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Frazer, you do like complicating things don't you! Nah, you are right... more explanation needed; especially with your second point....


1/ This is a bit hard to grasp but what I am trying to get across is the feel that you get from the PUSH that Torque gives you in real life.

Some people think the PUSH comes from Horsepower and if that was the case then the PUSH you FEEL on the bike should get progressively greater as the revs rise.... and looking at the graphs the Horsepower at high revs is 4 times the Horsepower at low revs so if the PUSH came from Horsepower then the PUSH at high revs should be 4 times greater than that at low revs.

This is not the case... the PUSH FEELS pretty consistant over the rev range so it is Torque that gives the PUSH not the Horsepower.



2/ Torque equates to PUSH or the amount of work that can be done.

Horsepower relates to how much work can be done per second. Loosely, yes it relates to speed.



Imagine you have a heavy load to lift with a rope going up and over a bearing and down to a winding handle. Winding the handle makes the heavy load go up. Let's imagine it will go up 10 feet and the load is 100 pounds.

Now it doesn't matter whether the load goes up slowly and takes a minute or goes up fast and only takes one second; the AMOUNT OF WORK DONE IS THE SAME. Take a moment to think about this because it can be hard to understand but is critical to understanding. If I lift a heavy load up in one minute and you lift the same load up in one second then we have both done the same amount of work, it is just that you have done it quicker.

So how much work have we done? Well we have both lifted 100 pounds up 10 feet so we multiply the figures and we have done 1,000 foot-pounds of work... ie we could say the PUSH we gave the weight was 1,000 foot-pounds or we could say the TORQUE we applied to the hande was 1,000 foot-pounds... they are all the same thing.

Note... we BOTH APPLIED THE SAME TORQUE but I spent longer doing it.


So where does Horsepower come in? Well, I am old and unfit but I am strong and managed to lift the weight slowly. I can also lift another weight straightaway again and keep doing it. I can lift one weight up every minute. So if I keep applying the same Torque to the handle for one hour then I will have lifted 60 weights.

You on the other hand, are young and nimble and but you are no stronger than me so you can't lift a weight any heavier than I can but you can lift that weight quicker. If you lift weights up for an hour you will keep the handle turning with the SAME TORQUE as I used but at the end of the hour you will have lifted 3600 weights.

So we both gave the same push to the weight but you could give more pushes over a period of time.

In Horsepower terms you are producing 60 times more Horsepower than me even though we are both producing the same Torque.



So yes, Horsepower is a measure of how quickly the Torque can be used and is related to SPEED.



5/ The bit that I have ignored in the example above is the starting and stopping of the weight.

When we both start turning the handle the speed of the weight going up is zero and the handle is not going round. We both need to get the handle turning but you need to get it turning far faster than I do because your advantage over me only occurs at high speed.

Obviously, just like on a bike, to get the weight moving initially you are going to need to put some gearing into the handle so the handle can go round at the high revs that suit you even though the weight hasn't started to move yet.

And then once the weight is moving you can change to another gear, and then another, and another.... and then as the weight nears the top you need to slow down so you need to change down through all the gears.

I think you can realise that although you are beating me while the gearing is not there, as soon as the gearing slows the speed of the weight down then you are coming down to my level... and in the real world you the gearbox will be sapping your strength because you must do somework to turn a gearbox.


Without going into the maths or any more detail the reality is that when a heavy weight must be moved slowly it is better to use a deisel engine producing 50foot-pounds of Torque at 4,000 revs (which works out at 38bhp) and when a lighter weight must be moved fast it is better to use an engine producing 50foot-pounds at 10,000 revs (which works out at 95bhp).



In fact, I've just thought of an analogy that might explain this...

Imagine a race track where two competitors must carry 50 tonnes of rocks once around the circuit and each competitor is limited to an engine with peak torque of 50foot-pounds.

One competitor uses a diesel engine (50foot-pounds at 2k revs giving 19bhp) to slowly drag all the rocks around at the same time but the other uses a motorbike (50foot-pounds at 10k revs giving 95bhp) to carry each and every small rock round once but does each lap very fast.

Both competitors do exactly the same amount of work and (ignoring friction) both would finish in exactly the same time.... but the biker had more fun





3/ In a serious answer to Knoxy, based on the graphs I have seen of an FZ6 and FZS600 dyno'ed back to back last year it is clear from the steeper HP curves at higher revs, that providing each bike keeps the revs above 7,500 rpm the FZ6 wins hands down... but then I'm assuming that neither rider is a wuss!!

