Pick up any motorcycle magazine today and they'll tell you at length about what a fantastic machine the YZ400/426 is. Sent down from heaven on a beam of blue light, the Yamaha has it all; speed, agility, and most importantly, it has four separate strokes. It's true; everybody likes to twist the "loud handle" on a YZ. They look good, they sound good, they are sure fun to wheelie and they do accelerate like crazy, but is this machine really the phenomenon that everybody seems to think it is? Or more realistically, are people just thrilled that the motor vehicle industry started to upgrade the technology of dirt bikes? I may be the only one, who feels this way, but to me, the YZ400 is a long way from being the perfect fourstroke, much less the perfect two-wheeled missile that everyone seems hypnotized into believing. Let me explain why.
I hold dirt bikes up to be measured by three fundamental rules.
Fundamental number one is this; weight always hurts you; it never helps. With all the advancements in our sport in the last decade, how everyone can make such a fuss over a bike that still weighs nearly 280 lbs wet is just beyond me. When you look at the complexity issue, and then factor in what it does to the weight of the machine, it is even clearer that the YZ is not the heaven-sent perfect bike. You know your buddy that's totally into mountain bikes? He spends hundreds and hundreds of dollars on lighter parts just to save a few GRAMS! And we load our dirt bikes up with about every gizmo that the engineers, (or is it the sales department) can think up. In 1975 we had dirt bikes that weighed less than 200lbs, don't tell me that we can't design one today. Really, if you use a chromemoly frame, keep the engine's overall size down by using a three or four-speed tranny, and make an effort to design things smaller and lighter rather than the other way around, it can be done. I'd enjoy seeing some exotic metals like carbon fiber rods and ceramic pistons; maybe even some Ti now that Russia is selling it for far less money. What is the weight of a stock YZ engine now, something like 90 lbs? Let's try to get that down to about 50, (which is still 10 lbs heavier than a 250 twostroke). Then see how it feels to fly on a bike that's only 210lbs, rather than 280.
Fundamental rule number 2 is that complexity will always return to bite you in the ass. Take a look at the YZ engine for a minute. Five valves, two cams, a computer controlled carb, and more wires, hoses, and gadgets than my Ford van. Friends, what we need in a dirt bike is much less of this unnecessary over engineering and a return to dirt bike simplicity. More parts means - more parts to break. Our shop sees tons of bikes for broken gizmos. Was Yamaha was just trying to impress us with their technology, rather than design a really innovative and practical engine? If so, all they got was complexity, not new technology. The formula car guys are experimenting with rotary drum valves that don't reciprocate at all, so there are no cams, valve springs, etc to adjust, wear out, or to limit the revs. That's a prime example of a simpler but more advanced system. I'm not advocating a return to the XT500, but sometimes I think that would be better than what we've got now. Look at the old 84 Husky 500 fourstroke. It used a twostroke bottom end, and it didn't even have an oil pump, but it ran hard and lasted forever. They ran the oil up the cam chain, and all the top end parts were roller or needle bearing mounted, so it didn't need much oil anyway. And I know there's a big debate about whether fourstroke carbs need accelerator pumps or not, but the roller-flat-slide carb on my YZ makes me nauseous. Honestly, if you were going to have all the 3D mapped ignition curves, wouldn't you be better off with fuel injection?
Fundamental rule number 3 states that if you're going to build a fourstroke, make sure it has a fourstroke powerband. As any YZ400 rider knows, if you don't keep it spinning it's going to stall, usually in the middle of a crowded turn or at the bottom of a hairy step-climb. I even ride twostrokes like they're fourstokes, using a high gear and lots of throttle opening, but the YZ400 is one fourstroke that must be ridden like a twostroke. It has very poor power down low, and it makes most of it's power up higher than God intended fourstrokes to be revved. The key to acceleration is more about how much power you can put to the dirt, not how much peak power you can build. I've had the pleasure to ride a few factory built 250 supercross bikes, and they're the opposite of what you'd think. They were all bottom end and tractability, and as flat as Kansas on the top. They would have made the most fantastic trail machines ever because they were so easy to get traction and so fast out of the turns. This is more what I expect out of a fourstroke, and I'll absolutely guarantee you that built the right way, a fourstroke can rev no further than 7000 rpm and still accelerate faster than any twostroke on the track. If you look at the original Vertimati's, they had two and three speed gearboxes, and it's said that they only needed 1st and 2nd for starts; they could race they entire MX course in third, and they kicked ass on the twostrokes. Just close you eyes and imagine THAT kind of wide tractable torque. It'd be fun, right? Not much like a YZ400, is it? I rest my case.
My point is this; Yes, I think the YZ is the best fourstroke on the market today, and it's not likely to be challenged anytime soon, even by the Cannondale (don't get me started on that!). But what we want is not an 11000-rpm street bike engine in a frame with long suspension and knobbies. What we need from a four stroke is simplicity, lightweight, and tractability above all else. So while I'm out riding on my YZ, I'm still searching the heavens for another beam of light.
