Setting the record straight on the 495cc KTM Assisting us in the top speed run was Rod Bush (now gone, but not forgotten). Paul Clipper and I set up the course and did the timing. The facts and figures you read here made up the bulk of an article done on the record ride. So when you read certain things, bear in mind that were talking about 1981. Also, bear in mind that this record still stands and has yet to be beaten by a real dirt bike as of this date. Wed heard about those Baja bikes hitting 115 mph or more, while some experts have flatly stated that no production motocross dirt bike will run over a hundred per. Even with the tallest possible gearing to be had. Well sir, the arrival of a 495 KTM and a genuine maniac Six Days rider appeared to us to be the perfect combination. Rod Bush is the Service Manager of KTM, U.S.A., and has a pretty good track record to back him up. Three golds, a silver and a bronze. Hes also the eleventh-ranked enduro rider in the country. A 16-tooth countershaft sprocket was delayed from Austria, so we had to go with a 15-fang version. Internal changes were needed to make up for this. A 20-tooth fifth gear from a 390 enduro bike was slipped in. Primary drive was 31/79.The gearing at the rear was limited to 48 teeth. Not enough for what we had in mind. A YZ250G rear wheel was found to be a virtual slip-fit, just by making some simple spacers. This let us drop to a 44-tooth rear sprocket, which is just about worth one more tooth on the countershaft. To play it safe, we also installed a gigantic 150.80 x 18 Metzeler, two-ply, nylon tire. This massive tire is almost 29 inches tall and noticeably dwarfs a 4.50 x 18 Metz. A larger tire is much like gearing a bike up. Rod felt that he could get some extra rpm out of the engine by changing the timing. After the bike was thoroughly checked out and broken in, we headed out for famed El Mirage dry lake, home of many high-speed crazies. The lake was in reasonable condition, with a bit of mud and water at the edges. We had enough room for our needs. Two markers were set up and Rod took some initial passes. We checked all three stop watches and double-checked the distances. Our first dozen passes had us in the 108 to 110-mph range. Rod leaned out the main jet in the 40mm Bing carb and slipped into a set of Danaise road racing leathers and a full coverage helmet with a shield. He also felt he could get a greater speed with more distance available before the traps. Because of the limitations of the wet part of the lake, Rod had to try to get the bike up to a high speed on a bumpy fire road. We estimated his speed at near 90 before he got on the smooth lake bed. It worked! On his next pass Rod went over 120 mph! More runs and a semi lay-down position got the speed even higher. Our best run of the day was 123.75 miles per hour! Astounding! We felt that even more speed potential was there if wed have more room and taller gearing. So, whats the point of all this? Basically, we wanted to deal in absolutes. The 495 KTM is representative of a new generation of super bikes. The 490 Maico spearheaded the effort and other manufacturers are girding their industrial loins for the battle to come. In a very dramatic way, a top-speed run is the ultimate dyno. Just how much does it have? What will she do? Make the motor try to punch a hole in the wind. Slap enough gears on it to force the engine to grunt, moan and shudder as hard as it can. Whatll she do . . . indeed.
Posted on: Sat, 03 Jan 2015 18:46:10 +0000
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