Most economical speed for a bike?

[Ditto]

What is the speed on a motorcycle where you would get the best MPG?

In a car its usually around 56mph, but motorbikes rev much higher and have higher performance engines than a typical car, while being lighter etc.

So what is the best speed for maximum MPG?

I read that it is where the bike produces maximum torque, which on my Bandit is 8500rpm, or about 90mph (Off the top of my head)in top gear...which seems alot for good MPG.

Is this right?
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CG 125 > Bandit 600 > CBR 600 FY > Street Triple R

[The Shaggy D.A.]

It's not just where the max torque is, it's more down to how much air you're trying to push out of the way, how smoothly you accelerate and brake, volumetric efficiency of the cylinders, etc etc etc.
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Chances are quite high you are not in my Monkeysphere, and I don't care about you. Don't take it personally.
Currently : Royal Enfield 350 Meteor
Previously : CB100N > CB250RS > XJ900F > GT550 > GPZ750R/1000RX > AJS M16 > R100RT > Bullet 500 > CB500 > LS650P > Bullet Electra X & YBR125 > Bullet 350 "Superstar" & YBR125 Custom > Royal Enfield Classic 500 Despatch Limited Edition (28 of 200) & CB Two-Fifty Nighthawk > ER5

[N cee thirty]

usually half throttle in 5th at 50 on my cg gives me a quite good tank range
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'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[iooi]

I find keeping sub 4K rev's gives best MPG..

Then again I find between 4 & 8K gives more SPG

Don't take it to the red line in lower gears, half way is more than enough on most bikes. This will increase MPG and you will still beat just about anything on 4 wheels away from the line, unless they are really trying hard.
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Just because my bike was A DIVVY, does not mean i am......

[Alexio]

Depends on the engine surely.

I bet you could get 200MPG out of a 50cc ped, but at the same speed on a 1000cc bike still only 40 - 50 MPG, or tragically lower?

You need an engine that operates very efficiently at a speed where it's not trying to push much air out of the way. Like the CG


I look at it this way. The size of my 125cc engine means it doesn't suck in much fuel at all, but produces a whole 11 horse power. Those 11 horse powers are apparently the power required to hit 60MPH. Now take a 600cc IL4 engine and sit at 60MPH in the most efficient gear to do so, I bet the engine is developing a lot more than 11 horse power and hence having to use a lot more fuel to hit that speed.

I think the problem is that if you did give that 600cc engine exactly the same amount of fuel (as the 125cc sitting at 60MPH) and tried to gear it to 60MPH it would be pretty bad on the engine if it ever got there. It would also get there very slowly.
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will never give up his CG. I look at my fuel gauge more as a progress bar than a fuel gauge.
G: With my GSXR I do often effectively use it as a scooter with a clutch in town.
ms51ves3: why does it need 500 miles? Are you teaching it how to be a piston?

[Ditto]

Yeah my old CG used to be awesome for fuel consumption! Used to do about 170 miles for 13 litres I think.

Ill do about 100 for that now, but I am much less careful with the throttle. I didn't buy a 600 to go slowly after all.

I just do alot of motorway miles and wonder if there is a good speed to sit at to make good progress and also good on fuel.
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CG 125 > Bandit 600 > CBR 600 FY > Street Triple R

[Kickstart]

Hi

Depends on the engine and bike. Basic theory is that an engine is at its most efficient at peak torque, and has the least pumping losses on full throttle. But in real life the mixture will vary and probably use more fuel at speed, and also at full throttle. Also the faster you go the more you have to overcome air resistance. So while you might land with the engine marginally more efficient at a higher speed that higher speed means more throttle and fuel used anyway. Added to which is gearing. No point in going slightly slower if you are just dropping out of the power and having to drop a gear on every slight hill.

Not sure cars are better at 56mph. Just that happens to be one speed that fuel consumption was calculated at (ie, 90kmh) and some makers fiddled the cars to appear best at that speed. Likely any car useful in real life isn't especially better at 56mph.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Alexio]

[Ditto]

Cheers Keith, so there isnt a definitive answer really, depends more on smooth control, less braking and fitting one of these:

https://www.schultzengineering.us/tail1.jpg

Or even doing this:

https://upload.wikimedia.org/wikipedia/en/4/4a/Rollie_Free,_record_run.jpg


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CG 125 > Bandit 600 > CBR 600 FY > Street Triple R

[Kickstart]

[T0MMY]

Air resistance is absolutely critical on a bike as they are so un-aerodynamic. Given that drag increases with the square of velocity I would say the most efficient speed would be the lowest speed you can sit at in top gear with the engine feeling "happy" ie. not labouring at all.

[hellraiser]

Full whacks best!

Don't really think about it on the bike, too busy trying to enjoy it.
Matters a bit bit more driving the car though.
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1987 FZ750 - 1994 YZF750R

[T0MMY]

As someone said above though, the real key to fuel economy is not braking.

[tutton]

[radical]

My old VT500e will return 75-80 mpg @ 4500-4800 revs which is about 60-70 mph in top gear which is more of an overdrive than a gear.

