Electronics > Mechanical & Automation Engineering

Car Tire Tread Mounting

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bostonman:
I have a question regarding car tire thread angle. While this pertains to cars and car tires, I think it touches more upon the physics aspect; but also mechanical.

Recently I purchased new tires and noticed the threads are angled differently on both sides of the car. If I stand by the driver's side door and look at the (driver's side) tire, the threads are aimed upward. If I stand by the passenger's side door and look at the (passenger's side) tire, the threads are aimed downward (see attached photos for reference - named accordingly).

Both driver's side tires are aimed upward, and both passenger's side tires are aimed downward. I've looked at other cars and it seems to be consistent with my setup indicating a reason exists for having the thread angles not match on all four.

My question is: why are the threads aimed the same direction on every car I've seen? It seems this isn't an error and a performance reason must exist, however, I can't think of one.

If the threads are aimed upward, it seems water would come off the tire in a heart shaped pattern thus the water would channel back to the car; possibly onto the rear tires. The other issue: all four tires are not mounted with the threads in the same direction indicating one side is holding a wet road better. Whereas if all four had matching thread angle, all four tires would be performing equally.

IanB:
If you look carefully on the sidewall of the tire, you may sometimes see a directional arrow near the shoulder, or maybe some text saying "Left" or "Right". If you see nothing like this, then the tires are bi-directional (most are), and the direction of rotation does not matter.

(By the way, the title of "Care Tire Thread Mounting" was very confusing. "Car Tire Rotation Direction" might be clearer?)

TimFox:
Spell-check may be necessary, but it is not sufficient.
I assume he meant "tread", not "thread".

james_s:
I figured he was talking about the little stringy protrusions left from the molding process? I really have no idea though. I don't know what else on a tire could be called a "thread" and that word was used throughout the post so I assumed it was not a mistake.

TimFox:
I believe the "little stringy protrusions" are a just a detail of the molding process, the result of air venting during the molding, and have no effect on the performance of the tire.

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