Braking - interesting article

[slofox]

I dunno if this is a re-post (you can always ignore it if you've seen it before) but it makes for an interesting read - if you can wade through the physics.

I stumbled on it when I was looking up tyre stuff. The bit that intrigued me was the section "Can you brake faster than cars?"


Linky HERE (http://www.stevemunden.com/braking.html#carvsbike)

[Ocean1]

Good sumary, cheers dude.

[p.dath]

The maths in the two articles of his I read are fatally flawed and indicate a fundamental mis-understanding of friction and rubber. I would not rely on any information by this person on this subject. They have basically tried to apply simple high school physics to the problem

Specifically, the biggest mistake is trying to apply Coulombs and Amonton's laws of friction to rubber. This work was exclusively done based on solid non-flexible surfaces, such as steel.

It has been proven again and again (by the likes of world renowned tyre experts like Pacejka and Robert Smith) that the laws of Coulomb and Amonton don't apply.

More specifically, friction is not constant either laterally or longitudinaly in tyres. And this is primarily because tyres deform under load - which they must if you want to have any kind of decent handling.

If you are interested in this could I recommend "Analyzing Friction in the design of rubber products and their parted surfaces" by Robert Horigan Smith, or if you like some hard core maths, try "Tire and Vehicle Dyanmics" by Hans B Pacejka.


Smith's book also has an interesting section on the application of these laws by some law enforcement agencies around the world who still try and use Coloumb's and Amonton's laws to determine vehicle speeds from skids - and shows how these methods can give incorrect results.

[slofox]

The maths in the two articles of his I read are fatally flawed and indicate a fundamental mis-understanding of friction and rubber. I would not rely on any information by this person on this subject. They have basically tried to apply simple high school physics to the problem

Specifically, the biggest mistake is trying to apply Coulombs and Amonton's laws of friction to rubber. This work was exclusively done based on solid non-flexible surfaces, such as steel.

It has been proven again and again (by the likes of world renowned tyre experts like Pacejka and Robert Smith) that the laws of Coulomb and Amonton don't apply.

More specifically, friction is not constant either laterally or longitudinaly in tyres. And this is primarily because tyres deform under load - which they must if you want to have any kind of decent handling.

If you are interested in this could I recommend "Analyzing Friction in the design of rubber products and their parted surfaces" by Robert Horigan Smith, or if you like some hard core maths, try "Tire and Vehicle Dyanmics" by Hans B Pacejka.


Smith's book also has an interesting section on the application of these laws by some law enforcement agencies around the world who still try and use Coloumb's and Amonton's laws to determine vehicle speeds from skids - and shows how these methods can give incorrect results.

There are a couple of online discussions that have submissions that agree with your opinion - can't remember where I found them though...(probably due to that alz...thingie.)

I'd have to say that gut instinct tells me to doubt some of his assertions.

I still found it interesting though.

[george formby]

I just read the snippet on braking in a curve, yup, the bike turns in but, it does not have too, you can still brake & steer while cornering. Much to my amazement.

That reminds me, I need to do some practice.:yes:

[oneofsix]

Smith's book also has an interesting section on the application of these laws by some law enforcement agencies around the world who still try and use Coloumb's and Amonton's laws to determine vehicle speeds from skids - and shows how these methods can give incorrect results.

Of course our SCU wouldn't make that mistake?

[p.dath]

Of course our SCU wouldn't make that mistake?

Alas I don't know if our SCU uses the old flawed method or not.

[slofox]

Alas I don't know if our SCU uses the old flawed method or not.

Many many years ago, (1968) I was in court (never mind why!) and listened to a defence lawyer argue this very point in reference to his client's charge of driving at excessive speed - as measured by the length of the skidmark left on the road. Guess nothing is new.