Are there any cars that run on petrol or diesel and will achieve 60mpg+ at 100mph?

There aren't many cars that are rated to do 60mpg extra urban, and that's on a rolling road under ideal circumstances.

As speed increases aerodynamic drag increases exponentially, so you'd need to be significantly more efficient than anything currently available.
 
None are aerodynamic enough - the cars which are designed with high speed aerodynamics in mind don't have ecobox engines in them.

Saying that, dads 318d will do mid 60s on a run at 80-85, but I imagine there would be an exponential drop from there
 
I wouldn't say there's no point. That kind of efficiency would benefit everyone, the vehicles could potentially be achieving even greater MPG figures at lower speeds.

Besides, I'm sure most people cruising along at 80 or 90+ would be quite pleased with getting more than 25-30 MPG!

That's pretty damn good Iain. Making me wonder what the most efficient vehicle would be at 100mph (petrol/diesel of course, hybrids accepted).
 
It is pretty impressive, I think his average on the computer is sitting at about 60mpg, although he lives out of town so not much urban usage.

It's surprising that for an engine "similar" to mine (~2.0 single turbo diesel) that it can be so much more efficient. Mine will do 60mpg on a level road at 60mph but I'd never achieve that on any sort of run. As for most efficient at 100, difficult to find out as its obviously not something that's measured. My money would be on a modern twin turbo diesel but that's just speculation. I don't think hybrid would help as you won't be running on battery but you'll still be lugging them around
 
Shad said:
I wouldn't say there's no point. That kind of efficiency would benefit everyone, the vehicles could potentially be achieving even greater MPG figures at lower speeds.
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I'm not so sure - if it was geared to be very efficient at 100mph it would need an extra gear ratio to do it otherwise it'd be less usable at 70mph, surely?
 
I once had to rush back from London in mine up the M40 during a summer... sat 5-10 below that target speed and the trip average was 60.9mpg. Probably with a small diesel the car might do it. Lean burn goes out the window at that speed.

Would have been doing circa 3000rpm at those speeds.

Vehicle mass doesn't effect steady state speed other than rolling resistance. Not that a Prius is heavier than a golf diesel anyway.
 
[TW]Fox;23639566 said:
I'm not so sure - if it was geared to be very efficient at 100mph it would need an extra gear ratio to do it otherwise it'd be less usable at 70mph, surely?
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Hence potentially ;) If the vehicle needed to 'cheat' with gearing to hit the target then for sure it could be a very different story at other speeds. But if it was just a great engine and probably more importantly, a great body shape, then who knows. I wonder how a modern diesel would do in something like an old Citroen XM.

Jonnycoupe said:
I once had to rush back from London in mine up the M40 during a summer... sat 5-10 below that target speed and the trip average was 60.9mpg. Probably with a small diesel the car might do it. Lean burn goes out the window at that speed.
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Now you're talking. Is that the Jag? It makes a certain amount of sense in my mind that something (such as the Jag) built to easily run at 150mph+ ought to return pretty sensible figures at more useful speeds.
 
Shad said:
Hence potentially ;) If the vehicle needed to 'cheat' with gearing to hit the target then for sure it could be a very different story at other speeds. But if it was just a great engine and probably more importantly, a great body shape, then who knows. I wonder how a modern diesel would do in something like an old Citroen XM.
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Gearing isn't cheating, it's a crucial aspect of a car's efficiency. To attain the best efficiency at a given speed, you gear the car so that the engine speed is at the best rpm for efficiency, having also accounted for torque/power required at a given speed.

You could have the greatest engine in the world, with the most aerodynamic body shape ever conceived by man but if it was geared to attain optimal efficiency at 50mph, then it'll still be crap at 100mph
 
I wonder what the 535d would get.. 100 MPH is about 2350 RPM. Extra-urban is 52.3 MPG, so I reckon maybe 40-43 MPG. Bit far off the target though :p
 
Insight would get closest I think. Low drag and geared for 200mph in 5th.

In 5th it won't go below 50mpg even with foot to the floor
 
Kenai said:
Gearing isn't cheating, it's a crucial aspect of a car's efficiency. To attain the best efficiency at a given speed, you gear the car so that the engine speed is at the best rpm for efficiency, having also accounted for torque/power required at a given speed.

You could have the greatest engine in the world, with the most aerodynamic body shape ever conceived by man but if it was geared to attain optimal efficiency at 50mph, then it'll still be crap at 100mph
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My point was you could 'cheat' by gearing and tuning the engine such that it had a narrow band of best efficiency and that could only be achieved doing 100mph in top gear.

Anyway, I'm off to look for Insights on Autotrader :p
 
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