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I've always used a lock nut with a presta valve, but I know others who don't use it and leave the valve stem to protrude through the rim hole without fastening.

What, if any, are the advantages of not using a locking nut for a presta valve?

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up vote 10 down vote accepted

The advantage is that it's quicker and easier to get the tube out and tyre off, and you never have to deal with jammed nuts.

IME the nut will be wedged unbelievably tight the one time you get a puncture at an inconvenient moment, and you'll end up breaking the valve (if you have pliers) or not being able to get at the hole (if you don't). The problem there is that you do the nut up firmly when the tube is inflated to 100psi, then it goes flat and without the air pressure "firmly" becomes "OMG".

The fix for that over-tight nut is obviously to inflate the tube. Which is fine if there's a wee hole somewhere away from the valve, but if the tube burst or you brought a spare tube instead of a patch kit you just have to somehow get the value out of the tyre. Which is surprisingly hard to do if the only tools you have to hand are whatever is on the side of the road.

Disadvantages of leaving it off: The nut is slightly useful if you have a flat-section rim drilled for Schrader values, in that it stops sand and muck getting in through the gap between the valve and the rim and rattling round in a hollow rim or causing punctures. Obviously this isn't an issue if your rim is drilled properly, and a better solution is to buy tubes with Schrader valves.

The nut can make putting a loose tyre back on by holding the bead in place by the valve while you try to balance the bead around the rim so it doesn't blow off. But a properly fitting tyre doesn't do that. And you could carry one nut in your repair kit, rather than one on each wheel (a saving of at least half a gram!)

(edit) the nut has to be tight enough that it doesn't loosen when the tube is fully inflated, but not so tight that it's hard to undo when the tube is flat. But often when you tighten it with the tube flat, when you pump it up the nut turns out to be loose. So to get it right you need to let the air out of the tube, tighten the nut some more, then pump it back up. Possibly more than once. Or you can tighten it once the tube is inflated and hope for the best. In which case you can easily end up back at the start of this answer.

The other 99% of the time the nut does nothing harmful. Nothing very useful either. It's just there.

(edit) Note that the question is not "what are the advantages of using the nut" or even "how do you use the nut", it is specifically "advantages of not using the nut". I don't think "if you do this the nut works fine" is an advantage of leaving the nut off.

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+1 - it's just there! – PeteH Aug 18 '14 at 9:30
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But if you only do the nut up finger tight in the first place, before the tube is hard, you gain the benefit without the risk. My schrader tubes have nuts now as well and it does make getting inflation started easier (probably even more so than on the prestas). – Chris H Aug 18 '14 at 13:10
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Personally, destroyed tubes from poor "pump attachment": three. Jammed nuts: zero. – tedder42 Aug 19 '14 at 22:47
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@Mσᶎ I don't think it warrants a full answer- it doesn't quite answer the original question- but my experience is that a tight nut significantly reduces motion of the valvestem. – tedder42 Aug 20 '14 at 3:20
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I also agree with @tedder42. When the tube is deflated it makes attaching a pump much easier. I've never encountered a nut that was difficult to remove, but maybe that's because I always tighten them before inflating the tire. – Carey Gregory Oct 20 '14 at 14:52

I prefer having the nut, because it makes pumping much easier, especially road side with a frame pump. I put them on finger tight and then retighten after inflating, and I've never had one jam, or rattle.

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Yea, and putting the nut on makes fitting the tube and then tire easier. Without the nut one needs to be careful not to move rotate the tube while fitting, this removing the valve from the valve hole. – Vorac Aug 18 '14 at 12:39
    
@Vorac However, if you use the nut, you'll need to have the tubes powdered with talcum or some such to further prevent them from moving. Otherwise, the tubes may stick to the tires and move during a hard stop, ripping the valve out in the process. Very annoying, especially if you don't carry a spare. – arne Aug 18 '14 at 13:16
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@Arne - is this really a problem for normal cyclists (as opposed to professional racers?) I've used tubes with and without talc and have had my share of hard panic stops, but never had a problem with the steam tearing out of the tube. And I'd be surprised if the talc really makes that much difference when the tube is being pushed against the tube with 100+ psi of air pressure, it seems that if the tire does move, it's going to drag the tube around, talc or no talc. Likewise, nut or no nut, it seems that if the tube does shift, it's going to tear at the valve stem. – Johnny Aug 18 '14 at 14:20
    
@Johnny I have Presta valves on my MTB, and there I had the problem. On a road bike, you're quite correct; the much higher pressure will keep everything together nicely. – arne Aug 19 '14 at 6:31
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@Johnny How do you know the valve wouldn't be damaged by a hard stop, with or without the nut? What will the valve do if the nut is not there that prevents damage? The way I see it, it's a straight metal pipe protruding through two holes in the rim, and the inner tube is pulling on it at 90 degrees. – Kaz Apr 8 at 0:35

I suspect a big part of the reason people leave them off is because it's something 'real cyclists' do- along with leaving off the dustcap, lining tyre logos up with valves etc. IME there are no real disadvantages to having them on apart from maybe a few seconds in changing tubes, which might get you some tutting on a group ride if people are hanging around waiting for you but that's about it. That said I don't use them on my road bike, and I do line my tyres up with my valves!

