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by Matt Wikstrom
February 23, 2017
Photography by Matt Wikstrom
It is easy to overlook the humble valve stem, but should it fail, or worse, be too short to suit your wheels, then it can sabotage your entire ride. In this post, Australian tech editor Matt Wikstrom takes a look at one of the most trivial but important parts of your bike.
Once upon a time — let’s say in the ’80s — there was no need to worry about the length of the valve stem when buying a spare tube for your road bike. Low-profile box section rims were ubiquitous and a single valve stem length, ~40mm, could serve every road bike.
All of that changed with the introduction of high-profile aerodynamic rims, and more recently, the massive growth in composite rim designs. Now local bunch rides are populated by wheels with rims ranging in height from ~25mm to 60mm or more.
Such variation is a cause for confusion when it comes to buying a spare tube, especially for the uninitiated. In most cases, adding 15mm to the height of the rim is a reasonable rule of thumb when it comes to deciding on a valve length. That extra 15mm is important because it provides enough length to fit any pump head.
Valves come in a couple of different configurations and it’s possible to extend them to suit different rim profiles.
According to this rule of thumb, low-profile rims that measure around 25mm require a 40mm valve stem. For those wheelsets measuring 35-45mm, a 60mm valve stem will normally be long enough, while anything taller than 50mm demands an 80mm valve stem.
For those riders making use of very high-profile rims like Zipp’s 808, a valve extender will usually be necessary since tubes with very long valve stems are rare.
There are two kinds of valve extenders: there are those that thread onto the valve stem just like the valve cap, and then there are those that thread into the valve stem. For the latter, the valve must have a removable core, so won’t be compatible with all tubes (Continental and Schwalbe tubes typically have removable cores, bargain brands do not).
Of the two, the second strategy is far more robust, since the extension is less likely to leak and more likely to work accurately with the pressure gauge on a pump. And since the valve is situated at the top of the valve stem, it’s much easier to deflate the tyre.
For those that haven’t had much experience with valve extenders, here’s a quick overview of everything that you’ll need to know:
1. Know your valve extenders. A valve extender can thread onto the valve stem like a valve cap (left), or it can thread into the valve stem in place of the core with the help of a small tool (right).
2. Know your valves. Picking the difference between a valve stem that has a removable core or not can be difficult, however removable cores always have flattened sides on the upper thread, as can be seen for the lower stem in this photo.
3. Get the right tool. It may look insignificant, but this small plastic tool is all you’ll need to remove the core of a presta valve. Simply fit it over the upper threads and unwind it like a dust cap.
4. Remember the possibilities. For those extenders that thread onto the stem, only one can be used to lengthen the valve stem, while the alternative can be stacked.
Every road rider should be self-reliant, so with the rim height in mind it should be a simple matter for any rider to equip themselves with suitable valves. However, for those riders that participate in bunch rides, or join a regular group of friends for a ride on the weekend, it’s worth carrying a tube with a valve stem that will suit everybody’s wheels.
Punctures always happen, so rather than leave somebody with tall hoops stranded on the side of the road, carry a tube with a longer valve stem. Better yet, make sure it has a removable valve core so that a valve extension can be used if necessary.
As for those riders that ride on high-profile wheels, it’s worth keeping an extra valve extension (or two, one of each kind) in your saddlebag or jersey pocket along with a core removal tool. In this way, you should be able to convert any valve stem to suit your wheels.
Finally, valve extender can develop leaks after repeated use, but there’s an easy fix: just wrap some plumbers tape around the threads (in an anti-clockwise direction so it won’t unwrap as the extender is tightened) and that will restore airtight seal.