what I liked with this one (above of the very low price) that the spur gear fits well because it's wide. I attached to the engine inside-out, so the screw are far from the engine, makes it easy to mount, and because of the wide size, it still has full contact with the spur gear. I am using it since a few weeks on asphalt track with my xray, runs +80kmh on track, no problem whatsoever.