Lightening flywheels

[Eddieb]

Anybody done it?

Does it really make such a difference to how fast the motor spins up, how does it effect performance, what does it cost, etc, etc.

[duckman]

Anybody done it?

Does it really make such a difference to how fast the motor spins up, how does it effect performance, what does it cost, etc, etc.

Never done it myself, but as I understand it, with a lighter flywheel theres less weight to spin and so it revs up quicker.

Much the same argument as replacing stock wheels with lighter ones... I think it's called "unsprung weight".

Give it time and someone with some technical knowledge will reply.

[Big Dog]

Anybody done it?

Does it really make such a difference to how fast the motor spins up, how does it effect performance, what does it cost, etc, etc.

Yes, most factory setups are done with constant speed in mind. The objective is to smooth out the acceleration curve.

The whole ides is to give you less need to adjust your throttle position to maintain a speed.

The upshot is your bike will accelerate better but will require quicker reactions to such things as bumps and hills.

You will find more wear on chain and sprockets (and your neck) but draggers do it because it can shave 2 seconds off a 1/4 mile. Expect it to be one of the cheapest performance mods (depending on model some are harder to get at / some already have custom parts available), but expect the costs of maintenance to go up. Had it done to a car. No change to hp but it halved the time to get up to 100kph. Sparks needed cleaning/changing more often (as the amount of fuel being burnt changes faster than the supply of fuel can), and my tranny suddenly felt "looser".

For how I was driving it was good but it rendered my car incappable of safe towing as it lurched too much.

[Big Dog]

Much the same argument as replacing stock wheels with lighter ones... I think it's called "unsprung weight".

I may be wrong but I'm pretty sure your referring to mass displacement. Unsprung weight refers to weight that is below the shock absorbers and the suspension set up itself.
It refers to weight that if you pushed down on it whilst it was stationary on the ground would not move.

Mass displacement refers to the amount of mass your motor needs to move before any power is applied to the ground. Ie pistons, transmission, flywheel, crank, chain, cush, back wheel, rear brake, tyre, clutch etc.

[duckman]

I may be wrong but I'm pretty sure your referring to mass displacement. Unsprung weight refers to weight that is below the shock absorbers and the suspension set up itself.
It refers to weight that if you pushed down on it whilst it was stationary on the ground would not move.

Mass displacement refers to the amount of mass your motor needs to move before any power is applied to the ground. Ie pistons, transmission, flywheel, crank, chain, cush, back wheel, rear brake, tyre, clutch etc.

Oh shuddup, i was just starting to sound intelligent!! :sly: (not likely)

Thanks Big Dog - I learn stuff everyday from this site.

[Big Dog]

Oh shuddup, i was just starting to sound intelligent!! :sly: (not likely)

Thanks Big Dog - I learn stuff everyday from this site.

Wait...... wait...... someone is bound to shoot me down if we wait long enough. :eyepoke:

[Kwaka-Kid]

from what im told... im loosing flywheel completely on the racebike which on a 53hp 400 gives me another 2.5hp, and helps the bike rev faster, but looses a bit of torque and smoothness... i figure that i already have slightly more torque then others being on a V4 not inline4, and that has helped my racing as its easier (more broad power curve) but as i get better/more experienced i can deal with a smaller but higher bang of power sort of thing, i dunno, plus im bored and just wanna do muck around free-mods to the bike! -personally dont know if its worth bothering to lighten, just take it off all together, its All or nothing my friend!

[wkid_one]

Now coming from my big boy racers days - I had a lightened race flywheel in my VR4 EVo and it makes a huge difference to how quickly the engine spins up - but be warned it can equally affect to ability of the vehicle to pull up hill......

Also - it can weaken the flywheel to the point whereby you need to replace it more often....and can lead to more money having to be spent on other items of the clutch assembly and drive train.

If you think about the whole drive train as a balancing act - if you add or remove certain elements to it - this can create or remove stress from other items within the system. For example - cars with improved clutches etc often shit the selector fork as this is the next weakest link.

I also had a triple plate clutch etc etc etc. About $12k invested in the drive train.

