Outer Limits 4x4 Board

chimpboy wrote:Hmm, I dunno.

Maybe you can clarify something for me actually, as I'm not thinking clearly tonight.

Heavy wheels/tyres are going to chew more fuel on take-off for obvious reasons. But does it take more energy to go from 0-5km/h than it does to go from (say) 90 to 95km/h?

If it's the same, then I think heavy tyres could have an effect on fuel economy in all kinds of driving.

On the other hand I feel it might be different but I can't see why.

Either way I think it is a bigger issue than gearing.

The absolute worst case for rolling weight is it's worth twice as much static weight.
So an extra 10kg on your tyres is similar to 20kg on the vehicle.

If you take 100kg off a 2.3 ton vehicle, how much is your economy going to improve?
I'd wager an almost unmeasureable amount. It's not 5% of the total weight and weight is still a minor player, well behind aerodynamics.

If you'd like a quick lesson in the difference in rolling resistance of different tread patterns and pressures, try riding a mountainbike with a range of tyres.
You'll find that weight only slows acceleration and means nothing overall on a trip. But tread pattern and pressure can take almost 50% off your cruising speed.

KE70, you've missed the point about efficiency and gearing.

I cant relate directly to the Patrol, but in my Discovery2 TD5 I changed from 29" 235/70-16 Michelin 4X4XPC (HT/AT) to 33" 255/85-16 Cooper ST tyres (Open AT).

My findings were that on the hwy they used about 1l/100km less fuel and around town they used about 1l/100km more. When I changed the ST's for muds, Simex etc the economy was all down hill and it didn't matter what I did, the economy wasn't coming back. Later I regeared the diffs back to correct the 33's back to standard and the economy then became a lot more stable around town and on highway. However, my opinion is that tread pattern is the most influential aspect for overall economy and gearing affects the town/hwy economy balance. I tend to think this is partly why the keep throwing more gears into gearboxs and getting more powerful engines that are consuming less fuel also.

KiwiBacon wrote:If you'd like a quick lesson in the difference in rolling resistance of different tread patterns and pressures, try riding a mountainbike with a range of tyres.

Now THAT is a pisser of an example - something i can vouch for 100%.
I'm not exactly the fittest or strongest person in the world, however going from an agressive offroad tyre on my MTB over to a skinnier, road tread tyre made a MASSIVE difference. It was amazing. Its probably also the reason why some smart cookie invented the dual tread tyre (slick centre, knobby sides).

KiwiBacon wrote:

chimpboy wrote:Hmm, I dunno.

Maybe you can clarify something for me actually, as I'm not thinking clearly tonight.

Heavy wheels/tyres are going to chew more fuel on take-off for obvious reasons. But does it take more energy to go from 0-5km/h than it does to go from (say) 90 to 95km/h?

If it's the same, then I think heavy tyres could have an effect on fuel economy in all kinds of driving.

On the other hand I feel it might be different but I can't see why.

Either way I think it is a bigger issue than gearing.

The absolute worst case for rolling weight is it's worth twice as much static weight.
So an extra 10kg on your tyres is similar to 20kg on the vehicle.

If you take 100kg off a 2.3 ton vehicle, how much is your economy going to improve?
I'd wager an almost unmeasureable amount. It's not 5% of the total weight and weight is still a minor player, well behind aerodynamics.

If you'd like a quick lesson in the difference in rolling resistance of different tread patterns and pressures, try riding a mountainbike with a range of tyres.
You'll find that weight only slows acceleration and means nothing overall on a trip. But tread pattern and pressure can take almost 50% off your cruising speed.

KE70, you've missed the point about efficiency and gearing.

I think you've convinced me. In fact thinking back, a lot of fuel must have gone just to produce all that fricking road noise from the muddies.