A Must-Know Presta Valve Characteristics and a Genius Hack 

from Rookie’s keyboard

Hello, friends

Today, I will share with you a few important characteristics of presta tubes and a hack that you may find helpful in extreme situations.

Presta valves /French valves/ are strategically made slimmer than Schrader (auto valve) and Dunlop so that they can work with the narrow, deep, aerodynamic rims seen on road and track bikes. 

Presta valve outer diameter

Schrader valve diameter

The outer diameter of the Presta valve that I had is 5.92mm whereas that of the Schrader is 7.83mm measured below the threads.

A 1.92mm difference! It doesn’t sound like a lot but amounts to about 24.4%.

In short, a Presta valve is 1/4 slimmer than a Schrader one.

The length difference between a Presta valve (left) and a Schrader valve (right) is also noticeable.

The valve’s entrance point on the Schrader rim that I have is around 8.53mm.

Due to the different thickness of the valve stems, the Schrader rims have wider openings and are normally present on mountain bikes, city bikes, and hybrids.

A Presta valve can pass through a Schrader rim’s valve entrance, but the body won’t be stable.

And when you account for its length, the instability increases.

The good news is that Presta valves come with a tension nut stabilizing the valve when tightened down to the rim.

The tension nut helps but it operates only on the outside. There’s space between the root of the stem and the rim.

When inflated to greater air pressure, the tube will penetrate that space, and a rough edge might damage it.

The road vibrations increase the friction between the tube and the valve hole and may also lead to a puncture around the valve – the most difficult area to patch.

A “Valve Hole Grommet” seals the entire root of the valve and prevents the aforementioned outcome.

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.

But 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

DIY Fixes

The “patch” below is a temporary solution and doesn’t offer maximum security. But in extreme cases, it works well.

Inner Tube Patch

Placing a small piece of inner tube around the valve adds a decent 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 vulnerable 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 and use it as an internal seal.

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 nut won’t do its normal job, namely to stabilize the valve, but the pressure of the inner tube should be enough to hold the valve in place.

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.

The “nut under the rim” method prevents the tube from laying against the rim as intended. The result is an uneven surface. 

Hence 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 non-Presta rim.

Emergency DIY Presta to Schrader Adapter

If you are stuck with a Schrader-only pump, and you have a Presta tube, you will need an adapter.

The one in the image below screws onto the Presta valve and essentially turns it into a Schrader unit.

Presta to Schrader Adaptor

Some touring cyclists carry a Presta to Schrader adapter to have the option of pumping their tires with the air compressor found at gas stations if their pump fails or gets stolen/lost.

A cool way to always have a Presta to Schrader Adapter is to put it on a keychain.

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 placing it on the valve as shown below.

Here are the steps:

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 

4. Attach the pump and inflate the tire

5. Remove the pump, the adaptor and screw back the valve nut.

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 some of the air is still getting into the tube.

Don’t forget that this is an emergency fix after all. 


There’s a myth according to which Presta valvescan handle higher pressure (PSI) than Schrader.

The reality is that 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 a separate pump is needed for them.

A narrow road bike tire may need 120 PSI whilst a rear shock easily exceeds that even when the rider is light.

It’s not uncommon for a 160lbs rider to set the rear shock at 160 PSI or higher. Heavier cyclists would often reach numbers over 200 PSI for their rear shocks. All that pressure is handled just fine by a Schrader valve.

Presta Isn’t a Beginner-friendly Valve

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 road bike.

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.

The act of unscrewing and tightening a mini-nut is fairly simple, but 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.

Until next time,

– Rookie






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