Ajax Bay
Guru
- Location
- East Devon
Jan Heine (BQ Ed but also Compass Tyres) has written this article: why-slick-tires-dont-stick-well.
Key assumption is that interlocking (ie mechanical) element of grip rubber/road when cornering becomes important, along with the normal adhesion (rubber/road) at the molecular level. Therefore key deduction is that a tyre with small ridges (ie a fine tread) on its shoulders will grip better when leant over. However, unlike the superb work he's done on wider tyres/lower pressures and rolling resistance (taking into account the benefits of better (tyre) suspension on the body), there seems no science behind this; more 'feel'. Rather difficult to test friction thresholds in real life road surfaces. Extract(s) from article:
Shoulders
The tread on the shoulders provides traction when cornering, so it’s of great importance.
The best solution is to provide little ridges that “catch” on the road surface irregularities and thus interlock with the road surface. One advantage compared to the slick race car tires is that the ridges cut through the water when the road is wet, thus providing the interlock even in the rain. On wet roads, the coefficient of friction between road and tire is reduced by more than 50%, so the interlock between tire tread and road surface becomes much more important.
Since the pavement aggregate is random, you want to provide as many interlocking surfaces, oriented in as many directions, as possible. By making the tread as fine as possible, you have a good chance that a rib lines up with the edge of a piece of aggregate in the pavement. That is why small ribs work best.
A criss-crossing pattern of fine ribs maximises interlocking surfaces - standard on high-performance bicycle tires for so many years. In the old days, rubber compounds were much less evolved and provided less friction especially in wet conditions. Without the interlocking ribs, the tires would have been very dangerous in the wet. Modern rubber compounds have improved the coefficient of friction, but interlocking still is important for grip, especially in the wet.
Key assumption is that interlocking (ie mechanical) element of grip rubber/road when cornering becomes important, along with the normal adhesion (rubber/road) at the molecular level. Therefore key deduction is that a tyre with small ridges (ie a fine tread) on its shoulders will grip better when leant over. However, unlike the superb work he's done on wider tyres/lower pressures and rolling resistance (taking into account the benefits of better (tyre) suspension on the body), there seems no science behind this; more 'feel'. Rather difficult to test friction thresholds in real life road surfaces. Extract(s) from article:
Shoulders
The tread on the shoulders provides traction when cornering, so it’s of great importance.
The best solution is to provide little ridges that “catch” on the road surface irregularities and thus interlock with the road surface. One advantage compared to the slick race car tires is that the ridges cut through the water when the road is wet, thus providing the interlock even in the rain. On wet roads, the coefficient of friction between road and tire is reduced by more than 50%, so the interlock between tire tread and road surface becomes much more important.
Since the pavement aggregate is random, you want to provide as many interlocking surfaces, oriented in as many directions, as possible. By making the tread as fine as possible, you have a good chance that a rib lines up with the edge of a piece of aggregate in the pavement. That is why small ribs work best.
A criss-crossing pattern of fine ribs maximises interlocking surfaces - standard on high-performance bicycle tires for so many years. In the old days, rubber compounds were much less evolved and provided less friction especially in wet conditions. Without the interlocking ribs, the tires would have been very dangerous in the wet. Modern rubber compounds have improved the coefficient of friction, but interlocking still is important for grip, especially in the wet.
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