HondaRideRed, on 05 April 2012 - 05:14 AM, said:
I myself have never ridden a 2 stroke, everyone I know rides a 250f or a 450f. Everyone is always saying to me how they are out dated and hard to ride well. I am looking at going into my first year of motocross, I ride a 2009 CRF250R but since I'm really short and it's a pain to start. Though how everyone seems to make out that the 2 stroke is hard to ride puts me off buying one seeing as it will cost around $9000 for a 2012 150sx and if I don't like it or it's just not as effective as my 250f then I can't really resell it as I would lose a few thousand.
Well, welcome to the big debate! A debate which has been thrashed around the world of motocross for more then 10 years.
Now before I begin a multi-page diatribe on the pro's and con's of each bike, I will begin by saying one simple thing. If you plan on
racing motocross and you want to do well racing said motocross, I would put owning a small-bore (125/150) 2 stroke on the far back burner. Spend every dime you have, buy a 2012 KX250F, put a
Pro Circuit rear link, offset triples and exhaust on the sucker and go race. There is no debate, there is no conversation, that IS the bike and if you wanna race, its got your name written all over it.
Everyone is entitled to have an opinion on the subject, so let me try and explain a few things which make the whole 2 stroke vs 4 stroke "discussion" (argument) more understandable.
When a motor produces power every stroke (every time it goes up and down), it produces constant "electric" power. Its
smooth, its super crisp and it spins the rear wheel constantly. This is because there really isn't much of a break between the power pulses. When a motor produces power every OTHER stroke, (every other time the piston goes up and down) there are tremendous losses in the over-all power the motor can produce. It also means, there is a slight break in the power hitting the ground, this gives the tire a break under acceleration. Because of the losses associated with a 4 stroke design, it can't produce the power of a 2 stroke at the same CC level. So a modern 125cc 2 stroke (half the cc of a 250) has equivalent power to a 250cc 4 stroke. A 250cc 2 stroke has more or less equivalent power to a 450cc 4 stroke and so on. Now, 4 strokes drivetrain steals a considerable amount of power to run from the retaining springs it needs to push past, to the larger flywheel/crank it needs to keep running. So 4 strokes in general are more heavy and much more complex then 2 strokes.
Now, here is the real kicker... A 2 stroke motor is basically a big vacuum pump. The piston moves up and down, it sucks in fuel/air and it pushes that mixture out and into the combustion chamber where it explodes and produces power. But just like a vacuum pump, with less pressure, it doesn't do its job as well. The higher the pressure, the more sucking it does, henceforth the more power it produces. So in layman's terms; 2 strokes need to have more pumping action to produce power (its the same on 4 strokes to a certain extent). That means two things; the higher the RPM the more power you produce OR the bigger the bore the more power you produce. 4 strokes however, don't pump, they just suck and blow (no pun intended LOL ). So they suck in the air/fuel mixture through HUGE valves (ports) and then immediately compress it. Because of this and the power pulses, 4 strokes generally produce power at extremely low RPM's, making them extremely tractable. This is why a lot of people call 4 strokes "tractors" because you can literally stop in a corner without the clutch in and get on the throttle and it will "chug" you out of the corner. Where if you did that same trick on a small-bore 2 stroke (like a 125/150), you'd fall flat on your face the first time around. Thats because its just not moving enough air/fuel mixture around, it just can't produce the power with that little bore. At the same time the larger the vacuum pump (125 < 150 < 250 < 300) the more bottom end you make because it moves MORE air/fuel mixture at a lower RPM. Again, this concept is the same on 4 strokes, just a little bit less pronounced since 4 strokes only have have to suck and blow.
Now, when it comes to riding, a larger bore 2 stroke will obviously be more similar to a 4 stroke because as I said, the larger the bore, the more air it can move at lower RPM's. A 500cc 2 stroke has bottom end like a 450 does, its unbelievable. So the "happy medium" has been in recent years a 250 2 stroke. Thats about where the bottom end starts be enough that it can get out of its own way at lower RPM's without intervention (clutch use). Surprise, surprise, seeing a similarity? 250 4t's and 250 2t's being "lugable". A 250 2 stroke however does have a lot more power, more then any one of us would ever need, so its a double edged sward. The smaller the bore, the narrower the power band which means, you need to ride the bike faster in order to keep it in the right power range. You also are forced to learn how to use the clutch and the rear brake because both of those things are necessities for slowing down and getting a small-bore 2 stroke to "pop" out of a corner. When your physically riding the bike, there is less rotating mass, less gyroscopic force, so the bike will go anywhere you want it to go, literally. But at the same time, there is less stability because that gyroscopic force does help keep the bike upright.
Finally, lets look at the numbers (these are generic just for reference, so don't go looking for them)
150cc KTM 2 stroke produces 18.2lb torque at 6 - 8k RPM and 40hp at 9 - 10k where it signs off quickly. So as you can see, 6k - 10k not much power band
250cc KTM 4 stroke produces 18.8lb torque at 4 - 6k RPM and 38hp at 10k - 12k where it keeps pulling until the electronic rev limiter kicks in. 4k - 12k, much wider power band
So there are pro's and con's to each design. Obviously as you can read above, a 125/150 2 stroke is a lot more work to get around the track and mistakes can be the end of your race, even simple ones. However, they are extremely easy to operate and own from their simple carb's and much easier
maintenance, to the lower purchase price and TOC (total cost of ownership). 250 4 strokes cost more to purchase, they are also harder to tune unless injected, but they still have a much more maintenance.
Finally, I don't know one person who hasn't ridden a 125/150 and not fallen in love. The sound, the
powerband, the snappiness of the throttle, the rear wheel steering, the light-weight, they are so much fun to ride, its difficult to NOT own one. At the same time, I do think they are a lot of work to ride and that kinda means, you've either gotta be a better rider then your friends on the 4 strokes, or you've gotta ride a bigger 2 stroke, like a 250.
Edited by tye1138, 06 April 2012 - 09:09 AM.
