Car Tire Tread Mounting - Page 1
Forum section: electronics / general

author: bostonman
author_rank: Super Contributor
timestamp: January 10, 2023, 04:09:51 pm
content: 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.

author: IanB
author_rank: Super Contributor
timestamp: January 10, 2023, 05:16:55 pm
content: 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?)

author: TimFox
author_rank: Super Contributor
timestamp: January 10, 2023, 06:01:14 pm
content: Spell-check may be necessary, but it is not sufficient.I assume he meant "tread", not "thread".

author: james_s
author_rank: Super Contributor
timestamp: January 10, 2023, 06:04:10 pm
content: 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.

author: TimFox
author_rank: Super Contributor
timestamp: January 10, 2023, 06:20:17 pm
content: 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.

author: james_s
author_rank: Super Contributor
timestamp: January 10, 2023, 06:23:14 pm
content: Quote from: TimFox on January 10, 2023, 06:20:17 pmThat's my assumption as well, but I couldn't figure out what else he'd be calling threads.

author: bostonman
author_rank: Super Contributor
timestamp: January 10, 2023, 07:10:06 pm
content: QuoteSorry for confusing people - think it's due to seldom typing 'tread' and usually tying 'thread' to reference a thread on here.QuoteI 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.

author: bdunham7
author_rank: Super Contributor
timestamp: January 10, 2023, 07:23:57 pm
content: Quote from: bostonman on January 10, 2023, 07:10:06 pmTires come with a variety of mounting direction requirements. They can be:1) any way is fine2) 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 outside4) 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.

author: Gyro
author_rank: Super Contributor
timestamp: January 10, 2023, 07:24:53 pm
content: Quote from: bostonman on January 10, 2023, 07:10:06 pmYou 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?

author: bostonman
author_rank: Super Contributor
timestamp: January 10, 2023, 07:43:20 pm
content: 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.

author: Gyro
author_rank: Super Contributor
timestamp: January 10, 2023, 07:52:12 pm
content: 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?

author: IanB
author_rank: Super Contributor
timestamp: January 10, 2023, 08:03:20 pm
content: 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.

author: bdunham7
author_rank: Super Contributor
timestamp: January 10, 2023, 08:11:21 pm
content: Quote from: Gyro on January 10, 2023, 07:52:12 pmIf 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.

author: Monkeh
author_rank: Super Contributor
timestamp: January 10, 2023, 08:20:54 pm
content: Quote from: IanB on January 10, 2023, 08:03:20 pmTyres 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.

author: james_s
author_rank: Super Contributor
timestamp: January 10, 2023, 08:40:42 pm
content: 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.

author: Gyro
author_rank: Super Contributor
timestamp: January 10, 2023, 09:01:25 pm
content: Quote from: Monkeh on January 10, 2023, 08:20:54 pmI'venotoften 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.

author: james_s
author_rank: Super Contributor
timestamp: January 10, 2023, 09:04:20 pm
content: 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.

author: Monkeh
author_rank: Super Contributor
timestamp: January 10, 2023, 09:05:23 pm
content: Quote from: james_s on January 10, 2023, 09:04:20 pmWear on tyres isn't symmetrical, so it stands to reason they have their reasons.

author: james_s
author_rank: Super Contributor
timestamp: January 10, 2023, 09:17:43 pm
content: Quote from: Monkeh on January 10, 2023, 09:05:23 pmSo 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.

author: jpanhalt
author_rank: Super Contributor
timestamp: January 10, 2023, 09:22:14 pm
content: Quote from: james_s on January 10, 2023, 09:17:43 pmYes.

author: Monkeh
author_rank: Super Contributor
timestamp: January 10, 2023, 09:24:35 pm
content: Quote from: james_s on January 10, 2023, 09:17:43 pmWhich is why these are asymmetrical not directional.

author: bostonman
author_rank: Super Contributor
timestamp: January 11, 2023, 01:49:19 am
content: 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.

author: bdunham7
author_rank: Super Contributor
timestamp: January 11, 2023, 02:04:06 am
content: Quote from: bostonman on January 11, 2023, 01:49:19 amLooking 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....

author: IanB
author_rank: Super Contributor
timestamp: January 11, 2023, 02:05:16 am
content: Quote from: bostonman on January 11, 2023, 01:49:19 amThe 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.

author: bostonman
author_rank: Super Contributor
timestamp: January 11, 2023, 03:51:53 pm
content: QuoteCheck 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 wouldnotpoint downward; thus matching the driver's side.QuoteThis 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.

author: IanB
author_rank: Super Contributor
timestamp: January 11, 2023, 04:23:06 pm
content: Quote from: bostonman on January 11, 2023, 03:51:53 pmNo, this is not so. The grooves on the inside of the tire will always point downward no matter how you flip the tire. The only way the grooves on the inside will point upward is if you move the tire to the other side of the car. If you don't believe me, draw some grooves on a cardboard tube with a marker pen and try it out.

author: bostonman
author_rank: Super Contributor
timestamp: January 11, 2023, 04:33:44 pm
content: Uh?If I draw a 45 degree angle starting from the left and drawing down, and flip it 180 degrees, the downward part will now be on the left.

author: nctnico
author_rank: Super Contributor
timestamp: January 11, 2023, 05:08:21 pm
content: Quote from: Gyro on January 10, 2023, 09:01:25 pmThese are all season tires so they have grooving to deal with mud & snow and regular grooving. Basically 2 types of tires in one, or -put differently- only half a tire suitable for the situation. Personally I avoid all season tires because they suck. Especially on wet roads they are way worse compared to a good summer tire that can deal with water. Been there, done that.

author: Tom45
author_rank: Frequent Contributor
timestamp: January 11, 2023, 05:13:41 pm
content: Quote from: james_s on January 10, 2023, 09:04:20 pmThe Michelin XAS tire that was first sold in 1965 was reputed to be the first tire with an asymmetrical tread pattern:QuoteIt was the factory supplied tire on the new 1969 Alfa Romeo Spider I bought in 1969 and was a very good performer at all speeds and in all conditions.

author: IanB
author_rank: Super Contributor
timestamp: January 11, 2023, 05:52:13 pm
content: Quote from: bostonman on January 11, 2023, 04:33:44 pmOn the left, and pointing upwards!(If you draw a line that slopes down from left to right, then you can flip the tire any which way you like, it will always slope down from left to right.)

author: bostonman
author_rank: Super Contributor
timestamp: January 12, 2023, 01:49:53 pm
content: 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.

author: Gyro
author_rank: Super Contributor
timestamp: January 12, 2023, 02:22:10 pm
content: Your mistake is looking at the drawing bleeding through the post-it (notwhat 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.

author: IanB
author_rank: Super Contributor
timestamp: January 12, 2023, 03:38:57 pm
content: Quote from: bostonman on January 12, 2023, 01:49:53 pmBut 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.

author: bostonman
author_rank: Super Contributor
timestamp: January 13, 2023, 05:12:09 am
content: QuoteYou'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).

author: bostonman
author_rank: Super Contributor
timestamp: January 21, 2023, 01:47:20 pm
content: 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