An interesting comparison

Anything about BXs
jeremy
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Post by jeremy » Thu Sep 14, 2006 12:22 pm

In the mid 90's the method of calculating the official fuel consumption figures changed from the old urban, 55 mph and 75 mph figures to the current urban, extra urban and ??? figures.

What is interesting is if you take a BX and ZX 1.9D as being similar vehicles with similar consumptions the BX on the old urban figures was 43.5 and the ZX is 33.8 on the new. In practice there is very little difference between the ZX 1.9D and the BX DTR Turbo estate (urban consumption 40.9) and if there is an advantage I'd say it was in the ZX's favour.

The reason for the change was that manufacturers were tuning for impressive figures that bore little resemblance to reality. Is this happening again?

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DLM
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Post by DLM » Sat Sep 16, 2006 10:01 am

Has anybody ever read a car review (or driven a car) where the manufacturer's quoted mpg figures match up to what's obtained in practice?
Relying on two wheels and musclepower since the last BX (or any car) had to go.

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Post by jeremy » Sat Sep 16, 2006 10:19 am

Always reconed most were a bit pessimistic - after all if you drove some of the crap for a living you'd find your only amusement was getting out of it as quickly as possible.

Did several gentle runs between 50 & 60 in my Renault 21 - claimed 55 mph figure was 55 - and I was able to get 48 - which I couldn't believe when I tried to fill it the first time!

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cavmad
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Post by cavmad » Sat Sep 16, 2006 10:55 am

DLM, I seem to recall these things were often tested to see if the figures were correct or not.
Can`t recall who actually did the testing (pointless relying on the manafacturer), may have been a govt. dept. or possibly someone like Which? magazine.
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Way2go
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Post by Way2go » Sat Sep 16, 2006 12:41 pm

cavmad wrote:DLM, I seem to recall these things were often tested to see if the figures were correct or not.
Can`t recall who actually did the testing (pointless relying on the manafacturer), may have been a govt. dept. or possibly someone like Which? magazine.
Cav, I seem to remember this; wasn't it TRRL at their test track and HQ in Crowthorne? ----^
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cavmad
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Post by cavmad » Sat Sep 16, 2006 1:48 pm

I think you`re right, Way2go. I knew that they had to be tested and it`d be interesting to find out if it`s still done and who does it.
There were always rumours of makers tweaking cars for magazine road testers so they were faster than standard models and I`d bet they could also tweak cars to use slightly less fuel for the people who test mpg.
I`d like to think TRRL use cars from random showrooms to test fuel efficiency, anyone know for sure?
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Post by tom » Sat Sep 16, 2006 2:18 pm

DLM wrote:Has anybody ever read a car review (or driven a car) where the manufacturer's quoted mpg figures match up to what's obtained in practice?
Yes, regularly. My 1.9, The CX returned 47.5 touring which is very close, and an old Rover 2000 which at 230,000 miles made both its design speed and quoted consumption. No wonder stored examples tend to sieze!

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Post by tim leech » Sat Sep 16, 2006 3:09 pm

Dont I know it!

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Way2go
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Post by Way2go » Sat Sep 16, 2006 5:27 pm

cavmad wrote: I`d like to think TRRL use cars from random showrooms to test fuel efficiency, anyone know for sure?
Just had a look at their website and now privatised as TRL it would appear that such "policing" of published specs is not part of private enterprise. :cry:

Extract:
[Originally established in 1933 as part of the UK Government, TRL privatised in 1996 to become a fully independent private company. TRL is wholly owned by the Transport Research Foundation (TRF), a non-profit distributing foundation with no share holders, enabling profits made by TRL to be passed to TRF and re-invested in scientific research. TRF is comprised of over 80 sector members from the transport industry ensuring TRL continues to undertake the high quality research it is renowned for. ]
1991 BX19GTi Auto

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Post by Kitch » Sat Sep 16, 2006 7:55 pm

DLM wrote:Has anybody ever read a car review (or driven a car) where the manufacturer's quoted mpg figures match up to what's obtained in practice?
Not with regards to economy. Its either way under or way above.

But I got exactly the same 1/4 mile time in the 16v as it says in the book! :lol:

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DLM
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Post by DLM » Mon Sep 18, 2006 1:39 pm

Even if a quoted mpg figure is verified by an external body, most were pretty meaningless in the past (when the BX was a new car), as the kind of trials were quite divorced from "normal" driving. I have occasionally been surprised in the past, such as when I drove a Pug 106 1.5 diesel up and down the M4 for a period and found it returned about 60 mpg, despite the extra bodyweight compared to an AX. Performance - well, that tends to be in the eye of the beholder, particularly because speedos are pretty inaccurate.

Of course, every car of a particular model ends up having different performance and mpg figures, due to a complex mix of initial build, preparation, maintenance or lack of, abuse, care, driving style etc. etc. etc. Boring but true.

It can't be as bad as WW2-era military planes though, which were produced and assembled in a wide variety of shadow and alternative factories. Some of the variance here was startling - and potentially a lot more disturbing than a misleading mpg figure.
Relying on two wheels and musclepower since the last BX (or any car) had to go.