Bicycle Mechanics - Measuring thickness of tire

On an Armadillo or even a regular tire, is there a way to measure the thickness of the remaining kevelar/rubber to determine how much longer a tire will last? On the main surface area, how many mm's is considered unreliable?

A caliper would work great for measuring the thickness. You would probably need to be fairly careful in your method to keep the measurements consistent due to the squishiness of the rubber.

http://demo1.physics.wisc.edu/MDemos/Pics/B1p2.gif

As for what is reliable or unreliable, you can literally ride bike tires all the way to failure. Once you are all the way through the rubber and onto the cording or canvas underneath (the last thing before the inner tube), it's probably a pretty good idea to retire the tire (no pun intended). Contrary to what some people will tell you, the rubber in a bike tire has nothing to do with it's blowout strength. The rubber merely exists to get a nice grip on the pavement, whereas the actual strength to contain the inner tube comes 100% from the fabric or cording underneath the rubber.

The best indication of when a tire has surpassed it's useful life (so I'm told) is when you begin to get flats in that tire on a weekly basis, meaning that the rubber layer has gotten thin enough that smaller and smaller bits of debris are enough to puncture the tube. Basically, once it slowly starts getting flats more frequently than you'd care to repair, try a new tire.

I usually start replacing tires when I get inordinate amount of flats in one week.

+1 to what these guys said. Unless you've got dry rot, you should be able to ride until you see cord, or until you get 4 flats in 5 rides on that wheel, and realize something is very, very wrong.

+1 to what these guys said. Unless you've got dry rot, you should be able to ride until you see cord, or until you get 4 flats in 5 rides on that wheel, and realize something is very, very wrong.

I've never seen a cord...even when encountering a slice that exposes the tube. Also I'd rather be pro-active and change the tire before running into the tire changing marathon. It's no fun changing tires in the rain with cars wizz'n by.

The Caliper idea sounds good. Do auto parts stores sell those?

The Caliper idea sounds good. Do auto parts stores sell those?

What MacG showed was a micrometer. I don't believe they're available in most auto parts stores. Totally unnecessary for determining tire wear anyway though.

Car tires have wear indicators moulded in to the thread pattern, because that shows the minimum tread you need to prvent aquaplaning. Aquaplaning doesnt happen with bike tires, because of the narrow contact patch, so go on using the tire until you can see some fabric threads of the carcass.

i usually repalced tires when i feel that the tire is shot. ie. i can see the tire cord and/or i am getting too many flats.

I agree that seeing the cords is the indicator.

You could find out the thickness of rubber from the manufacturer, measure the new tire, then replace when it is at (new thickness - 1mm). But I think you will find that tires are not manufacured to extremely tight tolerances and/ or they don't wear evenly. When I see cords on mine, it is usually in a small patch or two. Not evenly around the whole tire. So you would have to take measurements all around the tire.

Or, instead of buying a micrometer, taking your tire off once a week, and taking a dozen measurements, you could just look at occaisionally.