335d/435d or 535d
Discussion
Fox- said:
Welshbeef said:
Bugger all difference as in £/ tank and also number of days commuting per tank is the same give or take.
However I've not done a whole tank at the 95mph range in fact personally I rarely get the chance with heavy traffic but when it does clear make the most of it.
So meaningless then?However I've not done a whole tank at the 95mph range in fact personally I rarely get the chance with heavy traffic but when it does clear make the most of it.
IIRC, the drag increases exponentially with speed - at the square I think? So adding 50% to your speed increases drag by 125% (to 225% of the original) - so there is no way that driving much faster burns no more fuel
I used to think that the 318iS I had in the late 90s was more economical at motorway speeds than going more slowly - but it was just that there was less stop / start / slowing down / speeding up when on the motorway (and more steady cruising in 5th) than driving round town
oop north said:
I think the words "give or take" suggest that he has not made any kind of accurate comparison to evidence his statement
IIRC, the drag increases exponentially with speed - at the square I think? So adding 50% to your speed increases drag by 125% (to 225% of the original) - so there is no way that driving much faster burns no more fuel
I used to think that the 318iS I had in the late 90s was more economical at motorway speeds than going more slowly - but it was just that there was less stop / start / slowing down / speeding up when on the motorway (and more steady cruising in 5th) than driving round town
Spot on re drag - but lots of people on PH can defy the laws of physics IIRC, the drag increases exponentially with speed - at the square I think? So adding 50% to your speed increases drag by 125% (to 225% of the original) - so there is no way that driving much faster burns no more fuel
I used to think that the 318iS I had in the late 90s was more economical at motorway speeds than going more slowly - but it was just that there was less stop / start / slowing down / speeding up when on the motorway (and more steady cruising in 5th) than driving round town
Bloody glad I only buy BMWs and don't have to sell them.
Edited to add: as a rough guide
UK Govt studies suggest the average MPG at 55 mph will decrease as follows for a typical car (it obviously varies with headwinds, drag coefficient etc)
- 3% less efficient at 60 mph
- 8% less efficient at 65 mph
- 17% less efficient at 70 mph
- 23% less efficient at 75 mph
- 28% less efficient at 80 mph
MPG at 95mph likely to be close to half that you would expect at 55mph - give or take
Edited by drmark on Thursday 26th February 13:32
drmark said:
Spot on re drag - but lots of people on PH can defy the laws of physics
Bloody glad I only buy BMWs and don't have to sell them.
Edited to add: as a rough guide
UK Govt studies suggest the average MPG at 55 mph will decrease as follows for a typical car (it obviously varies with headwinds, drag coefficient etc)
- 3% less efficient at 60 mph
- 8% less efficient at 65 mph
- 17% less efficient at 70 mph
- 23% less efficient at 75 mph
- 28% less efficient at 80 mph
Doesn't gearing also come into it - ie lets say if the gearbox wouldn't engage the overdrive 8th or 9th gear until 70mph then the above would be flawed. The above assumes the same gear for. Each speed increment. Bloody glad I only buy BMWs and don't have to sell them.
Edited to add: as a rough guide
UK Govt studies suggest the average MPG at 55 mph will decrease as follows for a typical car (it obviously varies with headwinds, drag coefficient etc)
- 3% less efficient at 60 mph
- 8% less efficient at 65 mph
- 17% less efficient at 70 mph
- 23% less efficient at 75 mph
- 28% less efficient at 80 mph
Edited by drmark on Thursday 26th February 12:54
It is an inverted U shape curve with peak efficiency in the 50s mph zone for most cars. So less efficient at low and high speeds. The top of the curve being the sweet spot for gearing versus drag (around 55mph for most cars) but every model is different.
eg.
http://www.mpgforspeed.com/fegov_graph.gif
eg.
http://www.mpgforspeed.com/fegov_graph.gif
Edited by drmark on Thursday 26th February 13:37
Welshbeef said:
Doesn't gearing also come into it - ie lets say if the gearbox wouldn't engage the overdrive 8th or 9th gear until 70mph then the above would be flawed. The above assumes the same gear for. Each speed increment.
