CPI SM250 & related banter

[jaame]

I remember being confused when my dad told me that top level MX races were 250cc in the late 80s. Now I can fully understand it - there's no way you're going to be putting that power down on dirt. Say a 250 two stroke makes 50-60 hp, what does a 500 do? I seem to recall it's only a bit more at peak, nowhere near double, maybe just a better torque curve. Didn't Stefan Everts used to race a CR500 engine in a 250 twin-spar ally chassis when it was first released though? Could be a false memory.

Actually the first time I got on my DT125 I thought it was unbelievebly powerful, but after about a day I was pinning it, in a nice grassy field mind. I'd love to try a proper 2T crosser on an MX track or dirt oval.

[pommes king]

Say a 250 two stroke makes 50-60 hp

that'ld be a bit much - still, the question isn't what a 500 would do, but what does a modern 2-350cc 4stroke do...
Well, about the same, with twice the torque.

If you'ld ever be in Belgium when I'm there, I'll let you ride my WR450 motard - I don't know many who can bring any of those motards to its limits.... (certainly not me)

The nuttiest thing I ever saw was a german who bored his Husaberg motard out to a 800cc and about 80HP...

[maunaloa]

Didn't Stefan Everts used to race a CR500 engine in a 250 twin-spar ally chassis when it was first released though?

I don't remember the engine transplant, but Everts won 10 World Championships in GP and in MX. An amazing rider.

You can buy a new CR500. A large Honda dealer in Indiana bought the rights from Honda.
http://www.servicehonda.com/cr500af05.html

[jaame]

I don't mean to nit-pick, but I am positive that Kawasaki claimed 56hp from their KX250 back in 2001 or 2002. I had a brochure from the NEC show, I used to love those bikes and seriously considered buying a KX125 when I finished uni.

According to "motorcycle and scooter 2011" from Taiwan, the CRF250R makes 41hp, so not really the same. I won't argue that the the torque curve looks better, but 2 strokes make a shitload of torque too.

The other reason two strokes are better is because they are lighter, quieter, and more importantly, you can do no-hander-landers on them. Maybe a modern 4T crosser is similar in weight to a ten year old 2T, but it's got ten years more technology in it. I love the smell of two-stroke in an open space, it brings back a lot of memories. What are the FMX boys using, are they on 4 strokes yet?

I think there's a guy in Taiwan who has a KX250 motard. He's meant to be pretty handy with it too on the track at Longtan.

[maunaloa]

I think most FMX riders are still on 2Ts for power/weight reasons.
http://www.nightofthejumps.com/gallerys ... ?year=2011

[jaame]

I thought so, but someone told me the main reason is because you can't do no hander landers on 4 strokes - the engine braking makes you slow down too quickly when you land.

[jaame]

When I lean over to the right and then accelerate again, there is a weaving sensation coming from the back wheel. The tyre is down to canvas on one side, but has quite a bit of tread left at the other side. I don't think it's round and more, but could this small difference make it weave in that way? It doesn't seem to do it on left handers. What else could it be?

[pommes king]

The tyre is down to canvas on one side

change, then investigate again

[maunaloa]

Uneven tire wear can definitely cause weaving. With a rear tire in that condition, I would avoid metal grate bridges (if there are any in the 'wan), cross wet metal plates and wet road paint vertically... and replace the tire. If you can see fiber or steel fabric, you are WAY past safe.

[rk1951]

When I lean over to the right and then accelerate again, there is a weaving sensation coming from the back wheel. The tyre is down to canvas on one side, but has quite a bit of tread left at the other side. I don't think it's round and more, but could this small difference make it weave in that way? It doesn't seem to do it on left handers. What else could it be?

It is most likey that you need a new tire.