Originally Posted by
Amber1988
Check the PSI before the ride. The temperature also affects tire pressure.
Not as much as you might think. Going from 70°F at 100 psi to 90°F causes the pressure to rise 4 psi. Pressure rises with temperature but it’s just not that much of a change. If you wanted to double the pressure, you’d have to heat the tire to 500°F. The tires will likely burst into flames before that temperature is reached.
Originally Posted by
alank2
So I picked up a Bell Floor pump with gauge and I find it a little odd to use, but maybe I'm not familiar with 70 psi bike tires. I connected the end to it and it has a tab that locks it into place. My rear tire was at 60 so I decided to pump it to 70. The pump however is odd. I can get it about 70% of the stroke without much force, but it doesn't pump any air into the tire. Then the last 30% of the stroke takes some muscle to push, but it does increase the pressure. It doesn't take much air at all to go from 50psi to 70psi in the tire, maybe just one pump. Is this normal?
A bit of a science lesson is in order. A pump is nothing but a column of air in a tube. It’s at about 14 psi at sea level. If the plunger in the pump is 1 square inch in area, it’s experiencing 14 pounds of force. Now you push the plunger down and the pressure in the tube increases. That means that the force pushing back on the plunger increases so more weight is needed to overcome that force. At the very bottom of the stroke, the pressure is equal to the pressure in the bicycle tire. If the pressure is 70 psi and the plunger is 1 sq in in area, it needs 70 pounds of force to push the air into the tube. It’s not that you need more “muscle”, you need more
weight. Many people stop pumping when they feel resistance in the pump handle and pull it up. That will never get air into the tube. You
have to push the plunger all the way to the bottom of the pump.
You might notice that you can’t get more air in the tire than your weight if the plunger is 1 square inch in area. Higher pressure pumps use smaller plungers but put less air into the tire per stroke.