High gearing helps but only shifts the sweet spot up a bit. The drag increases so fast (as a square of speed) that it overcomes any advantage. An eight speed modern BMW may have a curve that is shifted a bit to the right but I would bet that mpg starts to drop quickly after no more than 65. But, as I say, this is just rough guide. You should try 10 miles at 55 in your car (when it will be in 8th anyway on the motorway) and then another 10 at 95 having reset the trip. If they read the same you are the proud owner of the Millennium Falcon Welshbeef said:
drmark said:
Spot on re drag - but lots of people on PH can defy the laws of physics
Bloody glad I only buy BMWs and don't have to sell them.
Edited to add: as a rough guide
UK Govt studies suggest the average MPG at 55 mph will decrease as follows for a typical car (it obviously varies with headwinds, drag coefficient etc)
- 3% less efficient at 60 mph
- 8% less efficient at 65 mph
- 17% less efficient at 70 mph
- 23% less efficient at 75 mph
- 28% less efficient at 80 mph
Doesn't gearing also come into it - ie lets say if the gearbox wouldn't engage the overdrive 8th or 9th gear until 70mph then the above would be flawed. The above assumes the same gear for. Each speed increment. Bloody glad I only buy BMWs and don't have to sell them.
Edited to add: as a rough guide
UK Govt studies suggest the average MPG at 55 mph will decrease as follows for a typical car (it obviously varies with headwinds, drag coefficient etc)
- 3% less efficient at 60 mph
- 8% less efficient at 65 mph
- 17% less efficient at 70 mph
- 23% less efficient at 75 mph
- 28% less efficient at 80 mph
Edited by anonymous-user on Thursday 26th February 12:54
Are you now saying that running at 56 in, say 3rd gear gives no better fuel consumption than 90 in top gear? Not that that wouldn't be an equally meaningless statement.
The fact is that less energy is required to propel the car at 56 than at 90. A lot less. Therefore given even close to reasonable gearing, i.e. letting the engine run at its most efficient for either speed, the fuel consumption will be a lot worse at 90mph.
The most economical speed always tends to be the lowest revs you can pootle along at in top gear.
Let's dig out some graphs.
This graph is not great, because it has the engine thrashing through the gears at high revs. But it does show the "tires" loss (actually that's the tyres, bearings and diff) gradually increasing with speed. The "transmission" losses are actually the whole engine (pumping, scraping, turning stuff and so on) and the whole gearbox. You can see that at low speed, the engine is the big draw on energy - not surprising really especially at high rpm.
This graph is more interesting. It's the same generic car (roughly a 330d on 17" wheels) but it shows the effect of keeping the rpm low. Obviously you can't go too low, because then power generation quickly becomes inefficient as the engine labours, or lower again and the engine stops making any power at all.
The 8th gear graph shows the effect of economy vs speed when steady state.
Let's dig out some graphs.
This graph is not great, because it has the engine thrashing through the gears at high revs. But it does show the "tires" loss (actually that's the tyres, bearings and diff) gradually increasing with speed. The "transmission" losses are actually the whole engine (pumping, scraping, turning stuff and so on) and the whole gearbox. You can see that at low speed, the engine is the big draw on energy - not surprising really especially at high rpm.
This graph is more interesting. It's the same generic car (roughly a 330d on 17" wheels) but it shows the effect of keeping the rpm low. Obviously you can't go too low, because then power generation quickly becomes inefficient as the engine labours, or lower again and the engine stops making any power at all.
The 8th gear graph shows the effect of economy vs speed when steady state.
REALIST123 said:
tjlees said:
Welshbeef said:
Well (I don't have Eco pro) but this morning country roads it took 8 miles from starting for oil to be at 100degrees.
