ASK THE MXPERTS: CAN YOU COUNT TO FOUR? DO YOU USE FIVE?
Why do current 450 motocross race bikes have five gears? I am a 40-year-old Vet rider and ride a 2013 KX450F. I’ve been to many tracks, and I always seem to spend 90 percent of the time in second or third gear (and occasionally fourth). I never get to fifth gear. The factories could make lighter and stronger three- and four-speed gearboxes that would be enough gears to be competitive. Why don’t they do this?
You might be surprised to find out that every KTM 450SXF four-stroke had a four-speed transmission when the 450 was first introduced in 2003 (and before that the KTM 525SX had a four-speed). Starting in 2010, all of the American 450SXFs were changed to five-speed transmissions; however, Euro-spec KTM 450SXFs, including the 2020 model, still have four-speed transmissions. Additionally, the first 2006 KX450Fs and Suzuki RM-Z450s came with four-speed gearboxes, but the KX450F was changed to a five-speed in 2007 (although all Kawasaki did was add a taller fifth gear on top of the existing four-speed) and the Suzuki RM-Z450 added a gear in 2008.
The reason most modern bikes come with five speeds instead of four speeds is because Kawasaki, Honda, Yamaha and Suzuki have no idea what the end user is going to do with the bike once he buys it. Because of this, they spec five close-ratio gears instead of four widely spaced gears. In your case, that provides you with gear ratios that work best on your track in second and third gear. If you had a four-speed gearbox, the gear spacing could be wider and taller in each gear—and perhaps not as usable on your second and third-gear track.
Additionally, lots of tracks do require fifth gear, and by shifting up through close-ratio gears, the rider can maximize the power on the way to fifth. With a four-speed gearbox, like on the 2010 KTM 450SXF, where first gear on the four-speed was actually second gear from the five-speed it could still produce the same top speed in fourth as the five-speed infifth. The end result for you would be the same. You’d still only be using two gears most of the time, but it might be first and second instead of second and third.
There have been three-speed works bikes, most notably Tim Ferry’s 2002 Yamaha YZ426 Supercross bike; however, it wasn’t a pure three-speed. It was a five-speed Yamaha transmission with fourth and fifth gears blocked out. In motion, that made it a two-speed, because Ferry never used first gear.