Weight of fly wheel different manufactures.

[lineaway]

 So what are you trying to figure out with the weight of mass for?

[leosantanalg]

My original question was confusing.  Is it about the power that the engine can generate or the inertia of flywheel and efficiency of clutch. Obviously I m talking about splatters, where all of us hold it wide open and just clutch on to launch... I swear the 4RT punch is higher than 2T. I mean, on my bikes was so obvious... that’s why I don’t get it... where is this disparity in power? 

[lineaway]

20 minutes ago, oni nou said:

Yes of course I am aware of the disparity between the 2T power unit and the 4T power unit as is shown in the junior champs where kids  can ride the 4rt against 125 2t's  but really I mean seriously he does not need  more punch as an amateur and this could be easily proven if we got Toni Bou to come and ride his standard 300rr bike in the expert class in a USA national against Pat Smage on a 300 2t Sherco .......my moneys on Bou winning on his gutless 300rr.

 And why do you think only 4 Montesa`s entered the British Championship?

[tony27]

3 hours ago, leosantanalg said:

It doesn’t.  But it’s know that more torque will come from more inertia. So, whichever bike can generate such with have a bigger punch correct? When you go for a splatter and accelerate the fly wheel clutch fully Off and then pop it, more inertia = more launch! Correct? 

Heavier flywheel doesn't change the amount of torque a motor has, a 2T should always have more torque due to firing every revolution. When people say 4Ts have more torque they are actually confusing flywheel mass needed to keep the motor turning during the non-firing revolution with torque

[oni nou]

6 minutes ago, leosantanalg said:

That’s what I think!! In the USA everyone seems to believe that this bike has no guts. I think it has much more than my previous bike: a 2018 300sherco factory. 

Well if you think that and you have ridden both bikes then that has a lot of weight to add to the discussion.

[oni nou]

14 minutes ago, lineaway said:

 And why do you think only 4 Montesa`s entered the British Championship?

They are harder to ride in muddy conditions and heavier in weight  plus not a lot of sponsored rides available on Montesas in the UK

Edited December 17, 2018 by oni nou

[lineaway]

1 minute ago, leosantanalg said:

My original question was confusing.  Is it about the power that the engine can generate or the inertia of flywheel and efficiency of clutch. Obviously I m talking about splatters, where all of us hold it wide open and just clutch on to launch... I swear the 4RT punch is higher than 2T. I mean, on my bikes was so obvious... that’s why I don’t get it... where is this disparity in power? 

The 4RT is really strange as it hits at just above idle and then it does rev out well. The initial hit is hard to control on clutch release. You can watch most 4rt riders as they will spin in places where most two stroke riders don`t. It`s always interesting to watch a Bou video because the sound never matches what you think the engine should be doing. And yes, if I had a 4RT I would invest in a pipe!  

[stpauls]

None of the above points about flywheel weight and torque are correct.

What IS important in not the actual weight of the flywheel, but WHERE that weight is located.  The more weight that is located at the outer edge of the flywheel, then the greater the inertia and torque forces. 

More weight (mass) at the outer edge of the flywheel = greater torque/inertia forces, and visa versa. 

Edited December 17, 2018 by stpauls
grammar

[sirdabalot]

If weight was added to the clutch inner hub or pressure plate, would it allow the engine to spin up quickly with the clutch disengaged then add the calming/inertia increase when the clutch was engaged? Would it serve any purpose doing so? 

[section swept]

Torque= Force x Effort. For example the longer the length spanner or lever used ndoing a bolt or nut the easier it is, whereas with a short lever or spanner the more effort you have to exert. Enger the Torque Wrench.

Old four stroke and two stroke engines had longer strokes than their modern day counterpart. With longer connecting rods the leverage against the crankshaft will be greater.....allied to this is the larger crank radius from main bearing journal to big end journal which of course adds weight and subsequently mass. With a larger and heavier flywheel this adds to the mass and it therefore takes greater effort to slow this rotating mass allied to the greater crankshaft weight and the greater ‘push’ on the big end journal of the reciprocating piston and con rod. Draw back is that to run the engine at 3,000 rpm the piston has to travel much further than a short stroke engine running at the same rpm. 

The modern four stroke has such a short stroke that the engine needs to be revved hard to generate sufficient inertia in all of its rotating mass to produce the take off thrust you need when the run up is very short! 

