Power Thrust Curves
Sat, 10/12/2011 - 19:54
#32
Re: Power Thrust Curves
Hi jag
Thanks for that.
Right, i now understand your graph! I was confused before, thinking that the lbs on the left (vertical) axis were thrust. But I now see that it is an expression of power/weight plotted against rpm. Obviously no need to know any gear ratios at that stage. When we come to over lay mph then we need to know ratios. Also I can now see that the graph will become way too cluttereed if we try to over lay each gear as mph. Effectively the green line will move to the right as we drop down the gearbox. You will need a separate graph for each gear to make it readable.
What I'd envisaged was a graph plotting thrust, in lbs, N or kg against either rpm or mph, with a curve for each gear on the same graph. That would, I feel, give a good indication of the sense of acceleration to be felt by the rider. Where my graph would come undone is that it wouldn't account for the weight of the machine (plus rider etc) or aerodynamic drag. For most road situations I don't think drag is a major worry. Because most of our accelerating (the feeling of which is what I'm trying to convey) is done at speeds where drag is not a major issue. I'm still left with how to factor weight into the graph. Or simply ignore it.
Instead of just having lbs thrust I suppose we could divide it by weight, but I think we'd end up with something which people couldn't relate to. If we just show thrust in lbs, at least people could relate to that. Admittedly thrust alone is not the full story without weight and drag.
At the end of the day there is no way to make these things palatable and take every factor into account. A compromise is needed. As long as we give people a good idea of what's going on I think that's fair enough.
Sun, 11/12/2011 - 00:09
#33
Re: Power Thrust Curves
Honda 2006 Blackbird 1100 vs BMW S 1000RR Thrust Curve Graph 6th gear 60 to 125 MPH
Below is the thrust curve graph of the Blackbird vs the BMW in 6th gear from 60 to 125 MPH.
The big difference between this graph and the others is that it is based on road speed rather then engine RPM. The total weights, including a 185 lbs rider, has been included.
As you can see the addition of both bike's gearing in 6th gear in the graph has made another big difference. The BMW, although it makes less RWHP than the Honda at these roads speeds, its straight line performance is much better than the Honda.
It's interesting to note that at almost exactly where the Honda power to weight ratio finishes at 80 MPH the BMW starts at 60 MPH.
This suggests that to match the performance of the BMW, the Honda may have to drop to 4th gear from 60 to 80 MPH.
Another way to look at it:
At 60 MPH in 6th gear the BMW has 44% more thrust available than the Honda.
At 80 MPH in 6th gear the BMW has 35% more thrust available than the Honda.
The real scary thing is that at these road speeds in 6th gear the BMW is not even close to its engine's maximum power torque band. This thing is NUTS!
On the feel good scale the BMW is at the "good" level and the Honda is at the "OK" level.
JAG
Sun, 11/12/2011 - 13:58
#35
Re: Power Thrust Curves
Re nc700
There's a power and torque curve on Kevin's test. I've found all the transmission ratios as well as wheel and tyre sizes on u tube of all places! I've a busy week ahead of me at work but after that I'll put some figures together ready to drop onto a graph. That's where I'll hit a problem, as my skills in producing graphs are positively Jurassic! Graph paper and flexicurve last time I produced a graph. And my flexicurve is no more. Guess I'll have to figure out how to do it on excell.
Sun, 11/12/2011 - 16:56
#38
Re: Power Thrust Curves
Honda NC700X crank HP graph
What we know so far.
The NC700X graph appears to be based on engine crank BHP, not RWHP.
We will need a correction factor to estimate RWHP. For a standard transmission I suggest a correction of about 12%.
Does this seem reasonable?
JAG
Sun, 11/12/2011 - 18:27
#39
Re: Power Thrust Curves
Yes, the power/torque figures are crankshaft. It's all I can find so beggars can't be choosers. I know a typical meshing gear set looses about 1 per cent, but we have a constant mesh gearbox so all meshing gears will loose something, if not the full 1 per cent each. There'll be oil drag. The rear chain will loose something like 3 per cent, as is substantiated by the fact they get so warm! There'll not be 100 per cent transmitted to the road by the tire( :) ) either, but how much "nominal" slippage... ?
Here's what I found on u tube.
Primary Reduction 1.731
Gear Ratios
1 2.812
2 1.894
3 1.454
4 1.200
5 1.033
6 0.837
Final Reduction 2.687
Final Drive Chain
Rim Size
Rear 17M/C X MT 4.50
Tyre Size
Rear 160/60-ZR17M/C(69W)
Happy number crunching!
