Quote:
Originally Posted by Thenorm
twedging the tire uphill (or over an obstacle) where a specific mention to mechanical advantage was made.
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Again you are focusing on something that has no bearing on the conversation.
Go by what he meant not what he said, an unpowered larger wheel has a larger mechanical advantage over a small one (think about a push cart).
When my car goes over a bump it wastes energy in the suspension and also slows the forward momentum of the car.
The larger the tire the easier it is to roll over obstacles whether they are bumps or cracks. The impulse duration is short so it is the horizontal movement of the car that pushes you over not the motor so the torque to the halfshaft is meaningless.
I know this because again push carts with bigger wheels are indeed easier to roll up door ledges and cracks in the sidewalk than small tires which sometimes require me to perform a vertical lift on the load to get over them.
So although a larger tire has absolutely no benefit in terms of the torque required to spin it, it definately has advantages in being less affected by changes in elevation due to the angle of approach of the tire surface itself.
The more gradual angle of the tire spreads the bump out over a longer duration and due to the dynamic nature of the rubber flexing it also results in less elevation change (compared to a smaller tire) Also a larger diameter tire flexes less when hitting an obstacle and the flexion of a larger tire is in a more favorable angle so less force gets directed opposite of the direction of travel in the form of vibration.
(I would almost bet there is some sort of illistrated video showing what a tire does when it tries to roll over a bump in slow mo so you can see the deflection in the tire)
So there is more to this and my only interest in the tire would be from the materials it is made of, not so much the size since it doesn't fit my cars. (with a wierd rim it could fit my old diesel suburban though (barely)
Has anyone determined what the weight ratings of these tires are? What are the inflation pressures?
Also I notice BMWs do occasionally come with 19" space savers, if we could find other cars like this and make a list, there might be hope of finding one in a junkyard with the correct lug pattern.
And no I won't hold my breath for I3 rims.
Cheers
Ryan