I’ve written about tires so many times in the past four years that I am wary of bringing up the subject again.   I have to wonder how many blog readers’ eyes have glazed over permanently.   But I keep learning new things, and I feel obligated to share them here in the hopes that these lessons will help someone else.

A few weeks ago I had mentioned on the blog that we had unusual tire wear along the outer edge of some of the Airstream’s tires, and this was the thing that caused us to go to Jackson Center for an axle alignment.   As it turned out, the axles were out of alignment. After the service, I resolved to keep an extra sharp eye on the tires, to see if the wear returned to a more even pattern.

This morning, after yesterday’s 350+ mile tow, I noticed the left rear tire was looking very funky.   Wear was occurring rapidly in isolated spots, and there was a distinct bulging in the tread.   Those are the signs of a belt breakage inside the tire, and I’ve seen them before.   We got some local advice and towed the Airstream a few miles over to Mill’s Fleet Farm in Wausau for a replacement.

These days, when I have a tire problem, it is my habit to remove and reinstall the tire myself.   This saves a lot of hassling and potential screw-ups by technicians who (a) don’t know the proper way to jack up an Airstream; (b) will use an air wrench to over-tighten the lug nuts; (c) want to argue with me about using tire pressure sensors (“Just throw those things away, they’re the cause of every stem failure I’ve ever seen.”)

So in the parking lot we removed the left rear tire (a Carlisle) and sure enough, it was a disaster.   The tire rolled like a jelly bean, and had bare patches on it.   It looked fine the day before, which shows how fast they can deteriorate once a belt starts to separate, break, or shift.   We rolled it over the shop, where it was quickly replaced with a fresh tire.

Then I took a careful look at the other tires and discovered that the left front tire (a PowerKing TowMax) also looked a little suspicious.   I asked Jason, the Service Manager, to take a look and he agreed it was probably also suffering belt breakage.   We removed it out of caution and confirmed that it was indeed out of round.   While it wasn’t as bad as the rear tire, it was heading that way and needed replacement.

So now the question was, why were these tires failing?   At first I was theorizing that the tires were stressed.   They had been wearing in a particular way before the axle alignment, and now they were being forced to wear differently.   Could the change in alignment be the cause?

Then Jason pointed out something interesting to me.   Both tires had been patched (we have rolled over a lot of road debris like nails and screws in the past year).   Both tires had belt separation centered in the exact spot where the patches were installed.   At last, we had a smoking gun.

The problem was that these were “flat patches”, meaning that they covered up holes from the inside of the tire like patches on your blue jeans.   Flat patches do a good job of holding air, but the original hole in the tread can still allow water to get inside the tread.   Over time, that water will rust the internal steel belts of the tire, and suddenly they break.   This is what I believe happened to my two tires.   Left unattended, the next step is a blowout.

The Rubber Manufacturers Association says not to use flat patches.   The recommended and best way to patch a tire is with a patch plug, which is a patch that also fills the hole permanently and keeps it dry. Too bad that the last few shops to work on my tires never mentioned this option.

Well.   I am glad that tire inspection vigilance prevented us from having a more serious problem, but on the other hand I wish I’d known about patch plugs before.   A pair of them might have saved us from buying $200 worth of new tires today.   I may begin carrying a patch plug in my spare parts kit, just so I can hand it to a tire shop guy if he doesn’t have one.

The two tires on the right side of the trailer are fine so far.   I don’t recall if either of them has been patched in the past, but they are wearing appropriately at the moment so I’ll just keep an eye on them.   Both of them, by the way, are Goodyear Marathons, and the rear one is actually nearly worn out, which suggests that it is approaching 30,000 miles.   My experience with numerous trailer tires over the years has been that no particular brand holds up any better than the rest, so I buy whatever is available.   At this point we have three different brands rolling on the trailer.

Interestingly, I had been noticing since Grand Rapids that our fuel economy was mysteriously declining.   We normally get 14-15 MPG towing with the diesel, and suddenly we were getting 12.5 – 13.3 MPG.   It seems that the tires were the problem.   Now that we’ve replaced the bad tires, we are back to normal fuel economy.   The broken belts “squirm” as the tire rolls, and in addition to causing rapid tread wear, this apparently increases the rolling resistance as well.

We are in Minneapolis tonight, parked on the street in a quiet neighborhood (with permission of the homeowners and their neighbor).   Local law says we can stay one night if we don’t unhitch, and that is our intent.   We had dinner on the deck with our hosts this evening on this balmy 82-degree September evening, and will be heading to Bloomington for routine car maintenance tomorrow.   Now that we are here, we are done with big-mileage days for a while.