Sun, 11/12/2011 - 19:16
#40
Re: Power Thrust Curves
Without cross checking, I get the following:-
Rolling circle of rear tire: 1.02 feet. (anticipating that our audience will still think in ftlbs!) no allowance made for tire "settling" with weight applied.
The following are the factor to multiply the engine torque in ftlbs to convert to thrust in lbs, allowing 10 per cent for overall losses.
1st: 11.53
2nd: 7.78
3rd: 5.97
4th: 4.92
5th: 4.24
6th: 3.43
Hope your figures agree as I've not cross checked my figures. Doing this hurriedly before sitting down for Sunday dinner. They're setting the table around me. Ha ha.
Sun, 11/12/2011 - 20:24
#42
Re: Power Thrust Curves
That was rolling RADIUS not rolling circle. Slip o the tongue. Sorry.
Sun, 11/12/2011 - 21:43
#43
Re: Power Thrust Curves
Think you may have a contender in the klr650. Not a uk model but that's not the issue.
Need to know mpg though as that is THE issue
Note how it suffices with 5 gears, something that you would think would suit the Honda
Just need to know if the mpg figure is worthy.
Mon, 12/12/2011 - 02:00
#44
Re: Power Thrust Curves
Kawasaki KLR650 MPG
I went on line to a few sites. The owners seem to get between 50 to 55 MPG in US gallons under normal highway speeds. The most common was about 53 MPG per US gallon.
53 MPG in US gallons works out to 64 MPG in Imperial (UK) gallons.
I would not consider the KLR a pretty bike. Its design refects what it is ment to do.
As Captian Scarlet would say, "it's a tall rounder". I tend to think of it as like a two wheeled jeep.
There are usually a good selection of good used KLR's available. Typically a low mileage bike a couple of years old runs about $5000 to $5500 asking price in CAN dollars. Sometimes you can get a new last year model at a pretty good price.
Many of the owners consider the bike a very good commuter bike. Its been around for a very long time so it's well sorted out. It's no fire ball but it will get the job done.
I believe the US has a military model where the engine was modified to a diesel. Its mileage is outstanding.
What is the NC700 new cost?
JAG
![images[1].jpg](http://www.ashonbikes.com/sites/default/files/images[1].jpg "images[1].jpg")
Mon, 12/12/2011 - 20:11
#46
Re: Power Thrust Curves
£5800 sterling for the nc700x
Wed, 14/12/2011 - 11:57
#48
Re: Power Thrust Curves
Nc700x
Max torque 44 ftlb at 4750 rpm
At max torque, rear wheel thrust, using method above, I calculate at:
1st: 507lb
2nd: 342lb
3rd: 262lb
4th: 216lb
5th: 187lb
6th: 151lb
A) I hope those are correct ! and B) I still intend to do full curves.
If anyone has any rear wheel thrust figures for any other bike, of any category, I'd be interested to compare the nc700. Just to give it a reference to anything else.
It's a shame that the lowest thrust occurs where you'd most want it to be the highest. That goes for all vehicles, not just this Honda!
If anyone has a way of reversing that, you need to ring the patent office immediately!
Wed, 14/12/2011 - 12:55
#50
Re: Power Thrust Curves
Hi jag.
The figures are for thrust, in lbs, not torque.
What I've done is calculate rear wheel torque for each gear, including losses at 10 percent, then divide by rolling radius in feet.
In my mind that gives a thrust load figure acting on the rear wheel spindle, parallel to the tangent of road/wheel. I've taken that to be the actual force moving the vehicle forwards. The torque is just the means to an end.
Does that sound right?
I think it's just coincidence that the rolling radius figure is similar to the amount accounted for by losses.
Wed, 14/12/2011 - 13:21
#52
Re: Power Thrust Curves
True. But max thrust will always coincide with max torque.
Geared correctly, top speed should occur at max power. No?
On modern high revving, mult cylinder bikes the max torque and max power happen at pretty much the same spot so it's difficult to feel the difference. Switching recently to a 1200cc twin I can feel a distinct difference to where max torque (therefore max thrust) and max power occur.
Wed, 14/12/2011 - 13:25
#53
Re: Power Thrust Curves
In fact even geared badly, top speed will occur at max power.
Good gearing will raise the potential top speed.
Wed, 14/12/2011 - 13:44
#54
Re: Power Thrust Curves
Pittsy: "top speed should occur at max power. "
Think I may be wrong with that one!
Pittsy: "In fact even geared badly, top speed will occur at max power."
And that one!
