More weight doens't make longer stopping

[dantama]

This is a continuation of a conversation with Blown Dodge about weight and stopping distances that we're spinning off of the car tire thread.


BD,

Here are portions of a topic from another site, I'll post a link at the end.

There seems to be a continuing belief amongst many of us that stopping distance increases as a direct function of increased vehicle weight. I would like to try again to put this issue to rest.

While it is true that a heavier vehicle requires more energy to brake to a stop than does a lighter vehicle, (there is, after all, more mass involved), that does NOT mean the heavier vehicle takes more time or more distance to stop....
Since you know that you can lock a wheel while the bike is still moving, you know that the braking energy you apply to your brakes is NOT WHAT LIMITS HOW FAST YOU CAN STOP! That limit is determined by the amount of traction your tires have.

Further, since it takes more braking energy to stop (lock) a spinning wheel than to merely slow it down, and because a sliding tire (the result of locking your brake) has less traction than one that is not sliding, your normally functioning brakes are NOT WHAT LIMITS YOUR STOPPING DISTANCE! That limit is also determined by the traction of your tires.

Traction, as we have discussed before, increases with weight. Thus, adding weight decreases your ability to slide the tire and, as a result, gives you the ability to stop more quickly while at the same time increasing the energy that must be converted to heat by your brakes in order to slow down. In effect, adding weight makes it harder to slow at the same time it makes it more possible to do so.

If you so severely overload your bike that the brakes are no longer powerful enough to cause a skid, then you know that the increase in traction gained by that added weight has finally overwhelmed the ability of your brakes and, thus, your brakes then become what limits your stopping ability (time and distance.)

Weight affects your ability to stop in TWO ways:

* It takes more energy (braking) to slow a heavier weight


* Traction INCREASES as a result of added weight such that more braking can be used without starting a skid.


Thus, adding weight essentially CANCELS itself out as an impact on stopping distance. All that you need to do is apply your brakes harder in order to TOTALLY compensate for added weight....

You know this already, of course. Else, for example, how could a car EVER stop as quickly as a motorcycle? Or, how could a heavy Valkyrie or an Ultra Classic Tour Glide EVER stop as quickly as a little 250 cc street bike?...

But, generally speaking, weight makes no difference in stopping distance because the brakes are more than adequate to handle any normal range of weight for that bike....


Taken from http://www.msgroup.org/Tip.aspx?Num=125&Set=


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A bike moving, say, 50 mph has four times as much kinetic energy as that same bike moving at 25 mph. In either case in order to skid your tire you need to achieve, say, 1.0 g's of deceleration. You maintain that the bike's brakes cannot do that at 50 mph because of the total amount of kinetic energy involved?

My experience is that unless you are moving at a speed that is beyond the capabilities of your brakes to handle in terms of dissipation of heat your brakes are more than adequate to LOCK your wheel which requires more braking energy than slowing down the speed of rotation.

Indeed, your brakes are more than adequate, assuming the coefficient of friction between your tires and the roadway is adequate, to scrub 20 mph of speed every second you use them. That is pretty close to 1.0 g's and to do so without burning up in the process.

Of course they get hotter when doing so at 50 mph than at 25 mph as they convert that amount of kinetic energy to heat in less time.

You could put the brakes from a Mack truck on a motorcycle and still only have deceleration rates of up to about 1.0 g's of deceleration capability as that is limited not by the brakes, but by the coefficient of friction available. Put the tiny squeeze brakes from a bicycle on a motorcycle and try that and they would fail - they are not adequate to the task. But *your* motorcycle brakes are.

http://www.msgroup.org/forums/mtt/to...TOPIC_ID=10818

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In a brief post he states,
The size of your contact patch does NOT determine traction. It is how much weight is being carried by each square inch of that contact patch that does that. A bigger contact patch merely means less weight per square inch as the weight of the bike does not change.

http://www.msgroup.org/forums/mtt/to...62&whichpage=2
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I didn't read through this one today, but I think it's the one where he got the MSF to change their position.

http://www.msgroup.org/forums/mtt/to...p?TOPIC_ID=918

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I don't like giving the guy props here, because he's and ass. But he seems to know physics.