Landracing Forum
Introductions => Formulas => Topic started by: sofadriver on December 20, 2014, 04:30:28 AM
-
Been a long time since Algebra 1.
Can anyone change this around to find speed?
speed x 336 x pri x gear x big
RPM = small
-------------------------------------------
diameter
Thanks in advance
-
mph = (rpm x tyre radius) / (primary x drive x final x 168),, 8-)
-
mph = (rpm x tyre radius) / (primary x drive x final x 168),, 8-)
Thanks, stay'tee.
Couldn't get that to work with the 168 (although 491mph would be coolish!).
Seems to work with 336, though.
I come up with 138mph and that works for me!
I've got more sprockets and more rpm than the figures I used.
But I'm still hoping for a little tailwind! :-D
-
http://www.cosportbikeclub.org/misc/SpeedCalc.html
This is plug and play - no algebra
-
Let:
S: speed (MPH)
D1: primary drive ratio (clutch wheel ÷ motor sprocket, etc.)
D2: secondary drive ratio (rear sprocket ÷ transmission sprocket, etc.)
G: individual transmission ratio (2.50, etc.), direct drive high gear = 1.00
T: tire diameter (inches)
R: engine speed (revolutions per minute)
S = (T × R × .002975) ÷ (D1 × D2 × G)
R = (S × D1 × D2 × G) ÷ (T × .002975)
D1 = (R × T × .002975) ÷ (S × D2 × G)
D2 = (R × T × .002975) ÷ (S × D1 × G)
-
interesting.......
sta'tee's method - 138mph
55chvr's online calculator - 178mph
panic's method - 144mph
:?
-
I'd use the 178 -- it's faster. Just say it's the Exit Speed if it doesn't match your time slip.
-
I'd use the 178 -- it's faster. Just say it's the Exit Speed if it doesn't match your time slip.
my choice, too! :-D
-
Here's one that covers just about ever variation you can come up with.
http://www.rbracing-rsr.com/gearspeed.html
-
Have you tried the gearing calculator that Sumner put together? It allows you change sprockets to compare in addition to transmission gears. It's down 2 threads here.
-
55chevr's page is correct - if you input your tire size and drive ratios correctly. The 178 mph result is a GIGO error.
-
whats a "GIGO" error, :?,,
in relation to the formula i posted, (primary x drive x final), "drive" is the ratio of the drivin gear, eg 5th @ 1.130,, "final" is the ratio of front to rear sprocket, eg 18/42 = 2.33,, :cheers:,,
-
Garbage in garbage out... :cheers:
Post the particulars and I'll put it thru our calculator
-
Garbage in garbage out... :cheers:
Post the particulars and I'll put it thru our calculator
Thanks, Stainless.
Final drive.....3.4
1st....2.54
2nd....1.89
3rd....1.5
4th....1.25
5th....1.09
6th....0.96
front sprocket - 17. rear is 35.
tire is 23.5" (120/60-17)
13,500 rpm
I'm going to try 55chevr's calculator again, too.
-
duhhhhh
i was entering tire diameter where the cosportbike calculator was asking for rim diameter
i'll go stand in the corner now
-
1 53.1
2 71.3
3 89.9
4 107.9
5 123.7
6 140.4
Max at 13500 in each gear, no slip compensation
I will send you an excel file that does the math if you would like... we have used it successfully for 20 years.
-
I will send you an excel file that does the math if you would like.
I think you already did it all !
Thank you.
As little power as I have, I think a little slippage on the way might help me hit 13,500 rpm in 6th!
-
i just done the calculations based on the info you posted (assumed stated final drive as primary), along with the formula i provided, result 140.56mph, (6th),, :-)
-
140 it is!
Thanks all :cheers:
-
Most of the tires I have used are in the 25 to 25.5 diameter
-
Have you tried the gearing calculator that Sumner put together? It allows you change sprockets to compare in addition to transmission gears. It's down 2 threads here.
