So my bike’s wheels say something like 40PSI, and when I feel the wheel is kinda deflated or not fully inflated, I use the bike pump and pump until the gauge indicates 40PSI, but since the gauge starts at 0, and there was already some air left in the wheel, does that mean I went over 40PSI? Or does the bike pump compensates for the leftover air somehow? How should I properly pump the wheels to the recomended PSI?
In: 6
Pump until it says 40.
It measures by measuring the back pressure as you’re pumping the air. Because air is a fluid, the pressure is constant everywhere, so the back pressure is the same as the tire air pressure.
When it starts at 0, that is because either the air in your tire is at equilibrium (atmospheric pressure), or it’s so low that it isn’t easy to see on the gauge.
The gauge didn’t start at zero if the tire is only kinda deflated. There is pressure in there when you start pumping. Pop the gauge on there next time it feels a bit flat, before you pump. You’ll see the pressure of the air currently in the tire. You are pumping additional air to reach a final pressure of 40 psig.
Pump until it says 40.
It measures by measuring the back pressure as you’re pumping the air. Because air is a fluid, the pressure is constant everywhere, so the back pressure is the same as the tire air pressure.
When it starts at 0, that is because either the air in your tire is at equilibrium (atmospheric pressure), or it’s so low that it isn’t easy to see on the gauge.
If you’re measuring pressure with a tire gauge and with your bike pump, what do they say when you finish pumping the tire? If they disagree, go with the tire gauge reading, not the pump gauge. Bicycle pump pressure gauges are notoriously inaccurate. Mine reads too high at low pressures and too low at high pressures, compared to a standalone tire pressure gauge.
The gauge didn’t start at zero if the tire is only kinda deflated. There is pressure in there when you start pumping. Pop the gauge on there next time it feels a bit flat, before you pump. You’ll see the pressure of the air currently in the tire. You are pumping additional air to reach a final pressure of 40 psig.
Pump until it says 40.
It measures by measuring the back pressure as you’re pumping the air. Because air is a fluid, the pressure is constant everywhere, so the back pressure is the same as the tire air pressure.
When it starts at 0, that is because either the air in your tire is at equilibrium (atmospheric pressure), or it’s so low that it isn’t easy to see on the gauge.
The gauge didn’t start at zero if the tire is only kinda deflated. There is pressure in there when you start pumping. Pop the gauge on there next time it feels a bit flat, before you pump. You’ll see the pressure of the air currently in the tire. You are pumping additional air to reach a final pressure of 40 psig.
If you’re measuring pressure with a tire gauge and with your bike pump, what do they say when you finish pumping the tire? If they disagree, go with the tire gauge reading, not the pump gauge. Bicycle pump pressure gauges are notoriously inaccurate. Mine reads too high at low pressures and too low at high pressures, compared to a standalone tire pressure gauge.
If you’re measuring pressure with a tire gauge and with your bike pump, what do they say when you finish pumping the tire? If they disagree, go with the tire gauge reading, not the pump gauge. Bicycle pump pressure gauges are notoriously inaccurate. Mine reads too high at low pressures and too low at high pressures, compared to a standalone tire pressure gauge.
A bit has to do with the design of the valve. Usually, it only allows air to enter, not escape. So if you put on your pump, the valve doesn’t release air into the tube, it just doesn’t do anything. Once you start pumping, you’ll quickly bring the tube up to the same pressure as the valve. So it goes from 0 to say, 20psi very fast on the gauge. If the pressure in the tube is higher than the pressure in the tire, the valve lets air in, but only as long as the pressure in the tube is higher than the one in the tire.
So you are measuring the pressure in the tube, which is almost exactly, but oh so slightly lower, the pressure in your tire.
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