Optimum Cruising Speed.

[ashypd51]

hi can someone sort this argument out. i have 1.9tdi 2001 6 speed gal ghia, my mate has the 2002 version. he reckons the optimum speed to cruise for max mpg, is at just under 60 mph (approx 1700 revs) in sixth gear, as the turbo doesnt kick in fully.

i am of the understanding that the max torue for the 1.9tdi is at approx 1950 revs , in which case my speed at that is just under 70mph. with the turbo working busily away.

we were going to do simultaneous and identicle journeys down the m6, but his trip computer isnt working , so we cant settle it that way.!!!

 

what happened to the industry standard optimum of 56 mph for best economy - what was that all about!

many thanx................... ashy

[Andrew T]

56 Mph was never a standard, it equates to 90 Kph , as 75 Mph equates to 120 Kph. It was used when the fuel consumption figures were first issued to tie in with industry norm in Europe at that time. The idea was simply to illustrate how fuel consumption deteriorates as speed increases.

[HJT]

50 mph in the middle lane :lol:

2 people doing the same speed on the same road will still give different figures. I find the cruise control will give me better mpg than me controlling the speed and when the wife drives I get the same mpg as the 2.3 petrol :(

 

Howard

[Guest MATT]

...the drivers driving style has a big effect on your mpg. example, there

[Masked Marauder]

If you are worried about fuel consumption then buy and fit a boost gauge and try to stay out of the red area, or if you have a VV turbo try staying off boost altogether.

[seatkid]

Maximum thermodynamic efficiency is around 1900 rpm which is where the PD engine can develop max. torque (at max. accelerator position) and has its lowest Specific fuel consumption measured in grams/kwh (not to be confused with fuel consumption - mpg or l/km)

Lowest fuel consumption (cruising) is dominated by rolling resistance,wind drag and transmission losses all of which go up with road speed. The lower the speed, the lower the consumption up to the point at which the efficiency of the engine drops off dramatically which in the case of PD would probably be 1200 rpm or less.

 

The answer to your question is "as slow as your engine will allow in top gear".

 

The curve below is not a VW engine (its a Mitsubishi diesel) but it shows the idea.

[Guest JBrannan]

zzzzzzzzzzzzzzzzzzz

[Ivor]

I just drove from Manchester to Preston this morning at 50MPH and got 64MPG.

 

Over 50 and it starts to drop to around 45 at 70MPH.

 

Why drive so slow?

Taking it in to dealer to sort coolant leak, didn't want to stress it.