Not that the spur gear alone makes that much of difference. With the standard 70t spur gear and the max. 25t pinion, your max. FDR is still limited to 7.28 - which is very short (unless you were planning to put a modified motor into that car - which I would not advise). The speed spur gear set has the advantage, that it allows a wider range of standard spur gears (even non-Tamiya) to be mounted, so that was a very good option part to get and install.