The MGA With An Attitude

At 12:55 AM 11/30/05, Greg Smith wrote:
>"I have spoke wheels on my GT. Why can't I install tubes in tubeless tires??"

Well, you can in a pinch, but you need to be careful about a few things. In general, tubeless tires do not need tubes, and you do yourself a dis-service by using tubes with tubeless tires. Tubes reduce the flexibility of tubeless tires, thereby increasing rolling resistance. This then consumes a bit more energy to make it go, which will consume a bit more fuel. The worse part is that this extra energy is turned into heat in the tire, and tires don't like extra internal heat. This could shorten the life of the tire rather dramatically if you run it anywhere near it's maximum load or speed rating.

As a rule of thumb, if you put tubes in tubeless tires you should de-rate the tire by one letter grade, or about 18 mph (30 kph) off of the rated 10-minute top speed. If you're talking about installing an "H" rated tire (130 mph) on your MG, you hardly have much to worry about if it gets de-rated by 18 mph to 112 mph 10-minute top speed capability.

>"I was informed by the "technician" at a local Sears store ...."

Translation: Someone trained to operate tire mounting and balancing equipment, and to look up standard tire size for your car in the data base. A Sears "technician" may know considerably less than you do about tires.

>"that I can not use tubes with tubeless tires due to the inability of the tube to fully inflate and support the more rigid design of the tubeless tire."

Ha, ha, ha, ha, ha, ha, ha, ha, .... Excuse me while I get up off the floor.

Tubeless tires have softer and more flexible sidewalls than tube-type tires (except for some very serious low profile autocross tires with steel reinforced sidewalls). Modern radials tend to squat under load and make the sidewalls bulge out a bit, This puts a larger footprint on the road, and the softer sidewall reduces rolling resistance, reduces heating, and improves fuel economy. When you install a tube in a tubeless tire you sort of defeat the advantages of the flexible sidewall, and the car will ride stiffer (more harsh on bumps).

>"As a consequence, the tire could possibly come off the rim while driving."

What a dope. The only thing you can do that would ever make a tire come off a rim is to run it with VERY low air pressure, like less than 10 psi. Read this article about the difference between J-type wheels and safety rims. I have been running tubeless tires on standard "J" pattern rims for more than 40 years. Nobody drives an MGA harder than I do, and I have never had a tire break loose from a rim.

The safety rim is designed for the idiot drivers who refuse to ever check tire pressure as long as the tire is still rolling in one piece. For the bloke who insists on running it at highway speed with 5 psi until the tire will self destruct, there may be some advantage to using a safety rim.

For dead serious off-road or non-paved road race and rally competitors, a tube may provide a small improvement in leak resistance in case they get some dirt crammed in between the rim and the tire bead. I have personally put 230,000 miles on my current MGA, at least 10% of that on gravel roads (or worse), and never had any problem with tubeless tires on J rims.

>"He went on to say that the tube tires were more "flexible" in order for the tube to fill and support the tire completely."

That's the flip side of the same idiotic un-truth. It's a lie, but the guy probably doesn't even know it.

>"I've never heard of this since I've had tubes in my tubeless tires for the last 20 years without a problem! Are these guys for real?"


>"Or did I just learn a new lesson!?"

Yup. If it sounds too stupid to be true, it probably is.

One serious note about use of tubes in general. Oversize inner tubes are a definite no-no, as any fold or wrinkle in the tube is almost guaranteed to split the tube. When installing inner tubes, inflate and deflate the tire a couple of times to allow the tube to settle in to a comfortable position without wrinkles or excessive stretching.

On using tubes in tubeless tires, older tube type tires were nearly as smooth as a baby's bottom inside. Modern tubeless tires are not designed to have tubes, so there is very little attention paid to manufacturing them with a smooth interior. As such, you may expect to find a lot of raised molding marks on the inside, like a rectangular grid of small ridges. Tubes tend to squirm around inside of tires as they flex under load. The little rubber ridges inside the tubeless tire can eventually abrade the tube to cause stress cracks and pressure failure. If you will be using a tube, you would be well advised to run a power sander all around the inside of the tubeless tire to remove the molding flash and leave the inner surface as smooth as possible. And NEVER leave any manufacturer's stickers inside the tire if you will be using tubes.

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