The Case of the Leaky Tires
It was a sunny, breezy day as Dabney drove his 1965 Sunbeam Tiger up to The Doctor's garage. Needless to say, Dabney was quite surprised when he saw Doc standing alongside his garage flying a rather unique looking kite. The kite was made of three wings and somewhat resembled a Fokker DR1 Triplane (of Red Baron fame), but without the fuselage.
Dabney got out of his car and walked over to The Doctor.
"Hey Doc, whatcha doin'? said Dabney still somewhat amused by the sight.
"I just thought I'd try out this new design I came up with for a kite. As you can see, the kite is made up of three wings. By pulling this second string I can control the angle of the middle wing against the wind and make the kite go up or down. As he was speaking, Doc pulled the second string, and sure enough the kite dipped, then as he let up, it started to rise again."
"By the way, Dabney, do you know what makes a wing fly. It's called the Bernoulli Effect and it's actually the same principle that makes your carburetor work."
Dabney was beginning to regret that he had come over. Not only was Doc winding up to get into his lecture mode, Dabney truly was not very interested in kites or wings or anything else that didn't remain firmly planted on the ground.
"I'd really like to stay and hear about it, Doc. But I got to get back to my garage to see if I can figure out why the tires on my Sumbeam keep leaking air."
The Doctor frowned a bit as he realized he'd just lost his audience.
"Ok, I'll tell you what. Let me reel this baby in and I'll ride into town with you. I got some errands to run and maybe I can help with your tire problem."
Doc reeled the kite in and put it in his garage and Dabney fired up the Sunbeam.
As they were going down the road, Doc said "So what's with the tires. I thought I just saw you putting air in them just a few days ago."
"Well, it was actually a couple weeks ago, Doc, but this car loses air in its tires pretty regularly," said Dabney. "I've taken off the wheels a couple times and re-seated the tire beads, but they still leak. Putting soapy water on the valve stems doesn't show any bubbles, so I suspect the tires themselves aren't up to snuff."
"But I can't believe the tires themselves would be so porous. The American Racing mag wheels look great. Where'd you get them?"
"Oh, I found them a few months after I got the Sunbeam," said Dabney. "You might recall that the Tigers came with disc wheels from the factory, but dealers often upgraded them with either the Shelby wheels or these chromed American Racing mags. I always liked the look of these things and found a set on an auction site on the internet. They're in perfect condition, except for this leaking problem."
They pulled into Dabney's garage. Doc got out and Dabney pulled the car onto the lift. As Dabney raised the car the Doc was silent. He appeared to be mulling over something in his brain, but he wasn't talking about it.
Let me pull off one of the tires while you're here and we can take a look at the inside of the wheel," said Dabney. As he did so the Doctor walked around the car to admire its striking resemblance to the 1955-57 Thunderbirds, remembering the story of how much Geoffrey Rootes (the Sunbeam's creator) liked the design.
Once the tire was removed from the wheel Dabney and the Doctor examined the inner surface. As Dabney had described, the wheel was in very nice condition and the chrome plating quite good. However, there were some surface cracks inside, as well as a little pitting of the chrome plating.
"I think the tires can't seal properly against the smooth chrome," said Dabney. "Maybe we can coat the inner part of the wheel with some rubberized compound. What do you think, Doc?"
"I think it's a waste of time," replied Dr. Crankshaft. "You're chasing the wrong problem. You need to learn a little something about chrome plating. It's obvious to me that the air is leaking out under the chrome!"
"What?" asked Dabney. "How could that be? The chrome is in great shape."
"That doesn't mean squat!" said the Doctor. "Chrome that looks good doesn't necessarily indicate that it is adhering to the metal all that well. Ya'see, chrome is plated by electrolysis. The chrome itself is in solution with an acid and electricity is passed through the tank. The wheel, in this case, is the electrical cathode and chrome molecules bond to it, eventually building up a thin surface of the metal. That surface is what plates the metal being chromed."
"I'm familiar with that, Doc, but what are you driving at?" said Dabney, thinking to himself that at least the lecture wasn't about kites.
"What I'm driving at is that the chrome is electrically attached to the base metal, not metallurgically attached. Over time the molecular bond deteriorates and the chrome can start flaking and peeling off. Corrosion takes place on the surface of the underlying metal and the chrome doesn't bond anymore. Those surface cracks and pitting indicate the chrome is lifting off the wheel's inner surface and air just migrates under it and out to 'freedom'," said the Doctor.
"You mean I'm going to have to spend the money to have these wheels re-chromed?" asked Dabney.
"Either that, or you can put in some inner tubes," replied the Doctor. "They used to do that with all tires awhile back, you know and it worked fine."
"I'm done here, I think I'll go do my errands, Doc added.
"Thanks, Doc," said Dabney. "And after you're finished with your errands, why don't you go fly a kite!" Dabney winked at Doc.
"I just might do that, Dabney," the Doc chuckled to himself.