MotoGP 2013

[tail_end_charlie]

Me too!

And maybe not...as I guess spinning = the same effect wether it's having power put through it or not? Confusing myself now. Easily done!

Yeah, I'm not sure that a power hit for every revolution of the crank would change anything. Like you say, spinning = spinning. More revs = more torque reaction though, so if you were to compare the 2-stroke and 4-stroke at similar revs, the number of power hits shouldn't matter.

I was thinking that maybe it was because of the overall weight difference between the 2-stroke and 4-stroke bikes of a similar age. To get near the same power out of a 4-stroke your normally need about 2x the displacement of the 2-stroke. So the 4-stroke bikes of the same era weighed more (heavier lever arm) and therefore didn't react as much to the torque reaction.

Or at least that's my guess, I'm not too familiar with the 2-smoke era, so I'm a little fuzzy on specs on the bikes from that millennium.

[tbs]

Yeah, I'm not sure that a power hit for every revolution of the crank would change anything. Like you say, spinning = spinning. More revs = more torque reaction though, so if you were to compare the 2-stroke and 4-stroke at similar revs, the number of power hits shouldn't matter.

I was thinking that maybe it was because of the overall weight difference between the 2-stroke and 4-stroke bikes of a similar age. To get near the same power out of a 4-stroke your normally need about 2x the displacement of the 2-stroke. So the 4-stroke bikes of the same era weighed more (heavier lever arm) and therefore didn't react as much to the torque reaction.

Or at least that's my guess, I'm not too familiar with the 2-smoke era, so I'm a little fuzzy on specs on the bikes from that millennium.

You're probably right.
Apparently the difference in torque reaction by reversing the crank rotation on an IL4 GP bike is worth about a 2kg weight shift front to rear. I wonder also if the more linear nature of the torque curve has something to do with it?

[bogan]

Yeah, I'm not sure that a power hit for every revolution of the crank would change anything. Like you say, spinning = spinning. More revs = more torque reaction though, so if you were to compare the 2-stroke and 4-stroke at similar revs, the number of power hits shouldn't matter.

I was thinking that maybe it was because of the overall weight difference between the 2-stroke and 4-stroke bikes of a similar age. To get near the same power out of a 4-stroke your normally need about 2x the displacement of the 2-stroke. So the 4-stroke bikes of the same era weighed more (heavier lever arm) and therefore didn't react as much to the torque reaction.

Or at least that's my guess, I'm not too familiar with the 2-smoke era, so I'm a little fuzzy on specs on the bikes from that millennium.

I reckon it'll be the crank inertia, did they put heavier flywheels on the 2Ts to dampen out the brutality a bit? Though the 2T crank is going to be a bit heavier anyway as they have to seal the crank volume for each cylinder.

[Mental Trousers]

A bang every revolution will be the reason there's a greater torque reaction for 2T's.

Each time there's a bang the head is being pushed in the opposite direction to the piston/crank. The crank is spinning. Alter the rate it's spinning and you get an opposite reaction.

[tail_end_charlie]

I reckon it'll be the crank inertia, did they put heavier flywheels on the 2Ts to dampen out the brutality a bit? Though the 2T crank is going to be a bit heavier anyway as they have to seal the crank volume for each cylinder.

Quite possible, like I said, I'm not up on 2-stroke internals, so I don't know about crank specs. But if they did have heavier flywheels on the cranks, then that would definately cause more torque reaction, which would mean a greater benefit of reversing the crank rotation. Its most likely a combination of that, plus 2-strokes being slightly lighter overall, and also a more savage power hit that would make it more difficult to try and manage the wheelie.

A bang every revolution will be the reason there's a greater torque reaction for 2T's.

Each time there's a bang the head is being pushed in the opposite direction to the piston/crank. The crank is spinning. Alter the rate it's spinning and you get an opposite reaction.

So you're saying that the 2-stroke would alter the crank speed faster than the 4-stroke, because it got two power strokes for every one of the 4-stroke? Right?
I agree with that, but I'm saying that if you were to take a instantaneous measurement of both motors at the same rpm, the torque reaction needed to resist the rotation of the crank would be the same (and only if the cranks had identical values of inertia, which bogon indicated that they were probably not).

[Mental Trousers]

It's the same, but it's happening twice as often.

[Crasherfromwayback]

I agree with that, but I'm saying that if you were to take a instantaneous measurement of both motors at the same rpm, the torque reaction needed to resist the rotation of the crank would be the same (and only if the cranks had identical values of inertia, which bogon indicated that they were probably not).

I guess it's the more frequent acceleration of the 2t crank that makes it more pronounced?

[tail_end_charlie]

Each time there's a bang the head is being pushed in the opposite direction to the piston/crank.

But this shouldn't matter for calculating torque reaction, this is all contained in the engine itself. So the fact that you're getting twice as many power strokes doesn't matter for actually calculating the torque reaction. Only the rpm and inertia value of the crank.

[tbs]

The torque reaction is caused by the inertia of the crank speeding up. At constant speed there is no reaction. When you give it some gas, the crank speeds up and uses the rest of the bike as a lever to push off, hence the lifting of the front even with the rear wheel in a stand. Does a peaky 2stroke spool up faster than a more linear 4 that can push from lower in the rev range? I'm guessing yes.

[DidJit]

Y'all seen the latest pics of Marquez testing the RC213V in Sepang? Methinks Jorge and Dani are going to have some regular company up the front in 2013...

[Crasherfromwayback]

Y'all seen the latest pics of Marquez testing the RC213V in Sepang? Methinks Jorge and Dani are going to have some regular company up the front in 2013...

Yeah looking good eh!

[DidJit]

Very.

[tail_end_charlie]

The torque reaction is caused by the inertia of the crank speeding up. At constant speed there is no reaction. When you give it some gas, the crank speeds up and uses the rest of the bike as a lever to push off, hence the lifting of the front even with the rear wheel in a stand. Does a peaky 2stroke spool up faster than a more linear 4 that can push from lower in the rev range? I'm guessing yes.

OK, so I slept on it a little bit. Torque reaction is cause by the acceleration of the crank, so the fact that a 2-stroke can accelerate the crank faster than a 4-stroke (because of more power hits per revolution of crank) is part of the reason why the 2-strokes seemed to suffer more from torque reaction. That and a heavier crank (more inertia) and their light overall weight to resist the torque reaction which all added to the problem.

That was what MT was trying to say as well wasn't it?

[tail_end_charlie]

Y'all seen the latest pics of Marquez testing the RC213V in Sepang? Methinks Jorge and Dani are going to have some regular company up the front in 2013...

.......Jorge and Dani and Rossi......

Eh? Eh? Whose going stand up and predict that there will be 4 aliens again in 2013?

[Mental Trousers]

OK, so I slept on it a little bit. Torque reaction is cause by the acceleration of the crank, so the fact that a 2-stroke can accelerate the crank faster than a 4-stroke (because of more power hits per revolution of crank) is part of the reason why the 2-strokes seemed to suffer more from torque reaction. That and a heavier crank (more inertia) and their light overall weight to resist the torque reaction which all added to the problem.

That was what MT was trying to say as well wasn't it?

Pretty much