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Pete Denison
A-Loop Offroad, Inc.
“The Artists Formally Known as Moose Offroad” www.aloop.com
<p align=right>12-07-1999 :Edited<p align=right>12-07-1999 :Edited
I hold dirt bikes up to be measured by three fundamental rules.
Fundamental number one is this; weight always hurts you; it never helps. With all the advancements in our sport in the last decade, how everyone can make such a fuss over a bike that still weighs nearly 280 lbs wet is just beyond me. When you look at the complexity issue, and then factor in what it does to the weight of the machine, it is even clearer that the YZ is not the heaven-sent perfect bike. You know your buddy that's totally into mountain bikes? He spends hundreds and hundreds of dollars on lighter parts just to save a few GRAMS! And we load our dirt bikes up with about every gizmo that the engineers, (or is it the sales department) can think up. In 1975 we had dirt bikes that weighed less than 200lbs, don't tell me that we can't design one today. Really, if you use a chromemoly frame, keep the engine's overall size down by using a three or four-speed tranny, and make an effort to design things smaller and lighter rather than the other way around, it can be done. I'd enjoy seeing some exotic metals like carbon fiber rods and ceramic pistons; maybe even some Ti now that Russia is selling it for far less money. What is the weight of a stock YZ engine now, something like 90 lbs? Let's try to get that down to about 50, (which is still 10 lbs heavier than a 250 twostroke). Then see how it feels to fly on a bike that's only 210lbs, rather than 280.
Fundamental rule number 2 is that complexity will always return to bite you in the ass. Take a look at the YZ engine for a minute. Five valves, two cams, a computer controlled carb, and more wires, hoses, and gadgets than my Ford van. Friends, what we need in a dirt bike is much less of this unnecessary over engineering and a return to dirt bike simplicity. More parts means - more parts to break. Our shop sees tons of bikes for broken gizmos. Was Yamaha was just trying to impress us with their technology, rather than design a really innovative and practical engine? If so, all they got was complexity, not new technology. The formula car guys are experimenting with rotary drum valves that don't reciprocate at all, so there are no cams, valve springs, etc to adjust, wear out, or to limit the revs. That's a prime example of a simpler but more advanced system. I'm not advocating a return to the XT500, but sometimes I think that would be better than what we've got now. Look at the old 84 Husky 500 fourstroke. It used a twostroke bottom end, and it didn't even have an oil pump, but it ran hard and lasted forever. They ran the oil up the cam chain, and all the top end parts were roller or needle bearing mounted, so it didn't need much oil anyway. And I know there's a big debate about whether fourstroke carbs need accelerator pumps or not, but the roller-flat-slide carb on my YZ makes me nauseous. Honestly, if you were going to have all the 3D mapped ignition curves, wouldn't you be better off with fuel injection?
Fundamental rule number 3 states that if you're going to build a fourstroke, make sure it has a fourstroke powerband. As any YZ400 rider knows, if you don't keep it spinning it's going to stall, usually in the middle of a crowded turn or at the bottom of a hairy step-climb. I even ride twostrokes like they're fourstokes, using a high gear and lots of throttle opening, but the YZ400 is one fourstroke that must be ridden like a twostroke. It has very poor power down low, and it makes most of it's power up higher than God intended fourstrokes to be revved. The key to acceleration is more about how much power you can put to the dirt, not how much peak power you can build. I've had the pleasure to ride a few factory built 250 supercross bikes, and they're the opposite of what you'd think. They were all bottom end and tractability, and as flat as Kansas on the top. They would have made the most fantastic trail machines ever because they were so easy to get traction and so fast out of the turns. This is more what I expect out of a fourstroke, and I'll absolutely guarantee you that built the right way, a fourstroke can rev no further than 7000 rpm and still accelerate faster than any twostroke on the track. If you look at the original Vertimati's, they had two and three speed gearboxes, and it's said that they only needed 1st and 2nd for starts; they could race they entire MX course in third, and they kicked ass on the twostrokes. Just close you eyes and imagine THAT kind of wide tractable torque. It'd be fun, right? Not much like a YZ400, is it? I rest my case.
My point is this; Yes, I think the YZ is the best fourstroke on the market today, and it's not likely to be challenged anytime soon, even by the Cannondale (don't get me started on that!). But what we want is not an 11000-rpm street bike engine in a frame with long suspension and knobbies. What we need from a four stroke is simplicity, lightweight, and tractability above all else. So while I'm out riding on my YZ, I'm still searching the heavens for another beam of light.
------------------
---------------------------------------------
Pete Denison
A-Loop Offroad, Inc.
“The Artists Formally Known as Moose Offroad” www.aloop.com
<p align=right>12-07-1999 :Edited<p align=right>12-07-1999 :Edited