Rotation of tires



Some additional bits of information on the subject:

Why is 2 /32nds considered Worn out? I don’t know. It predates my involvement. I just know that when the laws were first put into effect on tires (about 1968), they included a requirement for a wear indicator at 2/32nds for all street tires sold in the US.

Is it a law that tires have to be removed at 2/32nds? In most states, yes, but there are some that have no regulation, and some that have exceptions to 2/32nds. There is no Federal law on the subject.

There is a push to move from 2/32nds to 4/32nds due to safety concerns. The problem is that while tires have more wet and snow traction at 4/32nds, the point at which traction becomes dangerous is relatively arbitrary. The traction curve is smooth with no inflection points or discontinuities.

When the Rubber Manufacturers Association was updating their pamphlet on passenger tire usage, they wanted to include a statement about how to handle which end of the vehicle new tires should go on - and in particular, at what point did it make a difference in tread depth. Michelin did some testing and came back that they could not detect a difference at 1/32nd, but could at 2 /32nds - just like you’d expect: Small differences don’t matter, but large ones do.


Excellent point, Capri. And, as usual, an excellent post. :relaxed:
All I know is that when my tread blocks start obviously approaching my wear bars, I lose confidence in my tires’ ability to channel/shed water. I’ve noticed over my many years that tires getting worn as I described clearly no longer have the traction that fresh tires have. That’s enough motivation for me to get new ones. IMHO it’s cheap insurance.


Go out on a skid pad and measure the limits of traction.


Experience and a tire tread gage (only a buck or two at any parts store or perhaps even Walmart).


My safety, and the safety of my passengers is more important than trying to wring the last few thousand miles out of a set of tires.

I always replace my tires when they get down to 4/32, but in the case of some awful Continental tires that came on my car, I dumped them at 5/32, due to a total lack of confidence in their ability to resist hydroplaning.


LOL, I had a terrible experience with Continental tires. I wouldn’t put Contis on my car again if you gave them to me!


I know that I probably shouldn’t judge Continentals–in general–on the basis of their OEM-grade tires, but I had such a miserable experience with those tires that I just couldn’t get myself to buy Conti tires again. These were the only tires I ever had that wouldn’t “hold” their balance for more than a few thousand miles. I had a persistent high-speed vibration when I bought the car. The dealer did a Road Force balancing, and they were good. However, the improvement only lasted for a few thousand miles. So, with those miserable Contis, I had to pay for Road Force balancing once or twice every year.

Then, when you add mediocre ride and handling to the package, I just couldn’t wait to get rid of them. With Michelin Defenders on it, the car drives and rides totally differently than it did with the OEM Contis, and the Michelins have not needed to be rebalanced in the 3 years that I have had them on the car.


Ok, in an ideal sense. But in the real world, who drives the car during the test, and how many skid pads and how much time are need to test all cars regularly? And at what cost?

And if tires fail at 3/32, or 4/32, or 5/32 or more, is a warranty claim appropriate? Would tire makers have a problem?


You asked the question and I answered.
Or maybe this is a contest for who gets the last word.


No, I’m not trying to get the last word. I’m genuinely interested in how people can do better in managing their tires. It might even be self-interested because I use roads shared with others.
Measuring tread depth and hardness are do-able but don’t seem to provide an answer even in combination.

A skid pad test would work, but logistically and financially, I don’t think it works out.

And I am suspicious that tire makers are ok with some ambiguity on this issue because of self interest.


4/32 is enough for me to get new tires. No more detail needed. I think you’re over-complicating this.


You’re suspicious with good reason.

Not 1/2 hour ago a neighbor and friend stopped by and asked me to put air in her tires to the proper pressure. The tires looked old, so I decided it’d be a good idea to check their age. I wrote her alpha-numeric secret tire code down and came in to look up what they meant. I don’t deal with the age codes often. To interpret the code I had to go to and unscramble the secrets.

Why don’t they just put “51st week of 2007”? Why do they have this secret code?
I have a theory. My theory is that the legislator that wrote the law was trying to please both a consumer protection lobby and a tire industry lobby.
Now when he speaks to the consumer protection coalition he can say “I got a law passed to require the date of manufacture to be on all tires”.
And when he speaks to the tire manufacturers’ convention he can say “I made sure the law that got passed will not cause you problems and affect your tire sales” Who wants to buy a tire that’s already been sitting on the rack for two years when they can get a brand new one.

Thanks for tolerating the rant. I guess I’ll send away for my “secret decoder ring” now. :grin:


Minnesota has lots of money so MNDOT has gone nuts with those electronic message boards. The two new ones they put up have nothing better to say than “Ice and snow, go slower”. As a plus though they are placed soon enough so you have a chance to get off the freeway before a major stoppage traps you for ten miles with no exit. Hopefully they’ll use them. Used to be the signs were placed after the last exit when it’s too late to get exit unless you did an illegal U turn.

Personally I think they are a distraction since the lettering is too small, they try to say too much as you whiz by at 70 mph or my eyes are not what they used to be. Just the facts mam, “10 mile back-up ahead”.

What’s that got to do with tire rotation? If its rainy or snowy or icy, I slow down accordingly. Don’t need no manufacturer’s standards, or legal tread depth, or recommendation on where to put the new tires. And I wouldn’t go testing new tires on a skid pad for fear of flat spotting or stressing them.


Good for you. I do something similar. Do others on the road with you or yours do the same?


Not based on the evidence I’ve seen! :scream:

If you mean family members, I doubt if many of us know what their kids do. Mine live 3,000 miles away, one in the San Fernando Valley and the other in Portland Oregon. When I see them I have other things on my mind.


No, I meant those on the road with you or those you value (family, loved ones, friends).

And here’s a thought for those here who are mechanically inclined: how about a ‘reverse’ skid pad tester?
There are rollers for tires on cars when doing emissions tests or dyno tests.
How about a “roller” with surfaces that can be adjusted to detect traction by the tires? Power can be applied to the tires for drive wheels, while the roller could move for non-powered wheels.
The ‘roller’ would be in place of the ‘skid pad’.

For conspiracy theorists, maybe tire makers already have something like this. :wink:


Speaking of Continental tires . . .

Back when I was at the dealer, the cars came from the factory with either Michelin or Continental tires. Supposedly, the tires were comparable. Same measurements, same load rating, speed rating, etc.

I recall SEVERAL savvy customers hammering out deals, but with one important clause “I’ll only take the car with Michelins. Find me one on the lot with Michelins, or no deal.”

I also am no big fan of Continental tires. They didn’t wear as evenly as the Michelins, and they generally didn’t last very long, either. That prancing horse, which was the logo, I believe, was the only nice thing about them :racehorse: