Power Thrust Curves

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Thu, 15/12/2011 - 23:48
#61
pittsy
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Re: Power Thrust Curves

Going back to the nc700. I reckon, from memory, the max torque will be around the same as my 07 zx6r. The max torque and max power were very close together on the tacho on that machine. Whereas they're nowhere near on the nc700.

I'd like to have a crack at compiling thrust curves for the two machines to illustrate a few facts. Not least the perennial puzzle that is torque and power.

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Fri, 16/12/2011 - 11:39
#62
JAG
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Re: Power Thrust Curves

Hello pittsy,

"Your last paragraph is basically describing an over geared bike I think."

Basically, yes.

I don't want to give the impression that an over geared bike in top gear is a bad thing. It really depends on what you are looking for.

Do you want performance or good MPG?

Besides there's always the next gear down to select if you want better performance and acceleration.

I suspect the NC700 is very much like this in it's top 6th gear. The focus on an over drive type gear is not maximum road speed or good acceleration but efficent (good MPG) at normal highway cruising speeds. The RPM in 6th gear of the NC700 is a low 3000 RPM at 60 MPH. Lower engine speeds means lower engine HP friction and pumping losses than say like the KLR at 4150 RPM in its top gear at 60 MPH.

Lower engine friction and pumping HP losses means better MPG. Or simply the savings in HP friction and pumping losses can be applied to the rear wheel.

I don't mean that the friction or effort (torque)to turn the engine is less but the amount of time you have to turn it is less.

It's this less amout of turning (lower RPM) that allows you to get better MPG in top gear then if you operate the same bike at the same road speed in a lower gear. If you are travelling at a constant 60 MPH and it takes 12 RWHP, it doesn't matter what gear your in. It still takes 12 RWHP. The difference is the engine RPM. So if you get better MPG in top gear than at the same road speed in a lower gear its because the engine RPM is lower.

The down side is that an over gear will affect performance and acceleration. At high road speeds the air drag factor becomes too great which is trying to slow the bike down and as a result the bike cannot usually achieve the theoretical top speed.

An engine with an over gear usually needs a nice flat torque curve or a torque curve with good mid and low RPM power characteristics to minimize the down side affects of a low RPM at normal highwat cruising speeds.

JAG

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Fri, 16/12/2011 - 11:11
#63
pittsy
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Re: Power Thrust Curves

Found some info on zx6r 2007.

Max power 92kW@14000 rpm (96kW with ram air)
Max torque. 66Nm@11700 rpm

Primary i 1.9
1st. 2.714
2nd. 2.200
3rd. 1.850
4th. 1.600
5th. 1.421
6th. 1.300
Final i. 2.688

Rear tyre/wheel. 17". 180/55

I calculate rolling radius at 1.033 feet.

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Fri, 16/12/2011 - 11:27
#64
pittsy
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Re: Power Thrust Curves

Zx6

I get max rear wheel torque in 6th gear as 440Nm

Converts to 325 ftlbs

Less 10 percent is 293 ftlbs

Divided by rolling radius is 283 lbs thrust

That sound ok?

Much higher than the nc700 but no surprises there.

It would be interesting to compare their respective thrust figures at 70 mph in 6th gear. The 07 zx6 was slagged off big time for being gutless.

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Fri, 16/12/2011 - 12:36
#65
JAG
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Re: Power Thrust Curves

pittsy wrote:
Zx6

I get max rear wheel torque in 6th gear as 440Nm

Converts to 325 ftlbs

Less 10 percent is 293 ftlbs

Divided by rolling radius is 283 lbs thrust

That sound ok?

Much higher than the nc700 but no surprises there.

It would be interesting to compare their respective thrust figures at 70 mph in 6th gear. The 07 zx6 was slagged off big time for being gutless.

Sounds interesting so far.

Just remember, if you want to know how one bike will perform or accelerate compared to another you have to compare both bikes at the same road speed for each gear in question. Not engine RPM.

You also have to factor in total weight including the rider at that same road speed.

You want to know the power to weight ratio available at that same road speed of each bike in the gears you are interested in. Not what the maximum torque might be.

To get a better idea, base you thrust curve on a series of road speed data points. I suggest at least every 5 MPH for say over 30 or 40 MPH. The more the better. Depends on how much time you have for the calculations.

