Kyosho IS117 43T Hard Bevel Gear ST-RR Evo

A 43 tooth hard specification ring bevel gear for Kyosho's Inferno ST-RR Evo truggy differentials.

This is the large bevel gear inside the diff that the drive pinion meshes against, and together the pair transfer drive from the centre driveline out to that axle. On a 1/8 truggy it is a serious load-bearing component: all the drive to that end of the car passes through the mesh between two bevel teeth at any given moment, and the tooth form has to stay exact for the diff to run quietly and last.

The hard specification is a heat treated grade. Truggies are heavier than buggies and carry more rotating mass in their wheels, so the shock loading through the diff gears when a tire regains traction after a landing is substantially higher, and a standard gear wears faster under it.

Wear follows a predictable path: the tooth faces polish, then pit, then round off, and the diff gets progressively noisier under load until teeth begin to strip. Running this against a worn pinion just destroys it, so replace them as a matched pair.

It mates with the 10 tooth pinion for a 4.3:1 ratio.