What is rolling resistance?
Projecting a bike at 40km/hr on a flat road requires a power output of between 270 and 350 watts depending on factors like your weight and the weight of your bike. The biggest obstacle to edging nearer 45km/hr is wind resistance because air resistance rises in a squared ratio with increased speed; in short, the faster you go, the greater resistance from air. But up to around 17km/hr, rolling resistance is the dominant obstacle. This is the energy lost when the tyre is rolling, and predominantly derives from energy lost through the constant deformation of the tire.
Tire pressure, diameter, width, construction and tread all impact rolling resistance but, broadly speaking, on a smooth surface, the higher the inflation pressure, the less tyre deformation and lower the rolling resistance.
Tyre width is an important consideration – there has been adrift in popularity from 22/23mm to 25mm+ in recent years
Tire width is an evolving area of bike research. Over the past few years, 25mm versions have grown in popularity – compared to the previously more widespread use of 23mm– thanks to studies showing that, at the same inflation pressure, a wide and narrow tire have the same contact area. In fact, the wider tire could be considered a better choice as it deforms less, maintains its roundness and rolls better.
However, there’s a school of thought that says if you’re searching for all-out speed, narrower 22-23mm tires remain the racing choice. Narrow tires can be inflated higher – up to 160psi on some models – which equals less rolling resistance. This can result in a harsher ride; but how important comfort is to you when your race head is on is a matter of personal choice. The thinner profile also provides less air resistance and they’re easier to accelerate.
Vision Metron 55s are available in clicher and tubular options – here’s a close-up of a neatly-glued tubular
Types of tire
Your choice of tire is also down to the wheel you use. A clincher tire, like you’d use on Vision’s Metron 81 Clincher, is the most common, featuring beading that sits within the rim. This is prevalent because they’re (relatively!) easy to replace if you have a puncture. However, they can’t quite match the inflated pressure of tubulars (up to 160psi), like you might apply to the Vision Metron 55 Tubular, where the tire and inner are one and attach to the wheel via rim tape or glue. Still, with wheel technology evolving, there’s little in it these days between tubulars and clinchers.
Aerodynamic Metron 81s are available in both clincher and tubular variant models
Grip and compound
When it comes to racing, soft, gummy rubber compounds are the order of the day. This reduces weight and rolling resistance, and increases speed, but at the sacrifice of puncture protection. Racing tires often also have less tread as they’re designed primarily for the summer season. They’ll still provide grip but watch out for deep puddles!
Finally, all tires have multiple layers of threads holding things together. Two sheets of unidirectional threads laid across each other at right angles generally counts as one layer. Tire casings are specified in TPI (threads per inch) per sheet. The higher the number, the thinner the threads, since more of them can be crowded together. It’s generally accepted that a higher TPI (100-plus) is faster and more supple; low TPI (less than 100) is slower but more durable. The latter usually have thicker sidewalls, which makes them heavier but more resistant to cuts.
Right, now go and roll your Vision wheels to maximum effect. Happy racing…
If you also ride mountain bikes, check out our MTB tire tips on our FSA sister site.