Best MPG for cruising @ around 100-120mph

[McSam]

chard said:

Drive slower, doubling the speed requires 7x the power

Eight times, actually. Unless two cubed became seven while I wasn't looking

I really don't think the original poster wanted persistent bkings about the "stupidity" of the question; if it's not a massive fishing trip - I'd be wishing it was, because it's turning out to be a bloody good one - then someone drives quickly at night and figures saving a few quid in the process might be handy. Driving quick is the priority, saving a few quid is a bonus, hence the answer of "slow down if you care about economy" being silly.

The lowest-drag shape you can find, and then a medium-sized six-cylinder diesel will do it. Needs to be pretty powerful for a diesel, as top end isn't their specialty so you'd be using a lot of boot in, say, a 2.0TDI. Think E90 325d, I'd say, although I don't know how aerodynamically efficient it is, that's the sort of engine I'd go for. A 5-Series could easily make up for its extra weight if its aero is considerably better.

ETA:

OMNIO said:

Why are all these road angels harping on?

If she wants to drive at 120mph on a deserted motorway let her. Shes the one risking her licence not you.

Personally i think speed limits on a motorway between 8pm and 6am are a waste of time...

Fact is that at late night or early morning 90mph is a very achievable cruising speed, even on the M25.

Dare I say it but i find driving standards are higher at night. Theres no such thing a a 'middle lane moron' as everyone is in L1 until they reach a lorry, Doris and Bob arent sitting in their Jazz at 55mph in the outside lane admiring the view. No traffic wombles at 56mph with retards doing 57mph past them as they dont know the national speed limit.

Anyways... Fair play to your mate for using the road as its intended.

This

Edited by McSam on Tuesday 14th September 11:58

[8400rpm]

This thread is brilliant.

The OP is quite clearly taking the piss out of an earlier thread, with a similar question that was running about the same time this one started.

A lot of people in here have gotten carried away.

[CraigyMc]

zx10ben said:

The XF cruise will only activate upto 118mph unfortunately

My TT's Cruise works up to an indicated 250Kph. The other 8kph indicated you have to do with your right foot...

(I think it's about 145mph in real money, given that the speedo is as accurate as a Greek tax return)



Oh, and for the avoidance of doubt, this was on the A61 (autobahn)...

C

[CraigyMc]

8400rpm said:

This thread is brilliant.

The OP is quite clearly taking the piss out of an earlier thread, with a similar question that was running about the same time this one started.

A lot of people in here have gotten carried away.

I think it's quite an interesting question: "which car has the least drag at 100mph" would be my version of it.

Full expecting a thread soon asking for cheapest cruiser at 150mph...

C

[y2blade]

beanbag said:

zx10ben said:

y2blade said:

Trommel said:

zx10ben said:

I will cruise regularly in my Jag XFS between 115-125mph and achieve about 30mpg

I think that's fairly impressive.

me too


I'd like to see what mine does at 120mph on cruise

The XF cruise will only activate upto 118mph unfortunately

To be honest, 200kph on cruise control is quite scary and totally not recommended. My BMW will go as high as the car goes but I tried it at 210kph and I felt totally out of control.

160kph on cruise and thereafter I take control.....

Really?
mine feels totally solid and very stable at speed.

[Munter]

CraigyMc said:

8400rpm said:

This thread is brilliant.

The OP is quite clearly taking the piss out of an earlier thread, with a similar question that was running about the same time this one started.

A lot of people in here have gotten carried away.

I think it's quite an interesting question: "which car has the least drag at 100mph" would be my version of it.

Full expecting a thread soon asking for cheapest cruiser at 150mph...

C

Shirly the car with the least drag at 100mph is the same as the car with the least drag at 30 mph.

Something narrow, and low, and long, with stiff suspension, skinny tyres and tiny wing mirrors.

[hairykrishna]

We got 22mpg out of a 80's 500 SEL when cruising at 100mph+ through Europe; we averaged nearly 90mph through France, stops included...

It's an interesting question actually as it's quite different from the normal fuel economy requirements. Weight's largely irrelevant provided you're cruising for a long period and not slowing down/speeding up. Basically all about the aero I think. You could probably get a noticeable improvement by blanking off a good chunk of radiator grill - you won't need it at speed and it's a big contributor to drag.

[beanbag]

y2blade said:

beanbag said:

zx10ben said:

y2blade said:

Trommel said:

zx10ben said:

I will cruise regularly in my Jag XFS between 115-125mph and achieve about 30mpg

I think that's fairly impressive.

me too


I'd like to see what mine does at 120mph on cruise

The XF cruise will only activate upto 118mph unfortunately

To be honest, 200kph on cruise control is quite scary and totally not recommended. My BMW will go as high as the car goes but I tried it at 210kph and I felt totally out of control.

