Power Thrust Curves
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.
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.
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.
Straight line performance
As pittsy suggested there’s a lot more to consider then just RWHP when it comes to straight line performance.
In my graphs I tried to show that.
In fact, the traditional RWHP graphs based on engine RPM alone, when it comes to straight line performance, can even be miss leading.
Suggiemac may be actually right when he indicated that he places little value in just HP to RPM graphs when considering a bike’s performance.
RWHP to RPM graphs are important but they are only the starting point when it comes to straight line performance.
When it comes to straight line performance up to about 80 MPH you really do need to factor in total weight, gearing (road speed) and RWHP.
All have equal weight in your performance calculations.
At road speeds up to about 50 MPH air drag has little affect. Above 60 MPH it becomes more important. That's why I try to compare and include similar types of bikes in my graphs.
To minimize the rolling resistance and air drag factors you really need a second known bike of a similar type in your graph to compare with. That important known second bike also provides a baseline for comparison to get an idea how the other bike might feel.
At road speeds above 70 MPH air drag becomes a fourth factor and at very high road speeds the major factor that’s trying to slow the bike down.
For myself, I am interested in road speeds well under 125 MPH, especially under 90 MPH.
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.
Looks like you are well ahead of me.
If you could post the tansmission ratios and rear tire (TYRE crazy brits) size maybe I can help. I just have to find a good RWHP vs RPM graph of the KLR.
Wouldn't it be funny if the KLR works out to compare well with the NC700!
Hello again pittsy,
Sorry to bother you again.
Where did you get Kenin's RWHP graph for the Honda NC700X?
I can't seem to find it.
Thanks for your help.
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?
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
Final Reduction 2.687
Final Drive Chain
Rear 17M/C X MT 4.50
Happy number crunching!
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.
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.
At a 12% loss of 51 crank HP works out to a maximum of 44.9 RWHP at 6250 RPM for the NC700.
This would be for the standard transmission.
I think the KLR650 maximum RWHP was about 38 RWHP. I think the KLR weighs less than the Honda.
The Honda's rear tire turns 809.7 times per mile.
Based on your gear ratios I came up with an overall 6th gear ratio of 3.893 - 1.
Based on this the bike engine speed in 6th gear at 60 MPH works out to 3152 RPM.
1 MPH in 6th = 52.536 RPM
Theoretical top speed at 6250 RPM in 6th gear for the NC700 is 119 MPH. Sounds pretty high for a 44 RWHP 481 pound bike. I have a feeling the 6th gear is an overdrive gear for economical highway speeds and not for top speed. Maybe its top speed is actually in 5th gear like my old Honda V65.
5th overall gear ratio 4.8046865 - 1
1 MPH in 5th = 64.84 RPM
Theoretical top speed in 5th gear is 96.4 MPH. That sounds more like it.
If you want I will calculate the RWHP based on a 10% loss through the transmission.
That was rolling RADIUS not rolling circle. Slip o the tongue. Sorry.
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.
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?
Kawasaki 2010 KLR 650 overview
Total wet weight 432 pounds
Tank capacity 22 liters (4.8 UK gallons) I think Kevin designed the tank.
Bore 100 mm
Stroke 83 mm
Maximum HP @ 6000 RPM 38 RWHP
Overall gear ratios
1st 14.7552 - 1
2nd 9.4027 - 1
3rd 7.41015 - 1
4th 6.2120 - 1
5th 5.157 - 1
Rear Wheel = 130/80 - 17
Rear wheel turns 803.9 times per mile
At 60 MPH in 5th gear engine speed = 4145.9 RPM
Theoretical top speed in 5th gear at 6000 RPM = 86.8 MPH
The KLR makes less RWHP but it weighs less and has lower gearing. Especially in its top gear compared to the Honda.
KLR at 60 MPH = 4146 RPM in top gear
NC700 at 60 MPH = 3152 RPM in top gear (hope it has lots of mid-range engine torque)
£5800 sterling for the nc700x
NC700X & Kawasaki KLR 650
Total piston area 15.57 square inches
Piston speed at 6250 RPM = 2994 ft/min
Total piston area 12.2 square inches
Piston speed at 6000 RPM = 3268 ft/min
Both bikes have conservative piston speeds. The Honda especially, I have a feeling the Honda engine is more like a small economy tuned car engine in a bike.
You can see where the target market is for this bike. First time riders coming from small economy cars. They want a softly tuned engine they can forget about that won't challenge them. Coming from their car, it probably feels peppy.
A Ducati Diavel or 1198 is not what they are looking for.
The Honda engine has 28% more piston area than the KLR.
For example, if the NC700 was in the same state of tune as the VMAX 1700, the NC700 would develop 66 RWHP at 7900 RPM.
With the 73mm stroke, the Honda should still have good low and mid-range RPM torque characteristics.
Now if it could also loose about 80 lbs it would be quite the little rocket.
P.S. 5800 Sterling = $9273 Canadian dollars
Max torque 44 ftlb at 4750 rpm
At max torque, rear wheel thrust, using method above, I calculate at:
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!
Your torque calculations based on maximum torque of 44 ft/lbs at 4750 RPM appears to have not factored in the 10% loss through the drive line.
The problem probably started with my NC700 graph. I did not factor in driveline loses in that first graph.
Sorry I didn’t make that clearer.
90% of maximum torque of 44 ft/lbs = 39.6 ft/lbs
At a 10% loss that works out to 35.8 RWHP at 4750 RPM.
Maximum RWHP at a 10% loss works out to 45.9 RWHP at 6250 RPM.
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.
I think I can see where you are going.
In my mind its easier to just deal with RWHP. The only place I use overall drive train ratios and wheel diameters is in my road speed calculations for each gear.
RWHP is a measurement of "work". In my graphs all I care about is how much "work" can the engine potentially do at a given road speed in a given gear.
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.
In fact even geared badly, top speed will occur at max power.
Good gearing will raise the potential top speed.
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!
"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!
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.
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.
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.
Your idea of a thrust curve comparison between a Blackbird and BMW K1300GT is an excellent one.
What a thrust curve graph needs is validation. Can it objectively help a rider a little to understand real world riding straight line performance?
Having an experienced rider like you with extensive riding time on both bikes would be a big advantage and very helpful in answering this important question.
Having a thrust curve graph of the two bikes in question along with your real world input would be great.
A bike at a constant state of motion (at a constant speed) means that all the forces acting on it are in balance. So said a famous Brit a long time ago.
That means if it takes 12 RWHP on a bike to hold a steady 60 MPH on a level road, the total forces trying to slow it down are also exactly 12 RWHP.
So a bike will continue to accerate only as long as the force or RWHP from the engine is greater than the total forces trying to slow it down. The bike will stop accererating when the forces trying to accelerate the bike and the forces trying to slow it down are in balance or the same.
For a bike to accelerate, the RWHP at the rear wheel must be greater than the total forces trying to slow it down.
The greater the difference between the RWHP at the rear wheel and the total forces trying to slow it down, the faster the bike will accererate.
If there is less RWHP at the rear wheel then the total forces trying to slow it down, it will slow down. The bike will slow down until those opposing forces are again in balance.
So the top speed of a bike is the balance point where the RWHP at the rear wheel and the total forces trying to slow it down are the same.
If the engine has a maximum of 100 RWHP at a certain theoretical road speed, but the opposing forces trying to slow it down are greater than 100 RWHP at that same theoretical road speed, the bike won't reach that road speed.
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?
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