Car Tire Tread Mounting

[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.

[james_s]

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.

That's my assumption as well, but I couldn't figure out what else he'd be calling threads.

[bostonman]

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

Sorry for confusing people - think it's due to seldom typing 'tread' and usually tying 'thread' to reference a thread on here.

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.

I agree, however, as mentioned, I've seen multiple cars with the tread angled the same direction on the driver's side, and opposite on the passenger's side; and the angles match my car. The probability of different tire shops mounting them randomly and having them all match seems very slim which keeps me wondering if a reason exists they are mounted this way.

[bdunham7]

I agree, however, as mentioned, I've seen multiple cars with the tread angled the same direction on the driver's side, and opposite on the passenger's side; and the angles match my car. The probability of different tire shops mounting them randomly and having them all match seems very slim which keeps me wondering if a reason exists they are mounted this way.

Tires come with a variety of mounting direction requirements.  They can be:

1) any way is fine
2) one side is designated the outside with no rotational direction specified (which is common and will result in exactly what you see if the tread is not 100% symmetrical)
3) rotationally directional but no defined inside or outside
4) rotationally directional and a defined inside/outside--these tires will only work on one side of the car so they come in a left and right variety.

[Gyro]

Sorry for confusing people - think it's due to seldom typing 'tread' and usually tying 'thread' to reference a thread on here.

You could usefully remove the confusion by editing the thread title and your post then.

I still can't tell  from your photos, what you are actually talking about. It's very hard to see any relative angles from them. Maybe you could highlight the differences on them?

[bostonman]

I fixed the title and drew red lines to show the angles I'm referring to.

The red lines are a bit exaggerated to emphasize what I mean, but, if the tires were looked at directly, you'd see these channels are angled up on the driver's side and down on the passenger's side.

On some cars this is much more obvious whereas on mine the angle is a bit less drastic.

[Gyro]

So you have one of the tires with the outside [Edit: pattern] 'leaning' forward and the other with the outside leaning backwards (I can't see the inner side pattern). I'm trying (and failing) to get my head around what would happen if you turned one of the tires around (we're actually akin to screw threads here) - wouldn't the result be the same?

[IanB]

Exactly. Turn the steering wheel so the whole tire width is visible, and take a picture of the complete view, both inside and outside of the tire. I will guess it is symmetrical, so that if you turned the tire any which way the result would look the same.

[bdunham7]

So you have one of the tires with the outside [Edit: pattern] 'leaning' forward and the other with the outside leaning backwards (I can't see the inner side pattern). I'm trying (and failing) to get my head around what would happen if you turned one of the tires around (we're actually akin to screw threads here) - wouldn't the result be the same?

If you look at this picture, you'll be able to more easily see what would happen if you turned (this tire) around.  And putting a mounted tire on the opposite side of the car is indeed turning it around.  The OPs tires don't look like this--these would be directional but not have an inside or outside.

[Monkeh]

Exactly. Turn the steering wheel so the whole tire width is visible, and take a picture of the complete view, both inside and outside of the tire. I will guess it is symmetrical, so that if you turned the tire any which way the result would look the same.

Tyres are pretty easy to ID. These have an inside and outside, but are not directional. The channels push water out, but it doesn't really matter which way they're angled to my knowledge.

[james_s]

The tires themselves should all be identical, if they're not then they're either mismatched or there are serious quality issues. Is it possible one or more is installed the wrong way around? The tires I currently have on my car are directional, they have a large arrow prominently cast into the rubber sidewall indicating the correct direction of rotation so the wheels have to go on the correct side of the car.

[Gyro]

Exactly. Turn the steering wheel so the whole tire width is visible, and take a picture of the complete view, both inside and outside of the tire. I will guess it is symmetrical, so that if you turned the tire any which way the result would look the same.

Tyres are pretty easy to ID. These have an inside and outside, but are not directional. The channels push water out, but it doesn't really matter which way they're angled to my knowledge.

I've not often wondered whether the different tread sections on those asymetric tyres actually make a difference, or whether it's just the design guys getting bored. You think that if they were that worthwhile, the bolder patterns, like the arrow shapes on the AS4s would indeed face in the same direction.

You could have hours of fun phoning around tyre dealers and listening to their reactions when you tried to order left hand and right hand tyres. 

[james_s]

I'd never seen asymmetrical tires before now, that's strange, I can't help but think they are mostly a marketing gimmick. I don't think tire technology has changed a whole lot in the last 30 years.

[Monkeh]

I'd never seen asymmetrical tires before now, that's strange, I can't help but think they are mostly a marketing gimmick. I don't think tire technology has changed a whole lot in the last 30 years.

Wear on tyres isn't symmetrical, so it stands to reason they have their reasons.

[james_s]

Wear on tyres isn't symmetrical, so it stands to reason they have their reasons.

So do they make left and right handed tires? Reality prevents there being one tire with asymetrical and directional treads that can go on both sides of the car. In my experience the asymmetrical wear is usually mirrored, ie the outer treads of both front tires wear more than the inner treads.

[jpanhalt]

So do they make left and right handed tires?

Yes.

[Monkeh]

Wear on tyres isn't symmetrical, so it stands to reason they have their reasons.

So do they make left and right handed tires? Reality prevents there being one tire with asymetrical and directional treads that can go on both sides of the car. In my experience the asymmetrical wear is usually mirrored, ie the outer treads of both front tires wear more than the inner treads.

Which is why these are asymmetrical not directional.

[bostonman]

This is a picture straight on. If the tire is removed from the rim and flipped, the treads would be opposite thus matching the driver’s side.

[bdunham7]

This is a picture straight on. If the tire is removed from the rim and flipped, the treads would be opposite thus matching the driver’s side.

Looking at it you would think that there would be left/right versions of the tire and that it would be directional.  But according to Michelin, it is not.  I'm sure they have testing and data to back that up.  They have an obvious outside and inside though.  Definitely not the tire for those with OCD....

[IanB]

This is a picture straight on. If the tire is removed from the rim and flipped, the treads would be opposite thus matching the driver’s side.

The angle of the grooves on the outer tread pattern is rotationally symmetric. If you turn the tire around the angle of the grooves will still be pointing the same way.

But it is interesting that the tread pattern does vary from side to side in other details though. Someone with an eye for detail would mount the tires so that the outside tread on all the wheels was the same.

[bostonman]

If you turn the tire around the angle of the grooves will still be pointing the same way.

Check again, the grooves on the inside of the tire point downward, and the outside point upward. If I unmounted the tire from the rim and flipped it, the groves on the outside would not point downward; thus matching the driver's side.

But it is interesting that the tread pattern does vary from side to side in other details though. Someone with an eye for detail would mount the tires so that the outside tread on all the wheels was the same.

This was one of my points. The probability of mounting both driver's side so the treads face downward on my car and most cars I've seen while the passenger's side is facing upward on both tires, and on most cars I've seen, seems low.

If say three out of the four tires all went in the same direction, then one can say the tires are randomly mounted, however, it seems two match on the driver's side and two match on the passenger's side, and it's like this on most cars I've seen.