Motorcycle Racing News Motorcycle Gearing Calculator Demystifies Transmission Ratios and Calculated Top Speeds

Motorcycle Gearing Calculator Demystifies Transmission Ratios and Calculated Top Speeds

Not a math whiz? Does cold sweat form when you come down to calculating final drive ratios, top speed in each gear at the redline for your optimized track day set-up and so on?

Are you a techno-dinosaur who still thinks a circular slide-rule is advanced technology? Do you rummage through your collection of ancient Cycle magazines to find out what the top speed of some old motorcycle was in each gear instead of being able to figure it out? Yep—me, too.

Well, buck up, Bunky! That need not be the case anymore. It’s a new day and the mysterious world of all of that is now brought into focus with a free web-based motorcycle gearing calculator from an unlikely source called Blocklayer!

Indeed, the site has a variety of very handy calculators and technical support functions for the home handyman, contractor or would-be motorcycle performance maestro.

Here’s how it works:

For this example, I’m using the specifications from the factory service manual for my 1973 Honda CB500K2.

  • Sprockets: Drive 17 tooth, driven: 34-tooth for a final reduction of 2:1 (it can work with pulleys, too)
  • Primary reduction: 3.063
  • Gear ratios: First: 2.353 Second: 1.636 Third: 1.269 Fourth: 1.036 Fifth: 0.900
  • Tires: Front 3.25 x 19 Rear: 3.50 x 18

All you have to do is input this data to the application on the site and it produces an adjustable tachometer, speedometer, and graph where you can enter your shift points, and it plots the calculated maximum speed in each gear! It’s so simple, even a doofus like me can do it. Below are the two graphs the motorcycle gearing calculator produced for the CB500K2 at 8000 rpm and 9530 rpm.

1973 Honda CB500K2 Calculated Speed in Gears at 8000 rpm by Blocklayer online calculator

motorcycle gear calculated speed 8000rpm.png

1973 Honda CB500K2 calculated speed in gears at 9530 rpm by Blocklayer calculator online

motorcycle gear calculated speed 9530rpm.png

There are some caveats on using the calculator. For example, tire sizes in inches should be converted to metric for that part of the process to assure accurate results. Making sure the gear ratios for each gear, primary and final drive reductions are correct is also critical data for an accurate outcome.

Even if everything is spot-on in terms of the data entered, there will still be potential for differences between your calculated performance and the actuals that show up at the timing traps, on your GPS, on your tachometer, or speedometer.

Things such as track surface conditions and ambient environmental conditions will affect final performance, as well. The bottom line—this motorcycle gearing calculator is an enormously helpful tool for bike builders, tuners and owners interested in assessing the potential effect of driveline changes they have in mind before they spin a wrench.

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