160kph on cruise and thereafter I take control.....

Really?
mine feels totally solid and very stable at speed.

The car is perfectly stable at this speed but at 200kph, you want to be able to be able to back off the throttle instantly if you have to without touching the brakes. With cruise on it's possible, it's not the same and I don't think as safe. (IMHO)

[bobt]

[redacted]

[JonnyVTEC]

CraigyMc said:

8400rpm said:

This thread is brilliant.

The OP is quite clearly taking the piss out of an earlier thread, with a similar question that was running about the same time this one started.

A lot of people in here have gotten carried away.

I think it's quite an interesting question: "which car has the least drag at 100mph" would be my version of it.

Mk1 Honda Insight would be my answer, no only a low Cd. of 0.25 although when it was tested at MIRA it was 0.24, but a very low CdA as its a small car.

[y2blade]

beanbag said:

y2blade said:

beanbag said:

zx10ben said:

y2blade said:

Trommel said:

zx10ben said:

I will cruise regularly in my Jag XFS between 115-125mph and achieve about 30mpg

I think that's fairly impressive.

me too


I'd like to see what mine does at 120mph on cruise

The XF cruise will only activate upto 118mph unfortunately

To be honest, 200kph on cruise control is quite scary and totally not recommended. My BMW will go as high as the car goes but I tried it at 210kph and I felt totally out of control.

160kph on cruise and thereafter I take control.....

Really?
mine feels totally solid and very stable at speed.

The car is perfectly stable at this speed but at 200kph, you want to be able to be able to back off the throttle instantly if you have to without touching the brakes. With cruise on it's possible, it's not the same and I don't think as safe. (IMHO)

ah sorry I see what you mean and agree entirely

[Chris71]

8400rpm said:

This thread is brilliant.

The OP is quite clearly taking the piss out of an earlier thread, with a similar question that was running about the same time this one started.

A lot of people in here have gotten carried away.

Yep, I did get the reference to the 'cruising at 85mph' thread... Still think it's quite an interesting question though, once you're up to the sort of speeds that a PHer on a deserted motorway might consider doing it could throw up some interesting options!

[zakelwe]

I'm driving around in a superchips chipped Yaris Diesel 1.4 at the moment, it can't cruise at 120mph but toddling along at 55-60 it will do this

http://www.zen141854.zen.co.uk/mpg.jpg

That's a very boring 50 miles or so down the M20. Average for the tank was 69mpg. Don't all rush out and get one though. It will keep up with traffic quite well, but you'll be too asleep at the wheel to notice ...

Andy

[NoelWatson]

JonnyVTEC said:

CraigyMc said:

8400rpm said:

This thread is brilliant.

The OP is quite clearly taking the piss out of an earlier thread, with a similar question that was running about the same time this one started.

A lot of people in here have gotten carried away.

I think it's quite an interesting question: "which car has the least drag at 100mph" would be my version of it.

Mk1 Honda Insight would be my answer, no only a low Cd. of 0.25 although when it was tested at MIRA it was 0.24, but a very low CdA as its a small car.

CdA around 15% better than NSX

http://en.wikipedia.org/wiki/Automobile_drag_coeff...

[bobt]

McSam said:

chard said:

Drive slower, doubling the speed requires 7x the power

Eight times, actually. Unless two cubed became seven while I wasn't looking

This

Edited by McSam on Tuesday 14th September 11:58

I remember that generally drag is proportinal to speed squared, not cubed. Although in certain circumstnaces (speed, shape of object, bundary layer effects of aero aids etc.) it can be less, and in some cases be close to directly proportional or somehwere in between the two. And, whilst drag is the main force to overcome at speed, there is still the rolling resistance, and the mass of the vehicle which comes into play on even the slightest uphill gradient.

[GaryST220]

My VXR8 is pulling a lowly 4,000RPM at 160mph, which is the tallest gearing I know of - that said it's probably doing gallons to the mile

Edited by GaryST220 on Tuesday 14th September 13:03

[McSam]

bobt said:

McSam said:

chard said:

Drive slower, doubling the speed requires 7x the power

Eight times, actually. Unless two cubed became seven while I wasn't looking

Edited by McSam on Tuesday 14th September 11:58

I remember that generally drag is proportinal to speed squared, not cubed. Although in certain circumstnaces (speed, shape of object, bundary layer effects of aero aids etc.) it can be less, and in some cases be close to directly proportional or somehwere in between the two. And, whilst drag is the main force to overcome at speed, there is still the rolling resistance, and the mass of the vehicle which comes into play on even the slightest uphill gradient.