You graph will be very interesting to see.

I get that the ZX6 in 6th gear at 60 MPH = 5404 RPM

How much RWHP does the ZX6 make at 5404 RPM?

What is the bike's total weight plus the rider?

Divide the total weight by how much RWHP it makes at 5404 RPM. That's the hard part. To read a RWHP graph based on engine RPM to this level accuracy is HARD and takes time. I usually have to put the graph in PAINT and up scale it to at least 300% to 600% to create my own scale lines of reference.

You now have the power to weight ratio of the bike at 60 MPH in that gear.

Do the same for the other bike at the same road speed.

Which ever bike at that road speed has the lower or lowest power to weight ratio has more available thrust.

The greater the difference of the power to weight rato is between the bikes, the greater the acceleration rate difference will be between bikes. This will also apply to part throttle acceleration assuming both are at the same part throttle opening.

Have fun

JAG

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Fri, 16/12/2011 - 13:47
#66
pittsy
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Re: Power Thrust Curves

I've found a dyno curve for the 07 zx6.

Please correct anything you find to be wrong!

I'd already started crunching numbers based on 70mph so let's go with that for now. We're in a trough in the zx6 torque curve so anything above or below that speed will only be better.
One mile is 5280 ft so at 70mph we factor in 1.17 to get 6178 ft.

Zx6
Rolling circumference Rear tyre = 6.49 ft
Rear tyre at 70 mph = 951 rpm
Engine speed = 6314 rpm
Engine torque = 35 ftlb Dyno
Rear thrust = 224 lb. Not deducted losses as dyno reading

Nc700
Rolling circumference rear tyre = 6.41 ft
Rear tyre at 70 mph = 963 rpm
Engine speed = 3750 rpm
Engine torque = 43 ftlb
Rear thrust = 147 lb

Zx6 makes 1.52 x more rwhp in 6 th gear at 70 mph.
It is listed as 200 kg wet weight.
Some 25 or so kg less than the nc700.
Est 90 kg for rider.

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Sat, 17/12/2011 - 10:45
#67
JAG
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Re: Power Thrust Curves

Hi pittsy,

You do like the metric system.

I did some number crunching based on your numbers.

This is what I get.

ZX6

Total weight including a 198.4 lb rider is 639.3 lbs.

RWHP at 70 MPH in 6th gear at 6341 RPM is 42.1 RWHP

Power to weight ratio in 6th gear at 70 MPH is 15.2 lbs/RWHP

NC700

Total weight including a 198.4 lb rider is 679.4 lbs.

RWHP at 70 MPH in 6ht gear at 3750 RPM is 30.7 RWHP

Power to weight ratio in 6th gear at 70 MPH is 22.1 lbs/RWHP

On the "how does it feel" scale:

The NC700 in 6th gear at 70 MPH would feel "SLOW".

The ZX6 in 6th gear at 70 MPH would fell "OK". (very close to "GOOD")

My thrust curve of the BMW and Blackbird indicates that the Blackbird in 6th gear at 70 MPH has a power to weight ratio of 16.5 lbs/RWHP.

This would suggest that the ZX6 has more thrust available (can accerate faster) in 6th gear at 70 MPH than the Blackbird in the same gear at the same speed.

The BMW S 1000RR still comes out pretty good. At 70 MPH in 6th gear it has a power to weight ratio of about 11 lbs/RWHP. So it can accelerate much faster in 6th gear at 70 MPH than all of the above bikes.

Your numbers look pretty good.

You have come a long way in a very short time.

JAG

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Sat, 17/12/2011 - 11:20
#68
pittsy
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Re: Power Thrust Curves

Thanks jag

I'll try to digest what you've said number wise over the course of the day. I already have a pretty good idea where you're coming from but I need to try to fully get to grips with it.

The zx6 numbers look so good it makes me wonder if I've made a mistake. Although mine felt just fine at 70. It went banzai from 12000 to the redline. Epic!

Jag: "You do like the metric system."

Yes, I'm a crazy, mixed up kid. I can think in both imperial and metric but prefer metric. I wish my country had gone fully metric back in 1970. Because they didn't I still think in mpg, mph, miles. But in other things I think microns, mm, m. But not km! Crazy.

All converting does is increase the chances of a mysteak.

