xxChrisxx wrote:Stradivarius wrote:xxChrisxx wrote:Told you I was being a pedant
. Direct relationship is a well defined meaning. And gear ratios aren't variables, they are constants. You can choose different constants, but they are still constant!
Ok, let me be a pedant as well.
Each gear has a constant ratio and are not variables, but the total gear exchange ratio between the crankshaft and the wheel (which you see from the formula is what I am refering to) is not constant, as long as it is possible to shift gears. So the gear exchange ratio is in fact a variable. A parameter does not need to be continuous in order to be variable.
All this is highlighting two different philosophies of modelling. Top down or bottom up. Both will come up with the same answer and are equally valid.
edit. Bottom up is clearly superior though!! As you don't have black boxes in the model. Guess which I'm a proponent of.
What I am trying to point out is that these black boxes, as you call them, do not say anything about the performance. If they did, it would not be possible to determine the performance without them. So what is superior depends on what you want to do. If you want to evaluate the performance of a car, I would say it is better to remove all irrelevant information, such as torque and color (provided that you have the relevant information, if not, you can't evaluate the performance).
The whole idea of using the normalized curve and look at the ratios between successive gears rather than each gear exchange ratio itself, is to remove redundant and unnecessary information until it is not possible to remove anything more without loosing information about the performance. As it turns out, you can remove information about the torque, but you need to keep information about the power. What you are then left with is a set of a few parameters that uniquely define the performance and if you have this information, you can determine the performance. If you don't have it (either explicitly or implicitly), you can't determine the performance. I also want to point out that if you have this set of information, knowing the torque in addition does not add any more information about performance than knowing the color of the car.
It is, however, easy to imagine a context where knowing the torque is important. The torque is easy to measure, while power is measured indirectly by measuring the torque and the engine speed and multiply the two. So if you are tuning an engine, you don't need to know the power in order to conclude from the torque that you have achieved what you wanted. But this is only true if you are looking at the torque at certain engine speeds and that means the torque determines the power. You may also have situations where torque alone is an interesting parameter. If you are dimensioning the parts of the drive train, you need to make sure they are strong enough to handle the loads and that means you need to know the torque. But that is not related to performance.
