Kia Rio - Impact of Air Con and Tyre Width on your MPG

Honest John Back Room » Motoring discussion
What is life like with your car? Let us know and win £500 in John Lewis vouchers | No thanks
View Threaded
Fri 10 Jan 2014 00:19
Kia Rio - Impact of Air Con and Tyre Width on your MPG - Firmbutfair

My observations : Re various speculations on the impact, of using your air con, on fuel consumption or choosing wider (and therefore lower profile) tyres - most modern cars, even superminis, have air con either as standard or as an option. Clearly the entry level a/c sytems fitted to smaller EU cars do not have powerful compressors so the added 'burden' on the engine performance is not enormous and the a/c simply offers 'best efforts' in the spring and summer and usually very effective periodic 'demisting' in the autumn and winter. However some data are available e.g. see the entries (see link below) for the Kia Rio 1.1 litre CRDI 5dr manual in three columns - clearly showing a significant increase in fuel consummption when aircon is added (i.e. when going from Grade 1 to Grade 1 Air ISG or VR7) taking the EU Standard Test Procedure 'combined' figure from 88.3 mpg to 78.5 mpg I.E. a 12.5 % increase in consumption from 3.2 to 3.6 litres per 100Km - all running on 185/65 R15 tyres. Additionally when the same vehicle with air con is shod with wider 195/55 R16 tyres as in the Grade 2 model, there is a further degradation from 78.5 mpg to 74.3 mpg. I.E. a further 5.6 % increase in fuel consumption from 3.6 to 3.8 litres per 100Km.

www.kia.co.uk/new-cars/range/compact-cars/new-rio/...h

As always, real world fuel consumption is generally higher than the EU Standard Test figures but they give you some idea of the probable percentage impact of your choices on whatever your own real world figures are.

Other superminis are available - of course !!

Edited by Firmbutfair on 10/01/2014 at 00:25

Reply | Report as offensive | Link
Fri 10 Jan 2014 08:23
Kia Rio - Impact of Air Con and Tyre Width on your MPG - RT

The EC test procedure is done with aircon switched off - so apart from the effect of the marginally extra weight the inclusion of aircon makes virtually no difference to the EC test results.

Reply | Report as offensive | Link
Fri 10 Jan 2014 08:56
Kia Rio - Impact of Air Con and Tyre Width on your MPG - daveyK_UK

Im not sure what Mark of Rio you are refering to.

The mark 1 was respectable on fuel

The mark 2 in 1.4 petrol form was renowned for being awful on the fuel, averaging nearer 26/27mpg.

I havent tried out the mark 3, presume it must be a big improvement as the Rio is no longer made or sold as a budget world car.

Despite the bad mpg, the Rio has always been reliable.

Edited by daveyK_UK on 10/01/2014 at 08:56

Reply | Report as offensive | Link
Fri 10 Jan 2014 10:36
Kia Rio - Impact of Air Con and Tyre Width on your MPG - Firmbutfair

Im not sure what Mark of Rio you are refering to.

The mark 1 was respectable on fuel

The mark 2 in 1.4 petrol form was renowned for being awful on the fuel, averaging nearer 26/27mpg.

I havent tried out the mark 3, presume it must be a big improvement as the Rio is no longer made or sold as a budget world car.

Despite the bad mpg, the Rio has always been reliable.

In fact we are comparing the published data for various trim levels i.e. Grades 1, 1 Air, VR7, 2, etc as recently published on the Kia website for their new 5 door Kia Rio cars - not going back in time looking at previous models. I can say that there seems to be a very strong correlation between vehicle kerb weight and fuel consumption - just as one would expect from P = ma etc. Therefore the Kia Cee'd uses much more fuel than the Kia Rio and so on....

Reply | Report as offensive | Link
Fri 10 Jan 2014 09:35
Kia Rio - Impact of Air Con and Tyre Width on your MPG - Firmbutfair

The EC test procedure is done with aircon switched off - so apart from the effect of the marginally extra weight the inclusion of aircon makes virtually no difference to the EC test results.

Thanks RT, I had forgotten that, so the 12.5% increase in fuel consumption between the 1 and the 1 Air/VR7 models is not solely due to having a/c.

In fact Kia do reveal differences between the Rio 1 and the 1 Air/VR7 as in table below:

Kia Rio 1.1 CRDI Manual '1' - vs - Kia Rio 1.1 CRDI Manual ISG '1 Air' or 'VR7'

185/65 R15 on steel rims - vs - 185/65 R15 on alloy rims

Low rolling resistance tyres - vs - Standard tyres (with higher rolling resistance)

No Air Con - vs - Static burden of a/c compressor on engine

No a/c compressor - vs - Weight of a/c compressor and its accessories.

No electric rear windows etc - vs - Weight of electric motors for rear windows and any other accessories in the VR7 package.

