GU Patrol 285x75x16 tyre legality and engineering

Hi Bentaxle

How is your gearing now, it must have been affected by taller tyres. I have 3.0Ltr Diesel, wife 4 kids and fully loaded POD trailer and can easily cruise all day up and down hills in 5th gear without laboring, surely thats not possible with taller tyres and would then need to drop back to 4th gear at times? This will then affect fuel economy also, I currently get 9.5km to 10km per 1 ltr consistently to and from work 60-80km p/hr stop start, over 10km on open road w/out trailer.

Cheers Rob

I think its agreed that going to larger tyres will increase your fuel consumption but maybe not as much as you expect.

Yes your acceleration will be slower, you will need to drop back a gear earlier, the vehicle will be slightly higher resulting in more drag, but when crusing, the rpm of your engine should be closer to its most efficient speed. i.e. the point of maximum torque. Most cars even in top gear cruise above that rpm @ 100km/h so a larger diameter tyre is like having a higher 5th (or 6th) gear.

On a flat level road, with good pressure in the tyres, a reasonable fuel consumption can be acheived. There is probably more difference between the final drive ratio of a manual than of an auto. An auto generally has a much higher top gear resulting in a lower rpm @ 100km/h.

Also when making comparisons, users are often going from road tyres to larger AT or MT's. A larger road tyre would give a better fuel consumption difference indication, which has probably never really been documented.

I haven't noticed a dramatic increase in fuel consumption, the increase is very minimal. I have found that the acceleration is a slower, but at highway speed - 110km/h I fin d that the engine revs have decreased by 100rpm. As far as an increase in overall fuel consumption I haven't noticed any real change, when we head out offroad the old girl is pretty well loaded up, food water camping gear etc. and since I started to use the 285/75r16 tyres most of our offroad work has been in remote desert areas reuiring a lot of 4wd both high and low range and consequently fuel consumption had increased, my last remote trip to Carnarvon Ranges fuel consumption ranged between 4.2- 7.9km/L and was carrying at times as much as 3 Jerry cans of fuel and 100L of water pus usual gear

Cheers
Mike