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Jmac



Member Since: 17 Feb 2011
Location: South
Posts: 125

United Kingdom 2007 Range Rover Sport TDV8 HSE Stornoway Grey
Amazing decrease in fuel consumption!

This is very odd.. but brilliant! Since fitting my winter tyres which are on 19 inch wheels and a bit narrower than my summer tyres (on 20 inch rims), my fuel consumption has improved by almost 25%! They type of driving has been exactly the same..

I always have the 'fuel range' information displayed on the dashboard and also always re-set the trip meter whenever I fill up with fuel. Throughout the summer I always end up with around 400 miles when combining the two numbers - i.e. 135 miles range + 265 miles on the trip but since fitting the narrower tyres, the combined total is 490 miles!

Surely this can't just be down to the tyres? - I understand that the narrower tyre will offer less rolling resistance but surely it can't be affecting things this much?

Is there anything else I should be considering or am I just lucky?

Cheers,
J

P.S. My summer tyres (conti's) were all pretty worn out - does this have an effect on resistance? They were properly inflated though..

Post #320655 Thu Nov 10 2011 1:11pm
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gilford



Member Since: 07 Jan 2010
Location: Anglesey
Posts: 542

United Kingdom 2008 Range Rover Sport TDV8 HST Java Black

I think you mess up your MPG computer when you change wheel sizes?

Post #320681 Thu Nov 10 2011 4:11pm
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Jmac



Member Since: 17 Feb 2011
Location: South
Posts: 125

United Kingdom 2007 Range Rover Sport TDV8 HSE Stornoway Grey

gilford wrote:
I think you mess up your MPG computer when you change wheel sizes?


I totally agree that new tyres will give different readings when compared to worn out ones due to a different rolling radius but 20% Shocked ??? surely not... My speedometer seems to be the same - i definitely dont think im going 20% faster or slower!

Also, as the tyres are LR specification sizes for the car, I would have thought the car should be pretty accurate for both sizes..

cheers,
J

Post #320682 Thu Nov 10 2011 4:30pm
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JonnyDangerous



Member Since: 09 Nov 2009
Location: Reading
Posts: 57

United Kingdom 2010 Range Rover Sport 3.0 TDV6 HSE Stornoway Grey

hmmm - i always thoughts (maybe incorrectly) that the actual circumference of the wheel is the same if its a 19" or 20" rim as the inch difference on the 19" rim is made up by a tyre that is less low profile.

BTW - just about to make the exact wheel change on mine so interested in the outcome of this thread.

Post #320687 Thu Nov 10 2011 5:21pm
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Jmac



Member Since: 17 Feb 2011
Location: South
Posts: 125

United Kingdom 2007 Range Rover Sport TDV8 HSE Stornoway Grey

JonnyDangerous wrote:
hmmm - i always thoughts (maybe incorrectly) that the actual circumference of the wheel is the same if its a 19" or 20" rim as the inch difference on the 19" rim is made up by a tyre that is less low profile.

BTW - just about to make the exact wheel change on mine so interested in the outcome of this thread.



I thought the same and although there may be a difference it shouldn't throw out the numbers that much surely!

will be interested to hear if your numbers change too.. I'm using the vredestein wintracks (sp?)

Cheers,
J

Post #320688 Thu Nov 10 2011 5:25pm
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JonnyDangerous



Member Since: 09 Nov 2009
Location: Reading
Posts: 57

United Kingdom 2010 Range Rover Sport 3.0 TDV6 HSE Stornoway Grey

we can compare notes as that's the tyre i'm putting on too. Just need to wait for it to get a bit colder.