Here is a screen shot...
(http://1fatgmc.com/car/misc-pics-1/MC%20with%20Jack-Shaft-1.jpg)
...and besides the option to view multiple rear sprocket combintains at once as mentioned above (blue arrow area) you....
(http://purplesagetradingpost.com/sumner/bvillecar/Spreadsheet%20Car%20Image-2.jpg)
... can also see the speeds in any gear at any rpm without having to reload the rpm over and over. Also another helpful thing is that you can see the rpm drop after a shift in any gear and the new rpm in the next gear which can help determine if you are falling out of the torque/HP curve after the shift.
It is not interactive online so that is a negative but download it here...
http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html (http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html)
... and then use it (go down the menu a short ways to the motorcycle spreadsheets. If you don't have a spreadsheet program consider downloading Open Office....
https://www.openoffice.org/ (https://www.openoffice.org/)
...it is free and what I use (I do donate from time to time to them),
Sumner
-
I came late to this thread but sitting down in FL all nice and warm thought I'd run the numbers also and basically came up with the same as above or about 138.4 mph for the inputs...
(http://1fatgmc.com/car/misc-pics-1/MC%20with%20Jack-Shaft-2.jpg)
and you can see the rpm drop in each gear below if you shift in the 12,000 to 13000 range but pick what you would actually use....
(http://1fatgmc.com/car/misc-pics-1/MC%20with%20Jack-Shaft-3.jpg)
Sum
-
I use the the Bonneville formula to calculate speed. Really simple. Make a run, go back and collect timing slip and bingo you have your speed. This formula takes into account tire growth, wheel slippage and is 100% accurate.
-
I use the the Bonneville formula to calculate speed. Really simple. Make a run, go back and collect timing slip and bingo you have your speed. This formula takes into account tire growth, wheel slippage and is 100% accurate.
:cheers: :cheers: :-D :-D
Sum
-
I use the the Bonneville formula to calculate speed. Really simple. Make a run, go back and collect timing slip and bingo you have your speed. This formula takes into account tire growth, wheel slippage and is 100% accurate.
:cheers: :cheers: :-D :-D
Sum
Yeah, I know.
You never really know until it's done.
I have to prepare to be in the ballpark.
I'm obsessing about all this stuff (you guys don't know the half of it!) but..........it's what I do. :roll: :-D
-
It's OK... a little research to figure out where to start is something we all do... some more obsessively than others. It is a balance of what you want and what you need... getting there is the hard part... and the fun part... and the part that makes you crazy...
The time between races stirs the crazy pot... :cheers:
-
Salt time is valuable and getting hard to come by so being half way prepared can secure that record. you never know when the rain will come.
Jon
-
Salt time is valuable and getting hard to come by so being half way prepared can secure that record. you never know when the rain will come.
Jon
x2
When the time comes, you need to be ready enough to roll up to the line, and run a speed/time that is in your "ballpark". Otherwise you are just wasting your (probably limited) resources. Small changes or tuning to equal/exceed your class record can then be implemented.
That, in a nutshell, is the whole point of "planning".
BTW, "implementation" infers the execution of a decision or plan. Those who "fail to plan", simply "plan to fail". (W. Churchill) The BEST race teams I'm aware of: PLAN OBSESSIVELY . . . . go figure . . . . .
Pro teams that run less than competitively "right off the trailer" spend their race weekends playing "catch up". Trust me, nobody on those teams is happy about it . . . . . . especially if . . . :dhorse:
What say you Krusty?
:cheers:
Fordboy
-
Where is a good place to buy rear sprockets?
-
Try PBI sprockets and they are in Oregon
-
Sofadriver,,,,
What is your horsepower number and what is the exact horsepower rpm peak just have to work with ??
Robert
-
"Rebel gears" http://www.rebelgears.com/ will make sprockets which are not available from the big guys at about $50 each, for just about any bike ever made.