Piston Slap: A Cautionary Tread Wear Tale

Sajeev Mehta
by Sajeev Mehta
piston slap a cautionary tread wear tale

John writes:

Just a few days ago one of four nearly new tires developed a bubble on the sidewall. Thankfully, I purchased the roadside-whatever-the-heck when I bought them and got the replacement for the cost of shipping and had it mounted with decent haste – potential NJ turnpike crisis averted.

Now, I figure the other tires are at around 85-90% when this episode started. Is there a way to get the new tire to catch up with the others in terms of wear? Or should I leave well enough alone?

Sajeev answers:

The short answer is to leave well enough alone, it’ll be fine. Well, that depends on if your vehicle has permanent, full time AWD?

John answers:

Nope. FWD.

Sajeev concludes:

Well then! It’s not a problem, mount the new tire on the front axle and let it wear to match. At your tread depth, that tire could be mounted at any location, even on a four-wheel-drive vehicle. The folks at Tire Rack go into further detail than I’d prefer to in this column, including shaving a street (not race) tire to keep someone from replacing all four tires when only one is truly bad. So all roads point to you being fine.

Which begs a few questions: how many people rotate tires as per owner’s manual requirements? As AWD becomes more prevalent in affordable CUVs and sedans, are we gonna see more problems with mismatched tires? If so, what mechanical failures should we be on the lookout for?

Send your queries to mehta@ttac.com. Spare no details and ask for a speedy resolution if you’re in a hurry.

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7 of 32 comments
  • Slance66 Slance66 on Apr 11, 2011

    Mismatched tires were a significant cause of problems in our 2000 Volvo V70XC. Twice we had CV problems, and propeller shaft problems. We worked hard to keep tires rotated and of a similar circumference, even replacing them all when one was damaged with more than 50% tread life left. But the mechanical system in that Volvo had no ability to adjust. I was advised that the subsequent Haldex system would not react the same way and wouldn't treat similar differences in circumference is slip. I suspect that the modern systems, whether Haldex, Subaru, Quatrro or X-drive etc. can accommodate some variation more easily.

  • David C. Holzman David C. Holzman on Apr 11, 2011

    This suggests that some of those AWD and Limited slip dif cars should require real spares.

    On the other note, we got a bubble in the tire crossing the country in the old Studebaker back in '57.

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    • Ubermensch Ubermensch on Apr 11, 2011

      In case of Subaru's they don't have a full size spare (at least my 2006 Legacy doesn't). On the automatic transmission models which are electronic, you must insert a fuse to disable the AWD and make the car FWD if you need to drive more than a few miles. Another reason people need to read their manuals. Subaru also requires that all 4 tires not differ more that 1/4" in circumfrence.

  • Mikey Mikey on Apr 11, 2011

    I rotate front to back every 15000 KLM, on my Impala. I shudder at the thought of replacing those 18" tires. I'm trying to get as far as I safely can, with the originals. I used to do the same with my Jimmy. However the wicked cost of gas {almost $5 USD} finds the Jimmy not moving too far. I'm more concerned with flat spots on my pricey Michelins. As far as "johns" question goes, 10 to 15 percent difference? Don't sweat it. If it was 30+ percent buy another tire to match the axle.

    • See 1 previous
    • Mikey Mikey on Apr 11, 2011

      @WRohrl.....Thanks, might be a good plan? I do have some connections at the local Chev dealer.

  • ExPatBrit ExPatBrit on Apr 11, 2011

    My car manual specifies 1/8 inch max tread height difference. I rotate every 5000 miles . The problem is that many tire stores have a zero tolerance for "any" tread difference on an AWD car. They use this a marketing opportunity to have you replace all four, "it's not safe" unless you have the road hazzard warranty and then it's not so critical. I damaged a sidewall on one of my almost new Michelin Pilots (Car purchased used with them already installed so no warranty) . I ended finding a pair of matching tires with identical tread depth on E bay and taking the single wheel to the tire store to have it switched. I wonder how important this all is, since many people don't rotate and front tires wear out much faster any way. It also seems to me that depending on how many people are in the car the circumference of tire would change.