Post #320689 Thu Nov 10 2011 5:27pm
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npinks
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Member Since: 26 Nov 2007
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United Kingdom 

There is a tyre change button on my satnav, which resets it to new tyres thought is is the fl2

Post #320690 Thu Nov 10 2011 6:15pm
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Jmac



Member Since: 17 Feb 2011
Location: South
Posts: 125

United Kingdom 2007 Range Rover Sport TDV8 HSE Stornoway Grey

npinks wrote:
There is a tyre change button on my satnav, which resets it to new tyres thought is is the fl2


Hmmm. I do remember something about that. I will investigate in the morning. Cheers, j

Post #320697 Thu Nov 10 2011 7:15pm
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awd man



Member Since: 30 Nov 2010
Location: Malmesbury
Posts: 3355

2007 Range Rover Sport TDV8 HSE Java Black

iirc 20" rims read slightly quick on the speedo.

that coupled with new rubber on 19" would give quite a mpg increase I'd have thought RRS gone
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Post #320753 Fri Nov 11 2011 10:30am
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Beancounter_74



Member Since: 11 Oct 2011
Location: Down here now...
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England 

Interesting, mines got 20's as standard, so I would assume they have resolved this Confused
I'll check next time I go through one of those 'speed monitoring flash up speed safety sign' things Rolling Eyes

A near 25% change due to wheel size, does seem quite excessive though even if the above is true though. ON THE WAY: BMW F21 M140i
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Post #320758 Fri Nov 11 2011 10:43am
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awd man



Member Since: 30 Nov 2010
Location: Malmesbury
Posts: 3355

2007 Range Rover Sport TDV8 HSE Java Black

Sorry I should have clarified...

There is an adjustment in the gearbox module to correct the slightly smaller overall diameter of the 20's.

I didn't notice we were talking about a TDV8 which "should" come out the factory with the 20's as standard. RRS gone
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Post #320763 Fri Nov 11 2011 11:17am
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Jmac



Member Since: 17 Feb 2011
Location: South
Posts: 125

United Kingdom 2007 Range Rover Sport TDV8 HSE Stornoway Grey

awd man wrote:
Sorry I should have clarified...

There is an adjustment in the gearbox module to correct the slightly smaller overall diameter of the 20's.

I didn't notice we were talking about a TDV8 which "should" come out the factory with the 20's as standard.


My car had the 20s as std so that might be an explanation but the difference does seem massive..

Post #320787 Fri Nov 11 2011 1:18pm
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awd man



Member Since: 30 Nov 2010
Location: Malmesbury
Posts: 3355

2007 Range Rover Sport TDV8 HSE Java Black

so are we talking 20mpg to 24?

or 22 to 26

tbh, my D3 jumped from 23 to 26 just by having the gearbox module corrected (I was running 20's and the module was set to 18's)

That coupled with 4mm of extra tread and a slightly longer circumference could add 4mpg to the computer reading (not REAL mpg BTW, just what the car thinks it's getting, and hopefully slightly more accurate.. Whistle ) RRS gone
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Post #320803 Fri Nov 11 2011 2:34pm
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Jmac



Member Since: 17 Feb 2011
Location: South
Posts: 125

United Kingdom 2007 Range Rover Sport TDV8 HSE Stornoway Grey

awd man wrote:
so are we talking 20mpg to 24?

or 22 to 26

tbh, my D3 jumped from 23 to 26 just by having the gearbox module corrected (I was running 20's and the module was set to 18's)

That coupled with 4mm of extra tread and a slightly longer circumference could add 4mpg to the computer reading (not REAL mpg BTW, just what the car thinks it's getting, and hopefully slightly more accurate.. Whistle )


I don't look at the MPG reading as I know it's optimistic - I just add the two numbers from the range to go and distance travelled since I filled up. All I can say is that it used to add up to 400 miles and now it adds up to 490. If we assume the tank holds 84 (18.5 gallons) litres then that means a jump from 21.6mpg to 26.5mpg.. Seems like an awful lot to me for a very small change in diameter...

Post #320805 Fri Nov 11 2011 2:40pm
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awd man



Member Since: 30 Nov 2010
Location: Malmesbury
Posts: 3355

2007 Range Rover Sport TDV8 HSE Java Black

I'd not take too much notice of range either Mr. Green ..based on real time mpg that the module is telling the ecu... Whistle

Best and most accurate (if you really want to see the true effect) is to run it till the light comes on... put 60 litres in it and see how far you get till you get the light again.

then put your summers back on and repeat Laughing RRS gone
Audi SQ5...Gone Audi Q7 S-Line 240 3.0TDI Gone
Audi A6 Allroad Sport 270 3.0TDI

Post #320808 Fri Nov 11 2011 2:48pm
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