Monday, July 06, 2020

"My brakes were squeaking, so I sprayed oil in the calipers..."

Yes, it really happened. I didn't do the check in, but David told me about it.

"I think I made it worse," the customer concluded.

Gee, do ya think? So there's a set of pads headed for the trash.

The next day a customer bought three of the last four adult size bikes we had, and not cheap ones, either: two Specialized fat bikes and a gravel bike. She also asked if we could fix a flat front tire on a 650B mountain bike they already had. It had blown out when they were inflating the tires. This happens for various reasons, especially if the tire had been very low and the beads had come loose. The rider enthusiastically pumps it up and the beads fail to catch the rim because the tube is already sneaking out underneath the edge of the tire. Or the whole rig might be old enough that the tube has rotted out. We couldn't know for sure until we saw it.

The tire was off the rim in the classic explosive blowout position. The customer had left to transport two bikes home. She was due to return in an hour or so for the third new bike, and for the repaired bike if I could have it ready. I dug into it.

The blowout had damaged the bead of the tire, so I had to replace the casing as well as the tube. The blown-out section of tube was about 16 inches long, indicating considerable force. It had actually deformed a section of the rim. The side of the rim flared where the blast had originated.

I have reshaped damaged rims in the past using blocks of wood, and the vise, and large hammers, but that was usually when the rim was bent inward by an impact. Going the other way was going to be trickier. I needed the perfect block. A cut-off end of an adult-size wooden hockey stick turned out to fit. I put it into the rim channel and wrapped some cardboard from a parts box around the outside. Squeezing this sandwich in the vice coaxed the rim back to be usably near  parallel. I had to reposition it and repeat the squeeze a couple or three times, but that's what happens when you're using rectangular things to reshape something round.

When the customer arrived we reported on our findings. She told us that she had read that the tires take 90 psi. It was a classic case of too much information. The psi rating was written smaller than the load rating, so she saw 90kg and misread it as 90 psi, when the maximum pressure was actually supposed to be 50 psi. Many bike tires don't even have the load rating molded onto them.

"Did you put 90 in the rear, too?" I asked.

"Yes," she answered. Torin and I leaped simultaneously to disarm that bomb.

The customer is a triathlete, who is used to putting very high pressures in her skinny road tires, and hadn't bothered to think critically about volume and intended use. She just looked for a number and tried to follow instructions. Torin repeated several times that the fat bike tires would be rock hard and maxed out at 20 psi. "Keep them between 7 and 12," he told her.

1 comment:

Rob in VA said...

I want to be in the vicinity, but at a safe distance, with my cellphone's video recorder running, when they see "120tpi" on the sidewall of their fatbike tire and misinterpret that figure as psi. Could go viral on youtube.