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Message: <blockquote data-quote="Roberto" data-source="post: 708194" data-attributes="member: 8160">Bro Alan!Yes we should meet up for a tt one day, there is much that you can help me with.You've raised some interesting points and I thank you for your attention. However, I believe they are not significant to the issue. Let me explain further.------------------------And if you think about it, it is better to fit the callipers closer to the hats. There is less rotational force closer to the hats and thus less force need be applied to stop it. The reason they don't do this probably has something to do with metallurgy and not braking itself. The rotor probably deforms unevenly when you do this.  The centripetal force equation is F = mvv /r (i.e. m v squared, dunno how to type the square here sorry) / r....so the velocity of the rotor at that specific point contributes more to the force present than the distance to the centre. Wider discs will always require more force to stop them.So I believe you have understood it in reverse my friend. Please correct me if I'm mistaken.**The main thing about rotors with a larger diameter are 3 things :1. Large surface area dissipates heat better. This works because there is more physical metal in a larger rotor to dissipate heat from the pad-rotor contact point, and a large area in contact with cool air rushing by which means it can cool down faster.2. Bigger rotors enable you to create vents between both sides which are strong enough to withstand consistent braking. More vents = more exposure to air = better cooling = longer time to get to brake fade = better braking.Heat is a big enemy to efficient braking. Heat causes brake pads to glaze and thus brakes to fade. BMW builds their stock cars for hard drivers, so they will assume that you're going to do alot of braking while on the road not the track. So heat becomes a big issue for them to tackle properly.3. Large rotors of course enables you to fit larger brake pads and large pistoned callipers /pistons with a larger net application area such as multi pot pistons. More friction means better pre-abs braking times. And you might need that for that particular car. A vios does not need huge rotors to stop from 140kmh in say 50 metres. An E34 might. ------------------- And static and dynamic friction does not apply to our braking discussion. Static friction applies when both surfaces are not moving relative to each other. This is when the car and the road is at rest. When the car is in motion and the wheels are locked, the tyre is still moving relative to the road. It is just being dragged, as opposed to rolling over, the road. So in both locked wheels and unlocked wheels, you are talking about dynamic resistance, as long as the car is still moving. As long as there is movement, there is always dynamic friction involved. Alan I suspect what you're talking about is two types of dynamic friction : rolling resistance and sliding resistance. Rolling friction is what you get when the tyre rolls over the road without being dragged. Sliding resistance is what you get when the tyre is stopped from spinning by the wheels, and then is dragged across the road. Sliding friction is always higher than rolling friction. I'll use an example. Lets say the car is stationary, you apply the parking brakes, the transmission brake, and the foot brake. Can the car move ? Of course, but you will need a strong force to pull it forward before it even begins to move an inch. Now, release all the brakes and put the gear in neutral. A strong man can push the car and begin to get it moving. Much less friction. So that's the difference between rolling and sliding resistance. Wheels that are locked and essentially dragged across the road....slow down the car faster than ABS wheels which are kept rolling by the abs unit. However, in practice, when locking the wheels at higher speeds, the car also slides in odd directions causing the driver to lose control if he is not trained to react to that instantly (not a requirement to get a license ), and this causes accidents. So ABS braking, even if it results in less stopping force, is ultimately much much safer in practice as the driver maintains control.</blockquote>

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