• Welcome to the forum website of the Vincent H.R.D. Owners Club.

    Should you have any questions relating to the Vincent H.R.D. Owners Club, or Vincent H.R.D. motorcycles in general, please contact Graham Smith, Online Forum Webmaster by calling 07977 001 025 or please CLICK HERE.

    You are unrecognised, and therefore, only have VERY restricted access to the many features of this forum website.

    If you have previously registered to use this forum website, you should log in now. CLICK HERE.

    If you have never registered to use this forum website before, please CLICK HERE.

Rolls Royce Automotive study in MPH

champion

Well Known and Active Forum Website User
VOC Member
I was told of a study which is in MPH, last month, (Or possibly the previous one.)

It proposes the idea that as speed increases aerodynamic drag increases at a greater rate.
and that as speed increases, rolling restistance increases by an even greater rate...

Thereby making tyre choice more important for top speed than aerodynamics:

Problem is the artical says that aero drag increases by the power 3 and tyres to the power 4.


But doesnt aero drag increase by 2?

In which case is the part about tyres rolling resistance still true?

Really I would love to try and get hold of a copy of this report.

Only reason I ask is: I am currently doing my dissertation looking at motorcycle aerodynamics, and this would be a brilliant point to finish my conclusion on.

Alex
 

passenger0_0

Well Known and Active Forum Website User
VOC Member
Hi Alex. I you work from a free-body-diagram and apply basic physics you'll find that both form and skin drag increase to the square of the velocity. Obviously tyres experience centrifugal force which increased to the square of the rotational velocity but this is irrelevant to rolling resistance. Tyre rolling resistance may well be more complex given this is a function of sidewall distortion etc... Either way I think you'll find that aerodynamic resistance is several orders of magnitude greater than any form of rolling resistance - just sit up on an unfaired bike at 140 mph and you'll get the point. For a dissertation you'll need a robust derrivation of any model presented so I suggest you consult a relevant book. Good luck with your studies. Cheers David
 

vibrac

Well Known and Active Forum Website User
VOC Member
Verily it is said in the new testament Chapter XX P269(tuning for speed version 3 ) thou shalt add 2% for rolling resistance and air resistance is the square of the speed. as cast in the sacred formula Resistance= A x V Squared x C handed down from the mount at Caldwell
wherein A shalt be the frontal area of the hallowed machine V is its velocity imperial feet per second and C is the one indivisible constant known to mortals as "drag coefficient"
Wherein Bob Mac upon his Norton shall be 5 square feet and 4 1/2 square feet for Bill Ivy upon a 125 and the constant may be taken as .0008 for most mortals
so it is written
 

Albervin

Well Known and Active Forum Website User
VOC Member
Tim, be very careful about stating what is a "constant" in physics. Cd depends on so many things including atmospheric pressure, temperature, what you had for lunch, height above (or in Netherlands, below) sea level, whatever the machine is made from or coated with (paint, teflon, ceramic) and lastly, -ve or +ve lift. All in good fun but remember who went really, really fast with a 125 bike in 1955.....
 

champion

Well Known and Active Forum Website User
VOC Member
Wow, thanks guys - David you are right, I am on my way to the library now, to consult:
Race car Vehicle Dynamics by Milliken & Milliken as they seem to know their race car onions!

Are there any other books which you would recommend?


I have got a list of Cds from a book, however to validate them I have done a coast down test on a bike - Using an Iphone as a data logger (This method was validated by an Msc. Thesis in the summer of 2010 showing a difference of 5% between an expensive Motec logger and a £1.99 Iphone App.)

Problem is I only turned on the accelerometer and time loggers (recording at 40Hz) and forgot to turn on the GPS logger so did not get speed or distance. However if i know the speed and distance at the start are both zero, I could intergrate it to find speed and distance... Just got to remeber how to in Excel.

Anyway I digress..

http://www.amazon.com/s/ref=ntt_ath...-alias=books&field-author=Douglas L. Milliken
 

ET43

Guest
Hi Champion, You might find some more information in an article by Dennis E. Ortenburger about Frank Costin who I believe helped to design the Vanwall race car amongst other things. The article is called Flying on four wheels Frank Costin and his car designs. This article contains a load of technical guff that is way beyond me. I will bring it to Dick Sherwin's place on Sunday if some one wants to collect it. Cheers, ET43
 

champion

Well Known and Active Forum Website User
VOC Member
The VOC is one of the best motorcycle clubs I have ever seen! By such a long way....

I am also a member of another bike club (for an italian V twin without mentioning any names.) When you discuss anything else on thier forum other than Beer preferances or petrol prices all goes silent.....

Long live the VOC.
 

Comet Rider

Well Known and Active Forum Website User
VOC Member
Hi Champion,
Try and get a copy of "flight without formulae" by Kermode.

Lots of interesting stuff which may be of use.

Neil
 

passenger0_0

Well Known and Active Forum Website User
VOC Member
Hi Champion. I suggest you go for a slightly more theoretical book given you are writing a dissertation. Any fluid mechanics text, such as that by Frank White, will include the basis for what you're after. Albervin is correct in that drag is essentially a function of shear stress and this varies as a function of temperature and pressure. You'll need to show the difference between form and skin drag as this is an important point. For your comparative analysis I image fluid properties will remain constant otherwise you will have too many confounding variables. I don't think rolling drag can easily be calculated, given all the variables but you'll need some sort of law otherwise you'll not be able to compare the two with respect to speed increases. Cheers David
 
Warning! This thread is more than 12yrs ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Top