Can tread gauges vary that much?

[paulri]

In the last week or so, I had three different Americas Tire guys check the tread depth on my Goodyear Assurance tires on my Sienna. I got 3 different readings. One said 2 of them were at 2/32, and that no AT would rotate them because the treads were so short. I went to another location yesterday, and was told that they ranged from 3/32 to 5/32, but that because the treads were uneven, it would be hard for me to get a prorate (b/c the manufacturer would claim that it was operator error). Today, I went to that second location again, and was told by a third guy, that the front were 4/32, the rear were 6/32, and that I'd only get prorate on the lower two, but that they could be rotated, so the higher treads were up front--which I did--so the car should be good for several thousand more miles. The third guy assured me that the treads were not uneven. What is interesting is that I had actually ordered some Cooper tires, and was willing to buy them and have them installed, when I refused after learning that I wouldn't get prorate for all 4 tires. So this third guy actually talked me out of a sale.

My first thought was that the second guy was trying to scam me, just to sell me a new set of tires--and he did allow for a prorate once we got inside. I started thinking about buying my own gauge, and coming here asking for a good one that would stay accurate, when it dawned on me that perhaps the three guys had three different gauges that all had varying degrees of accuracy.

How likely is this last scenario? The first guy made no attempt to sell me tires--all I did was ask him to air them up (which he did), and he voluntarily measured them, and just said that two were too low to service any more. So I'm wondering if the issue wasn't simply inaccurate gauges. I certainly can't accuse the first guy (who said 2 of my tires were 2/32) of blatant dishonesty.

 

[Kestas]

You have a lot of variables here. You have four tires that can vary among each other. You have any tire that vary in tread depth within the tire. You have different people making these measurements. You have different tire gauges being used. I'm not surprised with the numbers.

In our lab we're studying precision and repeatability. What you just presented is a classic case.

It's not like tire shops are bound to a quality system that requires them to calibrate their gauges. And I wouldn't expect them to methodically take readings at three locations across the tire width, every 90 degrees, for all four tires to provide a complete and accurate report.

 

[paulri]

OK, but let's rule out four different tires--all 3 agreed that some of them had different measurements. That in and of itself doesn't mean that anyone's gauge was inaccurate.

But you did mention one thing that I hadn't thought of--tread depth varying within the same tire. In which case, all three could have been accurate.

 

[Snagglefoot]

Doubt there is anything wrong with the gages. They are totally simple. Sounds like BS at work.

 

[Rolla07]

Depends where they are taking the measurements from. Center or either side can vary if they arent wearing evenly. I measure in the center and both edges to be sure. Why not measure them urself or have the guy measure in front of you? Ask them to show you.

 

[paulri]

I don't recall if the first guy measured different treads on the same tire (I was in the car at the time), but the second and third guy both measured at least 3 treads in each tire, and I was standing watching them the whole time, as they walked around my car--I walked with them.

Originally Posted by Rolla07
Depends where they are taking the measurements from. Center or either side can vary if they arent wearing evenly. I measure in the center and both edges to be sure. Why not measure them urself or have the guy measure in front of you? Ask them to show you.

 

[eljefino]

I have a gauge that slipped 1/32 between the "guts" and the chrome outer part with the pocket clip. It gives the tire an extra 1/32.

The ultimate gauge is a $10 HF digital caliper with the far-end plunge depth mic. Accurate to 1/1000 inch, plus or minus the fudge factor of a human jabbing something into pliable rubber. Take a reading every 1000 miles and put it in your log.

 

[HangFire]

I had a bit of a scare this week when I first measured a tire on the Corolla, came in at something like 3-4/32". Turns out the gauge was sitting on top of the wear bar.

 

[Nick1994]

Buy your own gauge and measure them yourself. It's like $4-$5 on Amazon, I got my own.

The Discount Tire tech probably rounds the tread down to try to sell tires.

 

[k1xv]

Yep, buy your own digital gauge and judge it yourself. Very affordable car accessory.

 

[user52165]

A lot of depth gauges read both metric and in fractional inches. But there are 25.4 mm per inch and 32 32nds per inch.

So 8/32" would read about 6mm, 4/32" about 3mm.


Easy enough to read the wrong scale.

 

[JohnnyJohnson]

Originally Posted by user52165
A lot of depth gauges read both metric and in fractional inches. But there are 25.4 mm per inch and 32 32nds per inch.

So 8/32" would read about 6mm, 4/32" about 3mm.


Easy enough to read the wrong scale.


Especially when it supports a tire sale. My air gauge has two scales as well but I have no problem reading it and I'm not even a tire salesman.

 

[skyactiv]

Milton, made in the USA which means it's accurate and not cheaply made, $5.99, It is in my toolbox as a UPS semi mech and will never need batteries unlike something digital: https://www.amazon.com/Milton-S-448...096&sr=8-10&keywords=tread+gauge

 

[Ducked]

I use a cheap plastic vernier caliper with a depth gauge probe, and I measure across the tyre profile in each tread groove, at the circumferential positions corresponding to the 4 lug nuts.

I get quite a bit of variation. I think its mostly because there actually is quite a lot of variation in wear across the width of these tyres.

If that is your situation, without a standardised measurement procedure two people readings could easily be as different as you describe.

 

[DBMaster]

The best tread depth gauge for me has always been my eyes. But, keep in mind that some tires lose a very substantial amount of wet traction when there has only been a loss of half the tread depth. If you pay attention to the way the vehicle drives it matters a lot more than the tread depth. The tires that came with my Mazda3 (Bridgestone Turanza EL400) had lousy wet traction when brand new. The Michelins and Yokohamas I've had afterward were much better, even with substantial tread wear. Tread depth gauges are great for tire stores that want to sell tires and state inspectors who use them for pass/fail decisions, but not so much for those who are observant.

 

[paulri]

I appreciate the comments here---as always, you have given me some food for thought.

Having said that, I'm still not convinced that someone wasn't trying to snow me. If in fact my tires have varying tread depths, I think it is strange that 2 of the 3 guys didn't pick this up. And if it was a matter of people's gauges giving different readings--again, only one gauge gave different readings for the same tire, so I think there has to be more than just a difference in tread depth or measuring.

 

[paulri]

Because I did mention AT here, I want to post a correction. I went ahead and used my dad's tread gauge today, and sure enough, two were of varying tread depths--ranging from 4/32 to 6/32 (center treads were 6, the sides were 4). The tires with lower treads were more uniform--more like 4/4.5/4 32s--so the same pattern--center treads were higher, side treads were lower). Anyways, now I know that the one guy at AT who told me that I had varying tread depth on each of my tires was actually telling me the truth!

Now I don't have to stop buying tires from AT. I'm glad about that, as they are incredibly convenient to use.