Fuel save pro

Bigwheels1111

Don’t waste your money.
To save fuel, I drive at 62mph instead of 70 mph.
At 70 I get 45 mpg on the motorway, at 62 mph I get 54 mpg. 20% extra milage.

Mutton_Geoff

Bigwheels1111 said:

Don’t waste your money.
To save fuel, I drive at 62mph instead of 70 mph.
At 70 I get 45 mpg on the motorway, at 62 mph I get 54 mpg. 20% extra milage.

Why 62? The slower the better since drag (from wind) is a square of your speed. There isn't a sweet spot at 62mph, it's just that equates to 100km/hr, a nice round number from where manufacturers publish specifications so 62mph is bound to be better than 70mph.

chrisw

Mutton_Geoff said:

Bigwheels1111 said:

Don’t waste your money.
To save fuel, I drive at 62mph instead of 70 mph.
At 70 I get 45 mpg on the motorway, at 62 mph I get 54 mpg. 20% extra milage.

Why 62? The slower the better since drag (from wind) is a square of your speed. There isn't a sweet spot at 62mph, it's just that equates to 100km/hr, a nice round number from where manufacturers publish specifications so 62mph is bound to be better than 70mph.

Some people may remember the fuel crisis in the 70's when there was a national speed limit imposed of 50mph.

Some cars do seem to have a bit of a sweet spot though, mine seems more economical at 70 than 60 to 65 and a few people on the owners forums have commented similarly but no concrete proof.

Grey_Critic

Most cars these day seem to have a fuel computer so it is easy to see where all your fuel is going. Just try it.

[Deleted User]

Mutton_Geoff said:

Alanp said:

I’ve seen these things that plug into the cars obd port that save fuel. one was taken apart and it was basically just a few flashing led,s, , if you want to save fuel just drive gently and avoid harsh braking 

https://www.youtube.com/watch?v=azuB9ZJuDlM

I could tell from the off it was going to be Big Clive and if it wasn't, I'd have linked to him, the tear down is brutal, these things are such a scam

Stubod

chrisw said:

Some cars do seem to have a bit of a sweet spot though, mine seems more economical at 70 than 60 to 65 and a few people on the owners forums have commented similarly but no concrete proof.

...unlikely...I think the laws of physics would say otherwise??

Ebe_Scrooge

Stubod said:

chrisw said:

Some cars do seem to have a bit of a sweet spot though, mine seems more economical at 70 than 60 to 65 and a few people on the owners forums have commented similarly but no concrete proof.

...unlikely...I think the laws of physics would say otherwise??

It's an interesting question actually.  Yes, wind resistance increases exponentially as speed increases.  But any given engine (assuming we're talking conventional ICE) will have an optimum running speed.  So if you're labouring the engine doing 20 mph in top gear, or if you're revving the wotsits off it doing 90 mph in 3rd, both of those will be wasteful in terms of fuel consumption.  But doing, for instance, 70mph on a level road in top gear, could well be the optimum in terms of engine speed and load, for an individual car.

Obviously there will be many variables - the gear ratios, the engine size and power output, whether its petrol or diesel, the weight of the car ... but within a reasonably narrow range, it's not impossible for a particular car to be more economical at 70 than it is at 65, for instance.

Bigwheels1111

Mutton_Geoff said:

Bigwheels1111 said:

Don’t waste your money.
To save fuel, I drive at 62mph instead of 70 mph.
At 70 I get 45 mpg on the motorway, at 62 mph I get 54 mpg. 20% extra milage.

Why 62? The slower the better since drag (from wind) is a square of your speed. There isn't a sweet spot at 62mph, it's just that equates to 100km/hr, a nice round number from where manufacturers publish specifications so 62mph is bound to be better than 70mph.

Tried the same journey, a 350 mile round trip.

70 mph = 45 mpg

65 mph = 49 mpg

60 mph = 52 mpg

62 mph = 54 mpg, done by mistake.

I hit the cruise control at 65 mph, but dash cam and sat nav said 62 mph.

Just did 680 motorway miles and 120 miles of local runs and cold starts in a week.

54 mpg average.

Will be doing a 600 round trip in 2 weeks and hope to get 56/58 mpg as no local milage.

forgotmyname

Stubod said:

chrisw said:

Some cars do seem to have a bit of a sweet spot though, mine seems more economical at 70 than 60 to 65 and a few people on the owners forums have commented similarly but no concrete proof.

...unlikely...I think the laws of physics would say otherwise??

No mention of revs/gearing though.  when you take into account the revs/gearing/torque then its possible a higher speed maybe
more fuel efficient.  Maybe the revs/torque at 60mph in top gear is less than required but going upto 70mph brings it
into the sweet spot where the turbo is boosting higher giving an excess of torque.

When towing I don't use 6th gear, far more fuel efficient in 5th gear even though the revs are higher.  A few people on
the campsite with similar cars and they found the same. 60mph in 5th uses less fuel than 60mph in 6th, quite possible
that 70mph may use less fuel in 6th gear.

But the highest efficiency if probably more like 40mph in 4th, not tested my current car but had 76mpg on my old
car by keeping it to 40mph. 2L  diesel estate weighing over 1.5tons, amazing economy when older cars were
lucky to break 30mpg.

Stubod

https://www.youtube.com/watch?v=tqY-v2G0K0M&ab_channel=ScottyKilmer