Anyone thats watched Any form of road racing or dare I say it... race cars will have noticed that to actually pull away an awful lot of revs are needed. The flywheel of a formula 1 engine is no bigger than a tea cup saucer or a sandwich plate, producing so little inertia that the engine won’t pull below 6-8000 rpm. (example) 

Make the flywheel heavier on the 4T and the mass weight obviously increases but then the engine has to work harder to get that mass spinning, with a short stroke the con rod doesn’t have the leverage on the crank to produce the desired torque. The Mass just makes the engine take longer to decelerate from high revs. The 2T however has a longer stroke and hence more leverage on the crank. 

If you've ever tried to ride a kiddies bicycle (be nice and ask first) the pedal cranks are very short and your lickle leggies are going to go round at a fair old rate justto travel a short distance. Now jump on an adult size bike ( not one of those stunt things or trick trials cycles but a normal every day one) the pedal cranks are much longer and when you push down on the pedal you exert a much greater force....longer lever....Someone is going to have fun pulling this little lot apart?

Race engines have skimmed, lightened or alternative material flywheels and some are reduced in diameter, these mods then allow the engine to rev much more quickly or be more responsive. But they have little inertia and decelerate much more quickly due to less inertia. 

So thats my engineering doctorate thesis tsken care of......next patient please!?

To sum up....remove the 4RT engine, stick in a good Ariel 500 HT engine ( bloody great flywheels, dammed great long stroke generating armfuls of stump pulling torque) and away you gooooooo!?

[section swept]

8 hours ago, oni nou said:

So the stock 300rr  has less punch than an amateur rider needs then?  sounds preposterous to me.

Could be a ‘technique’ issue here, what do you reckon??

[jimmyl]

There is a whole lot more than just flywheel weight that effect engine response - porting/valve size (2t/4t), ignition map, carb size etc etc.

To compare flywheel weighs from one bike to another is like asking how much ingredients to put in a curry cos I put  3 tomatoes in my spag bolls.

Asking Altering flywheel weight on the same make and model will assist if you want to tweak things but I thing that is about as useful as you can go  

[leosantanalg]

13 hours ago, tony27 said:

Heavier flywheel doesn't change the amount of torque a motor has, a 2T should always have more torque due to firing every revolution. When people say 4Ts have more torque they are actually confusing flywheel mass needed to keep the motor turning during the non-firing revolution with torque

I have to completely agree and disagree with you. The heavier fly wheel can not generate torque indeed! torque is only generated by the engine.. The heavier flywheel will do is have more inertia. and that inertia means punch power when you let your clutch out with a full Throtle that has been wide open for 1.5 full second.  imagine that:  put your bike on a stand with the rear in the air in 3rd gear and clutch on wide open so the wheel will spin as fast as you can then suddenly press the clutch and jam the rear brake! that's replicating what happens in the flywheel/clutch.  Then do the same experiment but this time pack the rear rim with some lead weight distributed evenly. when you jam that brake, you better be holding the bike!!!   

[sirdabalot]

One of the Beta 250 Evo 2 strokes I had came with the detachable flywheel weight (UK model). At one muddy trial I did 2 laps with the weight then 2 without, one section had a straight steep 8' climb from a stream with a tight right at the top into some trees. A good hanfull of throttle got the bike up each time, the difference in flywheel inertia was more noticeable when shutting off to turn into the trees, the bike nearly overshooting due to the added built up inertia, I had to be ready to pull the clutch in to reduce the effect on deceleration. After getting used to it I preffered the additional weight as slower rear wheel response suited the conditions, some riders are clever enough to do similar by dragging the back brake or feathering the clutch. 

[cascao]

Power (torque) come from engine. It is'nt altered by flywheel.

Flywheel is a rotating mass that can store momentum. It has two effects:

1) when engine is comming from a lower RPM to a higer RPM: Engine will increase rpm slower since it has an added mass to accelerate. It can increase traction due a less agressive behavior and it will decrease power burst you have using throttle.

2) When engine is comming from a higer RPM to lower RPM: Flywheel will give energy to system. Rotating momentum can be used to drive the motorcycle.

An side efferct is the engine runnig in a more steady way when travelling during a rough terrain like over a bunch of loose rocks or loose terrain. On malleability deppartment, it can increase the "heavy feeling" on motorcycle just like we feel on a big bore engine.

Had played with flywhhel a lot and my feeling is: It only good in specific conditions (mud, senior rider, MX bikes on enduro). https://youtu.be/16d-ewfc8lU For average Joe, most of time, better stick with what come from factory.

Edited December 17, 2018 by cascao
highlighting important concept.