I was watching the Speed channel this morning and they were working on an old Mustang and were removing weight, they said that every 100 pounds you remove from the car it will take 15 less HP to launch the car with the same velocity. That equals 6.6 pounds per HP.
If 2 identical SEEG's are racing and one has a rider that is 80 pounds heavier it will take 12 more HP for him to accelerale at the same rate.
Black Dog [smiley=beerchug.gif]
It's true that the parasitic loss from extra weight at launch is important at the track. One of the most important things for someone really in to it actually. But even then it's not the only thing. Gearing, where the mill's power band goes through, where the stall is (if it's an automatic), and a variety of other factors all figure in. The Speed Channel is often entertaining. But it's not really a chalk board that presents physics too well.
But even then the weight becomes secondary as a source of parasitic loss of performance (not engine produced power, but overall performance) to the aero drag of the rolling mass going down the road. At the drag strip weight is so especially important because you're in an environment where the launch is sooooo important and you spend so little (comparatively speaking) time actually moving down the road.
In a different environment, however, there are particular circumstances where the weight has specific kind of benefits in terms of momentum. So you should always keep in mind that none of this stuff can stand alone and for every circumstance where an individual factor might be beneficial there's almost always some countervailing circumstance where a nearly opposite factor might also be important.
Some years back I used to be spend a lot of time at the track (oval and drags). Built a few cars and blueprinted more engines than I care to remember (it's a mind numbing exercise in details detail details). The scientific calculators and computers of the day were just part of what we did accounting for the total mass
and where it was on the car (which is also just as important). I personally only ever ran naturally aspirated and my best time was only ever an 8.48 at 163. So we were by no means running with the big dogs. But you still begin to get clued in.
For our bikes running around the street a difference of 40 pounds pulling away from the stop sign will be felt in the seat of your pants. Sure. But it doesn't have the continuous parasitic loss once you get moving that DJ was humorously suggesting when he figured that with the weight of he and his passenger and loaded bags that he'd actually have to be riding downhill and backward with a tailwind to have gotten anyplace. It just doesn't work that way. The overall weigt will affect us starting out and have an impact on rate of acceleration to a desired point. The faster you're rolling, however, the more important becomes the aero drag; especially for something as small and comparatively light as our bikes. And doubling your speed doesn't simply double your drag. No, we're not that lucky. But once you get to a given speed it takes far less power (from the engine) to hold it there than it did to accelerate to that point. So that extra fifty pounds on the saddle or in the tour pak makes a minimal to cruising down the road.
So I guess you might say that (for normal riding) we'd go on a diet and lose weight to get started faster. But to move faster or more efficiently going down the road it would be more important to be aerodynamically sleeker. And believe me, sleek is one thing this body will never be [smiley=huepfenlol2.gif]
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Topic: SEEG TOP DOG'S (Read 10117 times)