Dear Mr. Know-It-All,

What is the actual top speed of a modern 450 motocross bike? I’ve read on websites and YouTube comments claiming a KTM 450SXF is capable of 123 mph in stock form. I can’t see that being possible, as these bikes are geared to race on an MX or SX track, not drag raced. Could you please clarify?
via [email protected]

Well, Ken, while I don’t have the exact numbers, around the 120-mph mark is in the hunt for a top-speed run on a properly geared 450. The real issue comes with the gearing, setup and traction. About 10 years ago we were out with Robby Bell, who was testing his Precision Concepts KX450 for an upcoming Baja race. He and his mechanics had a radar gun and shot Robby, who was doing flat out in fifth-gear runs on a very long dirt road that had a slight rise going one of the directions. After a dozen runs, with each stint pushing the 103–104-mph mark, one of the tuners gave Robby a backpack full of rocks. His next run was 4 or 5 mph quicker both ways. I was informed that the rear tire was actually spinning rather than gripping at over 100 mph. The additional weight put more load on the rear tire, enhancing the grip, and therefore the top speed improved.

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