Speed Costs

[Dod101]

Having just spent almost £100 to fill my tank with petrol, I decided that given the fact that I am retired and do not need to get to many places in as great a rush as I may at one time have, I decided a week or so ago to cut my speed so that instead of setting my cruise control at 72/73 mph, I would cut it to around 65 mph just so see if it made any difference. Of course I am driving on motorways or dual carriageways. I am amazed to find that I am now getting almost 20% more miles per gallon than before. That is quite staggering to me, and it is much more relaxing to drive at that speed. I now feel sorry for those who go tearing passed me doing well over 70 and think of the fuel pouring through their engines. In fact, I am surprised that there seems to be no encouragement to drive at slightly slower speeds.

Dod

[nmdhqbc]

i go about 56mph. i must piss lots of people off. if you have time on your hands you could go to the station more often and only half fill the tank. lugging less weight around should help.

[DrFfybes]

I think we coveed this a while ago, certainly the Avensis is a lot better at 60mph than 70, but once down to 55 it struggles in 6th gear going uphill.

Air resistance is the square of speed, so 50mph has 250 'units' of air resistance, compared to 500 units at 71mph. Whilst engines tend to be geared for efficiency at a higher speed, for an electric vehicle that makes a huge difference.

[Dod101]

I think we coveed this a while ago, certainly the Avensis is a lot better at 60mph than 70, but once down to 55 it struggles in 6th gear going uphill.

Air resistance is the square of speed, so 50mph has 250 'units' of air resistance, compared to 500 units at 71mph. Whilst engines tend to be geared for efficiency at a higher speed, for an electric vehicle that makes a huge difference.

Sorry if this has been covered already. Air resistance of course may make a big difference. I drive an Audi Q5, a big heavy vehicle, although not as big as many, but I was really surprised at the difference a modest drop in speed makes. The wonderful thing is though that if I put my foot down it will take off. What that does to petrol consumption is another matter.

Thanks for the suggestion about only half filling the tank. Again I am sure that would help but as I live some way from the cheaper petrol stations, I prefer to fill up when I can.

Dod

[bluedonkey]

i go about 56mph. i must piss lots of people off. if you have time on your hands you could go to the station more often and only half fill the tank. lugging less weight around should help.

I tend to gravitate around that speed also. One aspect I'm aware of around that speed level is to either go faster than the long distance artics or slower, rather than about their speed as I then end up criss-crossing their paths along the motorway.

[monabri]

DrFfybes has covered the issue of 'drag' . I'd add that saving fuel is "one in the eye" for Mr Putin. I'd like to see the 70mph motorway speed limit reduced for this very reason (There's a petition to temporarily limit speeds to this effect).

https://petition.parliament.uk/petition ... %20Ukraine.

[Dod101]

DrFfybes has covered the issue of 'drag' . I'd add that saving fuel is "one in the eye" for Mr Putin. I'd like to see the 70mph motorway speed limit reduced for this very reason (There's a petition to temporarily limit speeds to this effect).

https://petition.parliament.uk/petition ... %20Ukraine.

Personally I would not go with 55 mph. I would though go with 60 mph, because people will not stick to 55 and anyway you are then up against the artics. The principle is right but not at 55 mph.

Dod

[pje16]

I prefer to drive fast (extravagant I know) but I do enjoy my car

[bungeejumper]

Different engines have their preferred speed ranges, which I presume depend on their torque curves as well as their aerodynamics? My 2007 turbo diesel Passat (with a mere 105 bhp on tap, no common rail and no DPF) would always return better motorway mileage at 70 mph than it did at 60. And my 1996 petrol Citroen Xantia would do at least 10% more to the gallon on the autoroute if I filled it with premium fuel, which cost only buttons more in France - and then drove it like I'd stolen it.

Almost as important as your speed, in my experience, is whether you're driving smoothly, and how much you're using your brakes. And whether you're thinking about what's happening half a mile ahead (and behind), so that you know where to be when the lane-swapping starts?

BJ

[pje16]

Great post BJ
On Motorways and major A roads I tend to accelarate, get up to the speed I want and then set Cruise Control
and then watch the revs drop as that manages fuel better than my right foot

[redsturgeon]

If I drive my 2007 Honda Accord diesel at 2000rpm on the motorway (about an indicated 70mph) then it will return over 60mpg. Turbo diesel 2.2 litre, 138 BHP and no DFP.

If I am travelling around town then I use my PHEV on electric only, don't want to let people breathe in my nasty fumes.

If I fancy a bit of fun then I take out the MX5 on the local B roads

If I want to feel really righteous I cycle.

John

[AsleepInYorkshire]

I think we coveed this a while ago, certainly the Avensis is a lot better at 60mph than 70, but once down to 55 it struggles in 6th gear going uphill.

Air resistance is the square of speed, so 50mph has 250 'units' of air resistance, compared to 500 units at 71mph. Whilst engines tend to be geared for efficiency at a higher speed, for an electric vehicle that makes a huge difference.

Sorry if this has been covered already. Air resistance of course may make a big difference. I drive an Audi Q5, a big heavy vehicle, although not as big as many, but I was really surprised at the difference a modest drop in speed makes. The wonderful thing is though that if I put my foot down it will take off. What that does to petrol consumption is another matter.

Thanks for the suggestion about only half filling the tank. Again I am sure that would help but as I live some way from the cheaper petrol stations, I prefer to fill up when I can.

