I just had my Pilot Sport AS 4's fitted. It is a bit early to report back but so far they feel pretty good.
I was planning to re-use my P-Zeros (8K miles) next Summer then refit the AS tires in the Fall.

However, while removing the PZ's, the tech managed to slice a cut along the wall of one of the rears.
The dealer has ordered a new free replacement but I am concerened about having mismatched tires when I re-install the PZs.

I have not had the reported handling issues with the PZs and they have worn very evenly both front and back.
At 8K miles the fronts have 8mm of tread left. The one remaing rear has 6mm.
So the question is whether I can run mismatched PZ rears (295/30R20Y) with 6mm and 10mm tread depths without experiencing a handling issue or problems with AWD?

Please do not tell me to just junk the crappy PZ's.
I have really not had any issues with them and would like to get another 8K out of them before I toss them.

 

I don’t think it’s ever recommended to run different wear depth tires on same axle. Maybe u can talk to the manager and get a new tire at their cost so u have 2 new tires?

 

I reckon it's OK with front tyres but not with rear tyres.
My front left tyre (Michelin PS4S) suffered a massive blowout just over two years ago so I bought a new replacement and had it fitted.
The other front tyre was some two years old and around one third worn at the time but I did not replace it.
I have not noticed the slightest difference or had any problems since fitting that new tyre and running with the "old" tyre on the other side.
I would not do the same with a rear tyre though as there could be a sizeable traction differential between a new tyre and a half-worn tyre, especially if you are talking about OEM Pirelli P-Zeros which are notorious for losing grip once half-worn.

 

Only acceptable if you drive like a grandma. Not worth the risk otherwise. Ask for dollar value back instead

 

Ask the dealer to get a pair of Michelins and sell them to you for a bit below cost. He can put the price of the P-Zero replacement towards the Michelins and it won't cost him anything. You avoid the mismatch, get an upgrade in the process, and save a buck on the eventual replacements. If, at a minimum, he agrees to sell the Michelins at cost (not more), take it. If he wants to insist on replacing a single P-Zero, tell him you want it in writing, signed by the GM that the mismatched tires are safe and will not impact safety/performance. (They won't sign.)

 

The real question is the rotational speed difference at the differential. Given how tender our rear diffs are, I wouldn't mess around. Scrap the P Zero's, get a discount on the new PS's and don't look back.

 

General advice on an all-wheel-drive car is if you have to replace one tire you have to replace them all if there is any wear involved otherwise you are likely to have serious problems with your drive train and void your warranty coverage. It's what got me off run-flats because having to replace four of those puppies if you pick up a nail was an expense I never want to repeat. Apparently you can't patch run flats. That was an Audi but I've since found that tire companies won't even sell you one tire if they know you have all-wheel-drive because it is a liability issue for them. By the way, neither of those tires are good in the winter. Winter tires are designed for the cold and will perform much better then. Given what it costs to fix that drive train I wouldn't take this risk myself.

 

But does that apply to the F-Type drive which is predominantly RWD? I can understand the tread depth having to be similar on the same axle, but front to back as well?

 

Both can be problematic for different reasons. Different diameters on the same axle, even a few mm, means tires rotate at different speeds which can be detrimental to the differentials if driven for any significant length of time or at speed. Different diameters on different axles can be problematic for traction control and/or torque-vectoring AWD systems because most rely on tire RPMs to determine wheelspin, etc. So if the computer thinks the front tires are turning faster than the rears (as a result of diameter differential), it may apply braking to the offending wheels (or retard throttle response) to correct what it thinks is wheelspin.

Replacing all four is the best, pairs on the same axle is second best, singles can be problematic if the wear is significant enough.

 

I've heard this argument often. But what's the science behind it? Even a very substantial difference in tire tread of say 4mm (ie 8mm in wheel diameter) makes a very small rotational difference (about 1%). So the wheel on one side would rotate 1% more times. What damage does that do to a diff? Cornering must create far greater difference in rotational speed from one side to the other - but that doesn't cause issues

I'd love to understand how this might wear the differential out. Does anyone have an engineering view here - and a real world example of it causing an issue?
I do remember my tire shop said they wouldn't replace the tire on just one side once for this reason. But the jag dealer said that didn't make any sense and was happy to replace just one tire

Any views welcome.

 

Inside the differential, the spider gears spin to make up the difference in wheel spin. When the wheel spin rates are equal (I.e, driving straight with equally inflated and worn tires), these don’t spin. So mismatched tires cause these to spin constantly, though probably at a low speed.

Does it matter? No clue. Having mismatched tire pressure has the same effect as mismatched tire wear, so you could perhaps overinflate the worn tire to compensate.

Here’s a good explanation of how a basic differential works. Note the mechanical and electronic LSDs are more complicated.

 

Thanks for all the input. It motivated me to go back my tire dealer.
Town Fair Tire has agreed to give me one free tire to replace the damaged tire, and to provide a new matching P-Zero 295/30R20 at 50% off.
I am happy with this solution.
Next Spring, I will mount 2 new rears and slightly worn fronts (8-9/32), and hope to get 2 more Summers out of them.
I would like to give a big shout-out to Town Fair Tire for the way they handled this issue.
They had the best price and service, and have shown themselves to step up when there is an issue.

Regarding other comments on this thread:

The Pilot Sport AS4's have very good ratings compared to other AS tires.
Admittedly they are not ice/snow tires but that is not what I need.
I just want to drive below 45F safely and not in ice/snow conditions.
https://www.tire-reviews.com/Tire/Mi...l-Season-4.htm
https://www.tirerack.com/tires/tires...t+All+Season+4
Having driven about 150 miles so far, the PS AS4's are responsive, a lttle firmer than P-Zeros and have a slight (rear) harmonic at 30-40mph.

Regarding the need to replace all 4 tires at the same time, while this may be the best possible solution, it ignores the fact that the F-type rears wear faster than the fronts.
At 8K miles, my P-Zeros fronts have 8-9/32 tread with rears at 6+/32. Wear is even - no sign of alignment/tracking issues.
So, during the normal life of a set of tires, the fronts will always be different to the rears, simply because they wear at different rates.
Presumably even the F-Type is able to handle this discrepancy.

 

This is correct, but also why the statement is true. Cornering is a transient event, and unless you're on a NASCAR track you probably take left- and right-hand corners at about the same percentage. So while wear absolutely happens on a differential during cornering, the duration is not sustained and wear is even in both directions (and it's designed for this). However, if you have unequal diameter tires, the wear--while much less dramatic than during cornering--is constant, often at higher speeds, and only in one direction. Picture a two-hour road trip on the highway at 80mph. While there will be some gradual turning, there is long sustained high speed uneven rotational wear.

Now the question comes down to 'how much additional wear.' I think most people sell or trade-in their vehicles long before accelerated differential wear would ever show on most 2WD vehicles. AWD may be a different story.

The other option here is to have the new tire shaved to match the tread depth of the used tire. Problem solved.

 

Hmmm...could unequal rotation L-R with the limited slip diffs, be a factor when folks find that the differential fluid has become 'sludge'?