Electronics > Mechanical & Automation Engineering

Car Tire Tread Mounting

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bostonman:
Maybe I'm totally wrong on this.

If I turn my wheels outward and look at my passenger tire from the front of the car to the face of the tire, the outside treads go upward (and the inside treads go downward).

If I ummount that tire from the rim, spin it on an imaginary vertical axis, and remount it to the rim without removing the rim from the car, the outside treads now become the inside treads. These treads will be aimed upward (just as they were when they were on the outside), and the inside treads that were aimed downward are now on the outside aiming downward.

If the outside treads are now aiming downward, they would match the driver's side.

I did draw this on a Post-it, spun the Post-it around 180 degrees on an imaginary vertical axis, and looked at the drawing bleeding through the Post-it. It was exactly as described above - although I had the image in my head already - just wanted to confirm on a Post-it.

Gyro:
Your mistake is looking at the drawing bleeding through the post-it (not what happens with the tyre). If you just rotate the top side by 180' (as you would be with the wheel) you would see what IanB shows. Looking carefully at the smudges, his images are clearly the same piece of paper rotated 180' on the vertical axis.

IanB:

--- Quote from: bostonman on January 12, 2023, 01:49:53 pm ---If I turn my wheels outward and look at my passenger tire from the front of the car to the face of the tire, the outside treads go upward (and the inside treads go downward).

If I ummount that tire from the rim, spin it on an imaginary vertical axis, and remount it to the rim without removing the rim from the car, the outside treads now become the inside treads. These treads will be aimed upward (just as they were when they were on the outside), and the inside treads that were aimed downward are now on the outside aiming downward.
--- End quote ---

But that's exactly what my pictures show. In case it's not clear, the pictures show an actual wheel, not just a flat piece of paper.

In one picture the red treads are on the "inside" (right) and pointing downwards. In the other picture I have rotated the wheel so the red treads are on the outside (left). As soon as the red treads are on the left they will be pointing upwards. There is no way to have the red treads on the left and pointing downwards. Geometry forbids it.

bostonman:

--- Quote ---But that's exactly what my pictures show. In case it's not clear, the pictures show an actual wheel, not just a flat piece of paper.
--- End quote ---

You've responded to other messages and provided some great insight. Just to clarify, I haven't been doubting you this entire time, I was uncertain whether my explanation(s) were making sense.

Anyway, I MUST be mentally using an incorrect axis to spin the tire. Although I didn't have much time earlier, I spent a few minutes tinkering with a spare tire laying around. I flipped it and rotated it, and the treads always aimed the same direction; this is where it occurred to me that I'm looking at things from the wrong axis.

This is where the confusion initiated from because my friend initially brought up this issue and we both agreed if the tire was mounted to the rim, we removed it, and flipped it (via an imaginary vertical axis), the treads would match the driver's side (or vice versa).

I'm thinking of it as a vertical rod, a piece of metal mounted to the rod at a 45 degree angle, and spin the vertical rod 180 degrees. If it starts from top right to down left, when the rod is rotated 180 degrees, the 45 degree angle will now be top left to down right.

I did a quick (rough) drawing of what I visualized (see attached). This is why I thought flipping the tire would cause the treads to change direction thus throwing water at the opposite angle (and matching the driver's side).

bostonman:
Thanks for the reply, however, I think you didn't read the entire thread and/or missed the point.

It has more to do with why all cars I've seen have one side angled upwards and the other side downwards. As it's been pointed out, by Ian.B, geometry forbids the angles changing if the tire is flipped.

In my head, and on paper (a Post-it), the tread angles would change direction as I pointed out in message #33 when I flip it on a particular axis. For whatever reason, I'm confusing which axis to rotate the object (tire in this case) so it matches not only what Ian.B stated, but what I visually saw flipping a spare tire in my garage.

On a side note, I keep meaning to flip the spare tire, however, it's been too cold (and wet) to deal with tire flipping at the moment. :)

Edit: changed thread to tread in the third paragraph

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