Heavy flywheel equals more torque? (2014)

Fast Eddie said:

worntorn said:

If light cranks are the way to go for racing, why did Nourish make his racing cranks heavier than stock? The Nourish crank seems to be the golden standard in competition cranks.

Glen

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Dave Nourish was very clear on this, his words went something like this:

"a heavy crank increases torque at the rear wheel" (note: he never said it creates torque, just increases what gets to the wheel)

"and give better drive out of corners"...

"There's more corners on a track than straights lad... its torque that wins races"

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Torque definitely wins races. I raced a 63mm stroke 500cc Triumph engine bike for 12 years which had a very light crank. It was simply a very nasty dangerous ride. My Seeley 850 has the standard commando crank balanced to 72 % and I defy anyone to out-ride me around the tight stuff on Winton Raceway. It would take a really god guy on an RS125 Honda. If you enjoy racing an extremely top end motor and can tolerate the uncertainty in corners, a light crank is OK. I think the crank in the Paton 500 would be extremely light, however I suggest a completely different style of riding is required compared to riding a commando engine bike. The light crank probably dictates 'point and squirt', so the bike's geometry and suspension also need to be different. If the bike tightens it's line in corners, you would not want it to be a twitchy bastard.

SteveA said:

worntorn said:

If light cranks are the way to go for racing, why did Nourish make his racing cranks heavier than stock? The Nourish crank seems to be the golden standard in competition cranks.

Glen

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I suspect it has more to do with how they are made than a deliberate attempt to be heavier, though since it works for some, who declare they are more rideable, you pays your money and makes your choice. The benefit of a billet crank over a 3 piece crank is less flex and less stress on crankcases, and they have been cheaper than Maney 3 piece items. And Nourish offered different crank firing angles, because that is easier to do with a billet item. Maney is 360 or.....360

With a Nourish crank you can set a tighter squish with the right rods, as always it is the sum of the parts, not the individual parts.

Steve likes lightweight, so that is what he makes.....except his crankcases!

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The only reason I persevered with my 500cc Triumph for 12 years, was it had the billet crank. You could race it forever without blowing it up unless you tangled the valves. It was great towards the ends of sweeping bends on a really big circuit when it was pulling a very high gear, it was easy to breeze past a lot of guys. Everywhere else it was bloody useless. It needed a 6 speed box. With the 4 speed CR box, if you geared it low you could out speed the others around the tight stuff and get blitzed at the ends of the straights. Gear it high, and you'd probably crash in the tight stuff. Effectively you could choose where you wanted to lose a race. I don't need that sort of stress in my life - the Seeley 850 is from another world.

What is the usable rev range of a Desmosedici and what shape is the torque curve ?

B+, forgive me if I dropped the flywheel ball but still have access to its water jet file and hard copy graph. Herb Becker and Doug McRae and Kenny Cumming might have a sense on this but could as well best like it opposite from each other too. With center flywheel a bit ligher allows putting heavy slugs in cheeks near bearing support to get desired BF but still similar spin inertia. Too much flywheel inertia is one reason the moderns developed slipper clutches as the multi's spin so fast for the gearing if they just let off throttle the rear skips out trying to speed up engine inertia.

[video]https://www.youtube.com/watch?v=X-WpReNmDhk[/video]

Fast Eddie said:

Dave Nourish was very clear on this, his words went something like this:

"a heavy crank increases torque at the rear wheel" (note: he never said it creates torque, just increases what gets to the wheel)

"and give better drive out of corners"...

"There's more corners on a track than straights lad... its torque that wins races"

Click to expand...

The crank stroke also is a factor. i.e the distance of the big-end axis to the out put shaft axis. 'Long stroke' engines effectively have a bigger lever than 'short stroke' so everything else being equal a long stroke engine will create more torque - torque = force x distance. A piston moves in a reciprocating motion and on it's own cannot produce torque. It produces a force to drive the cranked shaft which converts the reciprocating motion into a turning motion at the out put shaft - torque. So the crankshaft assembly including the weight of the flywheel, 'stroke', rpm, speed of flywheel circumference (which increases with diameter) are factors in creating torque.