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Lining the logos up is useful for finding what ever it was that put the hole in your tyre in the first place. – alex Oct 20 '14 at 7:45
    
Sure, that is helpful- and that's what I tell people if they ask why I care! But I think there's a big 'it just looks right' factor as well- it shows that you're paying attention to the details. – user814425 Nov 9 '14 at 16:46

The main reason I don't use them is that they rattle when they come loose. If you're heavy handed when pumping though, the nut is useful.

Just remembered one other reason to use them... removing them if you've got a tubeless setup is a recipe for disaster

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Heavy-handed is almost compulsory when using some of the little frame pumps (of course the solution is to get a better pump, as I learnt). – Chris H Aug 18 '14 at 13:11
    
Or a CO2 inflator! – Carel Aug 9 '15 at 19:05
    
> removing them if you've got a tubeless setup is a recipe for disaster Not familiar with this, but how so? The stem is just on the rim, and so if you don't have the nut, it can fall inside the tire? Or, worse, can you actually lose air: while the tubeless tire is inflated, and there is no nut, can the valve can be pushed inside, allowing air to escape? (On cars, the valve stem cannot move either way; it has a molded "gland" that grips the rim, or some such) – Kaz Apr 8 at 0:40

Some, especially little mobile, pumps do not have the tube and mount directly onto the valve which makes valve to move into all directions while pumping which is definitely not healthy for the place where your tube is connected to the valve. In fact I have managed to destroy a tube this way. The nut helps to avoid this problem by holding valve into the place.

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Advantages of not using a lock nut: faster tube removal, looking 'pro', possibly avoiding damage to tube due to overtightened nut.

Disadvantage: I run big tires and deep section rims. If I try and push the pump head on to the presta valve, it likes to bury itself inside the rim to hide.

Keeping the nut on there stops the vaulve from going down in to the rim. This is important when I'm doing a roadside repair and using a small portable pump with a tight fitting rubber gasket. I've bent the delicate little valve on tubes due to poor purchase with the pump head, so I want this little nut holding things so I don't mess it up. I could push the back of the valve with my hands while I try to fit the pump head on, but this really sucks with some tires, especially the very puncture resistant ones which are not very flexible (panaracer ribmo) and make it hard to do this because they don't want to push down between the rim walls.

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The nut is basically for ease of inflation when the tire is flat.

If you are a looks-oriented cyclist using one may make you look a little less serious, due to the implied fact that if you maintain your bike often you wont have flat tires from having your bike sit. If you have expensive wheels you might not want to use one for fear of it scratching the rim (cosmetic damage only, but still ...). Also, it is easier to take the tube out when you get a flat.

If you do decide to use one a little grease on the stem threads keeps it from getting stuck.

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It also holds the tire to the rim when you're inserting the inner tube into the tire, and you have the tire halfway mounted on the rim. You can go around and stuff the tire without the annoyance of the opposite side coming out of the tire – Kaz Apr 8 at 0:41

There is an advantage of the nut just being on the stem, simply because you know where to find it should you ever need it again. You will benefit from that helpful nut again if you have to take the tube off for whatever reason, and then put back the same one. For instance, patching that tube, or changing a spoke and nipple.

Now, some people believe there are certain risks, such as the nut becoming jammed (adding difficulty to tube removal), or contributing to valve damage in the event that the tire slips during hard braking, dragging the tube with it.

Whether real or not, you can eliminate the possibility of these risks by tightening the nut against the dust cap, rather than the rim, like in this image:

Presta valve with nut tightened against dust cap

The valve has two different sized threads. There is a small diameter thread for the cap, and then a wider diameter for the nut. You only thread the nut onto the the second thread by just one or two turns. Lightly tighten the cap, and then turn the nut left slightly to add that little bit more tension.

Of course, in this position, the nut interferes with pump chucks, and so you have to completely remove it to inflate. But that only takes one or two turns since it is right on the end of the threads, a noted.

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I've never known the dust cap on a Presta valve to be overtightened. I suppose one could do it if they really tried, but I can't see how it's a big hazard (and if it can be overtightened without the nut it can be overtightened with it in place). As to mounting a Presta valve in a rim drilled for a Schrader valve, one should use an appropriate grommet. – Daniel R Hicks Apr 8 at 18:27
    
@DanielRHicks Thanks for the pointer to the grommet. Some of those things in the image search are also called glands in electronics (rubber rings that fit holes in sheet metal, protecting cable shields from being cut). I want that now. – Kaz Apr 8 at 18:42
    
@DanielRHicks > and if it can be overtightened without the nut it can be overtightened with it in place Not in the same way (dome breaking right off the cap). – Kaz Apr 8 at 18:44
    
You can strip the threads. Or simply crack the cap open. – Daniel R Hicks Apr 8 at 18:46
    
@DanielRHicks The nut prevents the cap from moving down farther, so that the tip of the valve won't break the cap. But why would you keep tightening, when the cap is snug against the nut? The nut gives the user a clear target for how far the cap goes. – Kaz Apr 8 at 19:05

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