Tire pressure & fuel economy

2009 Triton 4WD 3.2 auto with ECU re-map, Dunedin to Alexandra nearly 11 l/100km on the trip computer read-out. Thought that was a bit thirsty for open road running as engine was purring nicely, scratched my head and read some threads in this forum, started wondering about tire pressures. Yokohama Geolandar G015 265/70/16. Checked and found all 4 about 29 psi, so blew ‘em all up to 36. Return trip Alex-Dunedin, the trip computer read 9.0 l/100km. Dunedin home is not much lower elevation than Alexandra, so not an uphill/downhill issue. Point well proved re tire pressure – although doubtless no surprise to some of you.

the harder they are ,the cheaper to run.......same as skinny tyres versus fatties.
get on your mountain bike with grippies,then try it with road slicks...HUGE difference.

Would the fact that you are running 65/70/16 might have something to do with it as well?
My 2010 Triton factory tyres were 245/65/17 - you are looking at a difference of 4% diameter and 15 revolutions per km (how accurate is the trip computer).

run them on the road at 40psi

There's more to it than "more pressure = less fuel burned" (unfortunately).

Lower pressure allows more contact with the ground (air down for sand etc) but places more load on the steering components and the engine to drive the thing forwards - also increases tyre wear towards the edges of the tyres. Higher pressure increases wear on the center of the tyre, and increases wear on suspension components, ball joints, wheel bearings and diffs and axle components. Running at higher weights needs more pressure, as does towing to stiffen the carcass of the tyre but can lead to worse handling in wet conditions (breaking free).

The trick is finding the trade off 'sweet spot' where you get the best run out of the tyres vs wear handling and fuel economy - and when you work out where that is check every week or two to keep them there. For standard utes on HT's and AT's - I would start in the 34-36 range and try up or down until you find where you and the ute likes it, and when you find that spot it's amazing how you can tell as soon as your tyres drop a psi or two in ride comfort and road handling.

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Originally Posted by Basenjiboy

Would the fact that you are running 65/70/16 might have something to do with it as well?
My 2010 Triton factory tyres were 245/65/17 - you are looking at a difference of 4% diameter and 15 revolutions per km (how accurate is the trip computer).

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Dash odometer matches closely with GPS speed, not sure what that means re trip computer fuel consumption accuracy which obviously also depends on reported fuel used. Anyway the point is, it’s indicating a gain of about in 20% fuel economy with tires blown up from 29 to 36.

Yep would stand to reason with what I've experienced with utes on average - although it's not a magic "36psi" golden bullet. Some vehicles might find better figures with more pressure without any unwelcome effects like lack of grip in the wet, cars might be better with 32. EV's are interesting, some are needing 40+ psi for best running and least tyre wear (now tell me again how good they are haha).

As @No.3 said you have to find the sweet spot. Only good way to check FE perfectly is tank full to tank full and then manually calculate or download som app. What I have seen trip computers usually exaggerate the numbers. Apart from that invest in a TPMS (Tyre pressure monitoring system) if your vehicle doesn't have it. It was pretty cheap from Aliexpress and likes. Helps keeping eye on each tyre.

just checked mine 30psi on Wildpeak AT3W's was wondering why the challenger was using abit more fuel lately up to 38 all-round , forgot to up the pressure after getting back from hunting in Taupo 3 weeks ago :D