This video helps to explain gyroscopic precession (e.g opposite lock steering) but also demonstrates torque produced at the axle, which is a product of wheel rim speed and also mass. http://www.youtube.com/watch?v=ty9QSiVC2g0

Al-otment said:

[
The crank stroke also is a factor. i.e the distance of the big-end axis to the out put shaft axis. 'Long stroke' engines effectively have a bigger lever than 'short stroke' so everything else being equal a long stroke engine will create more torque

Click to expand...

Yes and no.
If everything IS equal, then long stroke and short stroke engines will produce the SAME amount of 'work'.
The combustion gas pressure will see to that - and you can't get more power out of nothing...

The peak torque readings may be higher or lower for various configurations of engines.
But the differences are not great...

Back in the 1920s, JAP engines came in 2 varieties of sidebangers (1000cc v-twins).
Long stroke and short stroke.
The long stroke engine was the revvy racing engine,
and the short stroke engine was the torquey one, for road use.
Cams and valve timings maketh the man...

Then you add con rod ratio's into the equation.
The Commando has a low ratio which has a measured effect into and out of TDC plus the point that the con rod is at right angles to the throw which iirc has an effect on torque/leverage.

Ducati when they went to the 1000 (from the 864cc) engine in the mid 1980's by stroke retained the cylinder height but went to a shorter con rod which made it a mid range engine.
I'm sure JS can explain it in detail,con rod ratios that is.

I think the slipper clutches were fitted to moderns because many people don't know how to match the revs using the gearbox. If the ratios in the box are close there is usually no problem catching up with the engine revs with a long stroke, heavy crank motor. With a short stroke light crank motor, it can be a different story. If you are at extreme speed and cranked over in a corner and chirp a tyre on a gear change, you are often on the ground in a hurry. A lot depends on whether you use much engine braking as part of your riding style. I tend to use it if I have to change line to get around another rider in a corner, when using the brakes is a bad thing. I find that compared with my old short stroke Triumph, riding the Seeley 850 is much easier and much faster. The standard gearbox however, was a real bummer. I don't want to upset you guys, however I think there are much better ways to set up a Commando than as it comes out of the factory.

acotrel said:

I think the slipper clutches were fitted to moderns because many people don't know how to match the revs using the gearbox.

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I'm fairly sure the folk at WSB and Moto GP have downshifting under control,the slipper was a race only item to begin with.
http://s30.photobucket.com/user/manurew ... t=2&page=1
I modified a GSXR slipper unit to suit a TL1000,maybe I could put one into a Commando if the rotation is the same.

I always get amused at the moto ride days at Winton. Many of the kids have never previously been on a race circuit. There is one corner in particular where a lot of them change down two gears in about 10 metres. They just shut the throttle and click down two. I've sometimes seen their rear wheel hop off the ground. When I was a kid riding on those old tyres, that was an almost certain way to crash - when the engine stops the rear wheel. I think for those guys a slipper clutch would be good, however they would never learn to be smooth. It is like rev limiters - if you haven't got one, you have to learn self-discipline. If you get going fast enough, you will exceed all the aids. If you think back to the Manx Norton days, when you go fast enough all those old handling problems re-emerge.

Back to basic boys.

In race engines a light flywheel is used for a couple of reasons.

Firstly there is a large weight saving and secondly the engine can be used
more effectively for braking.

The flywheel is not for harvesting energy but was intended to "smooth out"
the drive and in some cases even kept the engine going.

Lots of pros and cons but to get the best it is not just a question of lightening
one component. Engine balancing involves many many hours of weighing parts
getting volumes correct and then adjusting timing and mixtures to get best
performance. For race engines well worth the effort but for a road engine !!!!!

