When to replace old tires?

[ucbalumnus]

@Iglooo

They are more worn on the outside than the middle. Is that cupping?

No. Wear on the the outsides of the tire is typical underinflation wear pattern. Underinflation makes tires less safe in various ways, as well as causing them to wear poorly.
https://www.knowyourparts.com/technical-resources/info/understanding-tire-wear/

[sushiritto]

Also, there are “tread wear bars” in the grooves. Have you worn the tire down to those “tread wear bars”?

[Iglooo]

What does it look like? I don’t see anything other the rubber.

[ucbalumnus]

5 Warning Signs You Need New Tires | HowStuffWorks has some photos of tires showing the wear bars that are 2/32" from the bottom of the tread.

[Iglooo]

I have a lot more than that. It is not bald anywhere at all. Tire on the front driver side show wear on the outer edge. That is about it. I think I can get another 5,000 miles out of it.

[evergreen5]

If the car was bought new, with whatever cheap tires the factory puts on, it’s possible it could be time soon - maybe rotate now? I have really stretched out my current tires, 27k on a car bought new. I was disappointed that they wore so quickly until I did a bit of googling and found that others with my car had similar issues with the tires on the new car.

[pishicaca]

What I would worry about most driving on tires with so little tread is hydroplaning when driving in the rain. If you live in a dry climate, you can probably get away with waiting a bit longer. In a wet climate, you may be tempting fate at highway speeds.

[anomander]

I let my tires go all the way down to the wear bars usually. But I live in Phoenix and I’d venture that 99.9% of my driving is in dry, sunny conditions. If I needed to regularly drive in the rain I’d change earlier with a few extra mm to spare.

If your tires are worn more on the inside and outside edges, then that classic underinflation. If they’re only worn on the outside edge, then unless you’re driving a sports car with aggressive camber like a Porsche you have an alignment issue.

[Iglooo]

It is some kind of sport model although I am sure it is nothing like a Porsche. I will drive another 5,000. It will still not go down to the bar. In addition to the expense, i would like to be mindful of landfill. If it is still safe to drive, wearing it down will fill landfill less.

[hebegebe]

@anomander

I let my tires go all the way down to the wear bars usually. But I live in Phoenix and I’d venture that 99.9% of my driving is in dry, sunny conditions.

I would do the same if I lived in Phoenix. Furthermore, tire performance in dry weather can actually increase as the tire wears down provided they are not too old.

But for people living where it rains regularly, change the tires at 4/32.

[sushiritto]

@hebegebe

Furthermore, tire performance in dry weather can actually increase as the tire wears down provided they are not too old.

This may or may not be true. Certainly race slicks have very little tread and are used for 1/4 mile drag strip races. And when the tires are new, they do need some wear to perform better.

But if you’re getting down at or near the wear bars, then no, dry performance isn’t improved. Better braking and handling require more tread.

Also, Phoenix and other hot climates regularly get to 100-120 degrees, which will also degrade your tires more quickly.

[sushiritto]

@evergreen5

I have really stretched out my current tires, 27k on a car bought new. I was disappointed that they wore so quickly until I did a bit of googling and found that others with my car had similar issues with the tires on the new car.

FWIW, depending on the manufacturer and model, new car tires and their manufacturer suggested replacements can wear more quickly than others. All tires come with treadwear ratings embossed on the outside of the tire. Generally, performance car tires (Porsche, BMW and the like) will have softer tire rubber compounds, while your typical family sedan will have a harder compound, which allows tires to last longer (more miles). Softer rubber doesn’t last as long as harder rubber.

One more TMI detail, since you said you have a “sport model.”

A few performance cars come with “staggered tire” setups, like a BMW M3, Mercedes AMG, Corvette, etc. for example. All that means is that the front tires are rear tires are different sizes. The front tires are a bit smaller than the rear tires, so no tire rotations. The overwhelming majority of cars and trucks do NOT have a staggered tire setup.

[hebegebe]

@sushiritto

But if you’re getting down at or near rhe wear bars , then no, dry performance isn’t improved. Better braking and handling require more tread.

This is generally not correct. Here is a snippet from the CR link that ucbalumnus posted, but you can find confirmation about this in many places.

Better dry-road performance. Bone-dry pavement is one place where less tread means more grip, since shallower grooves and sipes put more rubber on the road. That’s why mega-horsepower racing cars typically run on treadless “slicks” for all-out traction. It also explains why the half-tread tires performed better in our dry-pavement handling, cornering, and braking tests.

