17 hours ago, section swept said:

The bigger, heavier you are the bigger the ‘zap’ and ‘splatter’ when you fall off! ???

and the higher the bounce????

On 09/12/2017 at 9:39 PM, nhuskys said:

Riding at the Tryals Shop last Wednesday on the shop bike, a GG TXT320 instead of my usual 125(More bike than I want!)....  We got discussing various displacements, the owner Mike Komer( He has been riding trials for 40 years) said that a 250 was definitely easier to hop, than a 300. I'll trust him on that!

complete rubbish, in theory a 300 is no difference in weight maybe lighter? how can it be harder?

I have heard it called something like "moment of inertia" a combination of the mass of the crank, piston, flywheel, etc. in junction with the amount of fuel being combusted.

It is a bit more complex than I have writing skills to describe, but my best attempt is, that your working against more moving mass in a 300 so it's more work.  However, how much more I wouldn't be able to say but even between both my 07 Montesa 4RT and 17 Montesa 300 RR I believe I can feel a slight difference.

I think you're talking about "referred inertia". This is effectively a translation of the inertia (or "moment of inertia") of the rotating components into a value that can be added to the linear inertia of the bike and rider. This is what has to be accelerated when you open the throttle, or decelerated when you brake. I don't see that it has any relevance to hopping a bike, and anyway the rotating inertia of a 250 and a 300 would be so similar that it would be unnoticeable.

Actually I think there's something in this although some of it is in the riders head.

I went from a 250 to a 300 gas gas years ago and I couldn't chuck the 300 around like the 250. Some of it I think is just timing as the 300 was much quicker,  some of it is confidence / nerves as if you are trying not to open the throttle too far then you end up trying to move the bike more physically.

Can't argue that the actual weight will be almost exactly the same.

That's the trick there isn't it, it isn't just the mass and/or inertia, it's the package all together.  How it affects the spin up speed, the riders timing changes, etc.

And even a small amount of change can make it feel different tell you become acclimated to that change.

Erm, bigger piston equals bigger push down the cylinder bore equals bigger shove from the rear wheel. So a 250 has less shove than a 300. Otherwise what’s the point in the oversize engine? John Shirt when he was developing his 320 Majesty brought it to a weekend event I organised. This thing would go up any hill but the clutch was now the weak link as it developed so much torque. Bigger bore more torque more lugging power to get you through a section!

4 hours ago, baldilocks said:

some of it is confidence / nerves as if you are trying not to open the throttle too far then you end up trying to move the bike more physically.

I think you may have it there.

2 hours ago, section swept said:

Erm, bigger piston equals bigger push down the cylinder bore equals bigger shove from the rear wheel. So a 250 has less shove than a 300. Otherwise what’s the point in the oversize engine? John Shirt when he was developing his 320 Majesty brought it to a weekend event I organised. This thing would go up any hill but the clutch was now the weak link as it developed so much torque. Bigger bore more torque more lugging power to get you through a section!

 That`s just it, the bigger piston and rotating mass gives a heavy feel. This is modern bikes we are talking about and more lugging power does not get you through a section like it used too. We are talking about hopping the front wheel. Hopping was never the point in the old bikes. And yes, a 125 or 250 does feel lighter when hopping. Of course a 300 has it`s purpose. Some good some bad. But always makes more toque.

I know it would be easier for me if I lost my big stomach, so weight does matter! And there is my excuse!