Whenever we get the chance to ride an older bike here at SSB, the first thing we try to do is put some new tires on it. One of the areas of bike technology that has moved the farthest is the black, round, rubber parts that stick you to the ground.
Look back just fifteen years to a bike like the Yamaha FZR1000-a 130 hp sportbike with adjustable suspension, twin-spar aluminum frame, and more than enough performance for a fun ride even by today's standards. But if you tried to take one lap of your favorite track or canyon road on the original tires, you'd very quickly end up picking your nice classic superbike out of the dirt. Even sporty rubber from the past offered barely adequate grip in the dry compared with today's offerings. On track, there was often little warning before rear tires lost grip and flipped you over the highside. And, if you were unlucky enough to get caught out in the wet, then you were smart to park the bike and get the bus home. Similarly, the more basic roadster rubber fitted to sport-tourers and naked bikes was hard, unyielding, slow to warm-up, and as bad as the sportier tires when rain began to fall.
A lining machine lays down...
A lining machine lays down strips of rubber to form the tire carcass.
In comparison with those bad old days, it's almost impossible to buy a bad tire today. Even the base-level roadster rubber that comes on the most unassuming motorcycles like Monsters and FZ6s offers ample grip in wet or dry conditions, predictable handling, and excellent mileage. If you move up a level to a sport-touring tire like the Dunlop Roadsmart or Bridgestone BT-021, you get even more impressive performance in terms of grip. Click up another notch to a premium sport tire like a Bridgestone BT-016 or a Michelin Pilot Power 2, and you have a tire which could match a world-championship level tire of a decade ago. And by the time you get to the ultimate road-legal trackday tires such as the Pirelli SuperCorsa, Michelin Pilot Power Race and Bridgestone BT-003, you have rubber that is almost impossible to crash on, at least not due to a lack of grip.
But how have things changed so dramatically? Why is it that our engines have only put out an extra 20-30 percent peak power (compare 1989's 135 hp FZR1000 with the 160-odd hp R1 of 2009), yet tires have gone from barely-capable slip `n sliders to super-sticky marvels of engineering? There are several areas where tire construction has improved: the compound of the `rubber' used in the tire, the structure of the `carcass' that makes up the main body of the tire, and also the manufacturing techniques used to build the tires themselves.
Compounds
First off, the `rubber' used in your tires isn't just the stuff that grows on trees. It is in fact a complex blend of up to 200 chemicals, including natural and synthetic rubbers, carbon black as a filler, and a long list of other ingredients, like sulfur to vulcanize (harden) the rubber and anti-oxidants and additives to prevent damage from UV light.
The drum heater sets the rubber...
The drum heater sets the rubber in shape.
One of the most important ingredients, especially in terms of wet grip, is silica. This wonder ingredient is a filler, like carbon black, but it also improves the way the tire holds onto a wet road surface and is a large part of the improvement in wet weather performance.
Multiple Compounds
One clever way of getting more performance and mileage from a tire is to use multiple compounds in the tread. The idea is that the center of the tire doesn't need as much grip as the sides since the bike is upright when the contact patch is in the middle. On the other hand, the shoulder of the tire needs more grip, since this is where the contact patch is during hard cornering. So if you can use a harder compound in the middle of the tire and a softer compound on the edges, then you get increased mileage as well as amazing cornering grip.
Bridgestone was the first company to use this construction technique with its Battlax BT-50 tires of the early 1990s, and the firm now uses a `5LC' five-layer compound on its rear BT-016 sport tires. These have a hard cenrer compound strip with two increasingly grippier strips of compound on each side.
Carcass
The most important change came when Michelin developed the first radial ply tire in the mid 1980s. In this design, the threads of cotton (or polyester or rayon) that hold the rubber in the tire together are arranged in a radial layout-that's to say they run directly from one bead to the other, at 90 degrees to the direction the tire spins. This gives a lighter construction than crossply tires, and a lighter tire runs cooler. This, in turn, lets the designer use a softer compound for the same level of mileage. Older tires used `crossply' construction, where the threads are arranged at an angle across the tire tread. This makes for a heavier, thicker carcass that generates more heat, wears quicker, and requires a harder tread compound.
 Plies are laid down lengthwise...  Plies are laid down lengthwise across the tire for sidewall strength and stability. |  Steel belts are stripped on...  Steel belts are stripped on before the final rubber layer and help reinforce tire strength. |  |