1971 Experimental F750 Racer

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Dances with Shrapnel said:
The post where I introduced Phil Irving's reference titled Tuning for Speed is not edited. :oops:
:
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It doesn't SHOW as edited.
But if you alter it before anyone else posts, it doesn't record it as being edited.

I specifically went away and looked for my copy of Motorcycle Engineering,
and spent a couple of days searching ( a lot of stuff is boxed up)
Having found it, TFS was with it.
And nothing on P224 in either of them !

But we are raking over dead coals, its time to move on.
 
Rohan said:
Having found it, TFS was with it.
And nothing on P224 in either of them !
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SeeleyWeslake found it in his edition. Try page 244 as I was citing it from recollection or maybe it is not in your edition; suggest you look in the rear index of the book and search for terms like power, speed or drag coefficient. When I get back home in a few weeks I will scan it and see if I can PM it to you if you have not found it by them. Regardless, the essence of what Phil Irving presented I summarized earlier in this thread with the simple equation and terms of Area, Velocity and Drag Coefficient. Phil Irving presented the equation as force generated (lbf) for a given speed/area/CoD, cubing the velocity renders power required in lbf-ft/sec. Divide that by 550 yields RWHP. There was no mention of "rho" or mass density of fluid (in our case air) so I assumed it is rolled into his coefficient of drag value.

Rohan said:
But we are raking over dead coals, its time to move on.
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Now wait a minute, I was beginning to enjoy this.... but you are correct.
 
Rohan said:
Yes, we have dws ORIGINALLY POSTING
Dances with Shrapnel said:
Using your more common units of coefficient, reducing the coefficienct from say 4.0 to 3.5 yields a 12.5% reduction in drag.
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and its now been amended to - something less confused.... ?

Dances with Shrapnel said:
Using your more common units of coefficient, reducing the coefficienct from say .40 to .35 yields a 12.5% reduction in drag. Phil Irving presented a coeeficient of 0.0008 and I arbitrarily picked 0.0007 (net 0.0001) which yields the same percentage reduction. I have a hunch Irving may have combined a few terms; don't know for sure without digging into an old fluid dynamics text and studying it a bit.

So design or redesign a complete bike for 2" lower and maybe 5-8% reduction in drag or reduce the coefficient by 10-12 or more percentage points. It could be be as easy as adopting a different tuck in riding position or a modified tail piece.

Irving was pragmatic. Testing to measure results could/would be done on a flat out and read the tach.
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Yes, moving decimals one place to the left. That's what happens when you type on a cell phone on a bus and then catch it in the airport. The message is 12.5% reduction is 12.5% reduction, SI or Imperial :D
 
Dances with Shrapnel said:
The message is 12.5% reduction is 12.5% reduction, SI or Imperial :D
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We agree on that. And did from the start.
it was the math of getting there that raised the initial question.

Air Resistance is the indexed entry.
We found that days ago - its page 272, as SeeleyWeslake helpfully pointed out.
Always read the index from the very beginning, looking for drag or coefficient is too far down the alphabet !
 
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