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post #1 of 6 Old 05-09-2008, 7:12 AM Thread Starter
 
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Speed vs. drag

Here're the results of a little experiment I'm doing: comparing speed to road angle. Bike is a stock 2006 Blade, I weigh 187lbs, riding at sea level.

1) On a flat surface, the top speed I ever got was 166mph, and it takes a long time and road stretch to get there.
2) On a 1mile fairly steep uphill, I can hit 162mph!
3) On the same uphill with a 170lb passenger I got 147.
4) On the same hill going down, I max out at 159

So, going uphill I can almost do the same speed as flat road, and in a much shorter period. Going downhill, I can't reach neither the flat nor uphill speed.

I didn't realize wind drag made such a huge difference: the steeper the uphill, the less drag there is. Opposite goes for downhill.

Comments? If I'm right it means the double-bubble windshield I've ordered should make quite a huge difference?
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post #2 of 6 Old 05-09-2008, 2:29 PM
 
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Re: Speed vs. drag

First off I hope you were not on public roads doing this, and taking a passenger to those speeds is wreckless and ill advised.

Second angle of attack has no bearing on wind resistance unless it is blocking a headwind.

Third weight is also a factor in limiting top speed.

Drag is simple with every doubling of speed the drag force generated quadruples.

If it requires only 10hp to maintain 50mph it would require 80hp to maintain 100mph

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post #3 of 6 Old 05-09-2008, 3:06 PM Thread Starter
 
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Re: Speed vs. drag

Closed-down public road. Same rider, same weight. Wind-free. These speed figures remained consistent throughout the last few months. Although it doesn't really make sense, angle of attack is the only changed variable. Really puzzling.
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post #4 of 6 Old 05-10-2008, 2:00 AM
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Re: Speed vs. drag

To have anything even remotely accurate you need to do all the runs on the same day, at the same time and ideally very close to the same location.
If you're talking over a period of months it could be just about anything.
Worn or under-inflated rear tyre will give you lower gearing so you're speedo will read higher at the same speed. The weight of a pillion will change it even further and the pillion causes a lot more drag as well. Really low pressure could generate more rolling resistance and give you a lower speed. Over several months your engine tune will go off a bit or from a brand new engine it might even improve as it loosens up. Full or empty fuel tank should have an effect at top speed. Low oil level or even different oil could give another hp one way or the other. A different helmet, jacket or boots could also alter wind drag. Whether the bike has just been polished or is filthy would make a difference as well.
Way too many variables to take anything meaningful from it I'm afraid.
The double bubble _may_ make a difference but I doubt it'd be huge and it could even increase frontal area and create more drag. The only way to know for sure is to test it in a wind tunnel.

"I won't forget that ride for a while. Maybe you're right. Living fast might be worth the final crash. Maybe that's the secret you fliers know." - Flight of the Intruder
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post #5 of 6 Old 05-10-2008, 5:01 AM Thread Starter
 
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Re: Speed vs. drag

OK rephrase: go up the hill, get the reading, go down the hill, get the reading. 5minutes apart between the two. So no difference in any of those variables. And for each of those _sessions_ the relative figures remain consistent, maybe two or three mph out due to all the mentioned factors. The pillion figure was just to indicate the effect of added mass, not anything else.
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post #6 of 6 Old 05-10-2008, 5:39 AM
 
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Re: Speed vs. drag

where is this closed down public road pal? would love to test my bike out there as well.
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