Nooj, don't get too hung up about the low end Torque from that curve. The graph that Calz put up here does not show as much low down Torque.


I have resisted saying Torque = Acceleration because there are many variables that get in the way and reduce the feel. I have called it push and more push gives more acceleration.

A bike must get the available Torque from the engine into the tyre/ground and lots can get lost on the way so what you feel can be less than the curve would indicate.

Gearing is a classic area where Torque gets "lost" and there is always a doubt about where the best point to change gear would be. Lots more data is needed to be as knowledgeable about the bike as MotoGP engineers, for instance.

I seem to think that Debz changed the can on her FZ6 and as Calz's graph shows this can reduce the "power hole" quite considerably. The FZS will be affected by different cans as well (normally for the better, but it could be for the worse).

Look at Hamos's graphs and the Torque curve is much smoother than the stock curve.



I haven't got a chart for a stock FZS but if anyone can post one I'll have a go at explaining it.

Nooj... I agree that more is made off the bike's dip in performance than is necessary... if the bike feels OK to the normal rider then "nuff said" really.... but this is a discussion board....



TCat, thanks for the chart but unfortunately it is "useless" from the point of comparison with any other chart not produced by the same Dyno rig. If you look at your chart you will see that the Rev Limiter kicks in at 11.5k rpm whereas my (and I believe all) FZS600's kick in after 13.5k rpm.

Similarly if you look at Hamos's Stock Chart you will see that the Rev Limiter kicks in at 15k rpm which is, I believe, higher than reality.

I have been told that Dyno Rigs are notorious for being out of calibration and I would guess that neither chart has an accurate reading for RPM. Similar errors in the rig probably eplain some of the high torque figures seen in Hamos's hart at low revs.

Since Torque is based on RPM any figures taken from one chart cannot be related to the other chart.

Even though the actual values are incorrect the SHAPE of the HP and TORQUE CURVE are roughly valid (providing the errors in RPM are small) but they cannot be overlaid to get a comparison between bikes (unless someone has two charts of bikes measured back to back on the same rig?).




What the hell... do not put too much store behind these curves but if I make my own corrections to the RPM figures on both graphs I get curves very similar to two I saw last year from bikes done back to back on the same rig.




This supports a comment I made to Knoxy earlier that the FZ6 has the edge over the FZS600 is revs are kept between 8k and 11k.

Quote:

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Rubbermat,
The point you're missing is that hp/bhp is a 'leveller' - it's a way of comparing different engines on a sort of level playing field.
A 19bhp Diesel would get whupped by a 95bhp bike, all other things being equal.
The bit you've missed there is the gearing.

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Hi Allan, it is some time since I wrote all this so I'm stretching the grey matter to remember all the different sections I wrote.

My example of a 19bhp diesel vehicle and a 95bhp bike was carefully worded to include NO acceleration as I was merely trying to demonstrate the equal work done by the two engines moving the same weight of stone in different ways.

My example was intended to have both engines producing exactly the same torque but the diesel running constantly at 2,000rpm while the bike was running constantly at 10,000rpm.

If my "fixed rev engines" are put in your example then you are changing the system and we do not know enough about the specified engines to predict their relative acceleration as we do not know what bhp each engine produces at any rpm other than the 2,000rpm and 10,000rpm I specified.





I have also been careful to avoid the use of the word accelerate - prefering to use the word push - when talking about this subject.

Acceleration is only loosely related to torque and, in the real world, gearing does not affect a vehicle in the simple way that a school physics teacher may have us believe.

A bike with an engine with 95bhp at 10k revs can accelerate slower than one with an engine with 70bhp at 10k revs if the wrong gearing is selected.

The selection of gearing for a vehicle is very complex and has much to do with matching the power of the engine to the load. Ideally, the instaneous power of the engine needs to be matched through the gears to the load at the wheel integrated by time.

This is "impossible" to achieve for a range of revs in practical vehicles (remember the attempts to do this with the sliding rubber band in the 70's?) and so any gearing is a compromise. If you look at standing-start, fixed-distance figures for similarly weighted vehicles you will find many examples of the "less powerful" engine covering the distance quicker and with a higher terminal speed. There are some examples of gearing/acceleration issues on the web but they apply more to cars than bikes.


Likewise, relative acceleration is impossible to predict if you only know the two engines' torque at one fixed rev value.



PS: Ooops.... 26bhp???? I'd best go search and do some editing