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2018 Subaru Outback 3.6R, 2013 Porsche Boxster S
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Discussion Starter #1
Hey folks, I recently switched the stock wheel/tire combo for my 2018 Outback 3.6R to Method MR502 & Maxxis AT-771.

For highway driving, is there a rule of thumb that I could apply for tire pressure: long tire life vs best comfort ride vs. best mpg? Does a bigger all-terrain tire change Subaru recommended psi (35 front/33 rear)?

For light off-road driving on gravel, how much should I reduce tire pressure? I've read 25-28psi.

For winter snow driving, should tire pressure be adjusted?

Thanks in advance.
 

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2018 Outback 3.6R Touring WG/JB
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148 Posts
Just use the pressures recommended.

If you want to be more accurate you'll need a probing pyrometer and measure across the tread after you have driven long enough to heat up your tires under normal driving conditions. You want your tires inflated so that temps at the shoulders and center are roughly equal. Don't use a laser pyrometer. By the time you exit the car and measure the tire surface has already cooled and your reading will be inaccurate.

If you over-inflate the tires will bulge, and you'll loose significant traction – especially for wet handling – and the tires will wear prematurely in the center. If you under-inflate, the tires bulge at the shoulders, the sipes close up and you loose traction, including wet handling capability. The tires wear prematurely as well, but at the shoulders first.

When I tracked my cars, I measured tire heat on and off the track, and the correct pressure from those readings for normal driving on public roads were the ones stamped in the door...every single time (even when I sized up with performance tires)! I still have my pyrometer, but don't even bother using it anymore. I inflate to recommended pressures and never get uneven wear as a result.

Offroad may have other parameters, so others might have recommendations for that.
 

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Silver 2012 Outback 2.5i
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33 Posts
Sticker pressures are definitely safest. Going a few pounds higher will give better fuel economy but watch for uneven wear like previous poster said. For most dirt or gravel roads I’d run the same as you do on pavement. If you have a portable air compressor for real rocky trails or sand, reduce pressure but don’t go lower than about 25 psi otherwise you risk spinning the tire on the rim(Rock crawlers use special bead locked rims to keep this from happening when they run really low pressures.) Remember to reinflate before driving at high speed.


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2013 OB 3.6R (former)
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EDITED to make it shorter and clearer.

--on road/dirt roads: use the stock pressures though AT tires might wear better at slightly higher ones.

--loose hills, 20 psi hot.

--sand, 18 psi hot though 15 should be fine.

--really problematic sand: 12 psi hot but avoid all turns and do not make sharp ones. Return to min 15 hot asap.

--Jumping beads does not happen at 25. This is an issue under 10 COLD/12 HOT.

--However, most P-metric AT tires cannot be trusted under 25 because they have weak sidewalls.
 
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