J
Michael Press writes:
>>> Simon Brooke sent three separate statements each requiring
>>> explanation:
>>> 1. Contrary to common opinion, for any given rubber compound, (on
>>> bicycles) slick tyres are better in the wet than tyres with
>>> {patterned} tread.
>>> 2. They also tend to roll slightly better.
>>> 3. Bicycle tyres with {patterned} tread are only beneficial on
>>> soft surfaces, not on tarmac.
>> #s 1 & 3 are obvious on their face.
>> In the case of 1, slick guarantees more contact with the road. Bike
>> tires are too narrow to hydroplane, so there's no need for channels
>> to evacuate water.
>> As for #3, on soft surfaces, the ground deforms in deference to the
>> tire. On hard surfaces, the tire must deform in deference to the
>> road. So a slick tire at pressure low enough to deform (which also
>> increases the contact patch area) but not bottom out provides the
>> best traction.
>> I'll let someone else tackle #2, because I don't fully understand
>> the science of rolling resistance, and won't shame myself by, as
>> the Russians say, talking out my nose on the subject.
> Rolling resistance arises from flexing the tires. The tires are not
> entirely elastic and dissipate as heat some of the energy that went
> into flexing them. Tires flex significantly in the side walls and in
> the tread. If there is a relief pattern in the tread (e.g. knobs),
> additional energy is dissipated flexing the tread. Thin side walls
> and thin tread noticeably reduce rolling resistance.
Even with entirely elastic material, there are hysteretic losses that
dissipate energy (heat) when the material is deformed. The effect can
be felt by stretching a thick rubber band, sensing its temperature by
bringing it contact with one's upper lip to make heating and cooling
apparent.
Jobst Brandt
>>> Simon Brooke sent three separate statements each requiring
>>> explanation:
>>> 1. Contrary to common opinion, for any given rubber compound, (on
>>> bicycles) slick tyres are better in the wet than tyres with
>>> {patterned} tread.
>>> 2. They also tend to roll slightly better.
>>> 3. Bicycle tyres with {patterned} tread are only beneficial on
>>> soft surfaces, not on tarmac.
>> #s 1 & 3 are obvious on their face.
>> In the case of 1, slick guarantees more contact with the road. Bike
>> tires are too narrow to hydroplane, so there's no need for channels
>> to evacuate water.
>> As for #3, on soft surfaces, the ground deforms in deference to the
>> tire. On hard surfaces, the tire must deform in deference to the
>> road. So a slick tire at pressure low enough to deform (which also
>> increases the contact patch area) but not bottom out provides the
>> best traction.
>> I'll let someone else tackle #2, because I don't fully understand
>> the science of rolling resistance, and won't shame myself by, as
>> the Russians say, talking out my nose on the subject.
> Rolling resistance arises from flexing the tires. The tires are not
> entirely elastic and dissipate as heat some of the energy that went
> into flexing them. Tires flex significantly in the side walls and in
> the tread. If there is a relief pattern in the tread (e.g. knobs),
> additional energy is dissipated flexing the tread. Thin side walls
> and thin tread noticeably reduce rolling resistance.
Even with entirely elastic material, there are hysteretic losses that
dissipate energy (heat) when the material is deformed. The effect can
be felt by stretching a thick rubber band, sensing its temperature by
bringing it contact with one's upper lip to make heating and cooling
apparent.
Jobst Brandt