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Sat, 17/12/2011 - 13:23
#69
JAG
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Re: Power Thrust Curves

Hello pittsy,

The only problem I had was with the NC700 torque values.

I scaled up Kevin's NC700 crank HP graph curve and I came up with 29.8 crank BHP at 3750 RPM. 29.8 crank BHP works out to 41.7 ft/lbs of torque at the crank.

Could you be using PS HP?

I have a feeling your NC700 torque values did not include the 10% loss through the drive train.

At a 10% loss that gives a RWHP of 26.8 RWHP.

Based on a RWHP of the NC700 at 26.8 RWHP(or 35.9 ft/lbs)at 3750 RPM at 70 MPH the power to weight ratio in 6th gear at 70 MPH works out to 25.6 lbs/RWHP.

If you can post the HP graph of the ZX6 maybe I can help.

"Although mine felt just fine at 70."

The "feel good scale" would support your impression of how the ZX6 felt at 70 MPH in 6th gear.

"Yes, I'm a crazy, mixed up kid. I can think in both imperial and metric but prefer metric. I wish my country had gone fully metric back in 1970. Because they didn't I still think in mpg, mph, miles. But in other things I think microns, mm, m. But not km! Crazy."

I have the same problem except I prefer imperial. Shows my age. Thankfully there is the internet for easy convserions. At work I still like the imperial measurement, especially when measuring in less than an inch. At least you don't have to worry about US and imperial gallons.

Microns are pretty small and except for measuring particle contamination in hydraulic fluids, I don't use it much.

If I remember correctly a particle less than 40 microns in size cannot be seen by the naked eye. FYI before we put new hydraulic oils from the manufacturer into our equipment we have to be re-filtered it through two stages of filteration to clean them up before putting them into service.

These filters are much better (at removing small particles) than bike oil filters. Makes you wonder how much longer engines would last with better oil filters.

40 micron particles in a hydraulic system can do a lot of damage. Most wear occurs for us in the 10 to 15 micron size. The problem is that these particles create more particles as they impact surfaces and accelerate the "wear cycle". If your filter can't clean out these very small particles the wear rate increases. Changing the oil helps.

JAG

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Sat, 17/12/2011 - 14:25
#70
pittsy
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Re: Power Thrust Curves

I didn't convert into torque from the power curve, I read it straight from the torque curve. We're only just over 1ftlb out so that can accounted for just by slight differences in lining across the graph and in converting. Your figure makes it even worse! I didn't set out to make the nc700 look bad or anything. I just wanted to see how a "gutless" sportsbike stacked up against a bike with low down torque at half sensible speeds.

40 microns is just less than 2 thou in old money. So quite small.

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Sat, 17/12/2011 - 14:49
#71
JAG
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Re: Power Thrust Curves

pittsy wrote:
I didn't convert into torque from the power curve, I read it straight from the torque curve. We're only just over 1ftlb out so that can accounted for just by slight differences in lining across the graph and in converting. Your figure makes it even worse! I didn't set out to make the nc700 look bad or anything. I just wanted to see how a "gutless" sportsbike stacked up against a bike with low down torque at half sensible speeds.

40 microns is just less than 2 thou in old money. So quite small.

I agree 1 ft/lb is very close and can be accounted for by slight differences in graph reading. Really a very minor difference in the big picture.

At about 25 lbs/RWHP at 70 MPH in 6th gear the NC700 does appear to be well into the "SLOW" range.

I think we can safely say the NC700 6th gear really is for good MPG.

Don't feel too bad though, these numbers are probably close to a big HD at the same road speed in their top gear.

Compared to a small economy car I'd bet it feels pretty good.

The numbers really point out that weight and gearing make a BIG difference in straight line performance and the error of judging a bike's straight line performance just on traditional crank HP and torque vs RPM graphs.

JAG

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Sat, 17/12/2011 - 14:52
#72
pittsy
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Re: Power Thrust Curves

It seems to me that we need a rear wheel torque upwards of 250 ftlbs to start to feel a strong sense of acceleration. Wonder what rear wheel torque we're getting on these machines in, say 4 th gear at 50 mph.

