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Hi Guys - reading an old MCN [May 2007] noticed an article on Wind Drag - an aerodynamics bike expert [Alan Jenkins] talking on this subject mentioned a couple of things Q. why can't road bikes still get to 200mph in reality? A. Relative to race bikes the big difference is things like rear view mirrors and indicators which have a big impact on speeds. Mirrors can make a huge difference. The real horsepower available from a road bike fully homologated for noise and emission control is also much lower than quoted.I suspect that you need maybe 190bhp to do 200mph plus no mirrors and stuff like that. Q. What's the power to speed equation in simple terms? A. Aerodynamic forces including drag, increase as square of the speed. Therefore the drag at 100mph is twice what it is at 70mph and at 200mph it is nearly nine times that at 70mph!


Now i know why it seems all so gentle an' easy at 70mph and adarn site more 'battering' at 100mph+ on a naked bike with your knees out to dry - never seen 200mph on 2 wheels - what about you guys? regards tomba
 

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simple fact...at some piont in the past i think it was in the mid 90's the bike comp's got together and set a deal that all big bikes (900-1000)top out at 186 mph .... (300)kph 600"s below that
 

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hi i use to have an unrestricted busa and ive seen 200+ on the clock and just over 220 bhp thats with plenty of mods done


cheers steve
 

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Discussion Starter · #6 ·
Hi Stevei - wow that's a tad quick mate! - now i have this theory as i've never done it!! - that a quarter mile 200+ is easier that a road [private
road]200+ because by the time you committed the run it's time to give it a rest, and not enough time to scare the 'rap out of you! whereas winding the scenery up to warp speed over a few miles gives you time to realise just how fast you could hit something, and keeping that kinda pressure on you takes some doing so! which was it brave or mad or both stevei? - did the scenery warp? how did it feel? - i had longed to own a busa but the bandit moved scenery pretty quick and then the Warrior came into my life [to save it i think!?] - regards tom ba
 

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tomba said:
Q. why can't road bikes still get to 200mph in reality?


A. Relative to race bikes the big difference is things like rear view mirrors and indicators which have a big impact on speeds. Mirrors can make a huge difference. The real horsepower available from a road bike fully homologated for noise and emission control is also much lower than quoted.I suspect that you need maybe 190bhp to do 200mph plus no mirrors and stuff like that.


Q. What's the power to speed equation in simple terms?


A. Aerodynamic forces including drag, increase as square of the speed. Therefore the drag at 100mph is twice what it is at 70mph and at 200mph it is nearly nine times that at 70mph!


Now i know why it seems all so gentle an' easy at 70mph and adarn site more 'battering' at 100mph+ on a naked bike with your knees out to dry - never seen 200mph on 2 wheels - what about you guys? regards tomba




Idon'tagree with Alan Jenkins answer for question #2. I agree that theaerodynamic forces vary with the (velocity)2, butthe power required to overcome those forces vary with the (velocity)3. This is because drag is just a force andpower is a measure of how fast work is being done (by the engine) to overcome those forces. Maybe the poster didn't include Alan'sfull answer, but the question asked for arelation between power &velocity, not force &velocity. So to answer the original question, the power required at 100mph vs 70mph is ~2.9x, and for 200mph vs 70mph it is ~23x.


The drag forces (FD) can be written as: FD = 0.5·(CD·A·?·v2)


CD: Drag Coefficient


A: Frontal Area


?: fluid density


v: velocity





Expressing the Power in terms of Velocity (v)...


Power = Work/time = (force·distance)/time = (FD·distance)/time


Power = (0.5·(CD·A·?·v2)·distance)/time (NOTE: CD, ?, A, 0.5 areall constants. Let them= C)


Power ~ C·v2· (distance/time) (NOTE: distance/time = velocity)


Power ~ C·v3





Sometimes the values for the drag coefficient (CD) canbe estimatedfrom other similar, well known (aerodynamically)bodies,but for the most accurate estimates it mustbe evaluated experimentally ($$$).
 

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I've been over 200 on an unrestricted, slightly modified, Busa as well. Unless you are tethered to the grips you don't raise your head suddenly at those speeds, cause you'll about fly off.
 

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hi tomba well i would have to say its complete madness but what a buzz and iff you did hit something at that speed i dont think youd no about and youd probably slice a car in half like a hot knife through butter,but when you are at that speed its a weir feeling as you pass traffic it feels like there standing still and you could just get off and walk next to them thats about the best that i can describe it but i dont think ide do it again as its complete lunasy


cheers steve
 

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Discussion Starter · #10 ·
thanks stevei - i did wonder - i guess there should be a 200+ club badge but not many members yet huh!


The maths... brilliant i did try to follow it [honest] but idissapointed my dad with my maths [he wasa military surveyor here in uk] - I did copy the report as it was given, butobviously an oversimplified answer for the paper - regards tomba - just watched moto gpat indy - blimey those guys were doing 185mph in back end of Ike! - no wonder they red flaggged it - thanks guys
 
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