2015 Subaru Forester Tips For Airing Down Tires?

[Kemdawg]

Hey I just recently got a whole new tire, wheel, and lift set up. I'm running a 2 inch ReadyLIFT kit with 16 inch Motegi Racing Wheels and 235/65R16C Load Range E Falken Wildpeak AT3W Tires, Speed Rating: 121/119 R. (sorry I'm trying to be as specific in tires as possible).

Anyway my question is: What should my tires be inflated to for every day normal driving on regular roads in town and on the highway? they had them at 40 psi when they were installed. And what psi should they be at when I'm off roading on dirt roads? do I need to air down and what psi should I be airing down to?

 

[Kevin and Sara]

You might have wanted this post in general section here. But happy to help:

I would keep at 37psi for daily driving and depending on the dirt road, and how many rocks are in it 12-20psi. Low side for in sand and snow, around 15-18 for going over large rocks.

 

[M Kesik]

12 psi is a bit low, so something to keep in mind not to drive over 25mph and watch how sharp your turns are

 

[smritte]

You have about a 28 inch tire with about 6 inch of sidewall and a load rating of about 3000 lbs.

All of the above info is great. Your street air pressure is going to be based on how much weight is on the tires. Too much air and it rides like crap, wearing out the center of the tread. if these are on a light vehicle the psi may not be as high as you think.

To find out your street pressure there are several tricks. I use chalk. The kind you give to small children and let them draw all over the street works great. I fill to what the tire sidewall says (which will be too high normally) coat the tread as much as possible (one side front and rear), Pull forward about 30 feet. Look at tread. Drop 10 psi and repeat.
Too much air you see more of the center wearing, too little and its the sides. Ideally you want about 2/3 of the tread.
I normally find around a 20 psi window where the chalk doesn't change size. select that and watch your tire wear over time.
It just so happens, almost all of my offroad tires ended up being within a few psi of the door sticker when I was done.

 

[Pam H]

smritte, are you saying you recommend driving on 20psi all the time on the street? I ask because we have Nitto Trail Grapplers and another driver once told use to maximize tire wear on road we should be driving at 26psi and during offroad 8psi. We thought it was a little low so we kept at 35psi for on road. Was that guy right?

 

[smritte]

If I gave a set tire pressure without calculating and testing I would probably be wrong, unless I had the same vehicle with the same tires.

You cant really predict tire pressure easily on a heavier rated tire. If I understand your question about my post correctly, the twenty psi range I mentioned was while trying to determine where the pressure should be using the chalk.

If what I read is correct, that tire has a rated pressure is about 80 psi if you put 3000 pounds on each tire. Most of our tires are rated pretty high. That gives us more durable tires for the abuse we deal out. Were just stuck figuring out the best pressure at a lower weight.

Again, if I understand your question, here is a bit more info about the tire test. Im sure someone can word this better. I kinda suck at explanations sometimes.

If you started at say 50, you would see the chalk wear mostly center. drop to 40, the wear patch will grow outward. 30 it may grow a bit more(or not). 20 it will probably start wearing sides more.
That meant between 20-40 (20 psi window). I would start with 30 and watch my tread wear over time. You may find 34 optimum or 28. It all depends on the weight of the vehicle.

I had some 37 Nitto Mud grapplers on my TJ. I think they were rated 3500#@80 psi. 32 psi gave me even tire wear and I think the door sticker was 35psi for the stock tire. With all the armor and cage, I was about 5200# I think.
If my vehicle was heavier, I would have run more, lighter less.

To make it more confusing, my Cruiser is running a 33 KO2 and wearing great at 40 psi. My 33 " Coopers were too squishy on the street at that psi and I had to run 48. Same vehicle, diffrent tires. Off road the coopers were a bit unstable with 20psi over 40 and the BFG's are fine.

Edit: just noticed the "8psi" part. Ugh...I ran that on my Mud grapplers doing hard core rocks with a beadlock. Way heavier sidewall then the trail. I've never run the trail grapplers but, i'm sure I would only drop below 15 if I was on soft sand trying to not spin much. Figure I ran a 17" rim with 37's -39's. Nice tall sidewall to keep the rim from hitting the ground.
Across the board on all my vehicles (33"-39" tires) I normally don't run under 20 psi unless I really need the footprint.

Edit again: This is based on mostly desert driving with a small bit of forest.

 

[GrubWorm]

12 psi is a bit low, so something to keep in mind not to drive over 25mph and watch how sharp your turns are

2 years ago, a buddy was out at the sand dunes, had his tires aired down to 10 psi and he took at turn on the sand to fast and both passenger tires came off the rim! Talk about a mess he created. He was going way to fast as he admits.