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Fuel Consumption *CONFUSED*

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  • Fuel Consumption *CONFUSED*

    This may or may not sound silly, but i was just wondering about the Fuel Consumption of the VXR.

    I do alot of motorway driving and have always believed that the higher the gear the less fuel used...however when driving on the M1 this morning doing about 70-80 in 6th the trip computer told me i was averaging 30-35 miles/gallon, i geared down to 5th doing the same speed and to my suprise the miles/gallon figure started to rise!

    Is the trip computer wrong or is 5th more suited to driving at 70-80mph and 6th left for even higher speeds or something?

    Thanks in Advance!

  • #2
    Not silly at all. The gearing on many cars is such that dependent on road speed/throttle load at that time you'd be better off in a lower gear spinning slightly higher rpm but at a smaller throttle opening.
    Ultimately on a long trip at 70 + the 6th gear will be more economical but as speed drops - dependent on road gradient etc - you could be better off changing down.



    • #3

      thanks for the info...i'll give it another go tonight on the way home from work!


      • #4
        A common misconception is that fuel consumption rate is just directly proportional to revs, it is actually roughly proportional to the power output of the engine which is related to revs*torque, which is effectively mothership's point.

        Also in modern engines no fuel is used when the engine is acting purely as a brake, so if you downshift to slow down although it sounds like the engine is working harder it's just your car's kinetic energy that's driving the engine. I don't have one of these MPG meters on my car but I'd imagine it would go off the scale if your in gear with your foot off the throttle and slowing down.

        All you need to do is constantly drive downhill, and get out to push your car uphill.


        • #5
          That is indeed right and I've checked it with the test mode of the BC. Basically when slowing down on Motorway/Slip Road/Approaching lights if you lift off the throttle completely then the MPG goes to 999.99, and the test mode of the BC which shows the Fuel Injector Consumption goes to 0.0 ML per Sec. Round town I typically find that going into 6th gear actually increase my fuel consumption so only use 5th, and dependant on the types sometimes even 4th.

          Best method of getting used to driving it to is economical best (whilst not being a sunday driver) is to use the BC and test the same route a few times but driven differently. It will then tell you the average speed, distance covered, MPG achieved and the actual amount of fuel consumed. That's how I checked my thoughts on using 6th gear town, and confirmed I was better using 5th. Cheers.


          • #6
            Thanks for everyones replies...

            I tested the car in 5th doing 70mph on the M1 from Jct 37 to 34...The MPG was averaging 40-45ish!...

            Ah well...Looks like am gonna have to keep testing...not really a problem ofcourse, as getting into the car put a huge smile on my face


            • #7
              It also depends on atmospheric conditiond as well.

              So many peramiters the list gos on and on.

              Load, tyre pressure, road surface, wind, gradient,

              At the end of the day you got a VXR why worry about the consumption unless its stupid like 6mpg then you might have a problem if you wanted the looks and the economy the a T888 CDTi would have been a better option.


              • #8
                £48 in OPtimax..

                Gone in 110 miles, empty..... :wink:


                • #9
                  Originally posted by Daimo
                  £48 in OPtimax..

                  Gone in 110 miles, empty..... :wink:
                  Don't be confused by this folks, he was on the Snetterton race circuit!!! which was not exactly economical driving.


                  • #10
                    I was going to say flippin eck - but now makes sense......


                    • #11
                      Yeah sorry I should have added that small point.


                      • #12
                        Whats all this fuel economy chit chat ? boring.... buy a diesel... the VXR is a fun car



                        • #13
                          Good point like i said get the T888 then have the best of both.