Gearing - sprockets, ratios and what one tooth really does

The ratio

Final drive ratio = rear teeth / front teeth. A higher ratio means shorter gearing - more punch, less top speed. A change on the FRONT sprocket has a noticeably bigger effect than the same change on the REAR - because the front sprocket has so few teeth, adding or removing one tooth there shifts the overall ratio much more. The front is the sledgehammer, the rear is the fine adjustment. Rule of thumb: one rear tooth costs roughly 5 km/h of top speed and shifts every gear slightly shorter.

When to change what

• Tight track / kart track: +2 (up to +4) teeth rear - you want to use 2nd/3rd where the stock gearing forces 1st/2nd lugging.
• Fast layout: -2 teeth rear - stop hitting the limiter on the straight before you touch anything else.
• MX/enduro: terrain-driven - deep sand and mud like a tooth more rear (drive under load), fast hardpack a tooth less.
• LAISA encodes the mild version of this as condition rules (tight +1 rear globally, +2 supermoto; fast -1/-2) - the engine suggests, the chain decides.

The chain consequence

Plus/minus 2 rear teeth usually still fits the adjuster range; beyond that you need links (rear +3-4 = typically +2 links). Going DOWN in teeth needs the adjuster pulled back - watch wheelbase: axle further back means more stability, less agility, and more chain wrap wear. Racing chains: 520 pitch is the off-road and conversion standard (e.g. DID 520 ERT3 for MX); check pitch before buying sprockets.

Practical order

Fix gearing BEFORE fine-tuning suspension for a new track - wrong gearing changes where and how hard you accelerate and brake, which changes what the suspension sees.

Gearing by track and condition

The rear sprocket is your fine change; reach for it first. As a starting move off your normal gearing

• Tight / technical tracks and climbs: one tooth MORE on the rear. Shorter gearing gives more drive out of slow corners and up hills where the engine would otherwise lug.
• Fast / flowing tracks: one tooth LESS on the rear. Taller gearing gives more top end and stops you running into the limiter on the long parts.
• Deep sand and mud: one tooth MORE on the rear. The extra drive helps the bike pull under the constant load of soft ground.

The front sprocket is the COARSE change. Because it has so few teeth, one tooth there moves the secondary ratio (rear-sprocket teeth ÷ front-sprocket teeth) far more than one tooth on the rear. Because one front tooth is such a big jump, change the REAR first for anything fine, and only drop to a front-sprocket change when you need a big, clean shift in the whole gearing.