I have no idea what point there is comparing 5,000RPM to 15,000RPM...I was responding to the OP's question comparing the two...it's apples and oranges...

Yes, I made a broad generalization based on torque drop off...my bad...

I suppose the 'Busa gearing allows for the quicker launch...dunno, never really thought much about it...

 

Valid points and even more to ponder stuff by the seniors.

 

Actually, it’s not apples and oranges. But, whatever, I’m not going to beat a dead horse. I’ll just enjoy my Xl’s with peak tq in the 6000rpm range 😁

 

Do you really believe this?

OK, then explain something to me ...

Horsepower is torque times rpm, divided by 5252, right? I mean, that's the formula that describes the relationship between horsepower, torque, and rpm. You can look it up anywhere.

So now look at any dyno sheet ... here I'll just pick one randomly ...



Notice how the X axis says "Engine Speed". But this was a rear wheel dyno. That's power at the rear wheel. The rear wheel is going an entirely different rpm than the engine, right?

And yet if you pick any given spot on the torque curve, multiply it by the rpm, and divide it by 5252, you get the power at that rpm, right? Easiest place to see that is 5252rpm, because at that rpm, the rpm divided by 5252 cancels out and you're left with power = torque, if you remember your 8th grade algebra.

So how does rear wheel power and torque fit the formula with engine rpm? Doesn't it need to fit the formula at rear wheel rpm?

Rethink your conclusion that the dyno is showing rear wheel torque. It's not. It's showing engine torque as measured at the rear wheel, and that's an incredibly important distinction.

If this bike only has 82.3ft-lbs of torque at the rear wheel, a bone stock Honda mini-trail would eat it for lunch.

Torque drops after 5252rpm? Really?

That chart above is hitting it's torque peak at about 6200rpm. Between 5252rpm and 6200rpm, the torque is increasing. Was that dyno sheet faked?

I can show you a hundred sheets that have torque increasing above 5252rpm, without even trying.

 

This is the right answer. Gear reduction multiplies torque and divides rpm.

For a given rear wheel rpm, the 15,000rpm motor has 3 times as much gear reduction as the 5,000rpm motor.

So for example, if both are geared for 500 rear wheel rpm:

• 5000 divided by 500 = 10:1 gear reduction for the 5000rpm motor
• 15,000 divided by 500 = 30:1 gear reduction for the 15,000rpm motor

So the 5000rpm motor gets it's 100ft-lbs of engine torque multiplied by 10, giving it 1000ft-lbs at the rear wheel.
But the 15,000rpm motor gets it's 40ft-lbs of engine torque multiplied by 30, giving it 1200ft-lbs at the rear wheel

So the engine's torque number by itself doesn't tell you which bike accelerates faster. The rpm plays a role too. In fact, it's role is exactly equal to the role of the torque.

As it turns out, rpm and torque are completely interchangeable. Want more torque? Gear deeper. Torque will go up by the same factor that rpm will go down. If torque is all that mattered, no one would ever take their bike out of first gear. There's a reason you can pull a wheelie in first gear but not fifth. You have far more torque at the rear wheel in first gear.

Every time you upshift, you give up some rear wheel torque and you trade it for some rear wheel rpm.

So if the engine torque number is an incomplete predictor of the rear wheel torque, and you have to factor in rpm as well, then what we need is a new number. One that considers both torque AND the rpm of the motor.

That number is called "horsepower". It's literally torque times rpm (divided by 5252, but that's just to scale the number to what James Watt's horse could do ... conceptually you can think of horsepower as torque times rpm).

If we work out the math on the 5000rpm, 100ft-lbs motor, it calculates out to 95.2 horsepower.

If we work out the math on the 15,000rpm, 40ft-lbs motor, it calculates out to 114.2 horsepower.

So the torque of the motor didn't tell us which one is stronger, but the horsepower did. This is why horsepower is the operative figure for understanding the bike's acceleration capability (together with the mass of the bike of course).

 

Thank you for making the distinction regarding rear wheel torque measurement...it was what I had intended to convey and I thought that was obvious with the comparison to the flywheel measurement, but apparently not...

I have already addressed my generalization of the torque drop off in a prior post...mea culpa...

 

But the relationship you related was inaccurate, to wit:

The relationship between flywheel torque and rear wheel torque is not 15% at all. The relationship is to multiply the engine torque by the gear reduction to get rear wheel torque.

If, for example, the motor is making 100lb-ft, and the gear reduction is 10:1, then the rear wheel torque is 100 times 10 equals 1000lb-ft.

Gear reduction multiplies torque, that's the whole point here.

It also divides rpm at the same time. Therefore rpm and torque are totally interchangeable.

I can make a million ft-lbs of torque with a hand held battery powered drill motor, if I gear it deep enough. You'd have to time it with a calendar, but it could be done.

 

Thank you...I conflated torque and horsepower...again, mea culpa...

 

graphic rep of what you said !

 

Well ! I think I did find my config after a bit of an email swap with hammer - I think the 1275 kit with 570 cams gasket upgrade with oil pump gear upgrade is what will give me the max torque for the buck. This give a max theoretical torque of 93 with 101 hp as opposed to 96 to with 130 ish hp for the full kit.

now to get the quote and shipping tied up while this bloody Covid rages !