The Chainlink

Chainlink Tech Corner: Jam Nut or No Jam Nut...That is the Question

By Scott Wilson

What’s this thing for?

Here is a picture of a presta valve, exploded. You see the stem, the valve core, the cap… and that weird little nut.

This is an installation nut, or a jam nut. Its job is to keep the valve from sinking into the wheel when you try to pump up the tire. Once there is enough air pressure in the tire to keep the valve from going under, the nut’s job is done and it should be removed.

There are several good reasons to remove the jam nut after the tire is pumped:

  1. It rattles
  2. It can corrode and fuse to the valve stem, making a simple tire change into a Herculean task
  3. It adds weight
  4. In cold weather it’s one more little metal thing you have to take your gloves off to mess with to change a flat
  5. If it’s screwed down too tight it will squeeze the rubber tube against the edge of the rim hole and over many cycles of deflation/inflation and the normal wiggles and movements of riding it will cause a cut.

And there are a couple good reasons to keep it on:

  1. It’s shiny
  2. If you’re in the habit of letting your tires go completely flat, keeping it on might make re-inflation easier.

Most people these days are using extra-long valve stems and don’t need installation nuts at all. This trend is reflected by the increasing popularity of smooth, threadless valve stems.

There’s also a belief that that the installation nut will keep the valve from rattling. This is sort of true as long as the nut stays tight against the rim, but that picture above proves why that’s a bad idea. If you have problems with the valve shaking about, do like the pros and stack up a few layers of electrical tape, put a hole in the middle, and put that over the valve, like so:

But just because installation nuts aren’t particularly necessary doesn’t mean you should throw them away. They have lots of subsidiary uses, like acting as washers or spacers when installing a rack:

Or they can be used as bracelets for your doll collection:

Or you can make a necklace out of them. Be creative and post your installation nut uses in the comments below.

Scott Wilson is an MFA writing student at Columbia College as well as a seasoned professional bike mechanic. Scott’s “wrenching” experience includes bike shops, racing teams, and professional triathletes across the US. The aim of Scott’s technical articles is to explain in detail how bicycles and their individual components work...and in doing so, help you keep your own bikes running better and lasting longer.


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Comment by Jim Reho on June 9, 2015 at 4:07pm

Scott, I really enjoy your articles.  I've had reason #5 happen to me.  In addition to the picture of the doll, I got a chuckle out of reason #3 for taking them off.  I did so, and now that I've shed that .07 ounce (total) of useless weight, I'm really flying!  Now I need to take off the approximately 8,000 of those things that are hanging around my waist.  

Comment by daWillinChi on June 5, 2015 at 1:50pm

I like this article. I've been doing it wrong all this time!

Comment by Far'arned Retrogrumpalunkus #63 on June 5, 2015 at 11:27am

I have a couple of the stepped jam nuts that also serve as Schrader/Presta adapters in my tool box. Those used to be more common and would come on tubes every once in a while.   I've also got a bunch of the Wheels Mfg rim stem hole reducing bushings as well.  I've used both of these items for odd stuff over the years more often than the purpose for which they were intended.  Keeping do-dads around is handy. 

Here I am using the bushings to make a jig for smoothing out the inner sleeve of eggbeater pedals to get the deep scoring out that will make it hard to reassemble them without damaging the inner O-rings

Everything is useful, and can be made to serve many purposes...

Comment by kevin womac on June 5, 2015 at 10:35am

I often will screw the nut all the way to the tube if installing a presta into a schrader hole. This protects the area around the valve from tearing at the valve hole. This is if a valve shim is unavailable. Valve caps are also silly- but you know what? they help you remember to close the valve on a presta. There have been times I've noticed my own valves open days after refilling. Embarassing. Putting the cap on will deflate your tube if it's not closed. Be sure to close your valves!

Comment by Jonathan Quist on June 4, 2015 at 5:06pm
I'd be curious whether it makes any significant (i.e., noticeable) difference for wheel balance. Until recently I haven't owned a bike good enough to feel it.

The possibility of cutting the tube around the stem makes it worth consideration though. I'd rather think through small details than just do something "because I've always done it this way".
Comment by Far'arned Retrogrumpalunkus #63 on June 4, 2015 at 1:18pm

Of all the silly things to worry about on a bike, using a jam nut or not is so far down as to be a non-issue.  The whole issue has become another velo cult urban legend.  

Use it or not.  It isn't going to make much of a difference either way.  If you need to patch your tube and needed an "installation nut" as you call it, then you aren't going to have it.

As for the cap.  I keep them as well, and since I save tubes and patch them later, I re-use the cap when I re-roll the newly-patched tube back up, protecting the tube from being abraded in storage in the tool kit, and eventually re-punctured by the bare stem.  A spare tube that has been pre-holed is no good at all. 

Comment by Bob Kastigar on June 4, 2015 at 12:50pm

The added weight - another reason to stick with a Schraeder valve.

Comment by Lisa Curcio on June 4, 2015 at 12:26pm

"It adds weight"--No wonder I ride so slow! I'll be racing just as soon as I get those things off.

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