Yesterday, 11:09 AM
I believe there's oversimplification going on in that explanation of the physics.
Trying to dredge up my A-level physics memories, the concept of Ff=μFn is familiar (I remember the endless calculations of will the object on an inclined plane slide, roll or stay still...), but like many mathematical concepts that we know are true in a 'perfect world' we know are considerably more complex in reality.
Firstly theres static fraction, which I belief the above calculation is for, between two stationary bodies and secondly theres kinetic friction between two bodies sliding over each other. In the case of car tyres things get a lot more complex as the 'grip' we feel as a driver is generated by the slip angle of the tyre and the reactionary forces back through the tyre distortion to the wheel. It's considerably more complicated.
Put your fingertip on the desk in front of you, drag it across the desk with the weight of your hand pushing down, then do the same with your whole hand flat on the desk and tell me the surface area increase didn't make it grip more. Like the tyre your hand deforms and interacts with the table top in a much more complex way the the simple equation suggests.
Back on topic though... Not with an Austin 7 but in my '65 Fiat 500 (similar weight and power to a Ruby I believe?) I've also experienced just how much difference tyre pressure can make on top speed. I'd been experimenting with lower tyre pressures as many folks say it helps make the car less twitchy at speed, which it did, but it was knocking 5-8mph off my top speed. I opted to be able to cruise at 50-55 instead of 45-50 and to live with the twitchiness!
Trying to dredge up my A-level physics memories, the concept of Ff=μFn is familiar (I remember the endless calculations of will the object on an inclined plane slide, roll or stay still...), but like many mathematical concepts that we know are true in a 'perfect world' we know are considerably more complex in reality.
Firstly theres static fraction, which I belief the above calculation is for, between two stationary bodies and secondly theres kinetic friction between two bodies sliding over each other. In the case of car tyres things get a lot more complex as the 'grip' we feel as a driver is generated by the slip angle of the tyre and the reactionary forces back through the tyre distortion to the wheel. It's considerably more complicated.
Put your fingertip on the desk in front of you, drag it across the desk with the weight of your hand pushing down, then do the same with your whole hand flat on the desk and tell me the surface area increase didn't make it grip more. Like the tyre your hand deforms and interacts with the table top in a much more complex way the the simple equation suggests.
Back on topic though... Not with an Austin 7 but in my '65 Fiat 500 (similar weight and power to a Ruby I believe?) I've also experienced just how much difference tyre pressure can make on top speed. I'd been experimenting with lower tyre pressures as many folks say it helps make the car less twitchy at speed, which it did, but it was knocking 5-8mph off my top speed. I opted to be able to cruise at 50-55 instead of 45-50 and to live with the twitchiness!