Kolb Machine / Land Speed Racing: Why 125CC?

THIS 2011 Aprilia 125cc SuperMartXe' VIP Team / Paris Hilton.

NOT THIS

There are many good reasons why we run a 125 at Bonneville or on the track, here are a few:
1) My buddy Dwight had a 1996 Honda RS125 motor in my shop and it sounded like a good idea to build a land speed bike for this motor.... but it's actually much deeper than that...
The reason there were 125cc bikes in my shop was due to the acknowledgment by my friends that the only way to find out what it is like to ride a race-bike is through riding a Honda or Yamaha 125 or 250 GP bike that has been imported from the land of the rising sun. The key letters being GP, that is Grand Prix, the real McCoy, the shit. And in the words gleaned from an English cooking show, its fookin' pukka. I assume that means genuine or awesome. anyway...I had the good fortune of running a friends 96' RS 125 and within two laps i understood what they were getting at. If you have never had a go i highly suggest seeking one out at a track day and begging for a spin, like we used to do when the first dirt bike showed up in our neighborhood as kids.
2) This next bit is really going to offend the majority of racers: Street bikes converted into race bikes, and or track day bikes, are fookin' pigs. I don't care how much money you spend making the bike lighter and quicker it will never equate to the riding experience undergone while riding a purpose built race bike. Once I was tuned into this my track life changed for the better. It turns out this might be the least costly way to race and or do track days, the 125 that is-a 250 not so much. More on that later, for now a brief and slightly informed history of why the 125 is such a noble steed.

3) This is a 1996 Honda RS125 2-stroke GP motor. It weighs only 38 pounds and in a mild state of tune puts out 42HP at the rear wheel. A more potent, slightly more modern, and an extremely more expensive version might put out as much as 55HP at the rear wheel! With a proper chassis a complete bike weighs in at 150 pounds and in the GP stables they weigh even less. This is one reason a 125's corner speed is greater than a 600 and a 1000cc superbike, its all about the power to weight ratio. (Note: this is based on observation and hearsay, i have no actual speed gun readings of pro riders all going through the same corner on said bikes. If you have that info please post a comment so i can be humbled or more confident in my corner speed arguments.) Our current land speed bike weighs in at 200 pounds even, not bad for a motorcycle with a 104 inch wheel base.

Some historical perspective; I recently read Kevin Cameron's' book, 'Classic Motorcycle Race Engines' and discovered that Suzuki's GP125 single in 1962 had the same bore and stoke as the modern GP motors. That's fifty years ago! It was air cooled with a rotary valve and produced 22HP and would get up to 30HP after two more years of development which included water cooling. The bore and stoke of the Honda motor pictured above is nearly identical to the fifty year old Suzuki RT62 at 54mm x 54mm, and while this similarity might be layed in bedrock as a perfect engineering solution to what is needed from a 125, it most importantly bolsters our desire to get the most out of a historically significant displacement. Keep in mind this single cylinder format would be doubled and doubled again to create 250 twins and 500 fours, all three sizes becoming the GP standard race classes in the modern era of GP racing.

4) The 125 format is just plain handsome in its simplicity. This jewel is our newest 125cc motor which took us to a top speed of 155MPH at Bonneville last year with a new AMA record of 149.907. With 48HP at the rear wheel at sea level and probably 42 or so at Bonneville elevation we are nipping at the heals of bikes with 8 times our displacement. We will be running the bike on the dyno to verify these dubious horsepower figures next month. The Rotax bottom end design goes back to the 80's i believe. The Aprilia cylinder and BRC head are both from the last 5 years or so.

So for all the dopes who have made faces and or scoffed at what we do at Bonneville, history and the pragmatic engineering of a 125cc 2-stroke motor is on our side while we very quickly approach the AMA land speed records of most 600cc four strokes and have surpassed all but two of the 1000cc AMA records held by Harley Davidson's. Two more miles per hour and those two Harley records are done for. That might sound childish but I can't wait!