Forester: TPMS FTW, Sorta-Kinda

According to the Forester’s manual, the Tire Pressure Monitoring System kicks in after the car reaches 25 mph. It evidently takes a while to figure things out after that, because the TPMS light blinked on a mile from home on the way to Mary’s Vassar Farms garden. I pulled into the next parking lot, measured 20 psi in the left rear tire, then found this staring me in the eye:

Forester - left rear tire with screw
Forester – left rear tire with screw

Well, that certainly simplified the diagnosis!

I unloaded two bags of shredded leaves and a pile of hoses, swapped in the (limited use, donut-style) spare tire, and continued the mission.

The TPMS light wasn’t on when I drove to Squidwrench the previous evening. Judging from the wear, that screw appeared during the various errands following our 800 mile road trip, which is good news of a sort, and depressurized the tire over the course of a day or two.

The receipt from the fix-it folks cautions that a plug is a temporary fix, because “the injury has compromised the integrity of the tire”. On the other paw, the Forester manual tells me “All four tires must be the same in terms of manufacturer, brand (tread pattern), construction, and size. You are advised to replace the tires with new ones that are identical to those fitted as standard equipment” and then provides a checklist:

When you replacing or installing tire(s), all four tires must be the same for following items.
(a) Size
(b) Circumference
(c) Speed symbol
(d) Load index
(e) Construction
(f) Manufacturer
(g) Brand (tread pattern)
(h) Degrees of wear

There’s absolutely no way to get an identical replacement tire, let alone one with the same tread wear, but I am so unready to replace all four tires after 12 k miles / 2 years.

We shall see how this works out…

19 thoughts on “Forester: TPMS FTW, Sorta-Kinda

  1. I’ve had spotty results with those rope-tar plug repairs. Some lasted for the life of the tire, some had maddening slow leaks that drove me to distraction. Naturally, the tire dealers I tried insisted that all the tires had to be replaced simultaneously on my SUV. Seems like a conspiracy between the car and tire manufacturers.

    1. I can see a slash wrecking the tire, but I’m desperately hoping a simple in-and-out puncture won’t pose any challenge to modern adhesives.

      For all I know, though, that screw did a lot of thrashing around while seating itself. [sigh]

  2. I’ve had good luck with hole plugs in general. The most difficult part has been in getting someone to do the repair in the first place in these days of liability awareness. So I go to the local filling station rather than use the big auto tire chain where the tire came from. Everybody seems happier that way :-)

    1. The corner gas station is one of the few with actual repair bays and guys with grease under their fingernails. They did good work on the Sienna belts, so I let ’em plug the tire.

      I can understand the motivation behind that disclaimer, though…

  3. I’ve had probably a dozen flats repaired with plugs over the years. They all worked pretty well. One of my current tires leaks a couple of PSI per week in the winter, perhaps due to a leaky plug, but I can live with that.

  4. I’ve been lucky with the road vehicles (the tractor manages to find vintage roofing nails every so often, but I can change tubes by hand…), but a few thoughts:

    0) There are Subaru Forester fora on line. I’m not familiar with them (subaruforester dot org showed up as the first hit) but it can’t be an unusual situation.

    1) The matching requirement is to reduce wear on the AWD system and the differentials by letting windup average out. A mismatch puts wear on one side or another of the gears. I’ve heard that it’s a Good Idea to match even on a 2WD vehicle’s drive axle for the same reasons.

    2) Back in the ’90s, some shops would do quasi-permanent repairs by dismounting the tire and putting a patch on the inside.

    3) Some tire shops have the ability to trim tire diameter to suit. This may have been intended for the street performance crowd, and I don’t know what precision is available, but it might be worth looking into. If you can get items a-g to fit, and have a shop to match wear, you should be fine.

    1. If you can get items a-g to fit

      Therein lies the rub. Perhaps I could get an identical tire from the dealer, but the TireRack “OEM” offering sports a different suffix and who knows what else. At nigh onto $200 from Tire Rack, I have a powerful motivation to see how well the plug works.

