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Discussion Starter · #1 ·
We've talked a lot about what causes a bike to accelerate; horsepower or torque. I propose a thought experiment that might help clarify the physics of this event.

Let's consider any manual transmission bike with a clutch that locks-up when released. Let's now perform two experiments with the same bike, same rider, same roadway.

Test 1: Put the bike in first gear and get the bike rolling so the clutch reaches "locked state". Get the engine speed up to a steady 2000 RPM. Immediately go to WOT and note the instantaneous acceleration force.

Test 2: Get the bike moving and up into fifth gear and establish a steady speed where the engine is @ 2000 RPM and the clutch is in a "locked state". Immediately go to WOT and note the instantaneous acceleration force.

Does the bike accelerate harder during Test 1 or Test 2? Of course, it accelerated harder in Test 1.

Since horsepower is dependent on RPM, the available horsepower was the same during both tests with the engine running @ 2000 RPM, how is it that the acceleration was higher in Test 1? What property was responsible for this?

Remember, HP=(Torque)x(RPM)/5252.
 
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Gear ratio
Wither the limited HP at 2k the lower gear ratio makes it easier for the motor to move the bike.
It also allows the RPMs to rise faster.

I think a better example might be....
2 bikes exactly the same.
Both running at the same low rpm up a steep grade.
1 bike has less HP but more torque than the other.
Witch bike will climb the hill with the feeling of having MORE POWER...
Key here is both bikes running at low rpm.....
 

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Discussion Starter · #5 ·
Gear ratio
Wither the limited HP at 2k the lower gear ratio makes it easier for the motor to move the bike.
It also allows the RPMs to rise faster.

I think a better example might be....
2 bikes exactly the same.
Both running at the same low rpm up a steep grade.
1 bike has less HP but more torque than the other.
Witch bike will climb the hill with the feeling of having MORE POWER...
Key here is both bikes running at low rpm.....
If the bikes have the exact SHAPED HP curves, with one being "down" 1 HP, then the lower HP bike's torque curve will also be suppressed. Remember, HP is a mathematical extrapolation of torque @ RPM.
 

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Discussion Starter · #8 ·
Yeah, but I wanted to keep the principle of torque generating acceleration clear and simple.

Perhaps they were running in a vacuum, like some people . . .
 

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Now FIX your little thought experiment and have 2 bikes with different torque at a given rpm and have them both roll on where they have the same HP at the same speed and roll on.. you'll be amazed that the 'monster torque' bike will accelerate the EXACT SAME as one with lower torque but higher RPM's.. until one or the other runs out of available rpms (read that as the bike that only produces torque till like 3500 rpm) in which case the OTHER bike that can still rev will walk away from the bike that has run out of steam. POWER = acceleration.. not torque. Torque X rpm / 5252 = power. <drops the mic and walks away>
 

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Discussion Starter · #12 ·
Sigh. @kaitiff Did you even look at the link I provided that discussed this???? Power (HP) is never mentioned, nor does it appear in the equation for acceleration.
 

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Have you bothered to look at ANY of the links explaining why you're argument is totally specious and out of context? You just tried in the other thread to tell me that a bike at rest WITH A RUNNING ENGINE has zero rpm... telling me you aren't getting what a LOT of people are trying very hard to explain.
 

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Discussion Starter · #14 ·
Have you bothered to look at ANY of the links explaining why you're argument is totally specious and out of context? You just tried in the other thread to tell me that a bike at rest WITH A RUNNING ENGINE has zero rpm... telling me you aren't getting what a LOT of people are trying very hard to explain.
My argument is engineering; pure and simple. The WHEEL that the torque is being applied to is at zero RPM.
 

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I was told by an engineer that a bumble bee couldn't fly because of something like mass ratio to wing span.
 

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Ok... then in your little thought experiment you have a rear wheel that not moving.. and a clutch that is going to be engaged at some point to apply power to that wheel... have you ever killed an engine by having the engine running to slow when you dump the clutch? Why do you have to rev the engine to pull away from a dead stop sometimes, even on a 'torque monster' bike? Because (yet again) Torque X REVOLUTIONS PER MINUTE / 5252 = HP! Jeez. A motor with a high torque makes it easier to pull away because it has more HP available to it AT a lower rpm.. but you can get the same effect by revving the engine and application of gearing with a LOWER torque engine.
 

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If you put enough thrust behind a brick it will fly pretty good. Think F-4 Phantom aircraft.
Trebuchet does a pretty good job also.

Seriously I am enjoying this thread & I am really learning a lot from both you & Kaitiff.
Like I said earlier I have always been on the practical side of things.
 
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