About This Site
EMoto Gearing Planner is two calculators and four explanations. The calculators work out gearing and chain length for Sur-Ron Light Bee class electric dirt bikes and the machines built to the same pattern. The explanations exist because the calculators make assumptions, and a number handed over without its assumptions is worth very little.
Why it exists
Gearing calculators for motorcycles are built around an engine, a gearbox and a mechanical redline. These bikes have none of the three. What they have instead is a single fixed reduction, one sprocket pair the rider changes, and an rpm ceiling that lives in the controller’s firmware rather than in the metal. Feed that machine into a tool designed for the other kind and you get a plausible-looking answer that is wrong in a way nothing on screen reveals.
Chain length has a parallel problem. The published tooth-count-to-link-count charts are correct for the bike they were produced on. They cannot see your swingarm, your axle position, or your tensioner, and they do not say so. This site asks for the measurement instead and hands back a range.
Who runs it
One person, independently. The site sells nothing, takes no sponsorship, runs no affiliate links, and has no commercial relationship with any manufacturer or parts vendor. It is not affiliated with Sur-Ron, Talaria, Segway, or any of the vendors whose published figures appear on it. Those figures are reproduced with attribution because attribution is how you check them, and their appearance here is not an endorsement of the vendor and not a claim of accuracy on our part — it is a record of who published what.
The editorial rule
One rule, applied everywhere: no number is published without a named source, or an explicit label saying it is a user input or an assumption.
In practice that means preset values in the calculator carry their source next to the field they filled. Figures we could not verify for a particular model are marked UNVERIFIED and show a warning, rather than being quietly presented as fact. The 0.97 rolling factor is labelled an assumption and left editable, because it is one. And where we have no figure at all — measured centre distances for aftermarket swingarms, rpm ceilings for aftermarket controllers — the site says so and leaves the gap open.
What it will not do
It will not publish estimated figures to fill a gap, because a plausible invented number is more damaging than an admitted absence: people use it instead of measuring. It will not tell you whether a part physically clears your bike, which is a question for a tape measure and a trial fit. It will not model acceleration, battery behaviour or thermal limits, which need instrumentation this site does not have. And it will not tell you your chain is correctly tensioned — the chain length calculator gives you a link count, and checking tension before you ride remains yours to do.
Found a figure here that is wrong? Corrections with a source are welcome and get acted on.