    2. #1: Correct, the spider gear specifically. It’s why it is recommended to move the spare to the rear in a FWD car
      #2: I believe Costco will do so, at least up here in Canada.

    1. Gotta love it: “Includes everything you need to quickly repair punctured tires on sedans, bicycles, SUVs, tractors …”

      They must have some seriously fat-tire bikes in mind.

      The tire plug kit I had in the drawer dried out long ago: this is the first flat we’ve had in maybe three decades!

  5. Around here (in Europe in general IHMO) it’s quite usual to patch tires in specialized shops. Tire is taken off the hub, hole is drilled clean through, new rubber compound is applied and then hot vulcanized. All that plus rebalancing and remounting takes 10-15 minutes and patch is considered as good as new. I’ve had more than a few over the years and never even heard of one leaking.
    They won’t patch holes on the edge of tire where sidewall meets the contact surface because that zone constantly deforms, and run flat tires receive some specialized patch from the inside.
    I don’t know if patch is certified up to full speed of the tire, but it’s not unheard for people to drive 100+ MPH down the autobahn and I’ve never heard about a patch letting go.
    I’m surprised you don’t have such service around US.

    On the other hand I’m pretty sure you can change only the front pair of tires or only the back pair, just put the new ones in the front. It’s quite normal for front tires to wear quicker due to braking and FWD. If you’re running AWD all the time they might wear more evenly but front ones should still be more worn. Center diffs in these cars are not normally made to split power 50-50 so difference in wear shouldn’t matter. Handling might suffer a little, but as long as the left-right pairs are matched you should be fine.

    1. I think the only failure mode would be having the steel belts chew through the plug and spit out the short end. So far, the pressure is steady …

      It’s an always-on AWD car, but I’d still replace just two tires, rotate in the usual crossover pattern, and hope for the best. A regular tire doesn’t fit into the spare tire recess, alas.

      1. I run directional tires often enough (popular for snow tires) that I just do a fore-aft rotation when it’s time to swap seasonal tires. Seems to work fine, and I don’t have to get very creative in marking tires: (date of tire/wheel and location at that time. Aluminum wheels hold sharpie marks at the hubs just fine, though black steel wheels are a bit tougher to read.

        I hate to dismount tires, so it’s standard for us to get snow tires and wheels for each new car. If I were sufficiently motivated, I’d go the TPMS route for the winter tires, but it’s a non trivial DIY task to set it up. At least on the ’12 Forester, only 4 tires could be registered at a time. The TPMS seems to be twitchy at the recommended pressure, being fine on an afternoon and triggering the next cool morning. After a few rounds of this, I went to [nominal value]+3 PSI for the tires. Our dealer has been known to use 35 PSI, and Tire Rack shipped winter tires at 40…

  6. When you do get tires consider getting new TPMS sensors at the same time. Our sensor warming came on shortly before I replaced the tires and I didn’t get it checked until later. It turns out those little sensors have +/- 5 year batteries and when the battery is dead the sensor must be replaced. You can save the cost of dismounting and remounting the tires by doing it all at once.

    1. Good point!

      As Pete pointed out a while ago, Subaru makes TPMS far more difficult than necessary. The car stores exactly four IDs: swapping wheels requires dealer intervention or $300 worth of DIY code readers / setters. I know which I prefer!

      The least horrible alternative may be a set of winter tires + wheels (plus the DIY TPMS gear), leaving the plugged tire to deflate (*) in peace for a few months every year. Given how little we drive, the batteries should live out their entire shelf life, whatever that might be.

      (*) Short term, the plug seems OK.

      1. My first winter, I was talking about the light with the service writer at the dealership. His advice: a small square of black tape for the winter. (Names withheld to protect the guilty. [grin])

        I skipped TPMS sensors for winter tires for both Foresters. Bad of me…

        1. Now that you remind me, I’ll go out and cover the bright orange “Passenger Air Bag Off / On” indicator. It’s way too conspicuous for the information it conveys…

            1. The other side of that panel has a vivid red indicator for:

              • Rump in passenger seat
              • Seat belt unbuckled
              • Ignition ON

              We call it the “Warning! Loose Passenger!” light …

Comments are closed.