I have a Volvo XC90, running Yokohama Geolandar G015 tires. Can someone suggest tire pressures to run on:
Forest service roads with speeds under 40mph?
Rougher roads with some bigger rocks?
Sand / mud / really tricky stuff?
How to adjust the above if I'm towing a 3.5K to 4K pound offroad trailer? This is where I really am not sure what to do!
On the road I plan to stick to the 38F / 38R recommended, perhaps bumping up the rear a couple PSI when towing.
I appreciate any advice!
Edit for clarity: I am running the Euro-Metric version of the tires.
Which size G015 did you go with? How are they handling/performing on-road and off-road? I've been looking at options for when stock street Pirelli Scorpions are done.
As for pressures, I've gone as low as 32 on our 2017 XC90 although it's been on the Pirelli so I've hesitated going lower to avoid exposing too much of the sidewall and given the relative low profile of 275/45 series on 20" wheels. If I had proper AT tires I'd likely venture with pressures below 30 if conditions required it like I've done on occasions with our 2010 XC90. FYI T8s have a higher recommended pressure of 42PSI front and rear which is what I run on the road. It’s not just for their added weight vs T6 but I’m sure to also lower rolling resistance.
Usually on forest service roads 36PSI is enough to take the edge off. Given the higher baseline that's more like 30-33 on yours which is more comparable to our 2010 XC90 weight wise I think. Even on the rougher roads and at that pressure the ride comfort has been very good and I typically travel in suspension setting of Hybrid on most service roads - I believe it’s equivalent to Comfort on yours. Am I recalling correctly you have air suspension? When it gets rough and I need constant AWD and finer pedal control and/or I need the added clearance I'll go to Off-Road drive mode. Although we're not on AT tires on the T8 (yet) we've not experienced traction issues with these pressures even climbing over big rocks.
Fully loaded this summer with our R-Pod I still dropped down to 36PSI depending on terrain and distance. For the R-Pod over smallish rocks like in the 4th pic below we slowly towed the R-Pod up that BLM trail it was the only time I had dropped pressure on the R-Pod to 50PSI from 65. It’s running on LT rated Nokian Rotiiva AT which I was pleasantly surprised at how compliant they are even though they are 10ply. It was a smoother ride at 50PSI than on the old cheap 6ply Mudstar it came with for which Forest River recommended 50psi pressure. We had started the trip with the Mudstar AT and early on dumped them for the Rotiiva (the original tires were wearing badly and made me uncomfortable 2k mi into our adventure - we got just over 13k mi out them). For road/highway I bumped up to 65psi to take the squish out of them. Their max weight rating is based at 80psi. It goes to show that pressures depend on tires as much as vehicle and sometimes you do have to experiment. The recommended pressure is a good starting point and then adjust within rated parameters - great when known. What’s cool is Nokian publishes their weight ratings by pressure - load rating drops with pressure. The R-Pod was packed out to about 4100lbs for our summer adventure.
When the going got more rocky and jagged, at 32psi on our T8 (without R-Pod) was enough to smooth out the ride and baby the Pirelli in conditions beyond their natural habitat. We saw sand, mud, clay, badly rutted terrain, large rocks, and sadly not a lot of snow.
Our complete summer adventure this year was just over 7k mi and 2 months. We enjoyed exploring state parks, national parks, NF, BLM, and everything in between. Even some state parks had overland trails which were great.
As for lower pressures and towing - when we went to YK and NT with our 2010 XC90 and had a T@B I dropped the General Grabber AT2 we had on our 2010 XC down to 30psi. Even when on we hit the Dempster Highway and we traveled at 50-60mph on it the lower pressure was not only a huge improvement for comfort and and wear, handling was great and we had no issues. It was a good thing too as on that leg we came across a couple of other travelers that had experienced flats and tire failures (those were traveling fully inflated on their trucks while hauling trailers or had truck campers). It seemed many of those failures were when they went over slate rock portions of the Dempster. One family had a flat and a failure fortunately at two different times and had managed to get a replacement tire at Ft. McPherson. For that trip we carried two full size spares and the stock donut. Thankfully we didn’t need them but we did use the Jerry cans a number of times.
On the 2010 XC90 with Grabber AT2 I've gone as low as 18psi (deep snow on forest service roads) and 25psi for soft sand although I was not towing when I went that low on them. Weight wise and pressure wise it's more comparable to your XC90 than our T8. Volvo recommends 36 to 39 on that one based on load.
On this outing chains ended up being a must to eliminate the pucker factor on the descent when the snow turned to ice. If I recall on that trip we lowered to 30 I think - I was trying to balance between traction and clearance. I probably could have gone lower.