on, no more problems.

+1
I keep a knurled nut on the tube in my flat repair gear for just this reason. It's easier with the tight fitting heads on most mini pumps to just use the nut when doing a roadside repair.

I've never used the rings (and never had a problem because of it) but always use the caps (although I can't see why leaving them off would hurt).

The bike would be NAKED without the little knurled nut and a valve cap.

I wouldn't let a bike go outside.

My stems are smooth so no nut, and no cap. While using a pump, wrap thumb over the top of the tire to stabilize and have at it.

You've hit on a topic that is almost as religious in nature as what to lube the chain with

I use them semi fanatically because I don't want a bit of grit sitting on the stem thimble to get blown into the valve and possibly cause a slow leak through the valve. Granted the end of the valve is no where near as exposed as the open cup of a schreader stem but I figure why take chances. On the other hand if I lose the cap during a trialside flat repair it's hardly the end of the world and I don't keep a half dozen spares in my repair kit.

But during a thread we had about this exact same topic roughly a year back a lot of folks said that they served NO purpose at all other than protecting the tube while in the box, that anyone using them likely has dork discs as well and that generally their IQ was lower than a snake's belly in a wagon rut for figuring they were worthwhile.

Oddly enough having had a chain eat an entire back wheel on one occasion when it slipped down between the big cog and the spokes I proudly run dork discs on all my bikes. I guess that pretty much answers those folk's opinion of me..... Geez, the sides of this rut sure are high....

I use the cap because I see no reason not to, and because more than once it's happened that when I've left it off, I've cut my finger on the metal flashing that's on the tip of the stem. But perhaps I'm more of an absent-minded clod than most.

If the couple extra grams using the caps is an insufferable burden for you, by all means leave them off. I leave them on because the extra mass means I'm training that much harder than the next guy.

Possibly the practice of not using the cap or rim nut goes back to the days of tubular tires. With tubulars, I never want anything that could trap the valve in the rim if I were to roll a tire. It could be the difference between riding a rim (and probably destroying it) and a locked wheel causing a more serious crash.

It's a habit that sticks with you, so today, even on my PV mtn bike tires, where it doesn't matter either way, I still don't use the cap or ring. As far as I'm concerned the only purpose of the valve cap on PV tubes is to protect the tube from puncture while it's still a rolled up spare.

My Old Bianchi came with mismatched valve stems (one for a deep V wheel one not), but both with Red valve caps. I continue this tradition and transfer them from tube to tube because they look bada$$.

It's a difficult decision, leave off the caps and save all that weight, or put them on for the streamlining effect, by covering up the drag-inducing pin and nut.

then you can take them off and drop everybody

for some reason, my bike has the knurled nut on one tire and it doesn't have it on the other. I haven't had to change the tubes or tires yet, so I couldn't have lost it, the LBS must have only put on one as some kind of sick joke.

But I haven't had any problems with either wheel, I'd say the nut doesn't do anything. But I can see how it could be useful when using a pump.

It also protects the small valve which is prone to getting bent if anything hits it.

Once I had a dude on the train point out that my nut was loose. That might have been the impetus for me no longer using the nuts.

LOL... I'd be in that camp.

If it's not necessary, it doesn't go on my bike.

Mind you, I did use the nuts on my old early 70s classic to hide the fact some dickhead had drilled out one of the rims to fit a shrader valve... they kind of added to period look, too.

Hehehe! I drilled out a couple of my rims back in the day in preparation for a tour. Figured I had to be ready for anything.