i started riding a CB500F, it has a flat torque curve, pretty much the same torque at 3k and 9k rpm, then why does the bike (in the same gear) accelate much faster at higher than lower revs?
In: 88
Higher revs means more power strokes per second, hence more power if all other things are equal.
So there is a mechanical link between torque, time, and horsepower. Torque is the ‘push’ in one rotation of the engine. RPM (revolutions per minute) is how many rotations you apply. In every Dyno (dynamometer, measures input power to a known system) there is a crossover where torque and HP are scaled equivalently.
More rpm = higher horsepower (torque / second) = go fast.
Smaller piston diameter = less internal friction, and therefore more efficiency.
Here’s a recent video I saw that can help.
You have discovered the phenomenon that torque and power output are both important for maximum acceleration, despite what some people say or believe.
Your maximum torque determines the maximum amount of force that your vehicle can exert at the wheels. If you exert almost no force at the wheels, you can’t really accelerate very much. But in order to accelerate, you don’t just need to provide a force. You also need to increase the kinetic energy of your vehicle (as well as overcome the energy that you are losing to drag and other sources of friction). If you can apply a tremendous amount of torque but very little horsepower, what that means is that you can tow a million pounds, but at 0.0000001 miles per hour. Horsepower (power) is the amount of energy you can add to the vehicle per unit time. You need a lot of horsepower if you want to accelerate quickly, because you need to add a lot of energy to your vehicle.
The reason your motorcycle can accelerate more quickly at higher RPM given that it has a flat torque curve is that, at a higher RPM, the engine is putting out more power. More fuel is being injected and burned in the same amount of time. Since the amount of torque it’s providing is the same, power output is what determines exactly how fast you accelerate.
E: to be clear, of horsepower and torque, the fundamental parameter of the engine is horsepower. Output torque can be changed to any arbitrary value you want (within reason) through gearing. An engine that outputs 1,000 horsepower but only provides one foot pound of torque at the crankshaft is much preferable to one that outputs 100 horsepower but with 10,000 ft lb of torque at the crankshaft if you want to use the engine to make something move quickly. You can design a gear train to provide the torque you need at the wheels, but no gear train allows you to output more power.
E2: it has been pointed out to me, and I agree, that depending on how you interpret your original wording, what I said is wrong.
If what you mean is that, with the motorcycle in the same gear, and at 5,000 RPM versus 9,000 RPM, that you observe more rapid acceleration at 9,000 RPM, then what I said is wrong. If that’s the case, what must be true is that, if you’re already operating at 9,000 RPM, pushing the pedal down a little bit more must be increasing both torque and power output more than torque and power output increase if you are at 5,000 RPM.
The way I interpreted what you said is that you were asking why, if you really push the pedal down and go from 5,000 RPM to 9,000 RPM, you end up accelerating a lot. That’s because you have to, because power output is higher. The fact of the matter is that torque curves are maximum torque curves, not actual torque curves. That is, your engine can produce far less torque at a particular RPM then the torque curve would suggest, because the torque curve is generated by putting the engine at wide open throttle and seeing how hard you have to brake it before it slows down.
Horsepower is torque divided by time. Make the time smaller, leave torque the same, and horsepower goes up. This is what happens when the engine turns faster, up to a point where other things factor in.
Torque times RPMs equals horsepower.
If you have a flat torque curve, you also have a linear increase in horsepower over that curve.
If your bike has the same torque at 3000 rpm as it does at 9000rpm, that means you’re getting 3x the horsepower at 9000.
Take this to the extreme. Imagine two engines that provide 1HP of power One has high torque and spins the flywheel (without resistance) at 1 RPM and one with low torque and 10,000 RPM.
The first engine won’t result in quick acceleration but no reasonable amount of resistance will impede the rotation of the flywheel. The second engine’s flywheel will spin so fast it will be a blur to your eyes but reasonable reasonable resistance can stop the flywheel from spinning fast.
For a fixed power output, higher revs means less torque. Torque doesn’t determine acceleration, it puts an upper limit on possible acceleration and possible speed at a fixed resistance. Acceleration is a function of power, torque, resistance and rotation frequency. Acceleration always, always, always requires an increase in power output.
In short, your bike is pulling harder at 9k vs 3k at the same gear because you are generating more power at 9k RPM.
It makes the same torque, yes, but at 9k RPMs you have 9000 of those torque moments per minute, whereas at 3k you only have 3000. More bangs per second = go faster
The CB500F torque curve is only relatively flat between 5500 and 7000 rpm. At 9000, it has dropped off and at 3000 rpm, it has not yet come in. If you look at the graphs on [this page ](https://motostatz.com/honda-cb500f-acceleration-top-speed/), you will see that the in-gear accelerations are just the torque curve which is being vertically scaled and horizontally squished due to the gear ratios, so the difference in any one gear comes from the fact that the torque cueve is not perfectly flat.
Imagine you have a hammer.
The strength you hit the nail with is torque.
The speed of the hits per minute is RPM.
Horse power is then how fast the nail goes down.
If you hit the nail faster (more rpm) with the same power (Torque) then it will “go faster”.
Horsepower is the work being done. Torque is basically how much work you can do at any given time. If the torque curve is flat, the horsepower curve will usually be a constant incline with rpm. So basically, as revs increase, it becomes easier and easier to do the same amount of work.
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