How do I work out theoretical rear wheel revolutions?

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[the_lone_wolf]

Originally Posted by stuartyboy

Hmmm. Didn't you ask what units to use and measured the tyre at 17 inches. That smell of wee is getting stronger.

yes, i made the mistake of measuring the tyre at 17 inches, i have since corrected the formula and shown it to corroborate my original argument

the reason i asked for units is that you didn't state what units you were using for the diameter in this formula:

Originally Posted by stuartyboy

rpm = (mph x gear ratio x 336) / diameter

not because i didn't understand what you were suggesting

i've no idea how much you've done regarding physics but they taught us back at GCSE that to not state units is about the most basic mistake you can make

then there's the fact that neither of your formulae hold up to scrutiny

mph * gear ratio * 336 gives a result of 17912 for 30mph in second gear, seeing as you've not stated whether "rpm" means engine rpm or rear wheel rpm i can only assume your diameter measurement is one of the following

in the case of you meaning engine rpm, diameter = 17912 / 5000 = 3.58units
or if you meant wheel rpm, diameter = 17912 / 407 = 44units

i suppose 44cm is closest

as for your other formula:

Originally Posted by stuartyboy

Wheel RPM = (RPM / Primary Ratio) x (Gear Ratio / Final Ratio)

i've already shown that by putting in some simple numbers that isn't true

as before you should be multiplying by the inverse of the gear ratio, it looks like you've got a bit jumbled up rearranging your multipliers, dividers and brackets

Originally Posted by stuartyboy

Wondered this myself tbh...but I'm very brainy and like showing off

well one out of two isn't bad

go back, check your formulae, show your working

4/10 - must try harder

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[the_lone_wolf]

Originally Posted by stuartyboy

How many bikes have you ridden with a 1.96metre diameter wheel?

That's taller than me!

should have read circumference, a typo

when you've finished picking up on irrelevant minor errors, could you explain the fundamental errors in your formulae and why they don't show anything like what is observed in the real world

ta

God I love maths.

Matt

[the_lone_wolf]

Originally Posted by alpinestarhero

God I love maths.

Matt

chemistry is physics with no maths

maths is physics with no point

[the_lone_wolf]

Originally Posted by the_lone_wolf

mph * gear ratio * 336 gives a result of 17912 for 30mph in second gear, seeing as you've not stated whether "rpm" means engine rpm or rear wheel rpm i can only assume your diameter measurement is one of the following

in the case of you meaning engine rpm, diameter = 17912 / 5000 = 3.58units
or if you meant wheel rpm, diameter = 17912 / 407 = 44units

i suppose 44cm is closest

ok, i'll show you where you went wrong:

a simple units calculation means that your formula is effectively

[(distance in miles / time in hours) * unitless * unitless] / diameter in ? = 1 / time in minutes


rpm is measured in revolutions per minute, ie: a unitless number per given time, in this case one minute

miles per hour is distance per given time, in this case one hour

therefore your diameter is in the correct units (a distance as opposed to unitless or inverse time) but you've mixed miles, hours and minutes in such a way that it makes no sense and produces incorrect results, your proportionality constant of 336 seems arbitrary, so i would look there for your error first

QFE:

Originally Posted by stuartyboy

I'm a qualified physicist, its correct...end of

anyway, the dog needs walking, see you again

I love maths too. Ten years ago I'd have been in the middle of this. But that's long enough my for the knowledge gained in doing my A levels in maths to have eporated. I watch numb3rs despite the really awful tag line "we all use math everyday".

Physics is theoretical engineering. Ie those that can do, those that can't talk about it.

I actually wrote a little speed/gear ratio calculator. I can email you the executable if you want?

It allows the user to enter in different sprocket combinations and revvs to ascertain what the speed would be in each gear. You can even save the results to a text file

I see wheel circumference has been discussed. This is an important factor and the only way is to measure it, there is no point trying to guesstimate from the code on the side as 2 tyres with the same code 160/55/17 could well be different ... also as the tyre wears its circumference lessens ... My rear tyre was 198cm circumference. The program allows the user to configure this.


edit:- here you go, I uploaded it to a share site where you can download it!!
http://www.sharebigfile.com/file/176...SV650-exe.html

If it isn't on your machine already, you might need COMDLG32.OCX for it to work, this can be downloaded directly from Microsoft
http://activex.microsoft.com/controls/vb5/comdlg32.cab

[the_lone_wolf]

Originally Posted by Blue_SV650S

I actually wrote a little speed/gear ratio calculator. I can email you the executable if you want?

how cool is that, is that in visual basic? - i've been getting to grips with the basics (no pun intended) but kind of hit a wall when i couldn't think of anything useful to apply it to...

have you seen this:

http://blogs.msdn.com/coding4fun/arc...8/1709215.aspx