Honda CRF250L · CRF300L · Gearing

Sprocket & gearing calculator

What a sprocket change actually does to your bike: the ratio, the trade between acceleration and top speed, the chain you will need, and how far out your speedo will read. Nothing here is a lookup table — it is worked from your own numbers.

1 · Your bike

Picking a model fills in the stock sprockets, chain and tyres. Change anything that does not match what is actually on your bike.

Model

Current front teeth

Current rear teeth

Current chain length (links)

Count them, or read the chain's own marking. This is what makes the new chain length exact rather than a guess.

Chain pitch

#520 — 15.875 mm

Every CRF250L, CRF300L and Rally runs #520. It is not a choice, so it is not a dropdown — and a wrong pitch here would quietly spoil every chain number below.

New sprockets

New front teeth

New rear teeth

Rear tyre

The rear tyre is what turns engine revolutions into road speed, so its size changes every answer below.

Width mm

Aspect %

Rim in

Squat %

Squat is how much the loaded tyre flattens. A tyre rolls slightly less far per turn than its free diameter says; 97% is the usual working figure. Set it to 100 to use the geometric circumference.

2 · Absolute speeds (optional)

Honda does not publish the CRF gearbox ratios, and guessing them would make every speed here wrong in a way you could not see. So instead: give one speed and RPM you have actually seen in top gear, and that single pair calibrates the whole drivetrain — more accurately than published ratios would, because it already includes your tyre, your sprockets and your speedo.

Indicated speed (km/h)

At engine RPM, top gear

3 · What changes

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Final drive ratio

—

Pull at the wheel

—

Change in mechanical advantage. More pull means more acceleration and a lower top speed.

Road speed per RPM

—

At any given engine speed, in any gear. Your top speed moves by this much if the engine still pulls to the limiter.

Speedo error

—

The CRF takes speed from the gearbox output, so a sprocket change puts the reading out by the same proportion as the ratio.

Chain

New chain length

—

Axle travel needed

—

How far the rear axle moves in the adjusters if you keep the same chain. Beyond about 25 mm you are usually out of adjustment.

4 · Speed in top gear

Fill in the calibration above and this becomes real numbers rather than percentages.