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Sat, 17/12/2011 - 15:32
#73
JAG
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Re: Power Thrust Curves

pittsy wrote:
It seems to me that we need a rear wheel torque upwards of 250 ftlbs to start to feel a strong sense of acceleration. Wonder what rear wheel torque we're getting on these machines in, say 4 th gear at 50 mph.

On the "feel good scale" GOOD acceleration requires a power to weight ratio of between 10 to 15 lbs/RWHP at 70 MPH.

This power to weight ratio would feel close to the VMAX 1700 in top gear at 70 MPH.

The VMAX 1700 60 to 80 MPH time in top gear was 2.7 seconds.

The average G-force would be 0.338 G-force.

This would suggest "good" acceleration feels like between 0.3 to 0.4 G-force. 0.3 to 0.4 G-force feels like about 1/3 of your body weight is trying to push you back as you accelerate ahead.

So we could convert these numbers to feelings if we wanted too.

Of course 4th or 5th gear would deliver even more RWHP at the same road speed and therefore potentially increasing the rate of acceleration.

This would especially be true if at that road speed, the gear you selected resulted in the engine operating at its maximum torque RPM.

JAG

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Sat, 17/12/2011 - 15:55
#74
pittsy
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Re: Power Thrust Curves

Zx6 / nc700 comparison

At 70 mph in 4 th gear

That seems to have evened things up. It can be accounted for because the zx6 has very close ratios so dropping down even two gears makes small differences. Also, even though the revs have risen, we've dropped deeper into the lull in the torque curve! Whereas riding the nc700 the ratios are a bit more spread out and we've just about hit peak torque. Actually we've just passed it, but still on the crest!

Results:

Zx6
Rear wheel torque 286 ftlb

Nc700
Rear wheel torque 230 ftlb

Note I've switched to torque now, not thrust! Previously I'd divided RWT by rolling radius. Rolling radius is a gnats over one foot so it hardly changes the figure.

With the nc700 you're desperate to change up a gear at this stage, whereas on the sportsbike things haven't even begun to start! That's horses for courses. You pays your money, you takes your choice.

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Sat, 17/12/2011 - 19:25
#75
MP1300GT
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Re: Power Thrust Curves

Pittsy - While I haven't gone thru all of your calculations in great detail, there is NO WAY any 600cc street bike could beat the Blackbird in 70mph top gear roll-ons IMO. Something must be off in your analysis.

It was in another league compared to my 1999 VFR 800 and definitely much stronger than any 750 Sportbike available 10 years ago.

Cheers.

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Sat, 17/12/2011 - 22:12
#76
JAG
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Re: Power Thrust Curves

MP1300GT wrote:
Pittsy - While I haven't gone thru all of your calculations in great detail, there is NO WAY any 600cc street bike could beat the Blackbird in 70mph top gear roll-ons IMO. Something must be off in your analysis.

It was in another league compared to my 1999 VFR 800 and definitely much stronger than any 750 Sportbike available 10 years ago.

Cheers.

Hello MP1300GT,

This is great!

A good healthy debate.

Maybe I can help a little. I kind of hope pittsy's little 600 cc bike does well.

Below is my data for the 2006 Blackbird. It's only about the top 4 gears.

Honda Measured RWHP

NOTE: The RWHP number will be the same at the indicated RPM regardless of the gear it is in. The power to weight ratio number indicated is for 6th gear.

