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What's going on with claimed MPG figures?

Piff

Piff

MB Enthusiast
Joined
Feb 24, 2005
Messages
2,742
Location
Suffolk
Car
Audi Q5 Vorsprung
<div class="bbWrapper">Recently browsing Autotrader, looking at GLC's. Puzzled by the different claimed combined mpg figures.<br /> GLC 250D 2017 (16 reg) 2.1L 201 bhp - 56.5 mpg<br /> GLC 250D 2018 (18 reg) 2.1L 201 bhp - 45.6 mpg<br /> GLC 250D 2019 (19 reg) 2.1L 201 bhp - 39.2 mpg<br /> GLC 220D 2019 (69 reg) 2.0L 191 bhp - 47.9 mpg<br /> Now I can see that the 69 reg is a different engine but according to the quoted numbers it is worse than the 16 reg car.<br /> Have I missed something?</div>
 
<div class="bbWrapper">Different testing standards?</div>
 
<div class="bbWrapper">Unless you know <u>exactly</u> how those figures were derived, they are meaningless.<br /> <br /> Why worry?</div>
 
<div class="bbWrapper"><blockquote data-attributes="member: 126251" data-quote="Rorywquin" data-source="post: 2828331" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=2828331" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-2828331">Rorywquin said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Unless you know <u>exactly</u> how those figures were derived, they are meaningless.<br /> <br /> Why worry? </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Because there appears to be an enormous difference between say a 16 reg and a 19 reg</div>
 
<div class="bbWrapper">WLTP applies to the 19 reg car (and whilst more realistic, is worse)<br /> <br /> The 16 reg will be on the older less realistic tests (that some manufacturers may have defeated.....)<br /> <br /> It's the same for many pre and post WLTP mpg figures</div>
 
<div class="bbWrapper">Check on ‘Fuelly’ <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f642.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":)" title="Smile :)" data-smilie="1"data-shortname=":)" /></div>
 
<div class="bbWrapper">My 2016 model was 'close' my 2019 is spot on. The new testing to WLTP is far more realistic...</div>
 
<div class="bbWrapper">Yep, different test methods give different results...</div>
 
<div class="bbWrapper">Not sure if manufacturers MPG figures even count theses day's, they lie about pretty much everything else they do so why should their MPG be any different ?<br /> <br /> My MPG test would consist of a car being delivered to me with a full and sealed fuel tank, I would drive it for a day, then you would drive it the next day, then you would give the keys to one of your mates he would then hand them to his auntie and so on until the thing ran out of fuel.<br /> <br /> Real world testing right there.</div>
 
<div class="bbWrapper">Fuel consumption is also going to vary according to driving style and traffic conditions. Before the advent of regenerative braking one way of measuring this would be brake pad wear. Every time you brake you are loosing forward momentum initially gained by burning fuel. I would offer that by measuring/comparing newly fitted brake pad wear after say 5,000 miles that might prove a useful metric for the poorer fuel consumption experienced by some drivers. No blame involved here just a measurement!</div>
 
<div class="bbWrapper"><blockquote data-attributes="member: 683" data-quote="grober" data-source="post: 2828392" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=2828392" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-2828392">grober said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Fuel consumption is also going to vary according to driving style and traffic conditions. Before the advent of regenerative braking one way of measuring this would be brake pad wear. <b>Every time you brake you are loosing forward momentum initially gained by burning fuel.</b> I would offer that by measuring/comparing newly fitted brake pad wear after say 5,000 miles that might prove a useful metric for the poorer fuel consumption experienced by some drivers. No blame involved here just a measurement! </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote><br /> As does everyone following. <br /> This of course applies to no one as no one can fault their own driving - or they'd do something about it. If you cannot perform the downshift to first gear on the fly (eg, approaching roundabout where forward motion can be maintained) rather than having to come to a halt to select it - you shouldn't have a licence to drive a manual transmission. Auto only. There's a massive fuel and emissions saving to be had right there - and where it matters most - built up areas.</div>
 