Seems like a big difference to Eco pro and clearly mine is then ready to use properly from that point. If someone is taking nearly 20 miles to get to operating temps and then turn it off I wonder if that's really the best option.
I think the reason that Eco pro takes so long to warm the oil is because it keeps the engine ticking over at around 1000rpm especially since i'm not doing more than 40-50 and its usually 5c or under when I start out - yesterday it was only 4c when I came back. Even at 70 in comfort you are at 1500ish rpm.Seems like a big difference to Eco pro and clearly mine is then ready to use properly from that point. If someone is taking nearly 20 miles to get to operating temps and then turn it off I wonder if that's really the best option.
Away 75% of the engine damage occurs during warm-up according to the oil companies, however other websites claim that running the engine at almost idle gently during warmup minimises wear. The only thing that seems consistent is running a cold engine hard causes lots of damage.
Because of the relatively bad comsumption on F335d in the winter so far, I've mainly reverted back to the other diesel which sees between 62-65mpg in the same conditions/journey and SWMBO gets to play with a straight six for her 70 miles round trip
Edited by anonymous-user on Friday 27th February 19:39
Edited by anonymous-user on Friday 27th February 19:50
More of a step down than that - I'm having the golf and she's having the Octavia diseasal! Was just thinking last night that 2.5 years/ 42k miles in the 640d didn't cost much more than the E46 330Cd vert we bought as a demonstrator and owned for 20 months (needed to get rid at that point and Junior was on the way...)
cslwannabe said:
More of a step down than that - I'm having the golf and she's having the Octavia diseasal! Was just thinking last night that 2.5 years/ 42k miles in the 640d didn't cost much more than the E46 330Cd vert we bought as a demonstrator and owned for 20 months (needed to get rid at that point and Junior was on the way...)
Your a brave man She who must be obeyed will want to correct that very shortly mark my words. I agree but apparently not - after 2 leased cars SWMBO wants a cheap runaround. I might be under pressure to get rid of the Boxster however...
Back to the topic - once I've racked up some miles in my first 4wd car I'd be interested to see how a 435d xDrive compares with both the 640d and R dynamically.
Back to the topic - once I've racked up some miles in my first 4wd car I'd be interested to see how a 435d xDrive compares with both the 640d and R dynamically.
The new Golf R is very well thought of, so no doubt you will have a lot of fun. I would be interested in how you are coping with the interior, after the 640, which in my opinion has one of the nicest interiors of the BMW range. The Golf on the other hand is well made, but a bit more mundane, having come from a 640 I think I would feel a bit disappointed with the Golf.
Soov535 said:
As an aside, when I was filing some new insurance documents last night for the 535, I found the key ring and key my Dad gave me on my 17th birthday almost 30 years ago.
The key was for his 1982 X reg E21 316. Henna red. He insured me from my 17th and taught me to drive in it. I drove that car as a named driver for a decade all through sixth form and university, and on occasions when I visited them once I'd moved to London. He kept it for 17 years.
He's gone now, as is the car, but what a lovely thing to keep with me all day.
Save me a seat at the bar, Dad.
Ah, nice touch Soovy. The key was for his 1982 X reg E21 316. Henna red. He insured me from my 17th and taught me to drive in it. I drove that car as a named driver for a decade all through sixth form and university, and on occasions when I visited them once I'd moved to London. He kept it for 17 years.
He's gone now, as is the car, but what a lovely thing to keep with me all day.
Save me a seat at the bar, Dad.
Edited by Soov535 on Thursday 26th February 10:02
ZX10R NIN said:
JNW1 said:
Wills2 said:
Indeed we are, and it doesn't do 62 in 4.7 seconds either, there is some utter tripe been spouted on this thread.
True but best not to let the facts get in the way of a good story!!!So if you can both explain the "TRIPE" you're referring to it'd be appreciated.
Edited by ZX10R NIN on Thursday 26th February 08:27
Although you've not been here long, I think you'll probably have worked out by now which chuckle brother spouts the tripe.
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