by Jody Weisel on 07/05/2010
Believe it or not, there is more than one way around a track.
There was a time when the only people who rode four-strokes were grizzled old prospectors tooling around the Southwestern desert (And some guy named Scott Summers) No more! The four-stroke has replaced the two-stroke. The two-stroke had been the bread an butter machine of the last 40 years. The vast majority of riders racing today learned how to ride on a 50cc, 85cc or 125cc two-stroke. Then when they decided to make the step up to the big time, they switched to a valve-and-cam machine.
It is culture shock to switch from two to four (or back again). You wouldn’t think that it would matter what type of engine was bolted between the wheels, but it does. The MXA wrecking crew wanted to delve into why the two-stroke and the four-stroke are totally different machines. And, while we can’t tell you which is better, we can leave a trail of bread crumbs for you to follow on your search for the best bike.
TWO OR FOUR: WHAT’S THE DIFFERENCE?
Listen and listen good! Two-strokes are “rear-wheel handling” machines-they are guided by roosting, railing and rocketing around a track by using the thrust of the rear wheel to bring about direction changes. True, the front wheel initiates turns, but then it gets out of the way as the rear wheel takes over. The typical two-stroke rider rails into a turn with the front wheel cocked in the hoped for direction of travel, and then grabs the throttle to bring the rear wheel around the apex.
Not so with a four-stroke. Four-strokes are “front-wheel handling” machines-they utilize, depend on and wear out front tires. True, a four-stroke’s rear wheel provides motive power, but the front tire plays a large role in direction changes. Four-strokes and two-strokes are like front-wheel-drive and rear-wheel-drive cars when it comes to cornering.
Why the difference? Two-strokes and four-strokes handle differently because of their unique power characteristics. A two-stroke has snappy power that lifts the front wheel, a quicker rev that allows the rear tire to skim across the top of the ground, and no decompression braking to bury the front wheel into the dirt.
Conversely, a four-stroke revs slower, which allows it to drive the chassis without sudden weight shifts toward the rear. Twisting the throttle of a thumper doesn’t lift the front wheel as much as it drives it into the ground.
Additionally, a four-stroke’s decompression braking creates a massive weight shift to the front end on the entrance to corners. With more weight on the front wheel, even the slightest turn of the handlebars rewards the four-stroke rider with instantaneous response.
IS FOUR-STROKE HANDLING BETTER THAN TWO-STROKE HANDLING?
Which is better, front or rear handling? It depends on track conditions.
Front wheel handling bikes (four-strokes) are better in four conditions:
(1) Off-cambers. On slippery, steep and angled banks, a four-stroke can walk across the top, while a two-stroke slides to the bottom.
(2) Hard dirt. The harder and shinier the dirt, the more a four-stroke likes it.
(3) Perfect traction. The quickest way around any corner is to follow the front wheel. On good dirt, a four-stroke goes where you point it-no push, no understeer and phenomenal accuracy.
(4) Stutter bumps. There is something about the gyroscopic effect, crankshaft weight, centralized mass, “every other” firing cycle and well aimed front wheel that makes stutter bumps disappear on a four-stroke (until they get too big-then watch the front wheel).
What doesn’t a front-wheel-handling bike do well?
(1) Sand. All that wonderful four-stroke steering input is confused by shifting terrain. It wanders, refuses to climb up on top of the grainy stuff and wallows. A two-stroke gets up on the sand and stays there.
(2) Mud. What good is the perfect steering input of a four-stroke when it’s so muddy that you can’t steer? And front-wheel steering is of no use when the front wheel is plowing a trench. In the mud, you depend on the rear wheel for everything.
(3) Big whoops. Rear-wheel handling bikes, like two-strokes, can skip across the top of big whoops because they are able to keep the front end out of harms way. Not so with the front-wheel handlers! A four-stroke likes to drive the front end forward (not up), and in big whoops, having the front end come in contact with the whoops is not a good thing.
(4) Potholes. Two-strokes can bunny-hop square-edged bumps, potholes and G-outs. Four-strokes just make them bigger.
WHAT DO REAR-WHEEL-HANDLING BIKES DO BEST?
Two-strokes like big whoops ( even if the rider doesn’t). They work well in loam, because that gives the rear wheel something to bite into. They love to fly (and are easier to manipulate in the air). They excel at quick direction changes through S-turns. They are superior in the first ten feet off a dirt starting line. They can get totally crossed-up in the rough and come out of it. The deeper the sand, the faster the two-stroke goes (because of it’s snappy power delivery and light weight allow it to get on top).
What don’t they like? Rock hard dirt, off-camber corners, concrete starting pads and straights where the extra displacement and higher rpm of the four-stroke make it faster.
PLEASE TELL US THAT A FOUR-STROKE HANDLES BETTER THAN A TWO-STROKE
No. It doesn’t. Plain and simple, a modern four-stroke is too heavy (and even when it weighs the same, it’s every-other-firing stroke makes it feel heavier). Pound for pound, a lighter bike is easier to work with when it comes to handling. While the four-stroke may stay planted to the ground with more authority than a two-stroke, that plus becomes a minus when it comes time to bunny-hop, get light over braking bumps or make quick flicks.
In the grand scheme of things, you give something to get something. When the conditions favor the four-stroke it is awesome to ride. When they don’t, a two-stroke is awesome to ride. But, when it comes to handling, no four-stroke can hold a candle to a two-stroke.
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