How do I work out theoretical rear wheel revolutions? - SV650.org

26-05-07, 07:04 PM

OK, messing about with stuff, and was just trying to work out how you calculate the theoretical wheel speeds for a known RPM and gear. I've got the gear ratios, and Primary and Final reduction ratio, but my brains tired, and I can't quite work out the figures.

Anyone got any ideas?

the_lone_wolf · 26-05-07, 07:39 PM

i would have though rear wheel rpms would be

RW RPM = (Engine RPM) * (1 / Gear Ratio) * (1/Final drive ratio)

Gear ratios:

1st = 2.461 (32/13)
2nd = 1 .777 (32/1

3rd = 1 .380 (29/21)
4th = 1 .125 (27/24)
5th = 0.961 (25/26)
6th = 0.851 (23/27)

Final drive ratios:

SV650 = 3.000 (45/15)
SV650S = 2.933 (44/15)

26-05-07, 07:41 PM

Ta

the_lone_wolf · 26-05-07, 07:50 PM

Quote:

Originally Posted by rigor

Ta

well i know that if i'm in second gear 5k rpm is as near as dammit 30mph

so, a bit of math

rear tyre is 17 inches in diameter, which = 0.432m, therefore the wheel's circumference is (2 * pi * radius) = (2 * 3.14 * (0.432/2)) = 1.36m

30mph = 48000 meters/hour = 13.3m/s

number of wheel revolutions per second = 13.3/1.36 = 9.78

therefore rear wheel rpm = 9.78 * 60 = 587rpm
______________________________________

now calculating the other way:

5000rpm * (18/32) * (15/44) = 958rpm

sounds reasonable to me

26-05-07, 08:47 PM

...

the_lone_wolf · 26-05-07, 08:51 PM

Quote:

Originally Posted by stuartyboy

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

units?

26-05-07, 09:26 PM

...

the_lone_wolf · 26-05-07, 09:30 PM

Quote:

Originally Posted by stuartyboy

Pounds and ounces lol

i meant the diameter...

using inches in this formula:

Quote:

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

gives you just over 1000rpm for 30mph in second gear - not right unless they accidentally put the cogs on my bike back to front...

26-05-07, 10:41 PM

Could I ask - why do you need this information? Will it materially improve your life?

TBH I've managed many years without even thinking of the calculation let alone trying it and I can't say I'm bereft

26-05-07, 11:09 PM

Isn't 17 inches the wheel diameter rather than the tyre diameter? And there's a primary gear reduction to factor in as well?
Anyway, my head's hurting and I can't find a late night kebab house in Willenhall that delivers and I've got to go to bed hungry so I'm in a bad mood

26-05-07, 07:04 PM	#1
rigor Guest Posts: n/a	How do I work out theoretical rear wheel revolutions? OK, messing about with stuff, and was just trying to work out how you calculate the theoretical wheel speeds for a known RPM and gear. I've got the gear ratios, and Primary and Final reduction ratio, but my brains tired, and I can't quite work out the figures. Anyone got any ideas?

26-05-07, 07:39 PM	#2
the_lone_wolf Captain Awesome Mega Poster Join Date: Jan 2007 Location: Hamble Posts: 4,266	Re: How do I work out theoretical rear wheel revolutions? i would have though rear wheel rpms would be RW RPM = (Engine RPM) * (1 / Gear Ratio) * (1/Final drive ratio) Gear ratios: 1st = 2.461 (32/13) 2nd = 1 .777 (32/1 3rd = 1 .380 (29/21) 4th = 1 .125 (27/24) 5th = 0.961 (25/26) 6th = 0.851 (23/27) Final drive ratios: SV650 = 3.000 (45/15) SV650S = 2.933 (44/15) __________________ Official "Dumbass of the Year" 2011 (•_•) ( •_•)>⌐■-■ (⌐■_■) Deal with it...

26-05-07, 07:41 PM	#3
rigor Guest Posts: n/a	Re: How do I work out theoretical rear wheel revolutions? Ta

26-05-07, 08:47 PM	#5
stuartyboy Guest Posts: n/a	Re: How do I work out theoretical rear wheel revolutions? ... Last edited by stuartyboy; 28-05-07 at 08:38 AM.

26-05-07, 09:26 PM	#7
stuartyboy Guest Posts: n/a	Re: How do I work out theoretical rear wheel revolutions? ... Last edited by stuartyboy; 28-05-07 at 08:38 AM.

26-05-07, 10:41 PM	#9
Ed Guest Posts: n/a	Re: How do I work out theoretical rear wheel revolutions? Could I ask - why do you need this information? Will it materially improve your life? TBH I've managed many years without even thinking of the calculation let alone trying it and I can't say I'm bereft

26-05-07, 11:09 PM	#10
$tevo Guest Posts: n/a	Re: How do I work out theoretical rear wheel revolutions? Isn't 17 inches the wheel diameter rather than the tyre diameter? And there's a primary gear reduction to factor in as well? Anyway, my head's hurting and I can't find a late night kebab house in Willenhall that delivers and I've got to go to bed hungry so I'm in a bad mood

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Cleaning all around the rear wheel / swingarm / rear brake caliper	Camel	SV Talk, Tuning & Tweaking	12	28-04-08 02:00 PM
Theoretical Questions You Need To Know The Answer Too.....	Welsh_Wizard	Idle Banter	20	04-12-07 02:19 AM
2 wheel junkies body work? ? would you?	John 675	SV Talk, Tuning & Tweaking	29	04-07-07 08:31 AM
Theoretical acceleration question	Warthog	Bikes - Talk & Issues	29	10-05-07 06:58 PM
Abba wheel spin.does it work?	ged	Ancillaries	8	03-03-07 10:32 PM