3200 RPM = 35 RWHP 6th = 57 MPH P/W of 21.2 lbs./RWHP 5th = 51 MPH 4th = 45 MPH 3rd = 38 MPH

3400 RPM = 38.1 RWHP 6th = 61 MPH P/W of 19.5 lbs./RWHP 5th = 54 MPH 4th = 47 MPH 3rd = 40 MPH

3600 RPM = 40 RWHP 6th = 64 MPH P/W of 18.6 lbs./RWHP 5th = 57 MPH 4th = 50 MPH 3rd = 42 MPH

3800 RPM = 43.1 RWHP 6th = 68 MPH P/W of 17.2 lbs./RWHP 5th = 60 MPH 4th = 53 MPH 3rd = 45 MPH

4000 RPM = 45 RWHP 6th = 71 MPH P/W of 16.5 lbs./RWHP 5th = 64 MPH 4th = 56 MPH 3rd = 47 MPH

4200 RPM = 48.1 RWHP 6th = 75 MPH P/W of 15.4 lbs./RWHP 5th = 67 MPH 4th = 58 MPH 3rd = 49 MPH

4400 RPM = 52.5 RWHP 6th = 78 MPH P/W of 14.1 lbs./RWHP 5th = 70 MPH 4th = 61 MPH 3rd = 52 MPH

4600 RPM = 56.9 RWHP 6th = 82 MPH P/W of 13.0 lbs./RWHP 5th = 73 MPH 4th = 64 MPH 3rd =54 MPH

4800 RPM = 60 RWHP 6th = 85 MPH P/W of 12.4 lbs./RWHP 5th = 76 MPH 4th = 67 MPH 3rd = 56 MPH

5000 RPM = 61.9 RWHP 6th = 89 MPH P/W of 12.0
lbs./RWHP 5th = 79 MPH 4th = 70 MPH 3rd = 59 MPH

5200 RPM = 63.1 RWHP 6th = 93 MPH P/W of 11.8 lbs./RWHP 5th = 83 MPH 4th = 72 MPH 3rd = 61 MPH

5400 RPM = 71.9 RWHP 6th = 96 MPH P/W of 10.3 lbs./RWHP 5th = 86 MPH 4th = 74 MPH 3rd = 63 MPH

5600 RPM = 74.4 RWHP 6th = 100 MPH P/W of 10.0 lbs./RWHP 5th = 89 MPH 4th = 78 MPH 3rd = 66 MPH

5800 RPM = 78.1 RWHP 6th = 103 MPH P/W of 9.5 lbs./RWHP 5th = 92 MPH 4th = 81 MPH 3rd = 68 MPH

6000 RPM = 83.8 RWHP 6th = 107 MPH P/W of 8.9 lbs./RWHP 5th = 95 MPH 4th = 83 MPH 3rd = 70 MPH

6200 RPM = 90.0 RWHP 6th = 110 MPH P/W of 8.3 lbs./RWHP 5th = 99 MPH 4th = 86 MPH 3rd = 73 MPH

6400 RPM = 96.3 RWHP 6th = 114 MPH P/W of 7.7 lbs./RWHP 5th = 102 MPH 4th = 89 MPH 3rd = 75 MPH

6600 RPM = 100 RWHP 6th = 117 MPH P/W of 7.4 lbs./RWHP 5th = 105 MPH 4th = 92 MPH 3rd = 78 MPH

6800 RPM = 102.5 RWHP 6th = 121 MPH P/W of 7.3 lbs./RWHP 5th = 108 MPH 4th = 95 MPH 3rd = 80 MPH

7000 RPM = 105.0 RWHP 6th = 125 MPH P/W of 7.0 lbs./RWHP 5th = 111 MPH 4th = 97 MPH 3rd = 82 MPH

7200 RPM = 105.6 RWHP 6th = 128 MPH P/W of 7.0 lbs./RWHP 5th = 114 MPH 4th = 100 MPH 3rd = 85 MPH

7400 RPM = 107.5 RWHP 6th = 132 MPH P/W of 6.9 lbs./RWHP 5th = 118 MPH 4th = 103 MPH 3rd = 87 MPH

7600 RPM = 110.0 RWHP 6th = 135 MPH P/W of 6.8 lbs./RWHP 5th = 121 MPH 4th = 106 MPH 3rd = 89 MPH

7800 RPM = 111.9 RWHP 6th = 139 MPH P/W of 6.6 lbs./RWHP 5th = 124 MPH 4th = 108 MPH 3rd = 92 MPH

8000 RPM = 115.6 RWHP 6th = 142 MPH P/W of 6.4 lbs./RWHP 5th = 127 MPH 4th = 111 MPH 3rd = 94 MPH

8200 RPM = 118.8 RWHP 6th = 146 MPH P/W of 6.3 lbs./RWHP 5th = 130 MPH 4th = 114 MPH 3rd = 96 MPH

8400 RPM = 121.9 RWHP 6th = 150 MPH P/W of 6.1 lbs./RWHP 5th = 133 MPH 4th = 117 MPH 3rd = 99 MPH

8600 RPM = 123.1 RWHP 6th = 153 MPH P/W of 6.0 lbs./RWHP 5th = 137 MPH 4th = 120 MPH 3rd = 101 MPH

8800 RPM = 124.3 RWHP 6th = 157 MPH P/W of 6.0 lbs./RWHP 5th = 140 MPH 4th = 122 MPH 3rd = 103 MPH

9000 RPM = 124.8 RWHP 6th = 160 MPH P/W of 6.0 lbs./RWHP 5th = 143 MPH 4th = 125 MPH 3rd = 106 MPH

9200 RPM = 125.0 RWHP 6th = 164 MPH P/W of 5.9 lbs./RWHP 5th = 146 MPH 4th = 128 MPH 3rd = 108 MPH

9400 RPM = 125.3 RWHP 6th = 167 MPH P/W of 5.9 lbs./RWHP 5th = 149 MPH 4th = 131 MPH 3rd = 110 MPH

9600 RPM = 125.9 RWHP 6th = 171 MPH P/W of 5.9 lbs./RWHP 5th = 153 MPH 4th = 134 MPH 3rd = 113 MPH

Thrust curve graph data for the Blackbird

MPH Honda 6th gear power to weight ratio
60 19.6
65 18.2
70 16.5
75 15.2
80 13.6
85 12.4
90 11.9
95 10.2
100 9.9
105 9.2
110 8.3
115 7.5
120 7.3
125 7.1

