How load is carried by tire ?
- Vatsal Jain
- Apr 12, 2020
- 2 min read
In your vehicle ,whether it's a car ,truck ,bike or bicycle ,the weight is acted and distributed on the wheels . It is interesting concept to know that the load on the tire is not supported by the bottom part of tire , instead the tire is hanged by the top part .
Let's first understand the physics behind the bicycle tire and after that we will see the Car tire.
In this figure we are having a bicycle tire on road. All the spokes attached to the bicycle tire are in tension.
For understanding ,i am taking out two spokes from the tire , one from above and another from bottom. Tension in above spoke is shown by T2 and tension in below spoke is shown by T1.
When the tire is placed on the road , it is compressed from bottom and tension in the bottom spoke decrease and the spoke is in relaxed position with tension T1. Here, nothing happens to the top spoke. So, as the tension in above spoke is T2 is greater then the tension in below spoke T1 , the net force is in above direction and this force is hanging the tire center from above and supporting the load W on tire.
Hence, the bicycle tire is not supported by the bottom, instead it is hanged by the top spokes.
Now, let's see what happens with the Car tire. Here in the figure , we are having section view of tire and rim ,with sidewalls ,beads ,tire & rim.
Beads helps tire to get perfectly attached with the rim. In bicycle tire , the tension is produced in spokes ,but in car tire tension is produced in sidewalls of tire.
Note:- Air inside the tire doesn't carry any load.
When the tire is kept on the road the ,sidewalls are compressed and the pressure inside the bottom part of tire decreases. This decrease in pressure at bottom ,increases the pressure at top,which stretch the sidewalls and generate tension in them . Now these stretched sidewalls pull the beads upward and the beads of tire which is attached to rim , pull the rim upwards.
So in the above part force acted by bead in upward direction is F and this will support the weight on the tire W.
Hence , pressure at top stretches the side wall , which pull the beads ,that will support the wheel axle from top.
So, tires are not supported from bottom , they are hanged by top part.
This explanation can't be correct. A pressure change in the bottom portion of the tire would propagate to the top of the tire at the speed of sound. (or close to it depending on how much volume of air needs to be displaced and the head losses from the flow, but WAY faster than the tire is rotating. Or, take as an example a tire that is not spinning and yet holding a load. The pressure within the tire would equalize).
from the text :When the tire is kept on the road the ,sidewalls are compressed and the pressure inside the bottom part of tire decreases. This decrease in pressure at bottom ,increases the pressure at top, which stretch the…