Abstract torque

[Dendrob]

When a bike gets tested on a rolling road dyno things get expressed in an odd way.

The hp we record represents that spent or absorbed at the rear wheel. Yet the graphs invariably have engine speed on the other axis.

This is slightly abstract, but ok because the power figure represents something actual. Power is a constant, minus the losses in the system, and this is what we are seeing. The trouble arises when we try to express the supposed torque from which this power is derived. Because we plotted the power (attained at rear wheel) against engine speed, we end up with a very strange torque value. One that doesn't seem to represent anything that actually happened. Very abstract.

I'm cool with it. I understand it. I'm just saying it is 100% abstract.

John Robinson referred to it as "effective engine torque" and, pushed to find a description of it, that's what I coincidentally came up with too.

[grumpyfrog]

At the end of the day, if we are all using the same baseline system to compare against then it does not matter. 5 ponies are always going to be more than 3 ponies, if the ponies are the same?

[Dendrob]

At the end of the day, if we are all using the same baseline system to compare against then it does not matter. 5 ponies are always going to be more than 3 ponies, if the ponies are the same?

I agree, yes. But that's not what my post is about. It's an observation on something (which I perceive to be) odd. Abstract.

Most dyno graphs have rear wheel hp on one axis and engine rpm on the other. You can get away with this by saying "when the hp is xx at the rear wheel, the engine is spinning at yy rpm". That's all that's needed with hp. But then most dyno graphs accompany the hp curve with a corresponding torque curve. Here the trouble starts, because we used a mismatch of rpm against hp the torque value gets distinctly abstract. We can't say "when the engine rpm is yy the torque is zz" because it isn't. The torque value is in no man's land. It isn't engine torque and it most definitely isn't rear wheel torque.

You see my point?

[darkember]

Then it will depend on the rider and the weight of the rider that will depend on the best use of the ponies

[Stephan]

The torque is exactly at the same place where power is, it is very real value. But as nobody wants to see torque which is determined by final gear ratio (changing), it is better to calculate constant value for the crank, by comparing crank and wheel rpm. And reversibly you can calculate torque values on wheel with all gears without measuring it on dyno.

[Dendrob]

The torque is exactly at the same place where power is, it is very real value. But as nobody wants to see torque which is determined by final gear ratio (changing), it is better to calculate constant value for the crank, by comparing crank and wheel rpm. And reversibly you can calculate torque values on wheel with all gears without measuring it on dyno.

Absolutely agree with that. Except that the torque value, if expressed as I've put forward in my example, isn't real. Obviously torque is intimately related to horsepower, as you say, but if you mix up rear wheel derived hp with engine rpm you get a weird torque value.

As you say, we can plot graphs which are a true representation of rear wheel torque, showing the curve for each gear. Or even converted to show forward thrust in each gear.

[bigtwinthing]

personally its the Buzz in my butt that works for me. BHP, Speed and all that stuff mean shite if it don't thrill you. My Fazer 1000 went like bloody hell with an Ivans jet kit etc, but bland and boring. The storm was great but buzzy for me. The CB best of both happy chap.

[Stephan]

The torque is exactly at the same place where power is, it is very real value. But as nobody wants to see torque which is determined by final gear ratio (changing), it is better to calculate constant value for the crank, by comparing crank and wheel rpm. And reversibly you can calculate torque values on wheel with all gears without measuring it on dyno.

Absolutely agree with that. Except that the torque value, if expressed as I've put forward in my example, isn't real. Obviously torque is intimately related to horsepower, as you say, but if you mix up rear wheel derived hp with engine rpm you get a weird torque value.

As you say, we can plot graphs which are a true representation of rear wheel torque, showing the curve for each gear. Or even converted to show forward thrust in each gear.

got your point. When you claim graph is showing values at rear wheel, power is the same as on crank. But you don't feel 100nm at wheel, thit is similar stroke as you can do on bicycle

[Dendrob]

...... power is the same as on crank. ......

If I'm honest, I didn't fully understand your reply. My apologies. But to pick up on the above point.

Power is lost through the system. So whatever power is measured at the rear wheel, at any time you can be sure that if you measured also at the crank the power would be higher. By around 10 to 12% in the case of an average motorcycle they reckon. This is why, if you plot crank rpm against rear wheel hp, the torque figure you get is not true. It is quite clearly not rear wheel torque. But neither is it crank torque either, because all the losses in the system have been taken off it. But the true crank torque is the first position in the system so the losses won't have happened yet.

So the torque expressed that way is not a true representation of what happened. Hence my use of the word abstract.

[Stephan]

Sure there are losses between crank and wheel. I just wanted to say that power is somewhat comparable.

The rest, depends on who measure it. Look at this dyno chart, showing values on crank. Power and torque, both comparable, you can check the calculation :-)

[Dendrob]

Sure there are losses between crank and wheel. I just wanted to say that power is somewhat comparable.

The rest, depends on who measure it. Look at this dyno chart, showing values on crank. Power and torque, both comparable, you can check the calculation :-)

Thanks for posting that. If the hp is representing rear wheel then explain to me what the torque figure is.

[Stephan]

122 bhp is just value on rear wheel I was told by dynoman.

Curves are on crank both, and max values are 133,29 hp, and 112,42 nm. And if I get curve with power at wheel from him, there will be corresponding torque value. Or torque curve would be the same?

[Dendrob]

122 bhp is just value on rear wheel I was told by dynoman.

Curves are on crank both, and max values are 133,29 hp, and 112,42 nm. And if I get curve with power at wheel from him, there will be corresponding torque value. Or torque curve would be the same?

The graph seems to be showing crankshaft hp then and not rear wheel.

[Stephan]

exactly, so you cannot say there is abstract torque.

[Dendrob]

exactly, so you cannot say there is abstract torque.

No. Not with respect to the graph you posted. But I have seen graphs which plot rear wheel hp against engine rpm.

Or let's put it this way, the people owning the graphs told me it's rear wheel hp.

If your info was obtained on a rolling road I wouldn't mind seeing the rear wheel hp graph. I'm assuming the graph posted was extrapolated from it?