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Saturday, July 11, 2020

Doug's Domain

Doug Vetter, ATP/CFI

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Wednesday, October 14, 2009

How NOT to Fix a Flat

As you may recall, back in June I suffered a flat tire and had it repaired. Unfortunately, during my routine tire pressure check last Sunday, I found the very same tire down to 24 PSI. I carefully surveyed the tire and found no obvious damage so I quickly concluded that the patch was leaking.

Given that I hadn't checked pressures in a few weeks I figured it was a slow leak and I could save myself the trouble of an "in the field" tire swap and wait until after I installed the winter tires in a few weeks to bring the tire to the shop for repair. I pumped the tire up a few pounds over the norm for good measure, resolved to check it regularly and get on with my life. When I arrived at work the next morning I looked back at the car and quickly noticed a conspicuous bulge in the sidewall. I let out a choice word and then took a pressure reading of 19 PSI, or a drop of almost 20 PSI overnight. I didn't have a means to pump the tire up in the field so I resolved to swap the tire with the spare over lunch.

This morning I took the flat back to the same company that "fixed" it last time. The guy I spoke to took a defensive posture and attempted to convince me that they did not, in fact, fix the tire last time. After I told him I don't make a habit of going around to tire shops and requesting free services he relented, but only long enough to suggest that it might be due to the valve stem. I acknowledged that might be a possibility but suggested he dunk the tire in the tank so we could both stop guessing. He rolled the tire away only to come back a couple minutes later and admit that the patch was leaking. I asked him to fix it properly this time by dismounting the tire, applying a patch from the inside of the tire, and then remounting & balancing the tire on the road force balancing equipment. He agreed to have it done later in the morning and I left for work.

At this point you might be thinking, how does a plug patch leak? Well, this wasn't a plug patch. More precisely this was what they call in the industry a "gummy string" which is the easiest / quickest repair technique available because it doesn't require dismounting the tire. This explains why they charged me "only" $10. Some research online suggested that gummy strings work in general but the failure rate is high enough to question their use, particularly on a high performance car where a sudden loss of pressure or blowout in a high speed turn could very easily result in loss of the vehicle.

Later in the day I went back to pick up the repaired tire and figured the worst of the day was behind me. Wrong. As I picked up the tire to put it in the trunk I realized the the tire machine retainer clamp had gouged a circular scratch through the clear and into the base coat of the wheel a few inches from the hub. I'll spare you the details of the verbal exchange that followed, but it suffices to say that I have no intentions of doing further business with this facility.

So what have I learned? Plenty.

Mileage: 183525