Originally Posted by
happygu
TD, you have to remember that the larger tyre size will give you more distance for every rotation of the tyre, so in fact fuel consumption may not end up more at all.
In the OP, the tyre sizes talked about were 265 and 285
In a 265/70R17 tyre you may have a rolling diameter of around 804mm ( depending on brand, of course )
For the same brand tyre in a 285/70R17, you will have a rolling diameter of 832mm ....
What this means, is for every time your engine is running, for the same RPM you were doing on the 265 - on the 285 you will go 28mm further ..... that is why bigger tyres suck more energy out of the engine because the extra power required to turn the tyre a complete rotation, it means the car has to travel further.
This means you are going 3.5% further ( than your odometer is reading and what you were on the smaller tyres ), and if your fuel consumption has gone up less than that, you are actually in front ....
My fuel consumption probably went up slightly, at around 4 - 5%, so for the minimal extra fuel use, I get around 20mm more diff clearance with the bigger tyres.
My opinion is to go for the larger tyres, but for years and years, I stuck with original size tyres and went all over place.