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Discussion Starter · #21 ·
Blake,


Check out the old Cycle World stuff in the middle 60's with Gordon Jennings. The Fairing is the same look as the Buell in the 80's. Big round and bulbus... if that is a word.

To go fast Jenning's found you needed to be round and fat, not edgy and sharp like today's look.


The more your learn, the old guys have been there and done that before...


I think the article with the best pictures was in 1966 with the testing of a Sportster engined race bike. That is the same fairing design used in the 80's for the Buell's


Phat is back!... and maybe for the street too, if some one would make a kit maybe it would sell...


They would sure look different...Phat Fairings...



 

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Re: Faulty assumptions

I greatly respect jmeyn's contributions ever since he impressed me with the top speed estimates in for each gear for the 600RR after somebody wondered aloud what they would be.

I am always interested in hearing the mathametics and/or "bench racing" stuff that he has to provide. Jmeyn, don't let this mope bother you.

--Foxy
 

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Re: Do-it-yourself drag calculation

OK for a back of an envelope calculation, but still over simplified. Dynamic pressure is proportional to the square of the velocity. Drag is proportional to the square of the velocity ONLY if the drag coefficient is constant.

For something that would have highly seperated/turbulent airflow, like a motorcycle and rider, drag coefficient will increase with velocity, probably very sharply after some speed. Drag increase due solely to the increase in dynamic pressure is small compared to the increase in drag due to increased flow seperation (i.e. increasing drag coefficient).

As a result, you will be underestimating the effect of aerodynamic drag with your method.
 

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Why is this a big deal??????? The very first sentence discredits the whole article, "becoming the first Harley-Davidson powered motorcycle of less than 1650cc to exceed a 200 mph record speed."



Why are Harley's catagorized by themselves? Why not just buy a stock Hayabusa, put a pipe, jet kit and K&N on it and do the same thing with a stock fairing on pump gas?



With the savings, you could buy a garage full of dirtbikes for the whole family. Plus, you could still ride the Hayabusa for years to come without parts falling off.









 

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Harley's are not classed by themselves. These speed guys have classes for every TYPE of motor. Thi bike runs in a PUSHROD class so any pushrod motor could be used, Harely, BMW, Moto-Guzzi, Triumph, small block chevy etc.



Almost everyone run these large displace pushrod bike classed uses Harely type motors 'cause you can get the part to build one. I don't think anyone makes a 100 inch BMW.



 

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SEe my post about classes but I have to add, There have been a couple of mostly stock "Busas and they can't do 200 mph at Bonneville.



You make less power at that altitude and you get some wheel spin.



I think one guy after much work cracked 200 with his.



There was a "Busa running nitorus that did break 200 and did it by a good margin.



BTW a stock Busa would get to run in a Production class instead of the modified class we had to run in.



These hot rodders have classes for everyone, one of our teammates now holds several LSR in 50cc sidecar classes!!!



Also was a guy running a Lakester (streamlined but with no covering on the wheels) powered by a 6 cylinder diesel.
 

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My point is that for the that displacement and cost, the speed isn't that impressive. I would never buy a Harley for power, performance or racing because they can't compete. I would buy one for the resale value, perceived coolness factor and looks.



I will keep my day job as a Mechanical Engineer and continue to buy products that are innovative and technologically advanced. It allows me to have a Vmax, CBR900RR, WR426, PW50 and XR50 for the kids.
 

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Re: Do-it-yourself drag calculation

1) The result is consistent with reality within about 5% either way in several speed tests on modified motorcycles and right in line with MotoGP bikes that have exceeded 200 MPH.

2) 5% is all you can expect given the difficulty of reaching and measuring top speed; repeated runs tend to vary that much.

3) Bikes are out of boundary layer flow and into turbulent flow from about 5 mph till the edge of the speed of sound. The method holds quite well over that range.
 
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