defenders....check your tyre size (-:

[Dean Lofthouse]

Ive been running on 225/75R16 for about 4 years which was the size fitted to mine when I bought it.

 

The last set of tyres I fitted before these were 225/85R16.

 

The difference between the two is the wall height, in other words one tyre is much taller than the other, by roughly 3".

 

So I did some calculations for the 20k miles that I have done on the 225/75R16's which have a smaller circumference than the 85's.

 

Circumference

75 = 2.23m

85 = 2.48m

 

Revolutions per mile

75 = 721

85 = 648

 

difference per mile = 73 revs

 

If I have my calculations right, that means that over the 20k mile i have done on the smaller tyres, they have cost me 93.75 gallon of fuel more.

 

I also would have travelled a further 2250 mile

[Dean Lofthouse]

BTW... I was bored

[Gray git]

Better service a bit more regularly but that's quite a difference.

You must have been very bored!

[nepia]

I'm not that bored but how far out would the speed reading have been?

[C.J]

It's not as bad as you think.

 

The theoretical circumference of your 225/75R16 is 2.34 meters.

 

So you would only have done an extra 1210 miles.

[Justme]

The change in the gearing would have an effect on the reaction to the throttle position. A faster running engine under a lower load uses less fuel than a slower one under a higher load. The tyre difference is unlikely to have made as much of a difference as you think.

 

Also the 10% difference in side wall height would not equal 3".

 

A 225 / 75 has a side wall of 168.75mm

The 225 / 85 has a side wall of 191.25mm

 

Thats just 22.5mm per side wall.

 

Thats 45mm or less than 2" total height difference.

Edited June 3, 2015 by Justme

[C.J]

22.5mm on top and 22.5 mm on the bottom so 45mm extra diameter.

[Dean Lofthouse]

I stood them side by side and measured their exact heights in inches.

 

75 =28"

85 =31"

[mendiplogs]

I stood them side by side and measured their exact heights in inches.

 

75 =28"

85 =31"

 

Hi DEAN I run 235x85x16 BFG MUDS mate thanks jonn

[Dean Lofthouse]

Hi DEAN I run 235x85x16 BFG MUDS mate thanks jonn

 

 

That's where I cocked up

 

It's 235/85 I used not 225/85