The perfect example is a motorbike compared to a tractor:
The bike has high HP, low torque. Fast acceleration, cant tow for jack!
Depends on the bike, and its motor ...
Tractor has low HP, high torque. Can't accelerate but can tow a house!
Actually, most tractors have very (relatively speaaking) low horsepower figures, but the figures quoted for them are
drawbar horsepower, which is almost directly related to torque for any given engine.
e.g. The big tractors that we had on one of our properties had a 90 HP, 3 cylinder GM diesel in it. It accelerated at a huge rate, but could only reach a very low speed because of its enormously low gearing.
Similarly, motorcycles have a very narrow torque and power band, but have gearing and mass that matches this to produce very high acceleration and top speed in any gear.
Please don't argue RB, this is a basic tenant learned in the first lesson. If you wish to disagree, you will be disagreeing with
every engineer everywhere in the world, everyone from car designers to the space shuttle
Generally quite dishonestly ... :lol:, which is why the definition of "
horsepower" used in the motor vehicle industry has changed so dramatically over the last 40 years - the latest change being in 2005 ... It seems that "... every engineer everywhere in the world ... " took a very long time to come to any kind of agreement about the subject ...
... specially with their marketing departments ...
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Some conversion formulae
here, for example. It is a tricky subject when one gets down to the nitty-gritty, but my statement is correct as a rule of thumb (heuristic).
Two identical vehicles can be posited, one of which has far more torque and the same mass, but with the same maximum power. The car with the greater torque will accelerate far faster, but they will both have the same top speed. If both have the same torque, but one has far lower power at the same rev point, both will accelerate equally fast (up to a point ... ), but the one with the lower power will have a proportionately lower top speed.
This example can be shown to be (relatively) true for all the permutations and combinations of mass, power and torque, with all other significant, non-random variables (mass, gearing, frontal area, rolling resistance, etc) being held constant. Gearing also has a major impact on any given variable set.
An added wrinkle in this is the rev range over which a given engine develops its usable torque and power.
A car's maximum speed is reached at the point where all these variables are just equal in effect to the maximum power of the engine, assuming that this maximum speed is not limited by gearing, or by other means (ECU programming, for example).
e.g. my SG Fox with its stock LR is speed limited by gearing in 5th/LR to around 188 kmh. It is also speed limited by the ECU programming in 5th/HR to about 198 kmh. Its theoretical top speed is a function of its gearing and the revs at which it develops its maximum power, or the point at which the variables mentioned above equal the power produced at the revs at which it reaches its maximum velocity. I understand that this maximum speed is around 212 kmh from a bloke in the US who had his ECU re-tuned to remove the artificial speed limiting program variable.
( we should also not clog up jf1sf5's thread, please move this to a new thread, I'm sure there are many others confused about this too)
Done. Quite correct :iconwink: :ebiggrin:
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