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Discussion
I've been worrying about the idea that wider tyres don't have more grip.
Lighter cars stop more quickly than heavier ones, because the tyre efficiency is higher at lower loads (ie the available force per unit load falls off with load). And load is proportional to mass, so lighter cars have greater deceleration.
If this is the case, then a wider tyre, with lower load, must also have greater efficiency. (Imagine two lighter cars joined by a bit of string -- they stop quicker than one car twice as heavy, and only have more contact area / disc area)
Of course a wider tyre is a heavier rotating mass, the rotational kinteic energy of which needs dissipating as well as its longitudinal kinetic energy.
Help - am I spouting bollox again?
Lighter cars stop more quickly than heavier ones, because the tyre efficiency is higher at lower loads (ie the available force per unit load falls off with load). And load is proportional to mass, so lighter cars have greater deceleration.
If this is the case, then a wider tyre, with lower load, must also have greater efficiency. (Imagine two lighter cars joined by a bit of string -- they stop quicker than one car twice as heavy, and only have more contact area / disc area)
Of course a wider tyre is a heavier rotating mass, the rotational kinteic energy of which needs dissipating as well as its longitudinal kinetic energy.
Help - am I spouting bollox again?
Wider tyres do have more grip...increased contact patch means more adhesive grip and although you have a lower ground contact pressure you have more area for mechanical locking so it tends to cancel out.
That said the increase in grip is somewhat less than huge so if you expect to be Michael Schumacher by fitting 345/35ZR19 tyres to a Vauxhall Nova - you won't (not that it stops some people local to me from trying!)
That said the increase in grip is somewhat less than huge so if you expect to be Michael Schumacher by fitting 345/35ZR19 tyres to a Vauxhall Nova - you won't (not that it stops some people local to me from trying!)
7db said:
Why's that, Pigeon?
This might be of interest?
""If you could look between the tire and road you would see that there are
gaps between the road and tire due to the roughness of both tire and road
so within the area of contact not all parts of the tire are actual points
of contact with the road. Narrow tires provide less opportunity for there
to be contact points but because the weight of the car is distributed over
a smaller region there is greater pressure on the road under the tire
which helps to create more contact points per unit area than with a wider
tire. Conversely wider tires provide more opportunity for there to be
contact points but because the weight of the car is distributed over a
larger region there is less pressure on the road under the tires so there
are fewer contact points per unit area than with a narrower tire. As a
result the number of contact points, hence traction, remains about the
same. Now if there were a way to increase the contact points by
increasing the pressure of the car tire on the ground or by increasing the
contact points without regard to the pressure or area then one would have
more traction.""
BOF.
7db said:
Excessively wide tyres are likely to be detrimental in the wet.
Why's that, Pigeon?
My understanding is that the wider tyre has to clear more water out of the way and has a greater distance to move it to get it out of the way, but has less pressure on the contact patch to do this, so it is better lubricated, and also will reach the point of aquaplaning sooner.
I'm expecting the answer to be on the changed ratio of chemical friction and mechanical locking.
That is to say tires get grip from two places:- chemical bonding between rubber and tarmac, and mechanical locking between the rough rubber and the rough road. It might be that the mechanical locking depends on pressure, and the chemical friction depends on area, so they vary against each other as the tire width increases -- with wider tyres depending more on chemical bonding than mechanical locking.
However, as things become wet (and tire width is held constant), the chemical friction decreases, whilst the mechanical locking remains roughly constant, so wider tires lose grip more than thinner tyres in the wet.
That is to say tires get grip from two places:- chemical bonding between rubber and tarmac, and mechanical locking between the rough rubber and the rough road. It might be that the mechanical locking depends on pressure, and the chemical friction depends on area, so they vary against each other as the tire width increases -- with wider tyres depending more on chemical bonding than mechanical locking.
However, as things become wet (and tire width is held constant), the chemical friction decreases, whilst the mechanical locking remains roughly constant, so wider tires lose grip more than thinner tyres in the wet.
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