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slightly bigger tyres, heavier fuel consumption

 
 
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Jim1064
Just got MTs


Joined: 22 Feb 2009
Odometer: 264
Location: Now living in Kent



PostPosted: Sat Jan 31, 2015 8:22 pm    Post subject: slightly bigger tyres, heavier fuel consumption Reply with quote

Question for Mr Tyre...

I replaced the 195/65R15 steel rims/tyres on my Renault Kangoo dci 110 van, with 215/50R17 tyres on alloys.

Result: fuel consumption drops from low 50s to mid 40s mpg.

I didn't expect that I must say. The old tyres ran at 2.5 bar all round, I have the new ones at the same pressure.

Can such a small change in size have such a big effect on fuel consumption?

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Xpajun
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Joined: 22 Sep 2008
Odometer: 3239



1988 Mitsubishi Shogun

PostPosted: Sun Feb 01, 2015 8:44 am    Post subject: Reply with quote

The bigger tyres will have also altered your speedo - you'll be doing less miles for the same distance...


for a 10% difference instead of doing 50 miles you'll only be doing 45 miles
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Jim1064
Just got MTs


Joined: 22 Feb 2009
Odometer: 264
Location: Now living in Kent



PostPosted: Sun Feb 01, 2015 9:22 am    Post subject: Reply with quote

The difference in diameter is only 2%
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cynic-al
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1989 Suzuki SJ

PostPosted: Sun Feb 01, 2015 9:59 am    Post subject: Reply with quote

I lost 3 mpg going size for size highway tread to all terrain. You've gone 10 percent wider so more resistance
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Mr Tyre
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Joined: 17 Jun 2002
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Location: Darlington Co Durham



PostPosted: Sun Feb 01, 2015 1:58 pm    Post subject: Reply with quote

I would expect some difference between the 2 sizes.As you say your speedo will read slow (1.9-2.0%).The difference in sectional width and overall diameter are a likely reason for the extra fuel usage, even though the differences don't seem to be that much.The difference in circumference between the two (the 215/50 is larger) won't help either.
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Jim1064
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Joined: 22 Feb 2009
Odometer: 264
Location: Now living in Kent



PostPosted: Sun Feb 01, 2015 10:55 pm    Post subject: Reply with quote

Thank you Mr Tyre. In your opinion, should I increase the tyre pressure, or stay the same (2.5 bar on all 4)?
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Mr Tyre
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Joined: 17 Jun 2002
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Location: Darlington Co Durham



PostPosted: Mon Feb 02, 2015 12:12 am    Post subject: Reply with quote

I would leave them as they are and see how they wear, if it looks like the centre of the tyre is wearing before the edges then lower all 4 to 2.3 bar, you may even find that if you don't carry much weight in the rear then drop the rears to 2.1 bar.
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