Hey Team, thx for another awesome video :) Would it maybe possible to get a video from Ari´s Shop Manual, of him doing an upside-down fork rebuild? I know there is an video during his old MM times, but thats 8 years old and was about an right-side-up one. Greetings an have a good one folks

i’m sure y’all have muted me but this video rly needs a rewrite if u want to avoid misinformation and actually elucidate the difference btwn torque and power for bikers who don’t know.. power = acceleration torque ≠ acceleration torque = where the power band is in the rpm power tells u how fast u can accelerate torque tells u what rpm range yr power band is at.. (a 200ftlb 100hp bike had a much lower redline than a 60 ftlb 100hp bike for example,, but w the perfect transmission they’ll have the same acceleration..)

Yes - holding the piston-con rod and the crank pin made the difference for me too. Have seen many videos on hp vs torque and the force x distance equation but somehow that visual made it click.

same was very helpful!

Indeed

Torque is just a force. I think the concept of force is quite intuitive. Power is the one that is less intuitive. In layman's terms, a powerful muscle can exert a lot of force. But when you say a powerful engine can exert a lot of torque, it can get confusing because of the power and torque numbers/curves in the specs/dyno sheets. The torque can climb down while the power still goes up, but all is relative to the rpm. In describing engines, compared to describing muscles, the term Power is more technical. A force causing motion in the direction of that force, is producing work. The higher the rate that you can do that "work", the higher is your measured power. Torque is the rotational force produced by the engine's combustion, causing the crank to rotate (revolves). The rate of crank rotation is in revolutions per minute. The higher the torque that your engine is exerting at a certain rpm, then the higher the power will be at that rpm. Suddenly, the term "work" here is not specifically mentioned anymore. If your engine crank is rotating at a rate 6500 rpm with a force (torque) of 500 lb. ft. behind it, then it is producing 619 hp. The terms that are constantly there is the torque (force) and the revolutions (motion) per minute (rate). Power is kind of just a "calculated" result.

“How rapidly the torque is applied” made a lot of sense to me.

Classic. Saying.

Worst analogy ever.

😂😂😂😂 what an awesome analogy.

@@doomman700how’s it wrong? I’ll wait.

@@nogginbonker76how is it wrong, start with torque is a twisting motion not push. Then the fact that momentum will be what carries that wall which means speed and Hp will push it farther. Need more?

It is a nice but completely useless analogy, because the torque as in the subject of this video is crankshaft torque, which is one of the most useless engine parameters, unless boasting and bragging are a virtue. Crankshaft torque cannot be compared to the runners "push-off" because bikes and cars, unlike runners, have gearboxes. Crankshaft torque is TOTALLY meaningless. At best, the SHAPE of the torque curve matters, but only a bit, and only for mediocre drivers that do not know how to use a gearbox (and I know that because I am one, hence my preference for older big twin sportsbikes like the 2-valve Duc's). The best practical example for the utter irrelevance of engine torque can be found in Moto Grand Prix racing in the 1960's and '70's: Despite fourstrokes being "torquey" and riderfriendly with a wide powerband, pulling like a freighttrain, opposed to twostrokes being peakey and high revving, narrow powerband and not all that much torque compared to the 4-strokes, without a single exception ALL manufacturers went with the 2-stroke for the simple reason that it is horsepower that wins races. Not torque. Even Soichiro Honda, who absolutely HATED twostrokes and tried to keep racing a fourstroke with the NR series, knew this (the NR was intended to extract 2-stroke horsepower from a 4-stroke engine). Honda had to cave and also changed to 2-stroke. Quite succesfully, I might add.

It's like money. USD 50000 is a nice amount but meaningless without time, is it per week, per month, per annum, over a lifetime? Similarly, torque is timeless, horsepower is torque over time.

How did you know the difference in application, but not understand the physics? Cart before the horse.

Well,if you ride a v twin and a sportbike i would say its impossible not to feel the difference@@gorillamoto5329

​@@gorillamoto5329easy, if someone tells you torque is strength and Horsepower is Power then you now know the difference in application but you still might not know the physics behind it. We all know what things do but don't know how many things do it.

⁠@@paulneedham9885torque is strength, Horsepower is power? 😂 Watch the video again. In simple terms, horsepower is torque over time.

Yes! God, yes. I wish Ari would just say this. Torque on its own is basically a useless number that doesn't tell us anything. The whole HP curve is what matters, because it's the *power output of the engine*. Torque = strength and HP = speed works in many cases as a simple explanation but is very misleading and leads to misunderstandings.

@@Wintersdarkand make sure the hp and tq graph cross at 5252 which is used in the computation. I’ve seen graphs published where this did not occur.

Yeah that line is not true. A bike acclrates faster in its powerband, it's weight and gear says the same. The only think it change was the amount of horsepower that was created.

@@pleasedontwatchthese9593 I get the simplification he's going for and I'm positive he knows the intricacies. It's difficult to tell a KZfaq audience to integrate the horsepower chart across the range of the intended powerband to determine average acceleration. The sentence just seemed like a misleading sound bite when later people take it out of context.

​@@joepelletier5381 I agree with you. My main point is it should have been left out because as you point out it will be misleading

True. Given perfect gearing, the engine that makes the most horsepower will also make the most torque. In real life though we have no perfect gearing so in many cases an engine that makes greater maximum torque is more useful.