[sushiritto]

@hebegebe

This is generally not correct. Here is a snippet from the CR link that ucbalumnus posted, but you can find confirmation about this in many places.

As I said above, drag racing (or autocrossing) event participants use specialized tires with soft compounds, “slicks,” where the participants can heat up their tires with burnouts for more traction. And they’ll also “heat cycle” the tires as well. So less rubber is better in those racing examples.

But that’s NOT your typical situation on neighborhood streets or freeways, in uncontrolled situations, with “50,000” mile tires (harder rubber compounds) and where tires are often over-inflated, under-inflated, poorly aligned with less than desirable road surfaces aka “real world” circumstances.

In this NHTSA study, Figure 5 (page 9) is Percentage of tires of tire-related crash vehicles in each category of tire tread depth

Tire Tread Depth / % of Tires in Tire-Related Crashes

0-2/32nds → 26.2%
3-4/32nds → 8.0%
5-6/32nds → 4.0%
7/32nds+ → 2.4%

CFA was conducted to study association of tread depth with tire’s crash role. The results in Table 5 show that significantly more than expected vehicles experienced tire problems when they were running on tires with tread depth between 0 and 4/32" (Z-values 24.8 and 3.9), where expected frequencies were obtained under the assumption that tire’s crash role has no association with tire tread depth. With tread depth above 4/32", vehicles experiencing tire problems were significantly less likely than chance (Z-values -5.2 and -10).

https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/811617

As you can see in this NHTSA study, more tread meant less tire-related crashes.

[hebegebe]

You presented a number of good reasons why the OP should swap tires well before they hit the wear bars.

We will continue to disagree regarding dry-weather performance of low tread tires that are still new enough that the rubber remains soft. While this might be a nice debate for us (and I suspect we can both go at this for a while), it matters to very few drivers out there.

[ucbalumnus]

@sushiritto

https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/811617

As you can see in this NHTSA study, more tread meant less tire-related crashes.

Overall, but doesn’t that combine dry, wet, and snow conditions?

[sushiritto]

@ucbalumnus

Overall, but doesn’t that combine dry, wet, and snow conditions?

Yes, “adverse road conditions” were included, but…

“The results of this analysis show that vehicles running under adverse roadway conditions may become more vulnerable to tire problems.”

[RichInPitt]

@sushiritto

But if you’re getting down at or near the wear bars, then no, dry performance isn’t improved. Better braking and handling require more tread.

This is simply false. Tread squirm does not improve the contact patch.

Check any car mag testing cars after their 40,000 mile extended tests.

No, it doesn’t mean 2/32 down to slicks is safer for everyday, all-weather driving. But it’s still factually false.

[RichInPitt]

@sushiritto

Also, search “panic stopping.” Less tread depth will affect braking distance. Roughly, every 2/32nd’s of tread depth is about 100’ +/- (more or less) of extra of stopping distance at 70mph.

After discarding the many search results with the aforementioned scary wet tests, as I referred to, I did read Tire Rack’s well-controlled dry braking tests, done in response to exactly these type of comments.

They confirmed 2/32” dry braking distances are shorter than full 10/32” depth, not the nearly 150 foot increase your claim would indicate. 4/32” as well. They also confirm improved handling.

https://www.tirerack.com/tires/tests/testDisplay.jsp?ttid=91

Their conclusion is pretty much exactly what I said

Though dry braking isn’t significantly affected by tire tread depths, if rain and wet roads are a concern, Tire Rack suggests that drivers consider replacing their tires when they reach approximately 4/32" of remaining tread depth.

(Yes, tire age would trump any of these recommendations. That’s a given. If you’re using less than 6/32” of tread in 6-8 years, you’re in a small minority with different considerations).

[Knowsstuff]

Lots of tire pros here. But put one of these in each car trunk then forget about until you need it.

Fix-a-Flat Tire Repair Aerosol

It happened to me over the summer and I was not in a good neighborhood at all. Ready to change the tire and noticed in my car bag I bought this probably a few years ago. Worked like a charm and I was able to drive 35 miles on it…

So now all our cars have one. Super simple to use.

Back to discussing tire treads it if it’s my car or my families just change it a bit early. Why risk death of you or the person you hit??