Quote:
Originally Posted by phr3ek
what type of bike did they get those numbers from?
stopping distance can be reduced with lighter bikes, better brake components, better tires and ABS
i personally dont bother with statistics, there are just too many factors that may not have been covered
i just go by personal experience, i know how much braking force i can apply before having the rear end slide, and i know how to control a fishtailing bike
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According to the guy who did the calculator, there is fairly little difference between bikes that matters. Most bikes have brakes that are capable of lock up of the wheels, so the real limiter is the tire. Motorcycle tires can, normally, provide about 1.1g of traction. That is, they can handle a deceleration rate of slightly more than 32.2 ft/sec/sec without beginning to skid. In order to stop in the fastest possible time and shortest possible distance, you need to apply enough braking force via your front brake lever and rear brake pedal to overcome the momentum of all of that mass and slow it down as close to 1.1 g as you can manage. And while there is a slight variation with tires (race tires can handle about 1.3g, for example), for most bikes the differences in bikes is going to be overcome by differences in rider skill and reaction time, which create such huge fluctuations in stopping distance that it really doesn't make sense to tinker with the stopping distances to change a few feet here and there by changing the calculator for different bikes.
As for bike weight mattering, it is a myth. While counter-intuitive, heavier bikes still have (for the most part) sufficient braking power to lock up the wheels. Heavier weight just means you need more pressure on the brakes to achieve the same stopping power. This is because heavier weight bikes offer increased friction that balances out the increased momentum of the bike. (F = mu*N where F = frictional force (braking force between the tyres and the road), mu = friction co-efficient (changes based on road/tyre condition), N = normal force (force acting directly downwards with gravity i.e., the mass of the bike and rider). Think of it this way: It takes more energy to stop a heavier bike than it does a lighter one, but at the same time your traction increases so that you can use that necessary additional braking energy without resulting in a skid. The added weight (so long as it is within normal limits) self cancels itself - because the brakes ARE (with a few exceptions) adequate. Its the tires that stop you. Again, reaction time and rider vigilance are going to be the big variations to care about, not the difference in bikes.
The larger point is that regardless of bike, small increases in speed result in large changes in your stopping distance. And (I've tried this on multiple bikes) around 30MPH (give or take) the distances become critical when one considers intersection width. You can pay attention to the statistics or not, but they can be instructive in determining how to lower the risks of riding. And it is pretty intuitive that if you need to stop better in the highest danger area, an intersection, a solution is to be more vigilant and go slower in the intersection. 30MPH, give or take depending on minor variations in bike tires and rider skill, seems like a good general target. That is all I'm saying.