Andy

THE Gravel trained me to never just down shift at much speed but always rev up so I get a bit of speed up when down shifting in a series at speed so no chance of letting rear engine drag get me down. THE Gravel also taught me never be slowing down into a turn but always be going slow enough I can hi power into through and out of a turn. If I am on an off slope banked loose climbing or descending Gravel turn I tend to stay in lower gears to keep some flywheel gyro going and have some slack if having to let going of throttle which seems to help keep bike up right even though tires aren't in traction enough on their own. The issue with skipper clutch need is just more evidence of how corner crippled everything else is to me and Peel, my regular Combat and spiffed up race tired SV650 included.

I started racing in '75 on a Fastback....going downhill into Mansfield at Cadwell Park the rear would skip....and I knew how to match revs....

In the end I found that by running the chain a little slack with tight Isos I could reduce the occurence.....but if you think it is only modern bikes that do it you are just wrong. It was a combination of braking and weight transfer that did not really occur at many other places on that circuit and on some circuits not at all. On my GSXR750F and GSXR750SRAD, racing and track daying, rear wheel skipping was never a problem with much less flywheel effect and double the rpms, but also better suspension, including a tailored Maxton setup on the SRAD, and properly rated springs and an R1 shock on the 750F.

The slipper clutch allows a rider to avoid blipping the throttle on downshifts, and they work in conjunction with quick shifts.....what they are trying to do is just go through the box quicker taking less time over gear changes. These components can improve lap times with the same bike and rider by a couple of seconds a lap or more, but they don't make an inexperienced or incompetent rider a race winner.

Rohan said:

Al-otment said:

[
The crank stroke also is a factor. i.e the distance of the big-end axis to the out put shaft axis. 'Long stroke' engines effectively have a bigger lever than 'short stroke' so everything else being equal a long stroke engine will create more torque

Click to expand...

Yes and no.
If everything IS equal, then long stroke and short stroke engines will produce the SAME amount of 'work'.
The combustion gas pressure will see to that - and you can't get more power out of nothing...

Click to expand...

If you've a 10lb weight (force - as gravity is acting on it) on the end of a 1ft lever connected to a shaft the twisting force (torque) must be greater than a 10lb weight on the end of a 6in lever. Torque = force x distance. I'll keep quoting that formula until everybody gives up .

Engine designs have good and bad points. Typically multi cylinder short stokers are gutless at low revs but pile on the power at the high revs the design allows them to achieve where they're breathing more air and sucking in greater quantities of fuel for more power. The typical one or two cylinder long stroker produces more torque at lower revs due to greater 'crank leverage' plus the designers favouring heavier flywheels (see above formula).

The topic of 'torque' has been debated long and hard on this forum before. I learnt two lessons last time:
1. No one... and I mean NO ONE argues their point from a position of being willing to change their mind based on the input from others.
2. The argument quickly moves away from, or forgets, the topic of 'torque at the rear wheel'.
Whilst it is now clear (to me at least) that torque is generated, and ONLY generated, in the combustion chamber (therefore crank weight etc has no effect on the actual amount of torque generated) this loses sight of the question of what increases torque AT THE REAR WHEEL.
Crank stroke and weight, rod length, gearing, etc, etc. There are many things which influence how, and the amount of, torque that gets transmitted to the rear wheel, and with what characteristics.
Regarding the topic of 'do heavy or light cranks win races' Ken in particular posted some very clear evidence on this previously, whereby riders loved light cranks, but lapped faster with heavy cranks even though they 'felt' slower.
My point (if I have one!):
This is a complex discussion with many, complex, interconnecting factors. And many, many firmly held opinions. So, debate away if you enjoy it, but don't do so expecting to change anyone's opinions!
Meanwhile, I'll await Alotments feedback after trying a light crank back-to-back with a heavy crank...

Just to confuse the issue, I will point out that torque is not some mystical commodity like Golden Amber. It is measured on a dyno by a simple equation using horsepower and rpm, or the converse can be done.
So when someone states and engine produces this much torque at this much rpm, we can quickly determine exactly how much horsepower is being produced at that rpm.
I know this is simple stuff and most people already know this, but many times I have been in a discussion with otherwise knowledgeable people who have a strange concept of torque that makes it somehow entirely unconnected with horsepower, kind of like a motorized form of Golden Amber.