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Sun, 18/12/2011 - 10:56
#77
pittsy
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Re: Power Thrust Curves

mp1300gt: "pittsy - While I haven't gone thru all of your calculations in great detail, there is NO WAY any 600cc street bike could beat the Blackbird in 70mph top gear roll-ons IMO. Something must be off in your analysis."

Please bear in mind I never said it could!

I have to admit to wishing maybe I hadn't dug myself this hole now though! I'm just fascinated by the whole thing but maybe I'm misusing a good forum sight. I'm also starting to realise that if you're going to get into number crunching in public, you'd better be squeeky clean or you may upset someone. Dunno?

It does take some believing and I do doubt my own calculations. But at the same time, a sportsbike is powerful, light and very well geared so anything is possible.

For myself, what I'd hoped to get out of this was a) what constitutes rear wheel thrust? b) let's do some off beat comparisons and try and bust some myths.

Regarding b) I now realise that may be dangerous territory!

Welcome your opinion...

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Sun, 18/12/2011 - 14:05
#78
JAG
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Re: Power Thrust Curves

pittsy,

I found a 2009 Kawasaki ZX-6R RWHP graph.

Maximum RWHP = 107.7 RWHP at 14,100 RPM
Maximum torque = 42.9 ft/lbs at 12,000 RPM

Measured RWHP at 6341 RPM = 39.3 RWHP

Engine RPM at 70 MPH I got 6,301 RPM - very close to your reading of 6341 RPM at 70 MPH.

Power to weight ratio at 6341 RPM with a total weight including a 198 lb rider is 16.27 lbs/RWHP.

Our readings of 15.2 lbs/RWHP and 16.27 lbs/RWHP at 6341 RPM are very close.

Based in this review it appears the Blackbird and ZX-6R at 70 MPH in 6th gear are very close to the same straight line performance. The difference coming down to rider weight differences and slight differences in rear wheel overall diameters between brands adn tank fuel levels.

pittsy wrote:

"For myself, what I'd hoped to get out of this was a) what constitutes rear wheel thrust? b) let's do some off beat comparisons and try and bust some myths."

I agree pittsy, we are trying to objectively understand straight line performance. It's a learning curve. If we don't try, we won't know.

I appreciate all your hard work, comments and findings. They have made my journey easier.

In the end it's just numbers. That's why we need real world experienced riders like MP1300GT. We need his inputs and comments.

JAG

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Sun, 18/12/2011 - 14:22
#79
MP1300GT
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Re: Power Thrust Curves

Pittsy - I'm certainly not upset at your hard work, just stating what I believe to be a fact. Did many roll-ons at the time of my Blackbird ownership and always came out on top, by considerable margins.

I always thought torque x gearing was the definition of thrust. I'm talking pure engine thrust, excluding weights. With torque & hp always crossing paths at 5250 rpm.

Cheers

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Sun, 18/12/2011 - 14:30
#80
pittsy
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Re: Power Thrust Curves

Thanks jag

You've put some serious effort into this! You crunching all those numbers by hand or a program? We should be grateful you've done that and reflect on the information.

