(hypothesis) Begin at the wheels...

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Jun 22, 2005 | 08:29 AM

#16

200000+F150

Elder User

Joined: Mar 2003

Posts: 788

Likes: 1

From: Hendersonville, TN

Picture a 21" centerline racing rim with a narrow or modest sidewall...

~Wolf[/QUOTE]
Yeah, my last project car(15 yrs ago) had Centerline Autodrags, and I want 'em for my next project except in 18", but they don't make 'em that big. What a shame. I'd think it'd be good for their sales to offer those(and good for my car too, as this one is going to be an "Efficient" Hot Rod).

Oct 3, 2005 | 11:15 PM

#17

J6Szczecin

Freshman User

Joined: Jan 2005

Posts: 39

Likes: 0

Quote:

Originally Posted by Greywolf

Wheels are the major 'unsprung weight' load on any vehicle. But they are also highly 'energy absorptive', and there are a number of theories as to how to reduce loading on a drivetrain by cutting the load right at the hubcaps. Any bicyclist knows well the difference between pumping big tires, and running on small diameter high pressure tires (road and touring bikes). The principle does not change just because we are looking at a truck instead of a bicycle - if anything, it brings to us a test sled on which to chase the idea even further...

We should explore this, especially now. What we learn and save could go right into the BANK!

The dynamics of a rotating tire are not what most people think they are. As a tire/wheel rotates, ALL of the mass it is made up of is constantly changing direction - and that requires an energy expenditure. THEREFORE reducing the total mass reduces the amount of energy required in order to just turn the wheel. This energy expenditure increases directly in proportion to increased RPM at the axles.

Bottom line here is that BIG tires should be reserved for slow going and off road use. For the highway - normal width, moderate sidewall, high pressure ('E' rated tires are pressurised to 80 PSI) tires on alloy rims are the best way to go.

NOTE: Taller wheels/tires have a lower overall rotation rate for a given speed of travel in miles/kilometers per hour.

-Comments?

Your logic is not entirely correct. While it is true that every part of a wheel is constantly changing direction, this does not mean that it takes energy to keep it rotating. The law of conservation of momentum basically states: A moving (rotating) mass will keep moving (rotating) unless some force (torque) is applied opposite to the direction of motion. For an easy demonstration, put a bike in a bench vise, and spin the rear wheel up, the tire will only slow down because of air friction and friction in the bearings. If this tire were in a vacuum, to eliminate air friction, and had magnetic bearings, to eliminate bearing friction, it would keep spinning forever. The only time the weight of the wheel comes into play is when you are trying to accelerate or decelerate the rotation. However, if you spin up a tire that is heavier, but has the same friction as a lighter tire, it will keep rotating longer because the momentum is proportional to mass and the forces opposing the motion are the same. This said, these observations have nothing to do with rolling friction. I just wanted to correct the false statement that it requires energy expenditure to keep a spinning mass spinning. Correctly stated this statement would be that it requires more energy to accelerate or decelerate a heavy spinning mass than a light one.