Just something to bear in mind is that upgrading one part - often means upgrading another

The exhaust is another common one.....manus spec the mapping to run off a set airflow in and out....change the airfilter and you need to do your jets or or or or or.

Flywheel changes are great - but only consider if you are looking to do the whole drive train......otherwise the changes can be more detrimental than beneficial.

[wkid_one]

I may be wrong but I'm pretty sure your referring to mass displacement. Unsprung weight refers to weight that is below the shock absorbers and the suspension set up itself.
It refers to weight that if you pushed down on it whilst it was stationary on the ground would not move.

Mass displacement refers to the amount of mass your motor needs to move before any power is applied to the ground. Ie pistons, transmission, flywheel, crank, chain, cush, back wheel, rear brake, tyre, clutch etc.

You are right - unsprung weight is everything that is not suspended by the bikes suspension.

The flywheel is actually referring to the principal of inertia - the lighter something is the less energy is needed to get it moving. Therefore if you expend the same energy moving something lighter - it will move quicker.

[wkid_one]

Much the same argument as replacing stock wheels with lighter ones... I think it's called "unsprung weight".

This has alot to do with gyroscopic forces also - and the weight something has when spinning.....the less weight the less gyroscopic force - there the easier it is to alter direction.

Pilots artificial horizons work with a 'gyroscope' - which is essentially a spinning disk spinning within a freely moving frame - this will always stay in its original orientation, therefore regardless of what way the plane moves - the gyroscope (artificial horizon) will remain in the same place.

A bikes wheel is the same - once spinning - it takes a lot more force to make it change direction as it doesn't want to change - and this increases as the speed of the spinning increases. Which is why is it easier to change direction the slower a bike is going. If you therefore reduce the unsprung weight - you in turn reduce the mass of the gyroscope - which in turn means you can change direction easier.

[wkid_one]

Please disregard my 'physics' as I have just come back from dinner and am slightly inebriated.

[Racey Rider]

Removed: No longer relavent

[duke]

I lightened the flywheel and removed the alternator on my racing Pantah last year. It's made it easier to keep on the redline and I've not noticed much loss of momentum at low revs. I've only used the bike on the track and think it was a worthwhile performance mod. The flywheel mod might be worth considering for the road if you don't need to do much stopping/starting and you red-line a lot
regards
duke

[merv]

-personally dont know if its worth bothering to lighten, just take it off all together, its All or nothing my friend!

I doubt you'll be able to do that as it more than likely actually makes up the alternator on your bike i.e. the magnet thingy spinning round the coil thingies and it will have the ignition timing sensor and stuff like that on it too. You'd have to be prepared to replace some of that stuff with some race kit gear instead, can't just take it off and throw it away. Duke talks of taking off the alternator and if you did that the bike would have to be set up to run off battery alone.

Also it is unlikely that no matter how light your flywheel that it will allow the engine to generate more peak power - as has been mentioned by others it would allow the engine to pick up quicker i.e. the power and torque will remain the same, the inertia they have to overcome is what is less, but once you're up to peak power revs and it aint accelerating much more it can't magically produce more power from somewhere. However, if you can remove the alternator you will recover the power required to drive it - not sure that would be 2.5hp though. Otherwise change has to be made to make better action inside where it happens i.e. boost the action in the combustion chambers - higher compression, better beathing, better carburetion, cam profiles, exhaust system or whatever.

I wouldn't be surprised that there aren't too many useful grams that can be shaved from your flywheel to make it go any better. The V4 should have inherently less inertia in the first place - shorter crankshaft less bearing friction and mass etc, but hey no harm trying but seek advice (probably internet search for engine mods) and don't just go for the doctor first off.

[Kwaka-Kid]

for sure merv, and yeah not so good on a street bike, but im cutting my whole loom right down and running a total loss system. Well the guy who told me i trust has he has a fully worked RVF400 that has had shitloads done to it back in Wales, and was put on the dyno and apparently alone, that loosing the flywheel (and alt etc) gave a 2.5HP increase, apparently the biggest engine mod you can do for free. -i trust the guy, and his bike just f***s off when we line up to nail a straight