Clearly this is all getting a bit silly, since we all know that manufacturers will do everything they can to achive that class beating 85 gm CO2 per km during the EU Test by using low rolling resistance 'energy' tyres pumped up rock hard, thin 0W-30 engine oil, fully charged battery, well 'backed off' brake calipers etc

Sadly, in real world driving, the actual fuel consumption will be much higher than the published figures - so switching the a/c on will not make much difference PLUS we NEVER take over 30 seconds to accelerate and brake from one speed to the next as the EU Test specifies etc etc !

Both the Honest John Real MPG and the What Car Magazine True MPG figures tell the real story fairly well. What next - a discussion on hyper mile economy techniques ?


Edited by Firmbutfair on 10/01/2014 at 09:41

Reply | Report as offensive | Link
Fri 10 Jan 2014 10:03
Kia Rio - Impact of Air Con and Tyre Width on your MPG - RT

"thin" 0W-30 oil is fine - I use exactly that all the time - my car is specified for 5W-30, many modern engines are, so I use 0W-30 to get quicker protection when the engine is cold.

Reply | Report as offensive | Link
Fri 10 Jan 2014 10:22
Kia Rio - Impact of Air Con and Tyre Width on your MPG - Firmbutfair

"thin" 0W-30 oil is fine - I use exactly that all the time - my car is specified for 5W-30, many modern engines are, so I use 0W-30 to get quicker protection when the engine is cold.

I agree with you RT, I am glad that the days of using Duckhams 'Q' 20W - 50 in my old Austin A35 van (to reduce oil consumption etc) are gone for good. I rebuilt the engine with new main crankshaft bearings, new hepolite 'oil control' piston rings, new exhaust and inlet valves ground in by hand and it still used 1 pint of Duckhams every 1500 miles but NOWADAYS - I enjoy driving my fantastic modern car with its 16 valve, DOHC 4 cylinder all aluminium engine using the same 5W -30 oil all year round (about 8000 miles per annum and oil still 'honey gold' 2000 miles after each oil change). Happy Days !

Edited by Firmbutfair on 10/01/2014 at 10:25

Reply | Report as offensive | Link
Fri 10 Jan 2014 15:11
Kia Rio - Impact of Air Con and Tyre Width on your MPG - skidpan

Clearly this is all getting a bit silly, since we all know that manufacturers will do everything they can to achive that class beating 85 gm CO2 per km during the EU Test by using low rolling resistance 'energy' tyres pumped up rock hard, thin 0W-30 engine oil, fully charged battery, well 'backed off' brake calipers etc

Read most of this before.The cars presented for testing have to be standard but if one manufacturer ups the tyre pressure and changes oil grade then they all will do it, all that means is at least the results will still be comparableand we will pay less VED every year.

well 'backed off' brake calipers etc

How does that work then, brake calipers have never been adjustable. They take up the wear automatically as the pad wears. You could push the pistons back in to ensure there was no pad to disk contact but it would soon be back to normal once the test was underway.

Reply | Report as offensive | Link
Wed 15 Jan 2014 01:23
Kia Rio - Impact of Air Con and Tyre Width on your MPG - Firmbutfair

Clearly this is all getting a bit silly, since we all know that manufacturers will do everything they can to achive that class beating 85 gm CO2 per km during the EU Test by using low rolling resistance 'energy' tyres pumped up rock hard, thin 0W-30 engine oil, fully charged battery, well 'backed off' brake calipers etc

Read most of this before.The cars presented for testing have to be standard but if one manufacturer ups the tyre pressure and changes oil grade then they all will do it, all that means is at least the results will still be comparableand we will pay less VED every year.

well 'backed off' brake calipers etc

How does that work then, brake calipers have never been adjustable. They take up the wear automatically as the pad wears. You could push the pistons back in to ensure there was no pad to disk contact but it would soon be back to normal once the test was underway.

Yes you are right skidpan, but I believe that the 'backed off brake calipers' and 'taped up body panels' may be applied immediately before the 'coast down' test that is used to determine particular values for rolling resistance and aerodynamic drag vs road speed for input into the rolling road simulator before carrying out the urban and extra urban exhaust CO2 measurements. The result of this special preparation is that the very lowest possible values will be recorded during the coast down test such that the smallest possible additional resitance is programmed into the rolling road for the urban and extra urban tests with their closely controlled periods of very gentle acceleration, cruising, very gentle braking and short periods with the rollers stationary.

Reply | Report as offensive | Link
Wed 15 Jan 2014 09:21
Kia Rio - Impact of Air Con and Tyre Width on your MPG - skidpan

'taped up body panels'

How will taped up body panels help, the test is carried out on a rolling road in a lab!!!!!

The bottom line is the figures are only there to calculate VED and company car tax. They are published to help people when they are buying cars but all the small print tells you the figures are not achiveable and should only be used for comparrions. Use them like that and you will be happy.