[Teflon-Mike]

OK, well 'Efficiency' is the thing that clouds this topic hugely, and the thing is that efficiency can be measured so many ways.

When people start talking about the 'best efficiency' corresponding to peak torque, that nugget comes from the fact that peak torque corresponds to the highest 'combustion efficiency'. Which is where you agre getting the most useful pressure from the charge burned.

This is 'interesting' and can have some relevence to the 'overall' efficiency of the machine, which is what MPG looks at, but not much.

When you look at power-traces, the peak-torque you see is that derived under very specific 'lab' conditions. The engine at full throttle under the maximum load it can take at that speed.

In the real world we ride on part throttle, and at part throttle, the peak torque will move up or down the rev range depending on the engine tune.

And riding for ecconomy you'll be trying to avoid using full throttle, so its not a good indication of what might or might not give you best MPG.

MPG is the bottom line here, and if you forget all the 'detail' and go back to basics, and some first principles of physics, it makes a LOT more sense.

Power = Force x Speed

Theres a very long, tedius mathmatical proof for that one, but if any-one is interested enough..... but it comes from the defanitiuons of Power and work. Work is energy, and power is rate of energy transfer

When we are riding engine does work, it makes a force that shoves us along. More force it makes and the faster it shoves us, the more power is being used, right? so that makes sense.

Now the force 'made' by the engine is used to over come 'drag'. Thats the resistance to movement.

Thats NOT all wind-resistance, 'drag' is the TOTAL restsitance to movement, wind resistance bing a part, and often a big part, but theres also friction, or 'rolling resistance'.

Power = force x Speed

Power = Fuel Consumption

Bit of a leap, but theres another mathmatical proof, for any one interested, but essentially, Power + rate of energy transfer, right? The energy we are using is coming from the fuel, and the MPG is the rate we are using it, so makes sense, dont it?

SO Fuel Consumption = Force x Speed

NOW!

The force the engine makes is used to make speed, right? Shove us along against drag.

So the engine force, or 'power' our engine is providing, must balence the drag force at the speed we are going, right? I mean, open the throttle, make more force we go faster, close throttle, make less force, go slower. Sucking eggs I know, but this is science at its basic level!

So, steady speed, Fuel Consumption = FORCE x Speed, that force is Either or BOTH the force the engine is making and the force of drag we are over coming.

NOW, we get back to wind-resistance.

wind Resistance increases exponentially with speed. That is, double the speed, you get MORE than double the wind resistance.

THIS is a bit more complicated to explain, so I'm not going to bother. You'll just have to believe me.

Other bit is its directly proportional to frontal area. Bigger the vehicle, more area more wind resistance.

On a car or lorry, of course the frontal area is 'fixed' by the sixe of the body, and it dont change much, short of lifting the sun-roof or sticking your elbow out the window.

On a bike, the frontal area is more variable. Most bikesm you have rider sat on the bike, and about half the area is the bike itself, half the rider on top and syuck out the sides.

Ans at this point I'd better mention stream-lining, and Co-Efficients of Drag. stream-lining is how 'slipery' the shape, Cd value an efficiency index to suggest HOW slippery it is.

But its a perverse index, and unless you know how it works, and I should do, I spent three years having to work them out at Uni... but it was SO bludy long ago, I cant remember, or be arsed to put myself through the torture of googling it and reminding myself JUST how bludy tortiouse they are....... they are pretty irrelevent! In the real world, on a MOTORBIKE.... means little!

The frontal area is pretty similar for almost ALL motorcycles. Yup, Barn-door fairing on a Guzzi Cali is a LOT bigger than the little fly-screen over the clocks on a 'zip' moped, but, give or take not a lot, a bike is ROUGHLY person sized in frontal area.

And as far as the aerodynamics go, they are a bludy nightmare. Cars are nice and easy, they are a nice neat box shape. Bikes, sort of neat, until you put a rider on them, then they are all over the place.

And FAR more influential on the drag, a person on a motorbike can move around and CHANGE the frontal area by crouching over the tank, or even lying down over it, completely 'prone', or go to the extremes I believe its Johnny allen did in that pic on the Vincent in his legendary Land-Speed record attempt for 'Fastest Production Bike'.

Take a typical 'naked' bike, and the aerodynamics are pretty poor, but you can reduce the 'drag' by as much as 30-40% just by ducking into the wind.

Take a faired sportsbike, the areodynamics are a lot better, but less variable, and with the riding possition urging a crouch, ducking down might not make very much difference to wind resistance at all. WILL make a difference to how much of it you 'feel' tigging at your leathers, but overall on the bike, it wont have AS much influence.

Right; THAT bit accepted, we get to a situation where:

Fuel Consumption = Frontal Area x Speed x Speed

So the faster you go, more fuel you gonna use, and if you want to reduce fuel consumption, you have to slow down.

Follow the equation, which defines something roughly the shape of a skate-board or BMX quarter-pipe, you dont find any 'optimum', it starts at the slowest speed the engine will go, in first at idle speed, and goes up from there, getting worse the faster you go.

