Motorized Bicycle Gear Calculator

GoldenMotor.com

Goat Herder

Gutter Rider
Apr 28, 2008
6,237
20
38
N.M.

Dan

Staff
May 25, 2008
12,765
115
48
58
Moosylvania
Thanks GH! I am going to try and trash infopath and see if it will ask me what to open with.

Can't we all just get along!? LOL, talking to my programs
 

thefruitgnome

New Member
Dec 20, 2008
14
0
0
UK
This is a great way to see "how fast" someone could relatively go on a motor bike at a certain rpm. I used it with a 26" rim 11tooth drive sprocket, 36tooth rear sprocket, and an rpm of 2200. It gave me the speed of 52mph. But somehow this does not seem right.
think its because its not taking air resistance or weight into account.
 

ducatiluke

Member
Jan 20, 2009
39
0
6
los angeles/ south australia
no thats not right

firstly
is the 11 tooth pully or sprocket mounted on the engine crankshaft or a gearbox?

if its a chinese 2 stroke motorized kit it uses a geabox so you will have to remove the gearbox cover and count all the teeth involved

i believe its somthing like 20 teeth on the crankshaft
then 90 on the clutch
 

atombikes

New Member
Feb 14, 2010
525
2
0
Northern VA
Ahhh! What am I doing wrong? I am trying to calculate final drive for a mid-drive (jackshaft) setup, to select the best gears on the clutch, jackshaft and rear wheel.

The problem is (and I obviously must be doing some wrong) that for instance, if I change the gears on the jackshaft around (i.e the input is a 13 tooth, output is a 18 tooth; then swap them round to a 18 input, 13 output) the resultant speed remains the same! Its like I can't affect the final drive ratio at all?? WTH?
 

Felton

New Member
Dec 17, 2009
92
0
0
GA
One ratio would be 18/13 or 1.385/1 and the other would be 13/18 and would be .722/1
 
Last edited:

Felton

New Member
Dec 17, 2009
92
0
0
GA
tell me what you have and what your tring to do and maybe I can help or are you tring to figure out what you need to get?
 

atombikes

New Member
Feb 14, 2010
525
2
0
Northern VA
tell me what you have and what your tring to do and maybe I can help or are you tring to figure out what you need to get?
Trying to figure out what I need to get, or more specifically, if some components I have sourced will work. From the HF 79cc Utility Bike thread, I said I found a Hilliard centrifugal clutch at Northern that has 12 teeth; also they have a jackshaft kit that has a 13 tooth and 18 tooth cogs in it. So I was trying to input those, along with an assumed rear wheel gear, to see if I was in the ballpark. I put in the 13 and 18 tooth gears in one way, and then when I flip them, the output on the calculator remains unchanged, which makes no sense to me? It's gotta be operator error, I just can't figure out what.
 

Felton

New Member
Dec 17, 2009
92
0
0
GA
Thats right the utility bike. I didn't put two and tow together. Sorry, most likely your first reduction will have to be at least 2/1. So a minimum of a 24 tooth sprock will be required (24/12=2/1). That sprocket would be attached to your Centi. clutch via chain. on the other end of you jack shaft you would want something around a 9-12 tooth sprocket. That would be run to your rear axle by chain.

You want to multiply your first reduction by your second reduction to get the total reduction.

So if your second reduction went from a 10 tooth to a 72 tooth (72/10 or 7.2/1) and your first reduction went from a 12 to 24 (24/12 or 2/1) your final reduction would be 7.2 x 2 which equals 14.4 or 14.4/1

Clear as mud huh???
 
Last edited:

atombikes

New Member
Feb 14, 2010
525
2
0
Northern VA
Thanks, Felton. So would it be easier for me to use the jackshaft to get to the right side and then drive that thru a freewheeling crankset, finally back to the rear wheel (ala sickbikes shiftkit)??? I can see how I might have issues getting large sprockets for a 5/8" jackshaft.
 

Dan

Staff
May 25, 2008
12,765
115
48
58
Moosylvania
Cobra found this. Looks pretty cool.


Here is a handy tool I found. Rake and Trail Calculator
RB Racing Rake and Trail Calculator

Just punch in your numbers and it will tell it like it is. You can change your input numbers to see what it will take for you to get to your zone.

I just did my bike with it and came to 2.28 (I said to Roland earlier that I thought it was 1.48 but I did my math wrong) It's very close to 2.5" . I'm not going to sweat 1/4". I'm happy with the handling right now.
Not gear related but thought it would go well with the other calcs
 

ducatiluke

Member
Jan 20, 2009
39
0
6
los angeles/ south australia
asuming jackshft has two equal sprockets
your final ratio will be 10 tooth / 54 tooth
=5.4 to one ratio
which is too tall for a 26" wheel
would be ok if your rear wheel was 20"

reduce the number of teeth on jackshaft sproket that connects to rear wheel