Tuesday, August 28, 2007

Q&A: Road tires and tubes: wear and pressure

Hi Jim:
When is a good time to change bike tires? Should we change tube when we change tires? I am preparing my bike for an Ironman and thinking of changing tires that can be pressurized to 140 pounds (up from 120). Should I change my tubes also?


You replace tires when they're worn out and they're worn out when the tread is gone or the sidewalls start failing. When that happens they look cracked and weak from age and sun and weather. It's best to check the tires when they're new so you can tell when the tread starts to wear away. For most road tires the tread lasts about 1,500 miles on rear tires and at least twice that on fronts, but it depends on how you ride, how heavy you are and the roads you ride on. A sign that a tire is worn is having frequent flats on an old tire. That tells you that the tread is getting too thin to protect the tube. Tread with lots of cuts in it is also a sign of excessive wear.

Tubes don't wear like tires. They will last indefinitely because they are protected inside the tire. There's no reason to change them unless you get a lot of flats and even then a tube with several patches will still keep working fine. I never change tubes unless the valve fails or the tube starts to fail at the seam.

Now, on changing tires for higher pressure tires, there's really no reason to do that. All the testing I've seen indicates that lower pressure provides lower rolling resistance (more speed) and a better ride. You should actually ride tires pumped to about 95 to no more than 110 pounds for most riders between 160 to 200 pounds. If you over inflate the tires up to 140 you end up with a tire that's so hard it bounces over even slightly rough pavement. This bouncing slows you down and makes for a rough uncomfortable ride, just what you don't want on a long tough event like an Ironman triathlon. So, I'd strongly recommend going with a nice, flat-resistant tire like the Continental Grand Prix 4000 and inflating it to a modest 95psi or slightly more if you're 185 pounds or more. I weigh 165 to 180 pounds and ride on 100psi in back and 95 in the front. If I was 200 pounds, I'd bump it to 110psi, but I'd never go anywhere near 140. That'll only slow you down and make you miserable at the end of the bike leg from the beating you'll take.

Hope this helps,

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