Limitations Of Car Tyres Air Pressure

racing bicycles have 110 psi tyres!

True and a road bicyclist feels every crack in the asphalt when their tires are at 110 psi.

The also have a much larger radius than car tyres, and lower forces are involved.

Racing bicyclists are willing to give up a lot of traction for a relatively small decrease in rolling resistance.

To a motorist travelling at much higher speeds traction or "grip" is more important.

Higher pressure = smaller contact patch and less deflection = lower rolling resistance, less traction, harsher ride.

The manufacturer's recommendations are usually the best compromise for normal use. They can be adjusted somewhat depending on how the vehicle is actually used.

...and the wheel is turned in the vertical plane as well as the horizontal one as the vehicle turns, bringing more tread into contact with the surface. That is not the case with vehicles that have 4 or more wheels.

Extrapolating:

The area of a rigid wheel in contact with the rail on a railway vehicle is less than that of a £1GBP coin. Such a wheel will slide readily with a coefficient of friction of 0.2 - 0.25 when the brakes are fully applied and the direction of the vehicle is regulated partly by the coning of the wheels and partly by the actions of the flanges. To do that on a road vehicle would mean that it would become practically uncontrollable.

An unbraked railway vehicle can be expected to run away on gradients as shallow as 1 in 250.

So if surface transport vehicle makers wanted solely to save fuel then a railway system is a far better prospect than roads.

ride quality

Quite right but this deserves a little more elaboration. The tire and its air pressure also add a dampening effect along with the shock absorbers to the "ride" of the vehicle.

great mileage, lame ride

Putting 110 PSI in a car sized tire would be like running on solid rubber tires. The ride would be harsh, the tire would wear just as much as an air filled tire, but would last longer. The solid tire would wear down until the bottom of the car would start to drag on the pavement.

The cost of replacing shocks and other suspension parts would be more than the money saved in fuel.

Like others have mentioned, the tire is a component of the suspension system. Make it rock hard, and the other components will have to made stronger.

There's also the "wear" factor. An auto tire at 110 psi will look like a big smile, with all wear on the center of the tire. To make it strong enough not to cup, it would have to be far heavier, more expensive, and it would decrease mileage.

The tire is part of the suspension....pull a wagon down the road with solid rubber tires, it's off the surface more than on at any speed at all.....

Here's a new tweel concept, this attempts to address both issues, with mixed reviews...

http://www.pakwheels.com/forums/wheels-tyres-suspension-brakes-steering/10519-michelin-tweels-new-generation-tyres

In order to find out what it would be like to ride on a vehicle-----> take a ride on a solid tire fork-lift with no shock absorbers, which most do not have. To further replicate the actual ride on these solid tires take the cushioned seat off of the fork-lift and replace it with a 1 inch piece of plywood or similar rigidity wood. If wood is not available use a 1/4" piece of steel. After a half hour ride your gluteus maximus will be extremely sore, probably like never before, and your back will be extremely painful from the ride and trying to move when you get off it. This is to say nothing about the extreme head ache you will have.

After trying this ride you will be convinced to reduce your tire pressure down to 10psi like used for vehicles that travel on sand.

Good Luck, Old Salt

I gave up racing in Go-Carts because of back problems probably almost 20 years ago because of the missing comfort shock absorbers on Go-Carts.....

It simply got too painful, so I simply stopped doing it...my back has not improved though....

I think that all the problems that were described here could be solved with good air cushions, all- except for one which was decribed in answer 10: In a curve bicycle tend to keep the traction patch by their inclination.

No, air cushions will not solve all of the problems described here. They can only solve the quality of the ride not the critical problem of traction. As JohnDG pointed out, tire traction handles not just the starting and stopping forces but also steering and skid.

One thing that you're missing with the bus and truck tire comparison, these tires are bigger. Now I have not done the math but I suspect that the nominal three to four fold increase in truck tire pressure does mean a smaller percentage of the tread area contacts the road with a truck tire. My suspicion is that the traction forces at the contact pad are similar. The fuel savings a bus or truck provides is purely because of the right tool for the job not tire pressure. In the fuel economy per vehicle competition, a car has a far better fuel economy than any bus or truck. A bus moves many more people and most truck owners will not drive their vehicle unless some payload is in the back for one of the runs.

Road Bicyclists wipe out on corners quite often, even on indoor tracks. Very often you can see the tires skid right out from under them. Most people in cars are not willing to do that on corners regardless of how fun it looks.

Az, Why not go to an isolated area & try it? you could be the first in your area to fly!

A car tyre is made to operate at a specific pressure & if you over inflate the centre of the tread will wear faster than the edges also if you under inflate the edges will wear more than the middle.

NB. don't try to inflate a car tyre to 110psi.

Bazzer

Though I'm an old ignorant farmer, I 'm not that stupid to try hazardous experiments- instead- I asking enlighted persons like you!

IMHO, the biggest reason for the differences in operating pressure is consumer safety. Imagine someone trying to inflate their tires to 110 psig on their Prius. The lawyers would be lined up around the block.

The real reason is tax money. Let me explain.

The presented argument sounds just like the old school mountain bike racers argument that raged for the last 20 years or so. So, I will try to go at this from the bicycle tire theory currently standing in favor, as I fully can appreciate this subject from a personal expenditure in the field.

Bicycle tires are now going lower and lower in pressure, particularly those for off road situations, since, and I can attest to the truth in this having tried both high and low pressure settings back to back, the time in the air when the tire bounces creates lost momentum and wasted energy. A high pressure tire will roll quicker on a perfectly smooth surface, but once you add bumps, keeping the tire in contact with the surface by lowering pressures does indeed save energy. The mountain bike tires for racing have gone from 40 psi to 20 psi with tubeless technology just in the last 20 years. It took a while to convince people, but reality is that lower pressure is faster and easier to pedal when irregular surfaces are involved. (the roadies are still going high pressure, but that surface is fairly smooth, but they do lower pressures for racing on cobble stones)

So, to relate to the automotive tire, if roads were as smooth as a good race track, the high pressure would be fine. But, have you looked at the roads lately? Every millisecond those tires are out of contact with the road surface, the energy going to turn the driving wheels is being wasted, and any time a non-driving wheel goes up, not forward, that too is momentum applied in the wrong direction and therefore lost.

You want high pressure tires on autos to save fuel? - then tax the crap out of everyone to build and maintain a race track like surface on the public highways. Let's see you get that past a voting public.

Another result of increased air pressure on tire performance is the decrease in sidewall flex. This causes the tires to lose traction more quickly and skip across the road surface in cornering situations. There is a fine balance between too muck sidewall flex and too little. Racing tires tend to have greater sidewall aspect ratios (the ratio of the tire section height to section width - the section height is the distance from the rim flange to the tread surface) than the low aspect ratios that you see on "high performance" street tires to allow for a more tunable (with air pressure) sidewall flex. This is what is happening with NASCAR tires when you hear the commentator talking about adding or subtracting air pressure from the tires. They are "tuning" the suspension by adjusting the air pressure and thus the sidewall flex.

The introduction of forward scanning electronic suspension might render the critics of the flex sidewall tyre obsolete in truth you only need the rubber to provide the traction.

There are many great videos of Model T's driving. Watch a few and then imagine riding any extended distance in one. Yes, those were pneumatic tires but more akin to the bicycle tires mentioned above.

Now add about a ton or more to the sprung weight and reconsider. LOL