Just pulling one example out of the hat... Blackbird at 70 mph in 3 rd gear. Round figures is in the region of 450 ftlbs rear wheel torque. Not a bad feeling me thinks! It's hang on tight.

Why do your figures stop where they do? Is that the limit of the blackbirds performance?

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Sun, 18/12/2011 - 14:48
#81
pittsy
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Re: Power Thrust Curves

Mp1300 gt. thanks.

Let's get into this thing and have a bit o fun!

Regarding thrust. To me the term suggest a linear force. Expressed in lb, kg, N etc. Torque (at the rear wheel) is more a measure of the bike's potential for "traction", which will be converted into forward motion.... Thrust. That's how I see it.

I think we should pursue the blackbird/zx6 comparison. The sportsbike has nearly the same power available, is lighter and has an excellent gear ratio and rpm spread available. It is very good at the thing it has evolved to be good at!

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Sun, 18/12/2011 - 14:55
#82
MP1300GT
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Re: Power Thrust Curves

Just found some data for the Blackbird, pulled from March 2011 issue of Performance Bikes. Top speed of 177.02, 1/4 mile exit speed of 137.04mph, 133hp & 81ftlbs of torque, 563lbs wet weight.

The ZX-6R, tested by Cycle World in Aug.2011 issue, did 161mph, 1/4 mile trap speed of 129.81mph, 112.0hp & 45.1Ftlbs, 426lbs wet weight.

The Blackbird is probably making more torque than the ZX-6R's maximum even at 3,000 rpm. Certainly a huge advantage which would be difficult to overcome.

Hope this helps.

JAG - your Blackbird gearing looks bang-on. Where are you in Canada. I'm originally from Toronto.

Cheers

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Sun, 18/12/2011 - 15:09
#83
pittsy
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Re: Power Thrust Curves

Mp1300gt: "The Blackbird is probably making more torque than the ZX-6R's maximum even at 3,000 rpm"

Yes it is.

And it is clearly the faster bike. A bike I would love to take out for a ride. Let's salute the sportsbike for what it is though. While it's still here! The blackbird has nearly twice the cc but only slightly more power. That is reflected in the speed trap. Personally, I think the sportsbike is a staggering thing!

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Sun, 18/12/2011 - 15:47
#84
pittsy
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Re: Power Thrust Curves

Technically I think torque is referred to as a turning or twisting moment.

Essentially leverage.

Force at a distance.

Caveman levering rock forwards with a tree branch. That's our engine turning our back wheel, which is levering us up the road.

At a rate of knots if we have a blackbird.

Or zx6.

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Sun, 18/12/2011 - 17:00
#85
JAG
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Re: Power Thrust Curves

Hello all,

Looks like we are all on the same page.

I selected the Blackbird because it is a GREAT bike. I tend to think of it as a sport/touring bike rather than a super sport bike like the ZX-6R. I would be interested in MP1300GT views since he has had so much saddle time with the bike.

I also suspect the Honda's 6th gear is, in a sense a compromise between a nice economical highway gear for touring and still have reasonably good acceleration. As a sport/touring bike this seems justified. Besides there's always 5th gear.

I live in Mississauga (strange name for a city) - near Toronto. I was born in Hamilton. MP1300GT, were you around in the 60's and the Copetown Races near Ancaster?

With the Blackbird in 3rd gear at 70 MPH I got a power to weight ratio of 8.9 lbs/RWHP. On the "how does it feel scale" this works out to "very good".

Based on my BMW S1000R and Blackbird thrust curve graph the Honda in 3rd gear at 70 MPH has a better RWHP power to weight rato (more thrust) then the BMW has in it's 6th gear.

In 3rd gear the roll on time for the Honda from 60 to 80 MPH should be better than the VMAX 1700 in its top gear.

The Honda specs were based on a RWHP graph I found on line. RWHP graphs from different sources are often not exactly the same. Often they are out a few RWHP from each other. I usually select the lower reading graph. Cycle World is usually pretty good though.

A thrust curve graph over several gears of the Blackbird, ZX-6R and the BMW 1300GT would be very interesting. Especially considering MP1300GT's experience.

If we can get through all this and can say our numbers reasonably refect real world straight line performance at typical road speeds (not high speed racing)then I would like to write a simple excel program with graphing that anyone could plug in the numbers and do their own comparisions.

