What’s the difference between “48 pitch” and “metric 48 pitch” gears, and how can I tell what’s in my car?
A gear’s pitch refers to its tooth size. The smaller the number, the bigger the tooth. In RC, we most typically see 32 pitch (common in high-power vehicles), 48 pitch (most 1/10 scale), and 64 pitch (generally seen only in pan cars). Each of these has a metric equivalent, or at least a rough equivalent. The correct term for the tooth size of metric gears is “module.” A 0.6 module gear is referred to as “metric 48 pitch” but is actually 42.3 pitch. Standard 48 pitch and “metric 48” pitch gears will not mesh together properly. Competition cars typically have standard 48 pitch gears, while sport cars from Tamiya and Kyosho are generally metric pitch.
As for telling metric and standard pitch apart when uncertain, the best thing to do is check your manual and the gears themselves for any labeling that indicates metric or standard pitch. If that doesn’t provide the answer, try meshing the gear with another pinion or spur that you do know is standard or metric. If the gears mesh smoothly, you’ve got a match. If the mesh feels notchy, you’ll know you’re mixing metric and standard pitch.
Tamiya cars and trucks, like this TT-02B, typically have metric gears. Both of these gears have 21 teeth; the silver gear is “metric 48 pitch” and is noticeably larger than the standard 48 pitch gear.