Chain and sprocket calculator

Final drive ratio = rear sprocket teeth ÷ front sprocket teeth. A 15-front / 45-rear setup gives 3.00. A higher (shorter) ratio means stronger acceleration but higher rpm at the same speed; a lower (taller) ratio means relaxed cruising rpm but softer acceleration.

Each extra rear tooth shortens the gearing by roughly 2%: the bike pulls harder out of corners and wheelies easier, but at the same road speed the engine spins faster — top speed, fuel range and chain life drop slightly. Going smaller at the rear does the opposite.

One front tooth equals roughly three rear teeth in effect, so the front is the cheap way to make a big change. But a smaller front sprocket bends the chain around a tighter arc and wears the chain and slider faster. For fine-tuning and cleaner wear, changing the rear is the better practice.

Usually yes. Bigger sprockets need more links; the rear axle adjusters give you 20-30 mm of slack to absorb small changes, but beyond that you need a longer (or shorter) chain. Use the link calculator above — chains are sold in even link counts.

It depends where the speed signal comes from. If it reads the front wheel or an ABS ring, nothing changes. If it reads the gearbox output or the rear wheel, the speedo will be off by the same percentage as your ratio change — correction dongles (speedo healers) exist for this.

Replacing a heavier 525 or 530 chain and its sprockets with a lighter 520 kit. It saves rotating mass and is popular on track bikes. Pitch must match on all three parts — chain, front and rear sprocket — so the whole kit is changed together.

Yes, as a set. A worn chain has stretched pitch and quickly chews up new sprockets — and vice versa. If you can pull the chain away from the rear sprocket at the 3 o'clock position and see daylight, the set is due.