@@LTVoyager I think my point is that this is only true (that we should compare just torques) if both bikes have the same redline and I'm afraid that wasn't clear in the video.

You hit the nail on the head. Peak torque is kinda useless figure and is only talked about because of momentum. It doesn't matter if it's a useful number to the maker if it sells bikes

​@pleasedontwatchthese9593 yeah, there are still a lot of dudes in comments thinking torque makes a difference in acceleration. If two bikes have the same hp then they will accelerate the same regardless of torque difference. Only difference will be bike with lower torque will have to rev lot higher.

​@@currycel470 the bike has to Rev higher to create similar torque, torque is the turning force of the engine, HP is how fast the engine can work. The higher the torque the faster you take off, how fast you can go is HP. So a Harley will beat a Sport Bike off the line but the Sport Bike will then pass the Harley. Harley high Torque low RPM, Sport Bike high HP high RPM.

@@currycel470bro it does😂, not a big difference, but it makes a difference

A bike in its power makes more torque too, than remaining part of the rev range. So he's not wrong.

That is what I "keep screaming" on all videos like this. They don't specify that "torque at the wheel" is important for acceleration, not at the engine. In a gearing calculation, power is same between input and output of a transmission (ignoring internal losses). But the torque and rpm "value" is what changes. Want more output rpm (=wheel speed)? Torque has to come down. It's why diesel engines are not used in (high-)performance cars.

But, as you gear it down for more torque you loose speed. To try and match the torque output of a large engine with a small engine you would end up needing to shift a lot as the gearing would be very short. Everything is a balance. That’s why heavier bikes do better with high torque engines that produce relatively less horsepower. You need that high input torque to get the mass moving. And, generally a heavy bike is going to be more about comfort where you don’t want an engine screaming at high rpm all the time.

@ In real life you won't find the same transmission ratios on a big and a small engine. The "design target" is a "target max speed" and spreading it between 5/6 gears based on power band (i.e.: not peak engine torque). I agree that the small engine will scream, but the wheel torque will be comparable (if the power is comparable). Edit: If you care about acceleration, then "as you gear down for more torque you loose speed" is not really logical. You downshift because you already lost speed and want to regain it asap. If you are at peak engine torque rpm, then downshifting will, most of the time, get you more wheel torque because you shift into higher power rpm. And that was my main point of "wheel torque", not "engine peak torque".

@@mateiberatco500 You have to account for input RPM and output RPM as well. At the end of the day it isn't that simple because when you gear down for more torque you loose output RPM which is the speed. Yes, if you're going up a hill you may need to downshift to maintain speed. But, when you downshift the engine RPM has to be higher to maintain that speed. At which point you would eventually need to upshift again because you will run out of engine RPM if you keep accelerating. I will argue that just wheel torque doesn't mean anything. I can gear down a tiny engine and get the same wheel torque as a semi truck. But, the output RPM will be very low. That's why you need to account for RPM and not just the torque numbers. It's also part of why a higher torque engine can pull heavy loads better than a low torque engine. You could gear the low torque engine so the wheel torque is the same, but you need the high engine torque in order to have high enough gearing to get the speed.

​@@NBSV1 First of all: I'm fighting against "big torque numbers" (instead of "power") and how that number should not affect buying decisions. That's from where I say "wheel torque" makes more sense. Granted, it's not a beautiful single advertisement-friendly number like engine peak torque, but I also want to see the engine graph when I shop for a vehicle (and if they would provide "wheel torque vs speed for each gear", that would be my auto p**n). "when you gear down for more torque you loose output RPM which is the speed" please stop saying this. The rest of that paragraph I agree. But the output rpm/speed will not drop unless the vehicle is in the air (or hard braking or some catastrophic failiure). Vehicle inertia si orders of magnitude bigger than engine inertia to raise it's rpm. Also "gear down for more torque" - if you mean engine torque (cause everybody assumes that when talking about torque in cars/bikes), not true in any cases. You gear down for more engine power, which leads to more wheel power, and that is proportional to wheel torque at the same speed (again, speed change is negligible during a shift). Now, regarding your 2nd paragraph: "I can gear down a tiny engine and get the same wheel torque as a semi truck. But, the output RPM will be very low." We really need to define what we compare. In the video they compare a 80HP/110Nm Harley with a 110HP/50Nm Kawasaki (not sure if torque is in nm or ft-lbs). If the wheel torque vs speed would be overlapped, I would expect both to accelerate similarly until Harley tops out, because the Kawa has gearing spread to an, at least, extra 50% top speed for it's +50% HP. And that is my point: engine torque is meaningless for comparison. You need to get wheel torque graph and compare them. Otherwise we would see diesel engines is all car races. PS: Acceleration is defined as force / mass (from F=ma), force is torque / wheel radius (from Tq=F*len). So how can you say "wheel torque" does not mean anything?

Decades? But this was explained in high school (at least from my part of the world). Force, motion, rate = power. Basically, power is the calculated result. Force, motion, and rate are its factors and are the ones that are quite intuitive to understand. More torque (force) at a certain revolutions (motion) per minute (rate), more calculated power.

EE Jason is brilliant👍