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Tech Info

GEAR RATIOS From Baker Drivetrain

This page explains GEAR RATIOS. This is the art and science of optimizing the transmission gear sizes to the desired RPM-vs-Speed performance. The variables we finesse to achieve the perfect balance are the motor sprocket, the transmission gearset, the transmission pulley/sprocket, the wheel pulley/sprocket and the wheel size.

The fundamentals of this mastery reside with the following two equations:

RPM = (S × Sr × Pc × G × 88.00) ÷ (Tc × Sf × Pm)
Speed = (RPM × Tc × Sf × Pm) ÷ (Sr × Pc × G × 88.00)

Use the diagram below to determine what your speed or RPM will be.


S	Speed (miles per hour)
RPM	Engine revolutions per minute
Sr	Rear sprocket tooth count, secondary drive
Pc	Clutch sprocket tooth count, primary drive
G	Gear ratio
Tc	Circumference of rear tire: (diameter (ft.) X 3.1416) Typical tire is 25” in diameter Example: 2.083ft. (25”) X 3.1416 = 6.54ft.
Sf	Front pulley/sprocket tooth count (tranny output, secondary drive)
Pm	Motor sprocket tooth count, primary drive

The baker Transmission guts
Now that you have the equation (above) to fine tune your drivetrain. Let's go deeper. Let's add to the math by introducing you to more variables to the equation: The gearbox ratios. Many treat it as Pandora's box for a reason. But we'll coach you through.

Below is a list of links that lead pages that have more details about BAKER transmission gearsets that fit within the Harley-Davidson transmission cases. In these pages the gear ratios for the according BAKER transmission will be displayed so you have the knowledge to make the best choice for your bike.


Direct Drive 6-Speed	Overdrive 6-Speed	Direct Drive 5-Speed

The Torquebox	XL6

Math is Hard - We're here to help.
we notice for some reason a lot of bikers don't do math. How odd. Now some do it well, but many don't. So, we're here to help you through this part.

Fill in the blanks on BAKER's RPM vs. Speed Calculator. This popular online tool allows you to finesse, massage, and work the numbers up and down until you reach the desired effect. Give it a pull

Launch the BAKER RPM vs. Speed Calculator
(If your Pop-up Blocker in enabled, you may have to hold down your "CTRL" key on the bottom/left of your keyboard to get this link to work).

Belt And Chain Drives

For Information on Belt and Chain Drives Download the PDF http://kopflex.com/eptroot/public/schools/beltchan.pdf This is a 10 pager with detailed tech info on belt or chain final and primary drives

Tranny OffSet

The Evo powered Harley Softail is the design basis for custom aftermarket components like frames, transmissions, and engines. The positional relationships between engine and transmission, engine and frame, and transmission and frame all go back to the Softail. The stock Softail from the factory is a well-balanced machine with no significant weight bias from the left to the right. If a wider than stock rear tire is used on a Softail, the powertrain (engine and transmission) must be moved to the left to allow the 1-1/2” wide drive belt to clear the left side of the rear tire. Moving the powertrain to the left is referred to as powertrain offset. Powertrain offset can be achieved by moving the transmission and/or engine to the left, away from the stock position. The math to explain this is easy; see the figure below. The stock H-D Softail has a 130 size rear tire that is roughly 5.5” wide. The 300 tire is roughly 12” wide, which means there is 3.25 more inches of rubber on each side. This means the powertrain has to move to the left about 3.25” or so.