Wed, 14/12/2011 - 13:50
#55
Re: Power Thrust Curves
"The vehicle's resistance can be shown as a rising curve that, at any point, is the sum of aero drag and rolling resitance. At the same time, we can also make graphs of the rear wheel thrust produced by the engine in each gear. At some point, the resistance curve and thrust curve cross (become equal). This is the maximum speed attainable."
Extract from Kevin Cameron's sport bike handbook. Helps focus the mind.
Who's to say they'll cross at max power!
Wed, 14/12/2011 - 15:28
#56
Re: Power Thrust Curves
Pittsy: "top speed should occur at max power. "
Think I may be wrong with that one!
Pittsy: "In fact even geared badly, top speed will occur at max power."
And that one!
IMO your first statement would have been more correct if you had said "theoretical maximum speed should occur at max power (rpm)". Perhaps I'm splitting hairs here?
In your second one "...even geared badly..."
The engine won't pull to max power (rpm) if geared too tall.
Cheers
Wed, 14/12/2011 - 15:37
#57
Re: Power Thrust Curves
I'd love to see an analysis of the Blackbird vs K1300GT since I have extensive experience with both. Here is an interesting note, although the Blackbird has 10lbs less torque and hp, it's taller gearing and superior aeros make it pull better at high speeds - IMO over 200kmh.
Wed, 14/12/2011 - 16:23
#58
Re: Power Thrust Curves
Mp1300 gt, no you're not splitting hairs at all. I'm happy to be corrected at any time. Each correction, as long as it's valid, is another notch on the learning curve gun.
What I was thinking was that the bike, left on full throttle for "x" amount of time, would settle to a speed that had to coincide with the maximum amount of power available. Having thought about Kevin Cameron's extract I can see that may not be the case.
A rear wheel thrust curve graph ought to illustrate the point well.
Thu, 15/12/2011 - 23:27
#60
Re: Power Thrust Curves
Thanks Jag
Most of what you have said amounts to what I quoted from Kevin Cameron. But it does no harm to reiterate it from several different angles. Helps to confirm. You've certainly done a better job than I did!
Your last paragraph is basically describing an over geared bike I think.
Or to look at it from the opposite perspective. If there is a speciic target speed to be achieved, an under powered bike!
This is fascinating stuff.
Does this demonstrate how the best engine for top speed is one whose max power and max torque occur at precisely the same point? And for even better effect that point should coincide with max revs too.
I wonder if that is ever possible?
Donate to the Kevin Ash Fund
Donate directly to the Kevin Ash Fund setup by the Telegraph to help with the education of his three daughters.
The Telegraph can only accept cheques and Postal Orders in Sterling. If you'd like to make a donation but you can't send a cheque or Postal Order then you might consider using PayPal, which will accept other methods of payment. A small percentage (about 3.4%) will be retained by PayPal for the service.
Kevin's family have been touched by the generosity and messages of support from people using the website and would like to express their gratitude to those who have contributed in any way.
The donations keep coming in, thank you so much, and the family especially like it when you leave a message.
Ads
NEWS...
* TRIUMPH TIGER SPORT
The Tiger gets a single-sided swingarm and another 10bhp!...(more)
* HONDA MSX125
Honda announces a spiritual successor to the iconic Monkey Bike!...(more)
* APRILIA CAPONORD
At last Aprilia goes for the GS too......(more)
* GUZZI CALIFORNIA 1400
Italy's biggest ever V-twin for the all-new Guzzi...(more)
* VESPA 946 FIRST PIC
Sleek new Vespa 125 based on last year's concept bike...(more)
Hi pittsy,
Below is how I get the thrust curve graph for 1 gear based on the above power to weight vs RPM graph.
I'm sorry, I still think in MPH.
Honda 6th gear
In 1 mile the rear tire turns 796 times.
In 6th gear 1 MPH = 56.2 RPM
The purpose of this graph is to show you one way to do your graphs to get a thrust curve graph.
This graph is not the final thrust curve graph.
The graph has lots of lines and is difficult to read. I have indicated with green lines how to read it.
The green lines show that between 60 to 80 MPH in 6th gear the "how does it feel scale" indicates that acceleration is "OK". For touring in 6th gear between 60 to 80 MPH the performance is "OK". This would suggest that for rapid acceleration you probably will want to drop into 5th gear at those speeds.
The graph also suggests that in 6th gear the bike probably accelerates better at 70 MPH then at 60 MPH.
Please note that the "how does it feel" scale is really based on speeds below 80 MPH. At high road speeds air drag becomes a very big factor. So even though the power to weight ratio is very good in 6th gear at the higher roads speeds the air drag factor chews up more and more of that good power to weight rato.
JAG