So the most efficient speed would be somethiing near walking pace!

Not very helpful... so stepping a little away from the pure 'science' nd at the real world.

Fuel Consumption = Power => speed

3bhp Moped will do about 30mph. Proving the exponential of drag putting more and more load on the bike, the faster you go, takes something like three times a mopeds 3bhp, something like the 10bhp of a typical commuter bike, to go double the speed, 60, takes something like three times THAT, about 30bhp to go just one and a HALF times as fast, about 90, and four times that, about 120bhp to get a motorbike up to one and half times that speed, around 150ish.

By that you can see that the wind resistance 'exponential' is working, but between 30mph and ABOUT 70 mph, the exponential isnt' ramping up TOO steeply against you.

And 56mph lies right in that band.

Strictly is is NOT an 'optimum', becouse in the consumption vs speed chart there is no maximum or minimum that corresponds to it; line starts low goes high.

The 'traditional' 56mhp speed comes from standards, and I do NOT know exactly which ones, BUT its probably NOT a co-incident that 56mph = 90KMh. OR that the US 'Double-Nickle' 55mph speed limit is almost identical.

And I KNOw that that one was worked out for the US Govt from a study done back in the 1960's to be the 'optimum traffic speed'.

NOTHING to do with engine efficiency, or fuel consumption vs drag.....

It was derived, becouse if you take a mile of road, and want to know how many cars you can safely get down it in one hour.... you find out that you get MOST cars down that bit of road if they all travel at ABOUT 56mph!

Why? Well, whats the stopping distance at 30? whats the stopping distance at 60? Whats the distance of the 'two-second gap'?

Faster the cars go, the bigger the gaps between them have to be, so the fewer cars you can fit on a stretch of road. Slower they go, smaller the gaps, more you can fit.

But what was important wasn't how fast they were going, or how many cars there were on the road, but the NUMBER of cars you got through that stretch of road in an hour. The flow rate.

So slow flow rate, lots of cars close together, fast flow rate, fewer cars more strung out, at WHAT speed do you get the MOST cars along the highway?

Answer, near as damn it 56mph!

So THAT was the speed the Federal Gov't imposed on US Interstates, and it became the standard speed at which people wanted to know the fuel consumption at.

So it has since been encapsulated into the standards for deriving fuel ecconomy figures and EVERY one tries to get the 56mph consumption as low as possible.

Some-One in the USA actually tried to 'repeat' the figures for I believe a chevrolet and found that when they tried on a closed oval speed-way..... the engine siezed!

Reason being that the manufacturers has made the fuel map SO weak at that exact speed the engine knocked chronically, and overheated! They did NOT expect any-one in the real world to ACTUALLY drive for sustained periods AT that speed, so deliberately put a flat-spot in the fuel metering there to get a better MPG figure!

However, while that EXPLAINS the 56mph speed / 'MPG efficiency' idea.... its not THAT helpful, EXCEPT to say that its NOT far off!

As said, there are an AWFUL lot of variables, BUT 56mph id 'just' on the bottom of that exponential ramp for wind-resistance, but it IS just about fast enough for MOST vehicles to be running in a high gear, if not top gear, at an engine speed close to optimum for ecconomy.

Probably NOT the exact optimum, but not far off, and as a rough reckoner, its almost on the nail for most vehicles.

YEs, bikes do have much broader speed ranges than most cars, and 56 is a LOT slower than they COULD go, so 56 is probably NOT got the engine working AS efficiently as they could, but for the efficiency of a typical bike engine probably makes little odds whether you ran one in 3rd gear pulling 5Krpm at 56 or in 6th pulling 1400rpm at 56... difference in MPG would be negligible.

MORE influential would be whether you were sat upright or crouched.

And either way, upping th speed beyond 60, you would almost CERTIANLY be burning more fuel for the same distance, up it to 90, even more still, becouse you are definitely well onto the exponential ramp.

Going slower, you might save fuel, BUT depends on the bike, and if you have a fast bike, then probably not a lot of difference, becouse the optimums in the engine are sop far up the rev-range for ths epeed you are going.

Smaller, lower performance bikes, probably bigger gains to be found going mroe slowly.

The variables are FAR greater on a bike and between bikes, BUT that magic 56 is rarely 'far' off the mark.

any-one still awake?
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[L4Isoside]

[Teflon-Mike]

[L4Isoside]

[The Original Muzza]

[Kickstart]

[The Shaggy D.A.]

[N cee thirty]

teflon mike,you should put a summary at the bottom of your posts
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'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[Ol]

[Alexio]

So the question is, when are we going to riding around on aero bikes with minimal drag but unstable trajectories (side winds) and fragile plastic? Maybe we could at least have bikes with down force someday, however ugly they are.
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will never give up his CG. I look at my fuel gauge more as a progress bar than a fuel gauge.
G: With my GSXR I do often effectively use it as a scooter with a clutch in town.
ms51ves3: why does it need 500 miles? Are you teaching it how to be a piston?