[font size="1" color="#FF0000"]LAST EDITED ON 17-Oct-01 AT 07:05 PM (EST)[/font][p]Wheel/Tire tips:


Among my other flights of experimental mechanics, I got caught up in the bicycling wave during the '70s. It taught me a lot...

When your own 2 feet are the motor, efficiency becomes a matter of GETTING HOME, MAN!!!

- And I was doing hundred mile rides back then...

Lessons learned:

Reducing the turning mass makes a lot more power available.

By building narrow, high pressure "skinny" wheels, I found I had made a bike that seemed like a razor when I went on long rides-
Every pound of force I laid onto the peddles went more directly into SPEED.

This is because of a very simple principle or two, and (cringes) in part justifies some of the lowrider doctrine.

Now- I don't favor lowriders, I think it's a way to degrade a truck rather than improve it. But the wheel science works like this:

A body in motion in a straight line, unless acted upon by an outside force tends to continue in a straight line.

There is a buried message here -

To change the direction of a mass in motion requires an energy expenditure. Wheels, because of the hub, constantly change the direction of the mass they are made up of, AND THIS REQUIRES THAT ENERGY BE EXPENDED TO EFFECT THAT CHANGE IN DIRECTION.

-It's basic physics...

The greater the mass of the turning (mass), the more energy is needed(or absorbed) and this is directly applicable to not only bicycles, but also automobiles, motorcycles, and (you guessed it!) TRUCKS!!!

So how can we reduce this gas-sucking effect?

Well, the options are these:

Aluminum weighs less than steel.
Rubber weighs far more than either of these things.
Less rubber, on a wider diameter ALLOY wheel will dramatically reduce the "turning force" needed to rotate the entire wheel.

Also, a thinner tread can cut through snow to grip the road beneath, and is much less likely to hydroplane in the wet.

Conversly, for offroad, more cushioning is needed, and for towing more traction from a wide rim is another advantage.
For jumping an offroad truck, strength is the main theme, and steel rims with a FAT tire would be ideal...
Kind of like it's "Mountain Bike" counterpart in the bicycle world. It works the same

So what I'm suggesting, I suppose, is that a seperate set of rims and tires might be the most economical way to get good mileage on trips, even though you wouldn't want them on the truck in the MUDD...

In fact: I remember a beautiful story I read about a restored chain-drive Mack truck in a town that got snowed in. Because the truck had the old fashioned tall iron wheels, and narrow (by todays standards) tires, it was able to run through snow that was ridiculously deep, and clear the roads with it's plow blade when the county trucks couldn't even get out of the maintenance lot... (And yes, that story warmed my heart but good!)

Tinker with these ideas, they have a lot of possibilities......

~ Wolf

 

I wonder what the gas savings might be with aircraft tires pumped up to several hundred PSI on our trucks?

Ok, bear with me as I think out loud (and correct me if I am wrong):

It seems there must be an ideal tire width for a particular weight of vehicle. If the tire is too wide, the road contact pressure per square inch of rubber would be too low. Then wouldn't traction be more easily lost? The wide tire would allow more area for trapped dirt (which is usually present on a road surface in some quantity) to lubricate the road contact patch, thereby reducing friction--this seems similar to the idea in the post above of the wider tire spinning out in the snow more easily.

Worse yet would be a tire too narrow, which though there is plenty of road contact pressure per square inch of rubber, the contact patch would be so small that likely it would result in loss of traction. Just think how easy it would be to lock 'em up with say a 2-inch-wide tire. In theory it shouldn't matter as a sliding object that is 4 inches thick and 8 inches wide (assuming all surfaces are flat and of the same material) should have the same total friction whether it is sliding on the 8-inch side or the 4-inch side. The 4-inch side would have twice the weight per square inch but half the number of square inches. But the greater frictional pressure on a narrower tire would cause the rubber to peel off more easily, which will then act as a lubricant, therby reducing overall friction.

 

Hmm, a larger diameter would also extend the tires "footprint", and tire pressure will affect it too since the rubber will flex.

Tread is another factor - the gaps in a tires tread affect the total contact surface of the "Footprint". I suppose it could be expressed as a percentage, where the tread that contacts the road is divided by the spaces between.

So Rubber/Spaces x the contact surface in square inches might best define it.

And then there is the composition of the rubber...

But for a stock width of tire, a taller rim and narrower sidewall should work out the same as the stock rating if the total wheel height is the same. The biggest difference would be the tires ability to absorb bumps without rim damage. You would only want to run it on smooth pavement.

But then, there would be a reduction in "Unsprung Weight" also. Since the wheel and tire combination weighs less, the suspension would be more responsive...

Quite a few trade-offs in all of this, aren't there?

 

"There are no solutions, only tradeoffs" --some economist of the Austrian school of economics, can't remember who.

The best traction is a slick on a nice smooth, dry, and clean road.

To reduce unsprung weight we could get little wheels like those found on garden tractors, but make sure you don't hit any potholes or goodbye wheel, tire, and all!

 

Tire size breakdown -

225/75/15 Would be a tire with a tread 225 cm wide, with a sidewall 75 percent of the tread width (168.75 cm), on a 15 inch rim.

bigger truck tires are a bit easier to read, the sidewall percentage is left off of it.

35/12.5/15 for example is a 35 inch tall tire, on a rim that is 12.5 inches wide, and 15 inches in diameter.

A 35/12.5/24 (if there is such a thing) would have a much narrower sidewall.

Similarly, the middle number in the first set of numbers I mentioned is the percentage of the tread width that the sidewall is tall. 75 and 65 are common numbers there, a 60 series is slightly narrow, a 45 series is very narrow. I have seen at least one lowrider that had a 25 series on it, and it looked like a marble on the road would be enough to trash the rims...

 

You guys have WAY to much time on your hands, LOL
you would'nt happen to be at work while you are doing this would you?, HAHAHA

Ben

 

This subject doesn't belong in General Conversaton. There is a tires, suspension and wheels Forum here for such topics. Thread locked.

Ken Payne
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