I am far from an excel expert. I am sure there are many members who could do a better job then I at writing it.

I agree MP1300GT, thrust is the amount of RWHP available at the rear wheel at that road speed.

I use RWHP because HP is a measurement of "work". For me it's just easier to see then ft/lbs of torque at the rear wheel.

Reading a HP graph to get data is also easier for me since the HP curve is usually always going up whereas the torque curve goes up and down. I get confused easily.

As I have said before:
Thrust or torque is the force what pushes the bike forward on a level road.
HP is how fast (RPM) the engine can supply that thrust or torque.

During acceleration it's the bike's and rider total weight, rolling resistance and air drag that is trying to slow it down.

A power to weight value (lbs/RWHP) combines both the forward thrust available and total weight thrust trying to slow it down into a single value.

To compare two bikes straight line performance together you need a value that both have in common at any one time regardless of engine RPM. That common value is road speed.

Air drag and rolling resistance are not included. To compensate for this we need another bike of the same type to compare too.

Regards,

JAG

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Sun, 18/12/2011 - 17:30
#86
pittsy
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Re: Power Thrust Curves

Not saying I'm right here but just how I see things.

Thrust is a force. As far as I can see, always a reactive force.

I can envisage a scenario where it is possible to have torque without power.

I can envisage a scenario where it is possible to have thrust without power.

Don't know if that changes anything already said? For myself, I just want to fully understand things.

Regarding graph. I've seen a graph format which I think ideally suits what we are trying to express. It is in Kevin Cameron's book sportbike performance handbook page 39. You can view it on google. I can thoroughly recommend buying the book. The graph plots hp against mph and overlays curves for each gear. It also overlays rolling resistance and drag. If we ever reach that level!

We do need an excel expert. I can add, multiply etc different cells but I've never tried doing a graph.

I look forward to reactions (pun) regarding thrust, torque and horsepower. It's a perennial subject!

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Sun, 18/12/2011 - 17:59
#87
JAG
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Re: Power Thrust Curves

Thrust (force) and HP (power)

Thrust (force) without power (HP), yes.

Power (HP) without torque or thrust (force), no.

If you apply a force (torque) and nothing changes (doesn't move) then you cannot measure the HP applied to move it, but you can measure the applied torque or force.

I guess you could argue that if the bike is applying 100 RWHP through the rear wheel to the road (earth), then the earth is applying an equal force in the opposite direction. Since the earth has a lot more mass than the bike (unless you are riding a HD) the bike moves more forward than the earth turns backwards.

That's probably why your bike accelerates so much better if the earth and you are going in the same direction. Of course if you are in merry old England and heading south it is all down hill anyway. ;-O

JAG

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Sun, 18/12/2011 - 19:35
#88
JAG
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Re: Power Thrust Curves

Pittsy wrote:

“Why do your figures stop where they do? Is that the limit of the blackbirds performance?”

The answer is quite simple.

The HP graph I was using started at 3200 RPM. The next limitation was me and available time.

Finally, my main focus was on straight line performance at road speeds between about 60 to 125 MPH in the top four gears.

At my limited riding skill level anything over 100 MPH scares the heck out of me anyway.

In the bottom two gears the bike’s acceleration at speeds below 90 MPH is probably only limited by your pain threshold level, tire traction and how quickly you can turn the throttle and shift gears.

JAG

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Sun, 18/12/2011 - 20:34
#89
pittsy
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Re: Power Thrust Curves

And the front wheel being airborne.

Jag: "If you apply a force (torque) and nothing changes (doesn't move) then you cannot measure the HP applied to move it, but you can measure the applied torque or force."

I'm being a little pedantic I know, but as well as lots of examples of power being used, force being applied but no movement occurring, I can think of occasions where no power is used at all but a force or torque is applied. I suppose that would be classed as static strain.

In the first case the power will be wasted in heat (and maybe destruction), in the second case nothing happens!

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Sun, 18/12/2011 - 20:57
#90
JAG
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Re: Power Thrust Curves

Could "static strain" be refered to as "potential engergy"?

Like a closed full oxygen bottle at 2000 PSI. Lots of potential energy but no movement so as long as the bottle of gas remains closed - no "work" is being done.

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