I get it’s a safety issue, but what is different between the tread and sidewall? Does sidewall get more pressure? If so how?
In: Engineering
The sidewall is thinner than the tread so many patch methods are not reliable. In addition, sidewall holes tend to be more of a tear than a puncture, making repair almost impossible.
The movement and manipulation of the tire shape while in use also affects the ability to repair the sidewall. Much like how a bandaid covers a wound on the flat length of your finger but does not work as well when the wound is at the joint where your skin moves and flexes as your finger bends:
The tread mostly remains in one shape
– flat on the road.
The sidewalls are constantly rolling and curving to absorb the weight of the car
– notice that tires appear fatter at the point where the weight of the car rests on the road. That bulge is always present so as the tire rolls around, the wall has to flex
– the sidewall also flexes as it absorbs impacts to the tire from holes and bumps in the road.
– the sidewall also flexes to absorb the side-to-side physical forces created while turning. (consider the 3,000 lb vehicle traveling at 50 mph while rounding a highway curve – the tire battles the inertia that wants to keep the car going forward as the driver turns the wheel – that force is applied disproportionately to the outside edges and sidewalls of the two tires on the outside of the curve).
These forces exceed the force from mere inflation pressure. The flexibility of the sidewall is crucial for accommodating those forces.
Next time you have a chance, look at a tire that is off the rim. You can easily push and manipulate the sidewalk, but not the tread because of the thickness and the steel component
The tire plug, for example, needs the glue to adhere to the interior of the hole it passes through as well as to expand into a bulb on the inside to completely seal the hole.
An interior patch may work for a sidewall hole, as will placing an inner tube inside the tire, but much more labor is involved and they are not reliable repairs for modern driving conditions.
Pressure would be the same throughout the inside of the tire.
The sidewall is constantly flexing, or bending, as the tire rolls down the road with so much weight on it. A patch would be a weak place in the sidewall and would probably fail rather quickly. Also, this flexing causes heat, so the sidewalls get hotter, which would also weaken the patch.
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