Bicycle Tire Optimized for Electric Assistance

Abstract

A tire (1) for an electrically assisted bicycle or wheelchair having tire a crown reinforcement, which is radially on the inside of a tread, with the tread being connected to two beads via two sidewalls. The tire has, on at least one of the sidewalls (3) and protruding from the sidewall, a strip (4) of a rubber compound with an axial thickness (ep) that is at least equal to 1 mm and at most equal to 4 mm, at least equal to 10 mm and at most equal to 30 mm. The rubber compound has a Shore A hardness of between 55 and 75, and a glass transition temperature of between ?15? C. and 0? C. The compound forms a smooth outer surface (5) that is intended to come into contact with a drive roller bearing a plurality of indenting elements.

Claims

1. A tire intended to be fitted to an electrically assisted bicycle or wheelchair, the tire comprising: a crown reinforcement, which is radially on the inside of a tread, said tread being connected to two beads via two sidewalls, wherein the tire comprises, on at least one of the sidewalls and protruding from the sidewall, a strip of a rubber compound with an axial thickness (ep), perpendicular to the sidewall, that is at least equal to 1 mm and at most equal to 4 mm, and with a radial height (Hr), perpendicular to the axis of revolution of the tire, that is at least equal to 10 mm and at most equal to 30 mm, in that said rubber compound of the strip has a Shore A hardness of between 55 and 75, and a glass transition temperature of between ?15? C. and ?0? C., and in that said rubber compound of the strip forms a smooth outer surface that is intended to come into contact with a drive roller bearing a plurality of indenting elements.

2. A lightweight vehicle, such as a bicycle, tricycle or wheelchair, comprising a tire according to claim 1, wherein a metal roller drives at least one tire of the vehicle by rotational contact with the strip of rubber compound arranged on the sidewall of said tire.

Description

[0021] The features of the invention are illustrated by FIG. 1, which is schematic and not drawn to scale.

[0022] The invention also comprises a lightweight vehicle such as a bicycle, tricycle or wheelchair comprising a tire as described previously, wherein a metal roller drives at least one such tire of the vehicle by rotational contact with the strip of rubber compound arranged on the sidewall of said tire, this tire being specifically designed for these applications in order to improve the longevity and the driving precision thereof in all weather conditions.

[0023] FIG. 1 shows a meridian cross section of a bicycle tire 1 having a carcass layer 2, sidewalls 3 and, arranged so as to protrude from one of the sidewalls 3, a strip 4 of rubber compound having a smooth surface 5 that can come into contact with a drive roller equipped with indenting elements. The height Hr of the strip is between 10 and 30 mm and its thickness ep is between 1 and 4 mm.

[0024] The development of the invention required tests in order to determine the rubber compound most capable of transmitting force without deteriorating over time. Several machine tests were carried out: [0025] A grip test in wet conditions: a bicycle wheel equipped with a dynamometer is driven by a motor equipped with the drive roller being tested. A smooth strip of the rubber compound being tested is adhesively bonded to the sidewall of the tire. The test is carried out with water being sprayed. Solutions that do not allow a torque of 20 Nm to be transmitted are eliminated. [0026] .Math.A 5000 km wear test is carried out on the same test bed but without water being sprayed. Solutions exhibiting wear are discarded.

[0027] For the contact strip of rubber compound adhesively bonded to the sidewall of the tire, 25 rubber compounds were tested. Their Shore A hardnesses were between 50 and 80, this parameter being linked to their stiffnesses, and their glass transition temperatures, this parameter being linked to grip, were between ?90? C. and ?10? C. The 3 satisfactory solutions for the two tests all have a Shore A hardness of between 55 and 75, and the glass transition temperature thereof, at which the dynamic loss tan ? is at a maximum, is between ?15? C. and ?0? C.

[0028] Experience has shown, for example, that the rubber compounds of bicycle tire treads, the glass transition temperatures of which are extremely low, usually between ?50? C. and ?60? C., do not allow the invention to work. This is because these compounds are designed to provide grip, at a high pressure of between 8 and 15 bar, on asphalt or bare ground and are not designed to be driven by a metal roller equipped with indenting elements that stress the compound at a different frequency to the intended usage of said compound. These compounds were quickly destroyed by the roller.

[0029] One solution, with a tire as described in the invention combined with a contact strip made of rubber compound having a Shore hardness equal to 63 and a glass transition temperature equal to ?5? C., successfully completed the selection tests.

[0030] A validation test on an electrically assisted bicycle in urban usage over 1500 km allowed the chosen solution to be validated in actual usage conditions.

[0031] The invention offers a solution to the problem while maintaining excellent handling in wet conditions since the indenting elements break through the film of water at the surface in contact with the tire. The flexibility of contact between the roller and the tire allows extremely simple positioning of one on the other. After 1500 km of urban usage, the rubber strip adhesively bonded to the sidewall of the tire exhibits no sign of wear.

[0032] The invention therefore successfully provides a solution that is simple to install, provides excellent grip in wet conditions and is beneficial in terms of wear and therefore durable.