MythBuster

The large diameter wheels or the small diameter wheels.

If you have imperfection on the wheel, the unbalance forces generated by rotation will be the same weather the wheel is small or large, providing that both wheels will produce the same end result on the odometer. That is because the force is in direct relation with the diameter and with the wheel rotational speed.

I also think that a smaller diameter wheel is more strong to road pumps and holes. I mean their symmetry will last longer.

So why large diameter wheels, is it the beauty of the wheel, or I am missing something?

Johnny

A lead weight applied to the rim of an unbalanced wheel would have a lesser effect on a smaller wheel than on a larger one. This is caused by of a phenomena called "moment of a force". The further a load (even if the weight is a balancing load) is from the center of rotation, the greater the moment of the force. Most people understand torque, but the physics term is a moment, and moment = Fd, where 'F' is the Force or applied load, and 'd' is any given distance from the pivot point. This is why it is easier to undo a bolt when the handle of the wrench is longer. Similarly, as a balance lead weight moves further from the center, its effect is magnified by its increasing distance.

So to answer your question, the larger wheel is more susceptible.

MythBuster

True

but the smaller wheel has to spin faster to travel the same distance

in a nut shell the forces have a linear relation to the product of radius times wheel speed.

That is why I said no difference between large wheel and small wheel

jlawr

I supect Burnaby is correct. If the outside circumference of the tires are the same, the weight on the 19" wheel would indeed exhibit more force and be more like to affect wheel balance as the tire tread wears down.

MythBuster

Is it

if it is then , I am not aware

Johnny

But you asked: "Which wheel is more susceptible to unbalance"

MythBuster

sorry Burnaby If I confused you.

I made the assumption that a larger wheel will use larger tire. If the larger wheel will use a larger tire, then there is no difference in the force exerted on the lead or imperfections.

However with the same outside diameter tire, then a larger wheel will produce more vibration force

MythBuster

Let me explain, I know I dont do a good job explaining my self so let me explain again

If 2 cars are traveling one mile.

if the ratio of wheel diameter to tire diameter is the same for both cars but one is tire is smaller than the other car tire

the small car tire will have to make more revolutions to cover the one mile

now if both cars have to cover the one mile in the same time

then the car with the small tire will have to spin faster to arrive on time with the other car.

And as you know the force is proportional to angular speed multiplied by the radius (or distance to the imperfictions)

the fact that the distance (to the imperfections)is larger in the case of the car with large wheel is counter balanced with the fact that the smaller wheel has higher angular velocity.

This is what I was trying to say in the original post.

Johnny

I think I understand what you are trying to say now.

My opinion is the difference would probably be negligible.

Interesting question though...

mitsuguy

iTrader: (2)

smaller diameter tire spins more times per mile than a larger diameter tire - it really has nothing to do with the wheel diameter...

the bigger the tire diameter, the less need to balance it at all... it just doesn't spin fast enough to have vibration problems at normal highway speeds... for instance - 44" diameter Mickey Thompson mud tires on a 15x12" wide wheel... mounted them, no balance, test drove - no shake, even at 70 mph... do the same without balance, and most car tires will start shaking around 40-45... most car tires are around 800 rotations per mile, whereas the 44" mudder is 460 rotations per mile...

wheel balancers use one set speed, they do not change their speed with differing tire diameters... if you were to try to balance that big mud tire, it would probably take pounds of weight, not ounces, but again, at normal highway speeds, it rides pretty smooth...

so, is there a difference, sure...

but most car tires are somewhere between 23 and 27 inches in diameter... truck tires somewhere between 27" and 35" for normal stuff (OE Hummer H2 size is 35" diameter)...

MythBuster

Many thanks mitsuguy for the very useful explanations.