So a 250 4 stroke equals a 125 2 stroke?

That's what a guy was trying to tell me.

WRXR wrote:

That's what a guy was trying to tell me.

Give or take a bit. Orginalted with motocross and what could run in what class.
http://www.dirtrider.com/features/141_0509_125_two_stroke_250_four/index.html

about 75% more for a two stroke (100cc equals 175cc...), give or take due to innefficient gas flow (better at high RPM)..

I don't know if it started in moto cross or not. I know it has deep roots in roadracing too.

Generally speaking it was an old-school rule of thumb in many cases.

Look at horsepower output and weight.

Many of the WERA and CCS classes had distinctions that were close to the general rule of thumb.

What does an off the showroom floor YZ125 make in terms of power? I've seen some estimates of around 34. Wiki says 33.

Most people here would KILL for a 34 horsepower wr250r/x right off the showroom floor.

Blackfoots YZ 250F's make well over 40 hp, the last year guys raced 125's they probably made the same but not really a fair comparison, race bikes have a lot higher output because they don't need to meet emissions
I think the BMW (Husky) 450 dual purpose bike makes 44hp if I remember correctly

Generally speaking a 250cc GP bike could destroy a 600cc superbike.

Technology is catching up....but I think the rough generalization still holds pretty close even though you're trying to compare apples to oranges.

Thanks. Wow.

I rode a 125 Honda once, it had a pretty good top end. Better than my WR. But in the lower rpms it felt kinda the same.

like someone said, your comparing apples to oranges when comparing a cr/yz/kx125 to a wr250r/x.

when you look at the hp numbers a yz125 is close to a yz250f and a yz250 is close to a yz450f. i've seen a dyno sheet done by a local dirt bike mag back in '03 when the 450 first came out. the 250 2T and the 450 4T were only like .8hp apart in peak hp, but the 4T had double the hp and torque to that point.

when it comes down to it racing, its your riding style that'll determine what you should ride. do you limiter bash and scream around full bore all day, then a 2T is for you. if your a bit of a lazier rider, or like to use mid range torque to drive through corners (or you like to compression brake) then a 4T is the bike you want.

the other arguement thrown around is 2T are cheaper to run and rebuild. i tend to disagree, sure it might be cheaper to do a 2T rebuild, but you have to do them 3-4 times more often.

Its really hard to compare the reliability of the two. Two very mildly tuned engines, I would say the four stroke will last longer. The higher the state of tune gets, the more I lean towards the two stroke because of less moving parts so less things to wear out when pushed to the limit.

Another thing is for a given CC the two stroke makes more power all over, most people don't know that. Most people don't know that two strokes make strong bottom end torque because they are usually tuned to keep up with four strokes twice their size, which means they are in a very high state of tune and all of their power is in the top end to match peak power numbers.

A large mild two stroke is a wondrous thing we rarely get to buy. For example, a 450 single. A 4 stroke 450 single making 55 hp is a high strung, unreliable, heavy, expensive, slug. A 450 2 stroke single, if tuned to make the same peak power, would be a light weight, extremely reliable, torque monster that would go twice as long between rebuilds and cost 1/4 as much to maintain.
A lot of people who have never ridden a KX500 or CR500 imagine them to have the same kind of powerband as a 250, only twice as much. Not so. They really don't make all that much more power than a 250, definitely not twice as much. They have stump pulling torque and lots of reliability. Since they aren't in a class competing against four strokes twice their size, they made them all around good engines instead of going for peak power.