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Does higher revving = quicker bike?

Like clutchslip said.

It's all in the math: HP = Torque x RPM ÷ 5252

How can two bikes have the same HP and Torque but that max HP is achieved at different RPM?
 
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clutchslip said:
Horsepower is JUST a formula. Plug the 70 ft lbs and 100 hp into the formula, solve for rpm, and you get 7503 rpm. Both bikes will make the same power at this rpm.
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Doesn't this assume that the rpm at peak torque is the same for both bikes? Is that necessarily true? Isn't is possible that depending upon the shape of the torque curve that you could have to engines with identical peaks for both rpm and hp reached at different rpms?
 
flying_hun said:
Doesn't this assume that the rpm at peak torque is the same for both bikes? Is that necessarily true? Isn't is possible that depending upon the shape of the torque curve that you could have to engines with identical peaks for both rpm and hp reached at different rpms?
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Yes, that's just one point on the RPM-curve and it's not realistic for the two theoretical bikes mentioned. Not just peak figures, but the shape of the curve makes a huge difference. If you have a wide and flat torque-curve, you'll have more thrust at the rear-wheel than a peaky curve that rises sharply and drops quickly. It's the area under the graph that counts.

While there are simple equations, they are just approximations because they don't integrate each little RPM slice individually. Case in point:
1986 Ferrari Testarossa has 390hp, weighs 3700 lbs, 1/4-mile = 13.4s
1986 Ferrari 288GTO has 400hp, weighs 2600lbs, 1/4-mile = 14.1s​
WTF? A significantly heavier car with LESS HP, does a significantly faster 1/4-mile time? The simplistic equations cannot explain these real-world situations because they make too many assumptions. The only accurate way to model this is to take take individual 100-RPM slices, calculate thrust at rear-wheel for that duration, calculate instantaneous acceleration. Then do the next slice, then the next, etc. Then add up all the slices. In many ways, it's simpler to just take them to the track and do real-world measurements.


Here's a list for bikes: http://www.sportrider.com/performance_numbers/146_motorcycle_performance_numbers/index.html
 
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Lumberjack said:
I was pondering this because of the recent Sportrider mag where we have this situation:

Quarter mile times for the 600's in the shootout were all mid 10's..

Quarter mile times for the FZ1 and Ninja 1000 were mid 11's..

The FZ1 and Ninja 1000 both make substantially more hp and way more torque than the 600's, but rev only to about 11,000rpm..

Now, I know the rider makes a huge difference, and aerodynamics come into play, and the 600's are about 60lbs lighter.. But I figured it has something to do with the high revving engine..

Or is it related to how fast the engine revs?
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Ah I see.
The problem here is that you've given us a different set of variables than you observed in the mags.

In the mags you saw different types of bikes, i.e. displacement, weight, gearing, etc. but somehow you came away with, "The only difference seems to be the RPM's".

To answer the real underlying question. They are different bikes, built for different goals. And as such, each variable is tuned for it's intended goal.

since sprotbiles are "intended" for high performance riding, the gearing is usually geared to keep the engine up in the revs and powerband. Gear spacing is usually closer so the rpm drops with gear changes are minimal. Things like this.

The FZ1 and Ninja 1000 are NOT intended as race replicas. They are tuned to be "lazier" in a manner that makes them more "pleasant and comfortable" in normal day after day use. This state of tune in those larger bikes is also evident in the total power these two particular liter bikes make, as compared to something like a GSXR 1000 or ZX10RR.

So in the end, it's an apples to oranges comparison.
 
Lumberjack said:
I was pondering this because of the recent Sportrider mag where we have this situation:

Quarter mile times for the 600's in the shootout were all mid 10's..

Quarter mile times for the FZ1 and Ninja 1000 were mid 11's..

The FZ1 and Ninja 1000 both make substantially more hp and way more torque than the 600's, but rev only to about 11,000rpm..

Now, I know the rider makes a huge difference, and aerodynamics come into play, and the 600's are about 60lbs lighter.. But I figured it has something to do with the high revving engine..