You're quite correct that drag is proportional to speed squared, so the force required to overcome the drag increases with speed squared. However, power equals force times velocity, so the power needed to provide that force also increases with speed, hence power needed increases with speed cubed.

Since the rolling resistance is proportional only to speed^1, it becomes fairly negligible at high speeds, maybe 1-3%. Gradients are something that I like to completely ignore in these calculations, there it can get complicated

ETA -

GaryST220 said:

My VXR8 is pulling a lowly 4,000RPM at 160mph, which is the tallest gearing I know of - that said it's probably doing gallons to the mile

I think I read that the second-gen Viper SRT-10 sits at 1200rpm in 6th at 70mph, which makes a mind-bogglingly lazy 2750rpm at 160mph! Geared to cross galaxies, that thing

Edited by McSam on Tuesday 14th September 13:07

[BlueEyedBoy]

CraigyMc said:

BlueEyedBoy said:

This is not entirely true. Gearing and aero play a large part. Most hybrids switch to leccy power when cruising at highish speeds.

I remember Clarkson in the veyron, I think be was cruising at well over 100 and only 10% of the engine power was being used.

Sorry pal but it *is* entirely true. The assumption is that you're in top gear anyway (120mph) and as for your point about cruising and hybrids, and especially the veyron comment, can't you see why you're actually backing up what I'm saying?

Maybe I am confused with what you are trying to say then. I thought you were trying to say that driving at 70mph will use roughly half the fuel required to drive at 100mph?

Edited by BlueEyedBoy on Tuesday 14th September 13:12

[bobt]

McSam said:

bobt said:

McSam said:

chard said:

Drive slower, doubling the speed requires 7x the power

Eight times, actually. Unless two cubed became seven while I wasn't looking

Edited by McSam on Tuesday 14th September 11:58

I remember that generally drag is proportinal to speed squared, not cubed. Although in certain circumstnaces (speed, shape of object, bundary layer effects of aero aids etc.) it can be less, and in some cases be close to directly proportional or somehwere in between the two. And, whilst drag is the main force to overcome at speed, there is still the rolling resistance, and the mass of the vehicle which comes into play on even the slightest uphill gradient.

You're quite correct that drag is proportional to speed squared, so the force required to overcome the drag increases with speed squared. However, power equals force times velocity, so the power needed to provide that force also increases with speed, hence power needed increases with speed cubed.

Since the rolling resistance is proportional only to speed^1, it becomes fairly negligible at high speeds, maybe 1-3%. Gradients are something that I like to completely ignore in these calculations, there it can get complicated

ETA -

GaryST220 said:

My VXR8 is pulling a lowly 4,000RPM at 160mph, which is the tallest gearing I know of - that said it's probably doing gallons to the mile

I think I read that the second-gen Viper SRT-10 sits at 1200rpm in 6th at 70mph, which makes a mind-bogglingly lazy 2750rpm at 160mph! Geared to cross galaxies, that thing

Edited by McSam on Tuesday 14th September 13:07

You are quite right. It was the 30 years ago I did this stuff, and I don't think the equations have changed!

So in theory about 50% more power required to go from 130 kph to 150 kph, and yet no more than 5% increase in fuel consumption. Maybe the drag coefficient changes a fair bit between these speeds? Ca't see the enigne getting generating 50% more power on 5% more fuel. Any thoughts?

[CraigyMc]

BlueEyedBoy said:

CraigyMc said:

BlueEyedBoy said:

This is not entirely true. Gearing and aero play a large part. Most hybrids switch to leccy power when cruising at highish speeds.
I remember Clarkson in the veyron, I think be was cruising at well over 100 and only 10% of the engine power was being used.

Sorry pal but it *is* entirely true. The assumption is that you're in top gear anyway (120mph) and as for your point about cruising and hybrids, and especially the veyron comment, can't you see why you're actually backing up what I'm saying?

Maybe I am confused with what you are trying to say then. I thought you were trying to say that driving at 70mph will use roughly half the fuel required to drive at 100mph?

I was talking about the amount of power required to maintain the speed, and also saying that the amount of power being generated is roughly analagous to the amount of fuel used.

A common misunderstanding seems to be that a 300bhp engine is somehow able to generate that power without burning fuel at roughly double the rate of a 150bhp engine of the same type.
All I was saying is that - if you want lots of power, you're going to be burning a lot of fuel to get it.
Since speed requires power, more speed requires more power requires more fuel. QED.

C