285's in C Load / Chalk Test

Hey all,

So I am 300 miles into having my BFG KO's (285/70R-17) in C-load. Tires were topped off at 39psi and it rides really well. I decided to chalk test it today and I get even wear at that pressure. I have read where some run all the way to 32psi with chalking still showing even wear. Anyone here running this load range tire at 39psi?

 

I don’t buy the chalk test.

I run those same tires in E at 36-38.

 

30-40 psi is the norm, really just really depends on you and your 4runner

 

The chalk test is ok for figuring out treadwear, but it won't tell you the right pressure to safely support a load.

LT285/70/17's should be run at 38 on our 4runners based on GVWR. But, a lot of people will run a lower pressure for whatever reason.

 

I did. (285/70/17 ko2 c load) Ran em at 32-33. Didn't ever care about wear, as they went over 60k for me, and still looked ok when I bought new rubber.

EDIT- chose the better of em all, and its now in the spare location, and i still have all the faith.

 

Ok was just curious thanks everyone. I remember the calculator telling me 39psi before I bought the tires so was surprised when the tire shop did that vs what they normally do which is fill according to the door sticker. I mean it rides wonderful at this pressure so zero complaints I just wanted to make sure as I do not want to start out with issues from incorrect pressure.

 

It should have said 38.

 

Same tire/size. 37PSI

 

I think 32 is underinflated for that tire.

 

Why...

 

I have the Falken Wildpeak M/Ts in a 285/70/17 load E on the Sema TRD 17”x7” wheels. I run the fronts at 45 psi. and the rear at 35 psi. If i run lower psi. It wears the outside edges of the tires, so this is my happy spot for inflation based on not carrying a load.

 

The weight of your truck.

I wouldn’t run that on an FJ cruiser which is much lighter.

 

good info to know. i noticed there is also an SL Toyo Open Country AT 3 in 285/70/17 (in addition to C and E load). so according to the calculator those would be run at 26 psi.

i wonder how many folks run the SL.... i'm guessing not many.

 

Clearly not many as evident from the lack of response on my other thread...
https://www.4runners.com/threads/tpms-pressure-threshold-reset.25795/

 

interesting. even more so since we basically have the same ride.

 

I will lower it to 38 and monitor.. Isn't there an ideal temp range as well which would be at all telling regarding incorrect pressure or am I just dreaming?

 

You're not going to see a difference between 35 and 40. Ive set mine at 37 when it's cali cold outside but most of the time the display shows 39-40.

 

I know everyone uses this metric as the factory P265s show a load capacity of 2205lb (with -10% derating), however the Limited runs a factory P245/60/20 at 32psi, which has a load capacity of 1794lb (with -10% derating).

So that puts your 285 C load at 35psi. Interestingly they also show 265 C loads at 35psi.

 

In 3.5 years of ownership, I’ve checked my tire pressures once. As I recall they were around 37 psi for 285 E rated.

 

That is weird. I wonder why Toyota didn't adjust the pressure for the Limited.

 

Ride quality for the skinny low profile tires?

 

Just fill your tires at 40 psi, drive it, then drop it 2 psi, once again test drive it, and continue this until your achieve your perfect psi or just get tired and say fuck it and run it at 32 psi cause it rides nice and handles even better

 

Yup....

 

Because they don't have to. Everyone thinks that the 32psi of the OEM 265s means the 4Runner must need a tire load capacity of 2205lbs. The GVWR of the 4Runner is 6300lbs, 4 tires at 2205lb is 8820lbs, way over GVWR.

Logically the 4Runner needs a tire load capacity of 6300lb (GVWR) / 4 = 1575lbs.

As far as I can figure the 32psi of the OEM 265/70/17s and 245/60/20s is used to achieve a good balance of tread wear, contact patch, fuel efficiency, and comfort. It just so happens that 32psi in those P metric tires have a really high load capacity compared to the GVWR of the vehicle. The LT tires aren't meant to run below 35psi so the load charts pretty much bottom out there, which is more than sufficient for the GVWR of the 4Runner.

Matching load capacity via tire pressure is just one of many variables. You need to take into account wet road traction, braking performance, etc. as well.

Go follow the tire pressure calculator, put 44psi in your 265 KO2s and go do some emergency braking and evasive maneuvers on a wet road. You'll be sliding all over like you're riding on roller skate wheels.


Now, all that goes out the window if you're not talking about a truck under the listed GVWR. It seems not uncommon for guys to be loading up their 4Runners way over GVWR with bumpers, armor, winches, RTTs, etc. Everything changes at that point.

 

Great post!

I was under the impression that the tire pressure was calculated by a percentage over GVWR, though.

Great point about wet traction. This could contribute to the reason some folks think KO2's are garbage tires.

I refer to the tire pressure calculator on Simpletire a lot because it's dummy proof. But, figuring out tire pressure by actual GVWR or running weight is a good way to go.

FWIW, I ran stock size LT/C KO2's at 35 with good results.

 

I alway thought that had to do with running the E-rated version instead of the C.

 

I think that's a factor as well. I thought I read that the tread compound is different (harder) on the E versions. That could definitely contribute to poor wet traction.