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MPH and Gear Ratios - Audi
Comments
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You could theoretically change the box, but whilst that might fix your 70mph problem the other ratios could fall outside of the optimum for your car. Best leave it really unless vag stuck a 6 speed box on the same engine at any point (think it was only 115, 130 and 150's that got this, not sure).
I must admit I find myself driving at 60/65 most of the time in my hairdressermobile as otherwise I'm sitting at about 3,500 revs - this combined with the wind / road noise means it's generally not worth it unless in a proper hurry...in which case it tends to be worth exploring higher revs.0 -
Upshot is that for best mpg at a given speed you need to be running the engine at the “sweet spot” speed and be in whatever gear you need to get the required road speed
Nope. Its all about engine load. I've done enough mileage having nothing to do but investigate this with an onboard computer that gives realtime consumption to have a bit of a clue.0 -
I'm assuming it's a 5-speed box?Bit nerdy this- but I have what is probably the best car I have ever had- An Audi 1.9 Diesel. However what absolutely ruins it is the gear ratio in top. I spend allot of time on the motorway doing Ahhh 70MPH and I keep wanting to change up- It would be loads quieter, more relaxed and get me lots more MPG. The engine is plenty torque'y enough at low revs.
Why did Audi do it that way? - and Is there a way the gear ratios can be changed easily?
A lot of cars could do with an extra ratio for high-speed cruising to be honest. I had an Alfa 145 and it revved at about 4,000-rpm as 70-mph!0 -
To expand a bit ….all engines have a “sweet spot” (or more realistically a fairly narrow range) of maximum efficiency.
There are some seriously hard sums involving about pumping losses, tuned inlet & exhaust pressure pulses, flame fronts, BMEP etc etc but generally the maximum efficiency point coincides with maximum torque production.
Upshot is that for best mpg at a given speed you need to be running the engine at the “sweet spot” speed and be in whatever gear you need to get the required road speed
Thanks I thought it was max torque too.
The reason for me asking Hammyman is that Diesels typically have flater longer torque peaks, so giving a broader speed range. Petrol typically having amuch narrower spikey peak IME.
Don't dispute the fact that if you have your pedal to the metal at low speed in a high gear, or at high revs (to maintain speed) on an incline it isn't going to be very efficient. Maybe it is being efficient, going up hill, it is just the fact you have to expend more energy to overcome gravity.
I would have thought this would be more of a problem with carburettors than injection. I thought diesel was fairly accurately pumped/injected and this was one of the reasons for it's relative frugality.:think:"If you act like an illiterate man, your learning will never stop... Being uneducated, you have no fear of the future.".....
"big business is parasitic, like a mosquito, whereas I prefer the lighter touch, like that of a butterfly. "A butterfly can suck honey from the flower without damaging it," "Arunachalam Muruganantham0 -
I'm assuming it's a 5-speed box?
A lot of cars could do with an extra ratio for high-speed cruising to be honest. I had an Alfa 145 and it revved at about 4,000-rpm as 70-mph!
I have a friend who has a 1.9TDI A4 estate with a five speed box. Not sure what power, mileage well into three figures, but his doesn't seem too short geared.
He does think mine is more relaxed on motorways at 36/37mph per 1000.
Maybe it is just a slightly smoother engine or better insulated?"If you act like an illiterate man, your learning will never stop... Being uneducated, you have no fear of the future.".....
"big business is parasitic, like a mosquito, whereas I prefer the lighter touch, like that of a butterfly. "A butterfly can suck honey from the flower without damaging it," "Arunachalam Muruganantham0 -
Probably better insulated, as 3,600 - 3,700rpm is still on the high side for a diesel engine (Especially given that the redline is probably somewhere around the 5,000rpm mark!).grizzly1911 wrote: »I have a friend who has a 1.9TDI A4 estate with a five speed box. Not sure what power, mileage well into three figures, but his doesn't seem too short geared.
He does think mine is more relaxed on motorways at36/37 per 1000.
Maybe it is just a slightly smoother engine or better insulated?0 -
Probably better insulated, as 3,600 - 3,700rpm is still on the high side for a diesel engine (Especially given that the redline is probably somewhere around the 5,000rpm mark!).
Meant to say 36/37 mph per 1000:doh:"If you act like an illiterate man, your learning will never stop... Being uneducated, you have no fear of the future.".....
"big business is parasitic, like a mosquito, whereas I prefer the lighter touch, like that of a butterfly. "A butterfly can suck honey from the flower without damaging it," "Arunachalam Muruganantham0 -
To expand a bit ….all engines have a “sweet spot” (or more realistically a fairly narrow range) of maximum efficiency.
There are some seriously hard sums involving about pumping losses, tuned inlet & exhaust pressure pulses, flame fronts, BMEP etc etc but generally the maximum efficiency point coincides with maximum torque production.
Upshot is that for best mpg at a given speed you need to be running the engine at the “sweet spot” speed and be in whatever gear you need to get the required road speedNope. Its all about engine load. I've done enough mileage having nothing to do but investigate this with an onboard computer that gives realtime consumption to have a bit of a clue.
Maybe I'm being a bit thick but what do you mean by "all about engine load"?0 -
forgotmyname wrote: »Same here 6th gear is 70+, In theory 85mph is more economical than 70. Not that i would travel that speed
of course, But it really is.
How can 85mph be more economical than 70mph?0 -
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