Hi there,
10 days ago i purchased a used Strida SX. I liked the colour and i like the concept of the Strida.
I have more than 5 1/2 decades of experience riding bikes but this was my first one with AV/Schrader valves.
After 5 1/2 decades with no issue or problem with any Sclaverand (Presta, SV, SV/Presta) or Dunlop (DV) valve and on my second day with my new AV/Schrader valves i found myself in all kinds of trouble with the AV/Schrader valves the Strida is delivered with.
AV/Schrader valves have not been designed to be used in bicycles. They have a rather strong spring inside of the insert and they need such a strong spring, because otherwise they would not work in their design application: cars.
So why do AV/Schrader valves have this strong spring?
Mounted inside of the rim of a car the valve has to do it’s job at high speeds and therefore in high accelerations.
It can be mounted inside of a car’s rim so, that the centrifugal forces act to open the valve and there must be an accordingly strong spring to hold it back in place to keep the tyre sealed tight.
A car might have a tire circumference of 2 m. At 200 km/h, that is 55,555… m/s, it’s wheels rotate 27,777… times per second.
With the radius of a 15" rim and a = ω² r we calculate the centrifugal acceleration a of 11606 m/s² or - divided by gravity of 9,81 m/s² - we get the g-force of 1183 g. Now thats quite some force, isn’t it?
That’s why Schrader valves have such a strong spring inside of the valve.
When i wanted to pump up my tyres with my handhelt pump (easily sufficient to pump up a road bike’s narrow tyre to 8 bar) i could not even brake loose the valves. With an AV/Schrader to Dunlop adaptor and the same hendheld pump it was the same.
With my tall workshop kompressor and the AV/Schrader to Dunlop adaptor i managed to blow some air into the tyres. I noticed, however, that it needed 6 bar to open the valve. Frankly: to put 8 bar of pressure inside those tubes, i would have to apply 14 bar on the compressor but this was out of reach. I ended up with some 10 1/2 bar at the manometer and some unknown pressure inside of the tyres. Best guess would be 10 1/2 minus 6 = 4 1/2 bar inside of the tyres with a perfecly sufficient equipment for filling up all kinds of bikes, including road bikes up to 12 bar, if needed - that is: Using Dunlop or Sclaverand valves!
The AV/Schrader is a spoil sport!
I thought that probably some weird error could be on my side so i purchased another 3 AV/Schrader inserts and i found another one in my collection of bicycle parts. I ended up with 6 AV/Scherader valves all showing the same frustrating behavior.
I purchased another AV/Schrader to Dunlop adaptor - the silver one in pic. 1:
It worked much better but still not satisfactory. You’ll learn why in a minute.
In pic 2 - on the left side - the same adaptors are shown: A brass coloured and a silver coloured with an inside mechanism.
The brass piston inside of the silver adaptor presses down the piston inside of the Schrader valve like every compressor at every fuel-station in the world would mechanically push open the Schrader valve. They have a second - low force - valve right behind the manometer that prevents the tyre from losing to much air when the compressor head is lifted from the car valve.
The same is true for the silver adaptor. It has an internal valve that does exactly the same.
However, when You screw the adaptor to the pressurised tyre’s Schrader valve, You hear a hissing noise. Unscrew the adaptor from the pressurised tyres valve You hear a hising noise, too.
In order not to lose too much pressure while removing the adaptor uncrew ist a quickly as You can! Now, how much pressure is left in the tyre? Quite a good question, isn’t it?
However, after a puncture and repair on the road, You’ll be happy to get ait into tyre good enough to go a few kilometers.
The situation with AV/Schrader valves on bikes - especielly folding bikes with small high pressure tyres - is frustrating. It might be less frustrating on low pressure high volume mountain bike’s tyres.
It doesn’t have to be this way.
Please refer to pic. 2 again:
AV/Schrader to the left, i show three differend kinds of Dunlop valves at the top. Even the good old “tube valves” work like a charm as compared to the AV/Schrader.
To the right we see a Sclaverand valve attached to a TPU tube, a Sclaverand insert and a dirt cap of a SC/Presta valve.
Take a close look at the SC insert! It has slack on both sides. I arrangesd it that way to show, that there is no spring inside a Sclaverand valve.
That’s why SC/Presta valves give You an accurate reading of the pressure while You pump up Your bike.
5 and a half decades of riding bikes showed me, that it doesn’t have to be as frustrating as with AV/Schrader valves.
That’s how a Strida should look like:
SV/Presta valves - i call them Sclaverand and the SV in the abbreviation stands for exactly this: Sclaverand Valve - and the trouble is gone!
From now on, I’ll never mount a tube with AV/Schrader to any bike. What a nuisance!
Dunlop really work well. Even the oldest or the cheapest ones. Not much of a problem.
But Sclaverand is the king and queen of bicycle valves. No trouble whatsoever, accurate readings of pressure, easy to refill the tyre on the road with a hendheld compressor. Most effortless.
best regards: Klaus