<div class="bbWrapper"><blockquote data-attributes="member: 683" data-quote="grober" data-source="post: 2828392" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=2828392" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-2828392">grober said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Every time you brake you are loosing forward momentum initially gained by burning fuel. I would offer that by measuring/comparing newly fitted <a href="http://shop.ebay.co.uk/?_nkw=brake+pad" target="_blank" class="link link--external" rel="nofollow ugc noopener">brake pad</a> wear after say 5,000 miles that might prove a useful metric for the poorer fuel consumption experienced by some drivers </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote><br /> I've recently had the wheels off to do some rust prevention before the winter salt. The front pads have a little over 20,000 miles on them and looked good for at least another 20,000. That must be one reason why I get very good MPG. Unless you are deliberately driving in a spirited fashion, heavy braking should almost never be needed.<br /> <br /> Other than a steep hill, I can't envisage a circumstance where my manual Mercedes would need to have 1st gear selected while the car is still in motion. It's a long standing Mercedes trait that 1st is so low that the owners manual suggests starting from a standstill in 2nd when the road is flat.</div>
 
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<div class="bbWrapper"><blockquote data-attributes="member: 107513" data-quote="190" data-source="post: 2828475" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=2828475" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-2828475">190 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Other than a steep hill, I can't envisage a circumstance where my manual Mercedes would need to have 1st gear selected while the car is still in motion. It's a long standing Mercedes trait that 1st is so low that the owners manual suggests starting from a standstill in 2nd when the road is flat. </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote><br /> Not every car is a Mercedes.<br /> <br /> What I'm referring to is those that lack the confidence to maintain momentum in 2nd gear and the ability to shift to 1st on the fly. So they stop, select 1st, and by the time they have - we all miss the gap in the traffic.</div>
 
<div class="bbWrapper">The figures from the new WLTP testing are quite startling, eg E63 AMG falling from about 30mpg on the old test regime to about 23-24mpg on the new test. Arguably closer to reality though.<br /> <br /> The talk about using braking to measure fuel consumption is interesting. I agree with the hypothesis - it’s clear to me that indeed braking more often will be a good indicator of more fuel having been burned. I don’t think this is about driving style though; it’s more about the roads used. A 200 mile motorway drive will achieve better mpg than 200 miles around town with stop-start traffic. The brakes will attest to that due to the need for frequent braking in urban driving. That’s not to say that a good driver who is light on brakes gets better fuel consumption- at least not from their braking habits alone...</div>
 
<div class="bbWrapper">More emissions control + it's getting a bit tougher to simply make shit up</div>
 
<div class="bbWrapper">Which? magazine had fun slating the old NEDC test for being hugely optimistic and unrealisitic. I cannot find the Which? article now but there's a good summary of it on Wikipedia (<a href="https://en.wikipedia.org/wiki/New_European_Driving_Cycle#Test_procedure" target="_blank" class="link link--external" rel="nofollow ugc noopener">New European Driving Cycle - Wikipedia</a>):<br /> <br /> <i>&quot;The UK consumer group <a href="https://en.wikipedia.org/wiki/Which%3F" target="_blank" class="link link--external" rel="nofollow ugc noopener">Which?</a>, criticized the NEDC test procedure as being out-of-date as its most recent update was made in 1997<a href="https://en.wikipedia.org/wiki/New_European_Driving_Cycle#cite_note-10" target="_blank" class="link link--external" rel="nofollow ugc noopener">[10]</a>; before hybrid cars and stop-start technology was generally available. Which? claimed the test did not replicate real-world driving conditions and had numerous loopholes which cause the results to be unachievable in practice. It was also claimed that no official body polices the tests and the vehicle manufacturers can arbitrarily reduce their results by 4% at the end of the cycle. Weaknesses noted are: (i) that tests are not necessarily repeatable and comparable; (ii) the test-cycle does not include sustained motorway driving; (iii) test-cycles can be performed using optional economy settings which will not typically be selected by drivers; (iv) the test-cycle is performed with ancillary equipment such an air-conditioning and heated windows switched off; (v) the tests can be conducted at 2 km/h (1.2 mph) below the required speed thus using less fuel; (vi) roof-rails and passenger door-mirror can be removed for the test, to reduce <a href="https://en.wikipedia.org/wiki/Aerodynamic_drag" target="_blank" class="link link--external" rel="nofollow ugc noopener">drag</a>; (vii) tyre inflation for the test can be set above the recommended pressure values to artificially reduce <a href="https://en.wikipedia.org/wiki/Rolling_resistance" target="_blank" class="link link--external" rel="nofollow ugc noopener">rolling resistance</a>&quot;<br /> </i><br /> It's no wonder the results came out detached from driving reality. The new WLTP test is supposed to fix that.</div>
 