I agree with Eddie and others, flywheels do not produce torque directly, but they do store energy so that it can be utilized to produce torque when needed.

Glen

andychain said:

Back to basic boys.

In race engines a light flywheel is used for a couple of reasons.

Firstly there is a large weight saving and secondly the engine can be used
more effectively for braking.

The flywheel is not for harvesting energy but was intended to "smooth out"
the drive and in some cases even kept the engine going.

Lots of pros and cons but to get the best it is not just a question of lightening
one component. Engine balancing involves many many hours of weighing parts
getting volumes correct and then adjusting timing and mixtures to get best
performance. For race engines well worth the effort but for a road engine !!!!!

Andy

Click to expand...

The flywheel stores energy, the gearbox determines how you use the stored energy. It depends on how you ride and the way the bike is set up. On a road bike changing from a standard set-up can be a pretty pointless exercise. Mr Norton build a compromise motorcycle which seems to fit a lot of roles fairly well. If you have a specific purpose for your bike such as road racing it is worth modifying it to suit. Otherwise if you keep your bike fairly standard you must eventually find the situation where it does not cope so well. If that happens only once in your lifetime, would you modify your bike in case you find it ?
With My Seeley 850, I only ever use it on a road race circuit. I've worked around the standard crankshaft assembly, and I am surprised that it is quite adequate for the purpose. With the heavy flywheel, small inlet ports, methanol fuel on standard comp. and two into one exhaust , it is a really great ride however gearing has been a major problem. It is extremely difficult to avoid over-revving it and every time I've dropped a tooth off the rear sprocket it has gained a higher top speed and accelerated just as fast.

Fast Eddie said:

Whilst it is now clear (to me at least) that torque is generated, and ONLY generated, in the combustion chamber (therefore crank weight etc has no effect on the actual amount of torque generated)

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Saying torque is generated in the combustion chamber is the same as saying a canon produces torque when it fires a canon ball. It produces work (Joules) which is force (exploding gunpowder) acting on an object (canon ball) x the distance that object (canon ball) moves. The same thing happens to a piston except the piston is connected to a cranked shaft which turns linear motion into a turning motion at the drive shaft - torque.

Every time we use a spanner we create torque at the bolt head the one end of the spanner is connected to by applying a force at the opposite end of the spanner x the length of the spanner. Same force on a different length spanner creates a different torque. All the theory/equations are in books and on the internet.

Al-otment said:

Fast Eddie said:

Whilst it is now clear (to me at least) that torque is generated, and ONLY generated, in the combustion chamber (therefore crank weight etc has no effect on the actual amount of torque generated)

Click to expand...

Saying torque is generated in the combustion chamber is the same as saying a canon produces torque when it fires a canon ball. It produces work (Joules) which is force (exploding gunpowder) acting on an object (canon ball) x the distance that object (canon ball) moves. The same thing happens to a piston except the piston is connected to a cranked shaft which turns linear motion into a turning motion at the drive shaft - torque.

Every time we use a spanner we create torque at the bolt head the one end of the spanner is connected to by applying a force at the opposite end of the spanner x the length of the spanner. Same force on a different length spanner creates a different torque. All the theory/equations are in books and on the internet.

Click to expand...

I agree.
But its also true that none of those things will have any effect on torque until that combustion chamber goes bang. And, whatever effect they do have, the power contained, or released, during that bang is what 'generates' that initial force.
I don't have any personal opinion on the effect of rod length and torque transmitted. But I do strongly believe that stroke has a huge effect, as it is, in effect, a longer 'lever' as you state. I also believe that a heavier flywheel transmits torque differently to the wheel, and I 'think' it does this in a way that is better for most uses. A further hypothesis of mine is a lighter crank feels more 'fun'.
Given that most of us use our bikes for fun, would suggest that they're a good idea!
Hurry up and get your bike back together so you can tell us what you think!