Pros and Cons buying a diesel

How on earth can you get so called "accurate figures"? Ignoring the usual misleading BS you get on internet forums, fuel consumption will vary signifcantly depending on the type of journey, and the driving style of the driver.

The official figure are a baseline guide you can compare different cars. They are achieved by driving in a very artificial way. Usually to get the max fuel economy out of a car, under those specific conditions. You can't expect to replicate them, if you drive in completely different conditions. Which may be more or less favorable than the official tests.
 
aircobra19 said:
How on earth can you get so called "accurate figures"? Ignoring the usual misleading BS you get on internet forums, fuel consumption will vary signifcantly depending on the type of journey, and the driving style of the driver.

The official figure are a baseline guide you can compare different cars. They are achieved by driving in a very artificial way. Usually to get the max fuel economy out of a car, under those specific conditions. You can't expect to replicate them, if you drive in completely different conditions. Which may be more or less favorable than the official tests.
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That's exactly my point: the official figures, although in theory an objective baseline, are in my experience pretty useless even for that.

The only meaningful figure is how much you use yourself. It's easy enough to measure how many litres of fuel you use to go so far. On the basis that my own driving or types of journey didn't change radically, I found that by going to diesel I was using maybe 40% less fuel (I can't recall the exact figure), for a similar sized car. From talking to others who've done the same, this does not seem to be unusual.
 
If the official figures for car A were 20% better than for car Car B. Your saying that baseline is not useful and/or is not accurate. Perhaps its not accurate, but I would say its useful.

How can you estimate how much diesel you'll use in a disimilar car. Considering it you'll drive it differently from your own. For example if you have a peaky 16v petrol you are going to rev it a lot more than you will a 2.0 TDi and cruise at a different speed depending how its geared etc. You just drive it very differently. Thats what I reckon anywayz.
 
fuels cost difference between diesel and petrol based on 18k miles per year and obtaining 45MPG and 35MPG for diesel and petrol respectively

Price €1.06 Diesel €1.14 Petrol
MPG 45 Diesel 35 Petrol
Annual Miles 18k
Total Fuel Price €1,927 Diesel €2,665 Petrol

Saving €738
 
I don't know where you buy your fuel (clare) but petrol seems to be about 2c a litre cheaper than diesel in the northeast.

45 mph = 9.9 miles/L 18k = 1818L diesel @ E1.2/L = E2181

35 mpg = 7.7 miles/L 18k = 2337L petrol @ E1.18/L = E2757

Difference = E576
 
aircobra19 said:
If the official figures for car A were 20% better than for car Car B. Your saying that baseline is not useful and/or is not accurate. Perhaps its not accurate, but I would say its useful.

How can you estimate how much diesel you'll use in a disimilar car. Considering it you'll drive it differently from your own. For example if you have a peaky 16v petrol you are going to rev it a lot more than you will a 2.0 TDi and cruise at a different speed depending how its geared etc. You just drive it very differently. Thats what I reckon anywayz.
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I'd say the official figures are not entirely useless, but they do tend to under estimate the benefits of moving to diesel.

I still say the only comparison that makes sense is the one I outlined: so what if there's some subtle difference in driving style between the two cars? I'm only interested in how much I pay at the pumps, not some notional objective figure, which will never be able to take personal driving style into consideration.
 
ang1170 said:
...so what if there's some subtle difference in driving style between the two cars? I'm only interested in how much I pay at the pumps, not some notional objective figure, which will never be able to take personal driving style into consideration.
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Driving style can make a big difference. You shouldn't drive a petrol same way as a diesel its inefficient. Subtle I don't think so...

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All I'm saying is the official figures are under test conditions. So theres some consistency in them. They are a useful baseline for comparision.

But if a persons own driving isn't close to those test conditions, they might never do urban journeys at low speed for example, then of course they'll better the official figures.

You said originally to ask someone who drives a diesel car. Thats like asking how long is a piece of string theres so many variables that could be a factor in someones fuel economy. He might be doing a 400 mile round journey twice a week. You might be parked on the M50 everyday.
 
Going on today's Sindo's VRT changes expected in the next budget, you'd want your head tested to buy a petrol car now.
 
aircobra19 said:
You said originally to ask someone who drives a diesel car. Thats like asking how long is a piece of string theres so many variables that could be a factor in someones fuel economy. He might be doing a 400 mile round journey twice a week. You might be parked on the M50 everyday.
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I still don't think you're getting what I said.

As you say, little point in asking someone what mileage they get in their car in the hope you'll get the same, as there are too many variables involved.

However, if you ask them how much their mpg increased from their previous (petrol) car, you should get a pretty good estimate of the potential savings.

My point (again!) is that when you speak to owners, the savings they quote are typically more than you'd expect from looking at the official and supposadly objective figures.

Not very scientific I know, but as I also said, I think real world figures are the only one's that matter in the end: how much do I save in my choice of car.
 
What you saying is if someone hammers their 1L Ibiza at 75mph home every evening getting 25mpg, then switches to 2.0 TDI and gets 55mpg.

Then someone who does the same journey in say a 1.6 Civic at 60mph getting 45mpg or better should get about 90~100mpg if they switch to diesel.
 
I think your figures are a bit unrealistic, there.

40% or better improvement would be a better figure to use, rather than over 100%. One other poster apart from myself has used this figure, which is somewhat better than the comparison based on official figures quoted by another showed.

If memory serves, it was actually better than this over the long term, but it's not a bad figure to start with.
 
Thats because to demonstrate driving style.
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So the guy getting 25 now gets 35
The guy getting 45 gets 63
 
Exactly: so if I happen to be getting (say) 30 mpg in my current petrol car, it's a good estimate that I'd be likely to get 42 mpg if I moved to a diesel (assuming a roughly equivalent car).

What the official figures say for either car is pretty much irrelevant, as they don't take into account individual driving style or journey type, and as I've said (many times at this stage) they seem to consistently underestimate the benefits of moving to diesel.
 
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