<div class="bbWrapper">It's very easy to just point at the vehicle OEMs and consider the whole thing to be a conspiracy on their part. <br /> <br /> When the regulations were drawn up, the test methodologies and instrumentation systems were not as advanced as they are today. In addition, the emissions being managed were much greater than those emitted by modern cars. As a result there were a number of practical considerations and tolerances built in just so that testing could be carried out in a standard way. The drive cycles ECE and EUDC were based on real conditions and some cars didn't have enough power to achieve some of the higher speed conditions.<br /> <br /> Over the years, vehicle CO and HC emissions have been very much reduced. The focus widened to include NOx emissions and then fuel economy/consumption analysis based on the emissions data. Then more interest in managing emissions CO2 (which correlates well with fuel consumption) was included. CO2 was always measured but wasn't (and still isn't) regulated as such.<br /> <br /> In the process, the manufacturers learnt how to exploit these tolerances to show their products in the best light versus their competitors. Test houses have also learnt how to give the best results to their customers, again within the tolerances allowed in the methods.<br /> <br /> Removing wing mirrors, and roof bars etc. isn't done during the emissions test. It's done when the manufacturers are determining the chassis dynamometer road-load model for the particular car. This is usually based on a series of coastdown runs carried out on a test track. When the car is operating on a dyno, some manufacturers utilise 'dyno mode' operation whereby things like ABS, power steering and sonon are disabled. ABS and stability control systems for example can react badly on the dyno.<br /> <br /> The new harmonised test cycle picks up on some of this, providing a new speed-time profile that puts more (realistic) demand on the vehicle which should mean tests that yield results that are more representative of what the vehicles would achieve/produce in normal use.</div>
 
<div class="bbWrapper"><blockquote data-attributes="member: 107513" data-quote="190" data-source="post: 2828475" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=2828475" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-2828475">190 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> I've recently had the wheels off to do some rust prevention before the winter salt. The front pads have a little over 20,000 miles on them and looked good for at least another 20,000. That must be one reason why I get very good MPG. Unless you are deliberately driving in a spirited fashion, heavy braking should almost never be needed.<br /> <br /> Other than a steep hill, I can't envisage a circumstance where my manual Mercedes would need to have 1st gear selected while the car is still in motion. It's a long standing Mercedes trait that 1st is so low that the owners manual suggests starting from a standstill in 2nd when the road is flat. </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Many auto box MB's pull away in second unless S is selected <img src="/styles/mbclub/smilies/thumb.gif" class="smilie" loading="lazy" alt=":thumb:" title="Thumb :thumb:" data-shortname=":thumb:" /></div>
 
<div class="bbWrapper"><blockquote data-attributes="member: 126185" data-quote="Petrol Pete" data-source="post: 2828794" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=2828794" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-2828794">Petrol Pete said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Many auto box MB's pull away in second unless S is selected <img src="/styles/mbclub/smilies/thumb.gif" class="smilie" loading="lazy" alt=":thumb:" title="Thumb :thumb:" data-shortname=":thumb:" /> </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote><br /> I owned a 190e auto for 21 years and could count on one hand with fingers to spare how many times 1st was engaged This obsession with a very low first gear disadvantages MB against other cars as it effectively reduces the number of gears available in normal use. Not a problem these days but it effectively made my 190e a 3 speed box for 99.999 % of the time.</div>
 
<div class="bbWrapper"><blockquote data-attributes="member: 107513" data-quote="190" data-source="post: 2828800" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=2828800" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-2828800">190 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> I owned a 190e auto for 21 years and could count on one hand with fingers to spare how many times 1st was engaged This obsession with a very low first gear disadvantages MB against other cars as it effectively reduces the number of gears available in normal use. Not a problem these days but it effectively made my 190e a 3 speed box for 99.999 % of the time. </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Is is because Stuttgart is close to the mountains and some severe gradients...?</div>
 
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