Random Thoughts on Rubber Tires

by Grant Petersen

The concept of rolling down the road on a cushion of air is what Dunlop-the-Scottish-veterinarian had in mind when he invented the pneumatic tire for his young son, a century or so ago. Over the years, part of the concept has been lost, as riders ride the skinniest, hardest tires their bodies can stand. It's not pure idiocy by any means. Road surfaces have improved, after all; but even on smoothish modern roads there are advantages to riding on 700x28s and 700x32s. Such as:

• More comfort. The more volume, the lower pressure you need. So, when you hit a bump, the bump compresses the tire and isolates you from most of the blow. It's the oldest, cheapest, lightest, lowest maintenance, most fine-tunable type of suspension you can ride.
• Longer lasting wheels. Puffier tires run at lower pressure protect rims and spokes from fatigue-inducing flexes and cornering loads. Fewer pinch flats. That's when you hit a bump and it pinches the tube between it and the rim. More tire pressure will prevent it, but if you have to load up your tires with 130 psi just to prevent pinch flats (and with skinny tires, you do), then you're doing it the hard way. A 700x28 with 100 psi, or a700x32 tire with 85 or 90, will do the job better and give you all those other benefits of volume.

Do wider tires have more rolling resistance? Yes, but it's mostly the lower pressure that does it, not the size, and it's the lower pressure that gives you all the benefits, too. Besides, the difference in rolling resistance between a hard skinny and a slightly puffier tires is infinitessimal. Fitness, body weight, and wind resistance each matter ten times more. In a group, if you're in the same shape as other riders, it's easy to ride the group's pace no matter what you're on, because you're drafting so much of the time.

Finally, on rough roads, you go faster on a softer tire. When the wheel hits a rock or a bump, the fatter, softer tire will deform and roll right over it, while the hard tire bounces and jars you. Are fatter tires heavier? It might seem so, but trust a scale more than your intuition. An Avocet 700 x 32 Fasgrip tire weighs 300 to 315g. There are fancy 700 x 25s that weigh more than that. The Avocet 700 x 28 foldable weighs between 230g and 250g; and there are fancy 700 x 19s that weigh more.

Two-colored, dual-compound treads are popular and an easy sale. The harder compound in the center increases wear, while the soft and colorful rubber on the sides grips the road with eraser-like friction. It's such a tidy package and an easy to grasp concept. I've been riding a bike as a racer, tourist, and athletic recreational rider for 30 years, and the only times my tires have actually slipped around turns have been on gravel, water, road paint, manhole covers, or oil. The crashes have always been caused by bad luck, bad planning, or bad technique, and I'm skeptical how much difference a softer rubber would have made. On gravel, oil, paint, and manhole covers, surely none. Maybe on a wet road, but even then, I'm skeptical. When it's wet out, that's no time to set another PR for lean angle.

Dry surfaces are another story. I've read lean angle charts comparing different brands and rubber compounds, but I've yet to reach the traction limit on a single-compound tire while leaning into a turn, and I've never seen or heard of anybody doing that. Not even fourth hand! It may be possible that one tire grips at 28-degrees, and another maxes out at 31-degrees, but I start to freak out at 45-degrees, and even old-fashioned crummy tires grip at that.

Grant Petersen is a California-based member of PPTC and founder of Rivendell Bicycle Works. Visit Rivendell Bicycles Works at www.rivendellbicycles.com