The Presta valve a.k.a French valve is commonly seen on road bikes’ inner tubes. The original intent behind its production was to use it on narrow rims. Hence why Presta valves are slimmer than Schrader (auto valve) and Dunlop.
The size differences between Presta and Schrader could raise a few compatibility questions such as whether a Presta tube can be used in conjunction with a rim designed for Schrader valves.
A Presta tube can be used with a Schrader rim but only with a special adaptor known as Schrader – Presta grommet which fills the space around the new Presta valve and secures it.
Without a grommet, the tube may puncture near the valve stem from excessive movement or from pressing against the edges of the entry point.
Presta Valves Are Long and Slim
Presta valves are engineered to work with narrow, deep, aerodynamic rims seen on road and track bikes. Hence they are so long and slim in comparison to Schrader valves.
The outer diameter of the Presta valve that I had at my disposal turned out to be 5.92mm whereas that of the Schrader is 7.83mm measured below the threading.
That’s a 1.92mm difference. It doesn’t sound like a lot but amounts to about 24.4%.
In other words, a Presta valve is 1/4 slimmer than a Schrader one.
Due to the different thickness of the valve stems, the rims designed for Schrader tubes have wider openings and are usually found on mountain bikes, city bikes, and hybrids.
A Presta body can pass through a Schrader rim’s valve entrance, but it won’t be as rigid as necessary. When you add its length to the equation, the risk of riding with an unstable valve stem increases even further.
Thankfully, Presta valves come with a tension nut, which stabilizes the valve when tightened down to the rim.
The tension nut helps, but it has one real downfall – it only acts on the outside. There’s still space between the root of the stem and the rim.
When inflated to greater air pressure, the tube will penetrate that space and may get cut on a rough edge.
The road vibrations increase the friction between the tube and the valve hole and may also lead to a puncture around the valve – a difficult to patch region due to the “relief” of the area and the stress imposed on it when cycling.
A “Valve Hole Grommet”, on the other hand, seals the entire root of the valve and prevents that from happening.
Therefore, if you want to permanently ride with a Presta valve combined with a Schrader rim, a grommet is the go-to option.
If the necessary adaptor isn’t available where you live, it would be better to just buy an appropriate Schrader tube instead.
Having said that, if a Presta tube is all you have, you could run it as an emergency fix while keeping in mind the increased risk of a flat tire.
Presta to Schrader Grommet
A Homemade Fix
Disclaimer: The text below contains a homemade fix that will minimize the likelihood of getting a flat while running a Presta tube and a Schrader rim. However, the “patch” is a temporary solution as it doesn’t offer maximum security.
Inner Tube Around The Valve
Placing a small piece of cut inner tube around the valve adds another layer of protection.
When the tire inflates and starts pressing against the valve entrance, this patch acts as a shield.
The piece should be long and wide enough to cover the most vulnerable parts – the base of the valve.
Tension Nut Under the Rim
If you want to secure the section even further, you can place the tension nut under the rim (opposite side) and use it as an internal seal.
Or in other words, instead of relying on the nut to stabilize the stem, lower it maximally and insert the valve through the entrance this way.
Since the diameter of the tension nut is larger than the entrance point, the tube won’t be able to penetrate the empty space.
The downside of using the nut this way is that it won’t do its normal job, namely to stabilize the valve.
However, the pressure of the inner tube should be enough to hold the valve in place if the terrain isn’t extreme.
Alternatively, if you have two tension nuts, you could put one “under the rim” and one above as intended.
Another option would be to use a washer under the rim and the regular tension nut above the rim.
Note: This “nut under the rim” method prevents the tube from laying against the rim as intended. The result is an uneven surface. Hence why I wouldn’t consider this hack the best option out there. Nonetheless, it greatly reduces the chances of getting a flat when using a Presta tube with a Schrader rim.
Emergency Presta to Schrader Adapter
If you’re trying to run a Presta tube on a Schrader rim, you may also be stuck with a Schrader only pump.
In that case, you will need an adaptor that screws onto the Presta valve and essentially turns it into Schrader.
Some touring cyclists carry a Presta to Schrader adapter in their toolboxes to have the option of pumping their tires with the air compressor found at gas stations if their pump fails or gets stolen (it happens).
A cool way to always have a Presta to Schrader Adapter is to put it on a keychain.
Nonetheless, if you don’t have the adaptor above or an opportunity to buy one, you can make a homemade version by cutting the top cap of a Presta valve and screwing it on top of the valve as shown below.
Here are the steps for this method:
1. Cut the thinner part of the Presta cap.
2. Unscrew the valve nut of the Presta valve.
3. Screw the cut cap with the wider part facing up onto the valve.
4. Attach the pump and inflate the tire.
5. Remove the pump, the adaptor and screw back the valve nut.
Additional notes
You will have to play with the position of the cap. In general, the top should be 1-3mm higher or lower than the top of the valve depending on the pump you have.
Also, you may notice that the rear of the cap is leaking some air while pumping the tire. That’s fine as long as most of the air is still getting into the tube.
Don’t forget that this is an emergency fix after all. In general, it’s better to buy an adaptor, but when you don’t have options, this hack is still a good solution.
Frequently Asked Questions
Are there any other disadvantages to using a Presta tube on Schrader rim?
Besides the risk of flats, another downside is the possibility of water and dirt getting inside the rim if the tension nut moves out of place.
What are the advantages of Presta valves over Schrader?
Presta valves have one main advantage over Schrader – a smaller entrance hole.
Presta valves require a smaller hole in the rim. This results in greater rim integrity and consequently allows the production of narrow rims.
When it comes to mountain bikes, however, this advantage isn’t as significant since MTB rims are wider, thicker, and can have plenty of strength despite the larger entrance point of a Schrader valve.
Is it true that Presta valves can handle higher pressure (PSI) than Schrader?
Not really. Schrader valves can handle monstrously high PSI. For that reason, air forks and rear shocks all use Schrader valves.
And shocks operate at a significantly higher PSI than a tire. Hence why a separate pump is needed for them.
A narrow road bike tire may need 120 PSI. Meanwhile, a rear shock easily exceeds that even when the rider is light.
For example, it’s not uncommon for a 160lbs rider to set the rear shock at 160 PSI or even more. Heavier cyclists would often reach numbers over 200 PSI for their rear shocks. All that pressure is handled just fine by a Schrader valve.
Which valve is more beginner-friendly Presta or Schrader?
Schrader valves are more beginner-friendly than Presta for two reasons:
Availability. Presta valves are an invention of the bicycle industry whereas Schrader valves are the automobile standard. A new cyclist may have never heard of Presta before buying a bicycle.
Ease-of-use. Schrader valves operate on the “attach and pump” principle. Presta valves, on the other hand, require you to unscrew the nut at the top of the valve before inflating the tube. Then, you have to tighten the nut after finishing.
While the act of unscrewing and tightening a mini-nut is fairly simple, a beginner may be unaware that they have to do that.
People who don’t know how a Presta valve operates may try to pump the tire without unscrewing the valve nut. This happens more often than one might think.