Dod

Hi Dod,

I hope you're well. I am enormously proud to say that I drive a five door white family saloon. It's diesel (sorry but I purchased it when I was doing 250 miles per day on the motorway). Anyway that aside I have achieved well over 75mpg when I've sat on the motorway at 56mph.

I've also achieved 46K miles on one set of front tyres and my brake pads and discs did really well too.

I pay no tax on my vehicle and the insurance is minimal.

Speed costs serious amounts of money and in today's over crowded roads I'm not really that sure it gets you where you want to go that much quicker.

Take care

AiY(D)

[Dod101]

Different engines have their preferred speed ranges, which I presume depend on their torque curves as well as their aerodynamics? My 2007 turbo diesel Passat (with a mere 105 bhp on tap, no common rail and no DPF) would always return better motorway mileage at 70 mph than it did at 60. And my 1996 petrol Citroen Xantia would do at least 10% more to the gallon on the autoroute if I filled it with premium fuel, which cost only buttons more in France - and then drove it like I'd stolen it.

Almost as important as your speed, in my experience, is whether you're driving smoothly, and how much you're using your brakes. And whether you're thinking about what's happening half a mile ahead (and behind), so that you know where to be when the lane-swapping starts?

BJ

I can't agree with that final paragraph, certainly not with my car. I am driving very similarly to before although when I think about it, a lower speed does induce smoother driving, both in acceleration and in breaking modes.I would be prepared to agree that the one helps the other.

Dod

[scotview]

I am driving very similarly to before although when I think about it, a lower speed does induce smoother driving, both in acceleration and in breaking modes.I would be prepared to agree that the one helps the other.

Dod

Interesting post.

I don't think any of the political parties really believe in climate change, and the life changing urgent action, otherwise, virtually overnight, they could have the maximum speed set to 55 mph. This would save hugely on hydrocarbon and electricity usage. Maybe having an even greater and more instant effect than the heat pump strategy..

As further measures they could:
1 Limit all future ICE vehicles to maximum of 1.6 litre engine capacity, with governed acceleration rates.
2 Limit all future BEVs and PHEV's to 180 PS with governed acceleration rates.

But, this would be political suicide. Climate change........nah !

[swill453]

I get about 33mpg in my diesel campervan if I go at (indicated) 70mph when cruising, vs. 38mpg at 65.

£130+ to fill the tank these days.

Scott.

[Dod101]

If I drive my 2007 Honda Accord diesel at 2000rpm on the motorway (about an indicated 70mph) then it will return over 60mpg. Turbo diesel 2.2 litre, 138 BHP and no DFP.

If I am travelling around town then I use my PHEV on electric only, don't want to let people breathe in my nasty fumes.

If I fancy a bit of fun then I take out the MX5 on the local B roads

If I want to feel really righteous I cycle.

John

You are of course contributing to the well known fact that B roads are the most dangerous in the UK. They are not roads where people should be having a 'bit of fun'. Roads are not for fun (as I expect you actually know)

Dod

[pje16]

You are of course contributing to the well known fact that B roads are the most dangerous in the UK. They are not roads where people should be having a 'bit of fun'. Roads are not for fun (as I expect you actually know)

Dod

But they were great fun in the 1st lockdown
I have one on the way to the suoermarket - no-one was on it for about a month

[GoSeigen]

Having just spent almost £100 to fill my tank with petrol, I decided that given the fact that I am retired and do not need to get to many places in as great a rush as I may at one time have, I decided a week or so ago to cut my speed so that instead of setting my cruise control at 72/73 mph, I would cut it to around 65 mph just so see if it made any difference. Of course I am driving on motorways or dual carriageways. I am amazed to find that I am now getting almost 20% more miles per gallon than before. That is quite staggering to me, and it is much more relaxing to drive at that speed. I now feel sorry for those who go tearing passed me doing well over 70 and think of the fuel pouring through their engines. In fact, I am surprised that there seems to be no encouragement to drive at slightly slower speeds.

Dod

Energy used should be roughly proportional to the square of the speed, so 20% is pretty close.

GS

[redsturgeon]

If I drive my 2007 Honda Accord diesel at 2000rpm on the motorway (about an indicated 70mph) then it will return over 60mpg. Turbo diesel 2.2 litre, 138 BHP and no DFP.

If I am travelling around town then I use my PHEV on electric only, don't want to let people breathe in my nasty fumes.

If I fancy a bit of fun then I take out the MX5 on the local B roads

If I want to feel really righteous I cycle.

John

You are of course contributing to the well known fact that B roads are the most dangerous in the UK. They are not roads where people should be having a 'bit of fun'. Roads are not for fun (as I expect you actually know)

Dod

It is entirely possible to have fun without either breaking the law or being a danger to others. Also as a cyclist I ride my bike on those same B roads for fun...in your opinion I should not be doing that either?

I suggest that you keep your opinions to yourself rather than casting around completely baseless accusations.

John

[kiloran]

I don't think any of the political parties really believe in climate change, and the life changing urgent action, otherwise, virtually overnight, they could have the maximum speed set to 55 mph. This would save hugely on hydrocarbon and electricity usage. Maybe having an even greater and more instant effect than the heat pump strategy..

I wonder if the saving would be that great overall.
For sure, it would be beneficial for those on a motorway, but I'd hazard a guess that the vast majority of road journeys are in towns and cities with constant stop-start and accelerating/deccelerating. Anything but very gentle acceleration has a massive effect on fuel consumption.

But, of course..... every little helps.

--kiloran