Rhothgar wrote:You cannot gain a huge benefit for slipstreaming a lorry because you would have to be dangerously close for the wind eddies to totally miss your car and being that close would not be conducive to planning well ahead.
Too true, I know from cycling and slipstreaming buses (tried it a couple of times, never again) that in order to gain anything worthwhile in reducing drag you have to be dangerously close to the vehicle ahead and positioned centrally, at least when cycling I could hear the exact moment the bus driver lifted off the throttle (rear engined) I could start to brake. As for positioning slightly offside to gain vision beyond the vehicle you're tailgating you've immediately lost at least half of the slipstream advantage.
The other thing to mention on this dubious tactic is that if you've ever followed a HGV/bus in a flat fronted van at speeds in excess of 40 mph you'd realise just how much debris they throw up into the path of your vehicle, they act as a vacuum cleaner picking up everything below them and project it into the path of the following vehicle. Whenever I'm following an HGV I always leave an extended following distance for the reasons above not to mention the benefits in improving my own vision beyond the vehicle ahead, to do otherwise in an attempt to save a couple of pennies is just plain madness in my books.
As mentioned earlier in this thread unless the roads have been cleared of all other road users including pedestrians it's impossible to replicate the same 'drive' twice along the same section of road as there are so many variable conditions/circumstances each time you drive it and it's that that makes it all but impossible to achieve the perfect drive, never observed or managed to do one myself.
As for how much time you save by driving at say 80 compared with 65, from my personal experience it's very little especially when you factor in the higher levels of concentration/stress required to maintain the higher speed, you may arrive 10 minutes earlier on a journey of say 80 miles but you then spend that gained time in de-stressing
The advantage blues and twos gives you is rarely having to stop, you have a legal exemption from most red ATS (not train/tram level crossings), speed plus keep left and provided the driver ahead actually uses their rear view mirror (quite rare for a significant proportion of drivers) you maintain a high average speed by not getting baulked by clusters of slow moving traffic.
I'd be very interested to know the reality of the the effect on fuel consumption of some of the tactics mentioned here such as rarely going above 2,000 rpm as causing an engine to labour can't be good for consumption, most new manual gearbox vehicles have an indicator to suggest the most suitable gear for the speed/circumstances and remaining in too lower gear can trigger the 'change down' indicator. I'd have thought that remaining below 2,000 rpm in a XUD TD would have a negative effect upon consumption as the peak torque figure is reached @ 2250 rpm. Another one I wonder about is slowing down on uphill sections, yes the mpg figure won't drop as low during the climb but as the climb now tales longer the lower mpg is maintained for a longer period of time so does that now have a negative effect on the average journey mpg compared with maintaining a set speed?
The key to achieving high mpg figurers is quite simple, use advanced driving techniques, lift vision, anticipate and plan for the road ahead.