Airing down weight question

[Mock Tender]

I really want to gain some of the low end performance back that would be provided with less tall tires. The switch to 295/75R16’s seems like a viable option.

I am looking at the BFG KO2 and the Toyo AT2. The impressions that I am getting from the local tire shops here in the Rockies, that handle both tires, is that the BFG has a lot less problems due to sidewall damage.
I have no experience with either company and know that both have good reputations. Toyo Tire has a spread sheet on the ratings of different sized tires that they make. BF Goodrich claims that their info is proprietary, but would share their numbers on the 295/75R16 over the phone only. Funny enough, they matched exactly with Toyo Tires.

So if both tires share the same specs, and the sidewall on the Toyo is potentially less stout: how would the higher PSI’s over a LT 315/75R16 effect airing down?
1) Would I get more tire spread from one over the other- Same PSI?
2) At roughly what PSI could I safely go to for sand and rocks?

In the year that I have owned the truck- I never needed to air down.
At the weight I run the:

295/75R16 would have the tire pressure set at 47psi on the fronts and 68psi on the fronts.
315/75R16 would have the tire pressure set at 43psi on the fronts and 57psi on the fronts.

(PSI) a) 35 b)40 c)45 d)50 e)55 f)60 g)65 h)70 i)75 j)80

LT295/75R16 (For both Toyo OC AT2 and BFG AT2)
a) 2240 b)2460 c)2670 d)2910 e)3070 f)3265 g)3415 h)3635 i)3815 j)3970

LT315/75R16 (My current Cooper ST/Maxx)
a)2535 b)2715 c)2950 d)3195 e)3395 f)3610 g)3860

Mark

 

[SkiFreak]

There is no "one size fits all" solution to tyre pressures. The weight of the vehicle plays a big role, as does the weight distribution over the axles.

 

[kmlacroix]

I switched to KO2's, E range. the recommended pressure for my JGC is 47 psi. I air down to 30 off road. The OEM tires are 34 psi. Traction is great. My tires are 265/65-18.

 

[dlh62c]

Considering that to rotate tires on a FUSO one has to flip the rims, I'd go with the Toyo AT2's without the raised white letters on the sidewalls.

 

[Aussie Iron]

There is no "one size fits all" solution to tyre pressures. The weight of the vehicle plays a big role, as does the weight distribution over the axles.

Exactly what has been said in all the other threads about tyre pressure.

Dan.

 

[jadatis]

First , if you would find a European pressure/loadcapacity list for the same tiresise and speedcode and Loadrange, it would give lower loadcapacity,s for for instance 40 psi.
the European formula is saver for that.

the tiremaker determines a maximum loadcapacity for the AT-pressure ( yours 80 psi=E-load/10 pr) and maximum speed , and goal of calculations for loadcapacity for lower pressure is to keep the deflection the same as for when maxload and maxloadpressure/AT-presssure .
Then for lower speed maximum load becomes higher, and on track they use 80% of the pressure for the speed of 65km/40m/h and in sand even 50% of pressure needed for 20km/12.5m/h.
Can tell you more but first diner ( here in Holland europe its dinnertime now).

 

[DzlToy]

You need a load and inflation table/index. Maybe that is what you asked BFG for, I did not search for one for the KO2. There is likely nothing proprietary about their construction that is going to affect weight carrying capacity for a certain size tire.

Weight carrying capacity is a function of several things:

Sidewall - compare a 275/60R17 to a 275/55R17 for example

Tire construction - ply rating in the tire carcass and the sidewall, 10/4 or 10/6 is a pretty heavy duty tire, for example.

Load Range does not tell the whole story, as I have seen Load Range D tires in a certain sizes with E load ratings of a similar size. Some off road tires (all terrain or mud terrain) are not available in E, as they are presumed to not carry heavy loads off road.

Wheel size plays a minor role - compare a 275/60R16 to a 275/60R17 and see what the difference is

Tread width or section width plays a huge role in the footprint of the tire, as pressures decrease. Many people think that a wide tire, something like a 13.50 (345 mm) is best for "floatation". It can be in sand and some mud and some snow, but there is no "one tire does everything" Some situations call for a tall narrow tire to dig into snow or mud for the best traction. A wide floatation tire is going to require a bit more power to push through the mud, etc. Look at old (underpowered) Land Rovers, they have tall skinny tires.

I have aired tires down to 8 or even 6 psi off-road in a lightweight (non-expedition) rig on numerous occasions, without beadlocks and 3-4 psi with beadlocks. There is very little carrying capacity as these low pressures and the speeds are walking pace at best. The traction however, is fantastic, especially in rocky or technical terrain.

That said, you should "presume" there is a safety margin built into the Load & Inflation Table data and not worry that if 20 psi holds 2000 pounds that you are going to destroy your tire at 2100 pounds and 20 psi.

Some examples follow. The sizes are different than yours, but the principle is the same:

Toyo Mud Terrain in 37x12.50R20E: #1930 (25 psi), #2225 (30 psi), #2470 (35 psi), #2705 (40 psi), #2925 (45 psi), #3085 (50 psi), #3335 (55 psi), #3525 (60 psi), #3750 (65 psi)

Toyo Mud Terrain in 37X12.50R18E: #2095 (25 psi), #2395 (30 psi), #2680 (35 psi), #2915 (40 psi), #3150 (45 psi), #3415 (50 psi), #3590 (55 psi), #3795 (60 psi), #3970 (65 psi)

Toyo Mud Terrain in 40X13.50R20LT: #2470 (25), #2815 (30), #3085 (35), #3425 (40), #3705 (45), #3970 (50 psi in D load range), #3970 at 55 psi – 65 psi for E load range.

A 10 ply MPT in 275/80R20 can carry #3300 per tire @ 35 psi on grassland at speeds up to 30 MPH. It can carry #3300 per tire @ 22 psi in mud/sand at up to 12 MPH. A 12 ply 335/80R20 carries #3600 at 30 psi and 30 mph on grassland, #3600 at 16 psi at 12 MPH in mud or sand.

 

[cnick]

...

Toyo Mud Terrain in 40X13.50R20LT: #2470 (25), #2815 (30), #3085 (35), #3425 (40), #3705 (45), #3970 (50 psi in D load range), #3970 at 55 psi – 65 psi for E load range.

A 10 ply MPT in 275/80R20 can carry #3300 per tire @ 35 psi on grassland at speeds up to 30 MPH. It can carry #3300 per tire @ 22 psi in mud/sand at up to 12 MPH. A 12 ply 335/80R20 carries #3600 at 30 psi and 30 mph on grassland, #3600 at 16 psi at 12 MPH in mud or sand.

I understand the weight limits and pressures are coming from Toyo's Load & Inflation Table Application Guide. What formula is being used to calculate the maximum speed for a tire running less pressure?

 

[SkiFreak]

If you install a TPMS then you can adjust the tyre pressure according to the temperature.
Some testing with your own vehicle should give you the optimal pressures you can run at the speed/terrain you are going on.
As has been mentioned numerous times on this subject... you need the correct tyre pressures for the setup on your own truck.

 

[DzlToy]

You need to get accurate weight, speed and pressure info from the OEM. I don't know of a way to calculate or extrapolate that information. A tire temperature system or checking along the way is certainly not a bad idea, but that may require a bit of trial and error.

As long as the tires are not over heated or under inflated to the point where the tire is damaged, I would presume a reasonable safety margin, but that is upto you, your truck and the conditions you are in. I am not a tire engineer