Or is it related to how fast the engine revs?
Click to expand...
Upper 10s is about right for a 600 supersport. Mid 11s is way high for an FZ1 (I don't know about the Ninja 1000, but I expect that it's quicker than the FZ1). This is in comparison to Motorcycle Consumer News, for which I have 15 years of history.

Two examples from MCN:
2009 CBR600RR: 10.89 @ 125.53, 2009
2009 FZ1: 10.74 @ 123.22

For whatever reason Sport Rider didn't get best performance out of the FZ1 and Ninja 1000, so it's not a fair comparison.

In general, the best predictor of quarter-mile performance is horsepower divided by weight (full tank with rider). Where that goes wrong is when the bike is hard to launch. I was recently asked about performance of a bike that has an excellent power-to-weight ratio, but is so tall that it wheelies much too easily to turn a good quarter-mile. So it underperformed bikes with similar power by a half-second.
 
Thanks, DD. :cool
 
what if the vehicle as an airplane and it was trying to take off while on a conveyor belt?
 
xgambit said:
what if the vehicle as an airplane and it was trying to take off while on a conveyor belt?
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With or without monkeys flying out of the driver's butt?
 
DannoXYZ said:
Yes, that's just one point on the RPM-curve and it's not realistic for the two theoretical bikes mentioned. Not just peak figures, but the shape of the curve makes a huge difference. If you have a wide and flat torque-curve, you'll have more thrust at the rear-wheel than a peaky curve that rises sharply and drops quickly. It's the area under the graph that counts.

While there are simple equations, they are just approximations because they don't integrate each little RPM slice individually. Case in point:
1986 Ferrari Testarossa has 390hp, weighs 3700 lbs, 1/4-mile = 13.4s
1986 Ferrari 288GTO has 400hp, weighs 2600lbs, 1/4-mile = 14.1s​
WTF? A significantly heavier car with LESS HP, does a significantly faster 1/4-mile time? The simplistic equations cannot explain these real-world situations because they make too many assumptions. The only accurate way to model this is to take take individual 100-RPM slices, calculate thrust at rear-wheel for that duration, calculate instantaneous acceleration. Then do the next slice, then the next, etc. Then add up all the slices. In many ways, it's simpler to just take them to the track and do real-world measurements.


Here's a list for bikes: http://www.sportrider.com/performance_numbers/146_motorcycle_performance_numbers/index.html
Click to expand...

Gearing and traction I suspect.
 
Is the quarter mile going downhill or uphill ?
 
As to the question of two bikes with the same torque peak, which one has the higher hp peak? The bike with its torque peak at the higher rpm will have the higher hp peak.

Formula: (Torque x Engine speed) / 5,252 = Horsepower

This formula shows that as the peak torque rpm is increased, the peak hp is increased.

This formula also shows that no matter what, at rpm = 5,252 the torque will equal the hp. This is ALWAYS true for any engine.

As others have posted (especially DannoXYZ) there is a lot more variables involved in going fast and 1/4 mile times than just peak torque and peak hp numbers.
 
Very interesting!

I'm a little confused though by what DataDan said - I thought a "taller" gearing meant that the bike would launch more slowly and manageably than a bike which is geared "short"? I thought short geared bike is one that will pull really hard from lower rpm and so have more "trouble" with wheelies when launched..

I.e. - an R1 vs the bike I'm riding, a Z1000 - the Z1000 is geared quite short, so it has lots of power down low in the rpm range, at the expense of the high rpm power, while the R1 is geared tall and so is quite weak below 5k rpm, but really rockets at higher rpm....
 
Lumberjack said:
Very interesting!

I'm a little confused though by what DataDan said - I thought a "taller" gearing meant that the bike would launch more slowly and manageably than a bike which is geared "short"? I thought short geared bike is one that will pull really hard from lower rpm and so have more "trouble" with wheelies when launched..
Click to expand...
Sorry, I meant taller in stature. Wheelieability is related to center of mass height / wheelbase. The "taller" it is in that sense, the lower the maximum acceleration possible.
 
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