Why do car tires take more P.S.I. than bike tires?

Question

Cause my car tires take 30 PSI and my bike tores take about 40-65 PSI? What is this all about?? Car tires are bigger than bike tires!

I meant ***LESS*** than bike tires!!!!!!!! Why do car tires take ***LESS*** PSI than bike tires, lol.

i still don't get why car tires take less air than bike tires. bike tires are small and thin, so why do they take more air?? than car tires?

Answer 1

Pressure and volume are two different things, junior. The tires on your car are designed to flex so that they can absorb impact, and also so that they flatten out a bit and you have a contact patch. If your car's tires were inflated to 90 pounds like a bike, they would be hard as rocks and perfectly round with no flex and a microscopic contact patch, just like your bike, which would be extraordinarily dangerous because you would have very little traction. However, if your bike's tires were inflated to 35 PSI, they would be so soft and flexible it would feel like you were trying to ride your bike through molasses. The volume of air in a bike tire is extremely small compared to that of a car, but the pressure is much higher in order to minimize rolling resistance, which is one of efficiency's biggest enemies. If you could switch and put four bike tires on your car and two car tires on your bike, you would realize very quickly why the designers of cars and bikes use the tires they do.

Answer 2

There seems to be alot going on with the tire. Too much physics for me, but I found a few things that might help explain it.
"Width and Pressure
Tire width and pressure are inextricably linked. It is a serious mistake to consider one independently of the other. Generally, wider tires call for lower pressures, narrower tires call for higher pressures.
The part of the tire that is actually touching the ground at any moment is called the "contact patch." Generally, the area of the contact patch will be directly proportional to the weight load on the tire, and inversely proportional to the inflation pressure. For instance, if the rear tire of a bike is supporting a load of 100 lbs, and the tire is inflated to 100 PSI (pounds per square inch) the contact area of the tire will be roughly one square inch. If the pressure is reduced to 50 PSI, the tire will squish out until the contact patch has become 2 square inches (or until the rim bottoms out against the tire.)

A common debate among cyclists centers on the issue of whether a wider tire has more or less rolling resistance at the same pressure. The constant pressure is proposed because it appears more scientific to eliminate this as a variable, but this is not realistic in practice. The short answer to this question is that, yes, a wider tire of similar construction will have lower rolling resistance than a narrower one at the same pressure. This fact is, however, of no practical value. If you are comparing two tires of similar construction, with the same load, and the same pressure, either the wider tire is overinflated, or the narrower tire is underinflated!

A tire is supposed to deflect a bit under load. This deflection the whole purpose of pneumatic tires. When you sit on your bike, your tires should visibly bulge out at least a bit under your weight. If they don't, they're overinflated."

The above is from http://www.sheldonbrown.com/tires.html

And check thois out about car tires.
http://auto.howstuffworks.com/question506.htm

It answered a few questions for me but I don't know if it is exactly what you are looking for. Still, very interesting stuff.

Answer 3

bike tires are thin and made of weak construction so they require a tube and high psi my bike tires take 115 psi most cars take 35 and big trucks take 80 and up

Answer 4

P.S.I. stands for pounds per square inch. since there are four tires on a car instead of two and those tires are larger there is more surface area. therefore more pounds of pressure overall. since the motorcycle tires have less surface area, more psi is needed for the same amount of pressure, and proper ride

Answer 5

Car tires are now almost all 'radials`, and are
designed to have more 'wall flex` than bike tires.
The same kind of flex in a bike tire would make your bike feel 'loose` and feel very uncomfortable.

Answer 6

Much smaller contact area on the road, and inside the tire - requires more pressure for proper ride.

Answer 7

Larger volume and larger surface area of the car tire.

Answer 8

more weight