Too hot?

you gotta be kidding!
I can do the math but to really play around with gear ratios
you get smart and use this program.
Instant results.........in all permutations.

calculate speed based on engine RPM, drive ratio,and wheel diameter.

Here is your Magic. Screw Math!

gear ratio calculator can be downloaded from:

http://jimsitton.net/ratiocalc/

Just right click on the file gearratio.exe and select "save link as" and put it somewhere you can find it again.

Once it's saved, double click on the gearratio.exe file and it will run.

The program allows for up to three ratios in series.
If you have fewer just leave the unused ratios set to 1:1.

The program will also calculate speed based on engine RPM, drive ratio,and wheel diameter. Be sure to measure the outside diameter of your wheel for accurate results.

KCvale said:

[FONT=Verdana, Arial, Helvetica]To travel one mile a 26" wheel requires 775.5 wheel revolutions.
That is the 'magic number' you have been missing for your speed math.

Your 4G transfer cases 20T/100T reduction is 100/20=5:1
Your 9T engines output to 44T wheel sprocket is 44/9=4.9:1 multiplied reduction.
5*4.9= ~25:1 for your total reduction to your wheel.
[/FONT]
@6800rpm your back wheel would spin 6800/25=272rpm.
Speed is measured in time so now we convert rotations per minute to hours.
272*60= 16,320 rotations per Hour.

Now that magic number...
16,320/775.5= 21mph@6800rpm.

Now that is @6800rpm 'spec' best power but as you know these engines can spin faster, you put out 7560rpm, just work the math yourself now that you know the math and 'magic number'.

See what just changing that 4G 9T sprocket for the 10T does on paper for example ;-}

The more gear change stages you add in the drive train the tougher it gets to do the math, but it's worth it.
My topic for 4-stroke shifter gearing is here http://kcsbikes.com/topic.asp?TOPIC_ID=942

Hope that helps.

Click to expand...

MotorBicycleRacing said:

Here is your Magic. Screw Math!

Click to expand...

Hehehe, that works too ;-}

Misunderstanding, you kept say you had 5:1, but with the transmission. You have 10:1, try a 10 tooth like KC said, see what happens.................Curt

If you don't know the math, a program or spreadsheet can lead you down the garden path.
Thank you guys for all the resources, math and cool links!

Steve

ishman said:

Those 4G belt transmitions come in 2 ratios, either straight shaft or tapered. 20T:80T (4:1) or 20T:100T (5:1).

Click to expand...

Actually there are a couple more ratios available but no WD's (Wholesale Distributors) in the US offer them.

I am pretty involved with 4G development, Don Grube and I are friends and when I was working my 10G long shaft design he put into production of my output shaft design for the 10G into all new 4G's, that mostly being how you can get the output sprocket where you want it on the shaft and 2 sprocket choices.

On another note the 'tapered shaft' engine just has a short shaft with the clutch pads on the engine and not really tapered.

This allows the clutch bell to sit on it's own dual ball bearing shaft and not have to do anything until you rev it up to engage the drum, which is always in perfect alignment with the second pulley, it's one unit.

I have said it before and will continue to say a straight shaft HS engine is a BAD CHOICE for a motorized bike!

It doesn't mater what transfer case you use, even a Skyhawk, they all have one common flaw, the clutch bell is attached to the engine output shaft riding on a brass/oillite bushing opposed to being isolated in the transfer case so everything is aligned in one bolt on unit.

Just a tip maybe someone can use before they buy, and no I don't sell parts but I sure use a bunch ;-}