Live Oak

Pretend you are planning a 3,000 mile trip in the Spring in the west, some mountain driving (but on good roads) and periodic rain likely.

Do you replace your (in my case, Michelin Primacy MXM4 ) tires when wear reaches the wear indicators, 2/32? Or how much before? 4/32? Even before?

sosh

when it reaches the wear indicators. Thats why they are there! If they are real close I would replace yours before you leave on your long trip.

CEB

No, no and NO!

The old school of thought was 2/32nds but that effectively meant that the tires had lost all ability to evacuate water. The new rule of thumb is that you replace the tires at 4/32nds.

By the time the wear bars are showing, you've lost all ability to drive in rain and even a water puddle can cause issues.

Don't believe me? Read it on Tirerack. Yes, they are in the business to sell tires but they are also the undisputed experts in consumer tires. I could show you NHTSA test results but they aren't in anything remotely resembling the English language.

RNBRAD

Yep I never wait till it hits the wear bars. I don't mess around with tread depth.

PHML

I never go by indicators.

Hydroplaning effect is a great indicator ... time for new tires.

mnje350

Ditto

I don't wait till the car hydroplanes out of control to replace the. Do it before you get caught in that downpour in the mountains.

Live Oak

OK, that all sounds like good advice. Now, assuming 4/32 is the standard, how many miles would you expect to get out of those tires, Michelin Primacy MXM4, at 4/32? For a very conservative driver.

CEB

I'd have to look up those tires specifically, but most new tires have about 9 or 10 32nds of tread, so 7 or 8 32nds available for wear at the old measurement which is still used for treadwear ratings until the law is changed.

For ease of measurement, let's assume 8/32nds and treadwear of 40k miles. Accordingly, each 32nds will give you about 5k miles - however - as tires wear, they become more susceptible to road hazards so you'll want to factor that in as well.

Me? I'd probably swap the tires out before the trip if they were at 4/32nds, but any non-paranoid sane person would probably keep them if they had even tire wear and we're at 4/32nds.

sosh

Totally disagree with you. What makes tire rack the "undisputed experts"? They will tell you what best serves them. Why do the manufacturers put the wear bars in place and why do lots of states pass tires for inspections if the wear is not down to the bars? What you are saying is wrong and is most likely self serving. You must work for Tire Rack. Many years ago I spent the 2 years after college and the military as an exec at what was the largest independent tire sales and retreading company in the US. It was owned by members of my family. Maybe the loss of ability to drive in rain with tire wear not down to the bars is your ineptness as a driver.

Busta Riles

Is it "necessary" to replace your tires before they get to the wear indicators? Probably not.

Would i take a 3000mile trip on tires that are borderline? Not a chance.

The tires you have on your vehicle can completely make or break your satisfaction level, in my opinion.

I've never received bad advice from a TireRack rep. In fact, i think they are the most knowledgeable and accessible people in North America for wheel & tire information. Self-serving is not an accurate description of TireRack. If you know of a better & more complete source, please share?

CEB

That is, without a doubt, one of the most ignorant statements I've read in a long time and shows that you have no clue about tires.

I do not work for TR nor do I have any affiliation with them. You don't like TR? Fine, then how about the German equivalent of AAA? ADAC states"
Profiltiefe

Bereits bei einer Profiltiefe von 4 mm nimmt die Haftung des Reifens, insbesondere der Breitreifen, bei Nässe deutlich ab. Die Reifen können den Wasserfilm nicht mehr verdrängen. Sie verlieren den Kontakt zur Straße, das Fahrzeug lässt sich nicht mehr lenken und bremsen. Deshalb Reifen nicht bis auf die gesetzliche Mindestprofiltiefe von 1,6 mm abfahren. Je nach Breite der Sommerreifen spätestens bei 2 bis 2,5 mm, Winterreifen bereits bei 4 mm Restprofiltiefe erneuern. "

For those of not able to read German, let me (loosely) translate.

Tires, primarily wider tires, already begin to lose grip in wet conditions at 4mm (about 5/32ns.) The tires are no longer able to evacuate water. They lose contact to the street and the car can no longer be steered or braked. Accordingly, you should never drive a tire down to the legal limit of 1.6mm (between 2 and 3/32nds.) At the latest, change the tires at 2 to 2.5mm tread depth (3-4/32nds,) and wintertires no later than 5/32nds.

OEAMTC,the Austrian Automobile club, recommends the 4x4x4 method of changing tires - all 4 at one time, no less that 4 mm tread depth and no older than 4 years. 4mm is roughly 5/32nds.

If you'd like it in English, the here it is from Tirerack and AAA who actually recommend 4 or 5/32nds but no later than 3/32nds.

But back to Tirerack and being the "undisputed" authority on tires. Every US car magazine links to TR tire testing and most magazines use the TR testing facilities to test tires, but that is really unimportant since neither ADAC, OEAMTC or AAA sell tires and they all say the same thing.

Whoops, I forgot Consumer Reports.

CEB

The old 2/32nds rule actually came about back when we were driving on skinny tires (when 175 was a "wide" tire.) As I'm sure you know from your vast experience as working as an "exec" at your family owned retreading business (shall we talk safety of retreads?) that as a tire gets wider, it becomes more susceptible to hydroplaning and it is more difficult to evacuate water. Pretty soon you'll see laws changing for that too.

Are you one of the guys on page 31?

CEB

His dad's retreading shop perhaps?

Busta Riles

That's some serious pwnage ^^^^^^^

mnje350

My dealer said that I have about 4,000miles left with 4/32 of tread. I also drive fairly conservative but am running a completely different tire so don't know if this estimate will help you.

blackbullit

I replace tires when I can see top of Washington's head when inserting a quarter in the tread. This is about 4/32" and gives a easy measurement. I live in Florida and you can tell with heavy downpours that tread depth is inadequate if it reaches this level. I would replace if any one of the tires are worn this far.

RNBRAD

I think it would be pretty much common sense to assume that a tires capability to evacuate water declines proportionately with miles on the tire. It's not that at 3/32 the evacuation is good and at 2/32 it's not. The chances of hydro planing under a set of cicumstanes will continually increase as the life of the tire is used. Now the decision is yours regarding where you want to draw that line and what you can or can't live with. If you want to wait till it hits the bars, go ahead, that your perogative. That risk may save you some money, or it may not. You decide!!

mnje350

^ditto

At these tread depths it is a role of the dice as to how much water you will encounter and the ability of the tire to deal with it at the speeds you typically drive at.

Busta Riles

Well put.