I think it comes down to driving style... which the HDi is very hard to do well due to very short gearing!
What you really need to do is be happy to drive at 60mph and not change speed. If you start speeding up/slowing for lorries passing or whatever else then you burn fuel and soon get down into the 50's.
Ie, lots of people run 195/50R15 Eagle F1 or PS2 or something sticky and sporty, wheras an eco 195/55R15 would probably see a 10% improvement right off the bat!
The super short gearing also costs you on cruise efficiency. Much over 60mph and you are just running higher revs than you could be to sustain the same rpm. Again, the often used lower profile tyres lower gearing even more making economy worse again (and making brim to brim refill method inaccurate due to rolling rad issues (unless you use GPS)
Get speed up much higher and engine revs higher = more friction. You need more advance on injections and thus want to run more rail pressure = cost on HP pump to deliver the higher pressure, so the tiny gains in torque you get are offset by higher parasitic losses, and also running the higher drags at 70mph vs 60mph!
All in there really isn't much to find vs just running good eco tyres, good state of service (oil and internal engine losses), and driving at a slower speed and not changing it much!
Remember when tuning/remapping for economy it's all down at sub 10mm.3 injections, they are tiny really at 60mph. The extra power needed merely to overcome drag goes up by the square of the speed change so 70mph vs 60mph needs 35% more injection. So simply dropping cruise speed down 10mph will save a great deal of fuel.
As per remap claims, that is all they are. Has anyone ever seen any real data? It's all just claims 'up to' or user reports which are not really reliable.
I remember someone on theywhoshallnotbenamed claiming a 33%+ boost with a remap from the king of economy boosts, while Pete and I have tinkered for 1000's of road miles and can't find anything more than a feint sign economy *might* have improved... hmmmm!
Dave
What you really need to do is be happy to drive at 60mph and not change speed. If you start speeding up/slowing for lorries passing or whatever else then you burn fuel and soon get down into the 50's.
Ie, lots of people run 195/50R15 Eagle F1 or PS2 or something sticky and sporty, wheras an eco 195/55R15 would probably see a 10% improvement right off the bat!
The super short gearing also costs you on cruise efficiency. Much over 60mph and you are just running higher revs than you could be to sustain the same rpm. Again, the often used lower profile tyres lower gearing even more making economy worse again (and making brim to brim refill method inaccurate due to rolling rad issues (unless you use GPS)
Get speed up much higher and engine revs higher = more friction. You need more advance on injections and thus want to run more rail pressure = cost on HP pump to deliver the higher pressure, so the tiny gains in torque you get are offset by higher parasitic losses, and also running the higher drags at 70mph vs 60mph!
All in there really isn't much to find vs just running good eco tyres, good state of service (oil and internal engine losses), and driving at a slower speed and not changing it much!
Remember when tuning/remapping for economy it's all down at sub 10mm.3 injections, they are tiny really at 60mph. The extra power needed merely to overcome drag goes up by the square of the speed change so 70mph vs 60mph needs 35% more injection. So simply dropping cruise speed down 10mph will save a great deal of fuel.
As per remap claims, that is all they are. Has anyone ever seen any real data? It's all just claims 'up to' or user reports which are not really reliable.
I remember someone on theywhoshallnotbenamed claiming a 33%+ boost with a remap from the king of economy boosts, while Pete and I have tinkered for 1000's of road miles and can't find anything more than a feint sign economy *might* have improved... hmmmm!
Dave