If the figures reflected exactly the average driver achived our VED etc would increase. take my Seat Leon, official combined is 54 mpg, I get 45 mpg (true calculated) which is excellent and better than I expected. The Co2 figure is 119 thus I pay £30 a year VED. If the VED was based on 45 mpg the Co2 would be in the mid 140's and my annual VED would be over £100 extra.

So keep the system as it is a just be realistic when you buy a car. Anybody who belioves they will get the official figures must be liviing on a different planet, the HJ Real MPG proves that.

Reply | Report as offensive | Link
Wed 15 Jan 2014 13:27
Kia Rio - Impact of Air Con and Tyre Width on your MPG - RT

'taped up body panels'

How will taped up body panels help, the test is carried out on a rolling road in a lab!!!!!.

All cars have to undergo a "coast-down" outdoor test to establish basic parameters for the rolling road tests.

Reply | Report as offensive | Link
Wed 15 Jan 2014 13:44
Kia Rio - Impact of Air Con and Tyre Width on your MPG - skidpan

All cars have to undergo a "coast-down" outdoor test to establish basic parameters for the rolling road tests.

Where is that is the rules for the EU test cycle. I have read it many times and it clearly states it takes place in a lab. No mention is made of the proceedure for an outdoor coast down test.

Reply | Report as offensive | Link
Wed 15 Jan 2014 13:58
Kia Rio - Impact of Air Con and Tyre Width on your MPG - RT

They can't "simply" do a rolling road test - they need to know what the aerodynamic drag is.

Reply | Report as offensive | Link
Wed 15 Jan 2014 14:04
Kia Rio - Impact of Air Con and Tyre Width on your MPG - skidpan

They can't "simply" do a rolling road test - they need to know what the aerodynamic drag is.

But where does it give the specifications for this aerodynamic test. If the test actually exists there must be a specification, if there isn't all manufacturers would make up a simple test to their advantage and then the test would be an even bigger joke.

The proceedure for the actual lab part is clearly set out, as I said there must also be a specification for the aeordynamic test.

Reply | Report as offensive | Link
Fri 17 Jan 2014 09:18
Kia Rio - Impact of Air Con and Tyre Width on your MPG - Firmbutfair

They can't "simply" do a rolling road test - they need to know what the aerodynamic drag is.

But where does it give the specifications for this aerodynamic test. If the test actually exists there must be a specification, if there isn't all manufacturers would make up a simple test to their advantage and then the test would be an even bigger joke.

The proceedure for the actual lab part is clearly set out, as I said there must also be a specification for the aeordynamic test.

I agree 'skidpan' - in fact the EU test has several obvious shortcomings and - I believe it is currently under review with the objective of revision towards a much more 'realistic' set of test conditions including realistic rates of acceleration and braking, not the 'pedestrian' envelopes in the current EU Test - however, the 'coast down' test is certainly part of the tests carried out in the USA.

Reply | Report as offensive | Link
Wed 15 Jan 2014 14:20
Kia Rio - Impact of Air Con and Tyre Width on your MPG - artill

I think to even use the official figures for 'comparison' would be very misleading. Cars with large engines often exceed their EU test figures by some margin, whereas cars with small engines miss by a large margin.

We have all read the awful real world figures of small turbos. We see much less often how good the old fashioned large engines were.

My own experience is around 30mpg from a 3.0 406 compared to the 26 quoted. 29 mpg from an S2000, pretty much 100% of the test figures. 24 mpg from a Monaro, the EU test suggests 18 mpg. A Peugeot 107 did 49 mpg, the EU claim is 62.

So my experience suggests you will get somewhere between 80% and 130% of the EU figures. I am sure there are cars much further adrift from these too. But even if these were extremes they are still far too far apart to make a 'comparison'.

Reply | Report as offensive | Link
Fri 17 Jan 2014 09:23
Kia Rio - Impact of Air Con and Tyre Width on your MPG - Firmbutfair

I think to even use the official figures for 'comparison' would be very misleading. Cars with large engines often exceed their EU test figures by some margin, whereas cars with small engines miss by a large margin.

We have all read the awful real world figures of small turbos. We see much less often how good the old fashioned large engines were.

My own experience is around 30mpg from a 3.0 406 compared to the 26 quoted. 29 mpg from an S2000, pretty much 100% of the test figures. 24 mpg from a Monaro, the EU test suggests 18 mpg. A Peugeot 107 did 49 mpg, the EU claim is 62.

So my experience suggests you will get somewhere between 80% and 130% of the EU figures. I am sure there are cars much further adrift from these too. But even if these were extremes they are still far too far apart to make a 'comparison'.

Your figures are very interesting 'artill' I too have been able to match the official combined figure for my car, in mixed brisk but not agressive driving without behaving badly or inconsiderately, and I am driving a mere 1000 kg, 1.25 litre NA supermini, carefully 'broken in' and now with 18,000 miles from new on the clock.

Reply | Report as offensive | Link

Looking for a garage you can trust? Honest John's Good Garage Guide has thousands of reader recommended garages, plus how-to guides and tips on servicing.

The Good Garage Guide