Safe Speed Forums

Well that's ruined MY day then!
I had a look on a US website devoted to my particular make and model of "performance" saloon from the early '90s and found various standing quarter times of around about 15.8 seconds and 90MPH!

Oh well, at least I know what a "Riceposeur" is now! Actually, now you mention it, I think I've heard my brother refer to his Skyline as a "ricer" / "rice rocket".

i've often wondered if this is an acceptable racial term....
seems to contain all the hallmarks of a racist stereotype to me.

where are we going with this anyway ?
what are we trying to prove ?

being alive isn't fuel economic ??

My fault. I was just trying to find an answer by thinking of ourselves as the engine and how the energy expended under different riding styles relates to the temperature of our bodies and efficiency over the same time and distance.

Short of using an F1 diagnostic lab, I don’t know how we’re going to get a definitive answer. Good question though

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

to an extent for running/walking what mole said holds true, its roughly the same calorie expenditure whatever the pace, although it would vary with pace a little depending how efficient that pace is for your physiology, certainly where those calories come from will vary with pace & distance (i.e. glycogen, carbs/sugars, fat).

for cycling speed & drag come start to become non negligible, but the mechanics of it is a bit simpler in terms of rider's power output vs load power (drag, rolling resistance, gradients).

assuming we're not prepared to make the ultimate green sacrifice and stop living, and assuming all people have a base intake of say 2000cals a day.... the question really becomes is it more economic to expend X fuel calories to get to the shops or Y food calories to walk/bike there..... and even then how far down the chain do you go? do you consider a proportion of the energy expended in building the car, processing & transporting the fuel.... and likewise energy expended producing and transporting the food to fuel the cyclist !


waaaaaay OT methinks

Okay, how about this then...

I have an electric drill with variable speed. I attach a small motor, the shaft of which is locked to the chuck, and connect the output of the small motor to a metal clad resistor which is immersed in a jug of water, the temperature of which I monitor over a set period of time.

The small motor will act as an electric generator, (the car engine), feeding the resistor, (our journey). I mimic the two scenarios by building up the speed of the variable drill gradually verses ‘accelerating’ quickly up to the set speed or rpm.

The resistor, acting as the load, will heat up the water. I record the temperature rise of the water after, let’s say, five minutes in each case indicating which method has expended more energy to complete ‘the journey’ in those five minutes.

If the results prove nothing conclusive at least I can make a nice cup of tea. (I know, I know - I need to get out more).

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

what you do in your own time is your business tone.

Awe come on ed, I was making a serious effort there trying to think outside the padded cell. I think we could expand on my idea; it deserves at least an 7 IMHO

Anyway, what happened to your avatar? If you haven’t got an avatar I don’t think you should be allowed to play.

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

I do not think your idea will really reveal anything useful unfortunately as it does not simulate an internal combustion engine or the acceleration of a mass against a steadily increasing load.

You would be as well simulating the journey with software. It would be simple enough to to produce a notional map of engine power output, fuel consumption and rpm from the graphs on the link I posted earlier. To keep it simple this 'car' would have a cvt gearbox so the same rpm could be maintained during acceleration. Acceleration could be determine from the engine output, mass and the speed dependant air resistance, distance travelled would be the area under the speed graph.

I do not have the time to do this properly, however I might try to come up with some figures with a very simple model where you can choose to accelerate gently at low revs, hard at high revs or using the best power to fuel ratio.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

Drat! So I just get a 1 for effort

Sounds like a job at NASA for you and YASA, my local Indian resturant, for me.

Software? My enemy.

10 INPUT NAME""

20 IF name = 'Tony' THEN GOTO 50

30 Execute faultless program and have a good day

40 END

50 CRASH!

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

hmmm.. i have a little spreadsheet here..... needs engine power vs fc maps tho

A chufty badge for anyone who can cram a good 'treadmill paradox' within it

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

How about this?

I am just trying to find some figures for power vs speed or drag vs speed to see what power output is needed to maintain the cruise speed and what surplus is available for acceleration.

Interesting page here too.

This page has a useful equation for power vs speed given CD and frontal area. I have put some numbers through for a couple of my cars that I have dyno figures and max speeds for and it looks a pretty good match.

This site has a graph for a VW diesel engine. He also makes the useful point



Remember this is not the total energy expended, you will need to burn fuel just to prevent the car from slowing whatever speed you are at instantaneously, but the additional energy needed to accelerate the vehicle.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

I have had a go at this using the Mercedes M271 graph on http://mark.tranchant.co.uk/2008/06/dri ... onomically

Assumptions for the car are-

Weight = 1400Kgs.
Cd = .35
Frontal area = 20 ft sqr.
Driveline losses = 25% (this means KW @ flywheel = Bhp @ wheel - near enough).
Only air resistance was allowed for.
Gearchanges are instantaneous and gear ratios allow the following-


Calculations were done for acceleration from 20 to 60 mph using 2nd/3rd/4th between 2000 and 3000rpm using 1/3 and 2/3rds load using averaged power and fuel use. I also estimated acceleration in 1st and 2nd gear at full load though the large variation in power and fuel figures mean this result is only a best guess. To normalise the results the fuel used to cover the distance which the low acceleration run covered to reach 60mph (3090ft) was calculated for the higher acceleration runs at 315g/kWh at 60mph and 13.16Kw. Final drive ratio used was 28mph per 1000rpm.

For 20bhp @ 300g/kWh the time was 45.4 seconds and the distance covered 3090ft using 75.1g of fuel.
For 40bhp @ 250g/kWh the time was 17.5 seconds to 60 and 39.5 seconds to cover 3090ft using 73.4g of fuel.
For full throttle I used and average of 90hp @ 320g/kWh, time to sixty 7 seconds and 37 seconds to cover 3090ft using 85.5g of fuel.

The full throttle run is very approximate, however common sense would dictate that this would always use more fuel, it is interesting that this only saves about 2.5 seconds in covering the distance compared with the medium run. The fuel saving between minimum and medium acceleration is small, much of this is down to the relatively poor efficiency of the engine at a constant 60mph compared with when accelerating at a higher load. In particular note that using medium acceleration is not only slightly more efficient but also saves nearly six seconds or 12.5% time to cover the same distance.

Hi my name is Toltec and I am a nerd.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

Hi

This is an easy one for any mechanic to answer....

The MOST economical speed is in your TOP gear at the lowest possible revs that will maintain a stable speed....

To get to that speed and gear in the MOST economical way, you accelerate as SLOWLY as possible, while still getting faster.

All the best Brett

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