Tire Pressure - BFG All Terrain T/A KO - 315/70-R17

[McDermott]

315/70-R17, 121/118S, Load rated "D".

2005 Ram 2500 QC, short bed, Cummins 5.9L, automatic. I bought the truck with these BFG tires already installed. The door jam says 60 psi front / 70psi rear, cold for the stock 265's. But the BFG 315's say 50 psi max.

What pressure do I run them at unloaded for daily driving?

Thanks for the help.

 

[SnoKing]

Load range D tires should not be installed on vehicles placarded for LRE tires.

Place pieces of white paper on smooth surface and drive over it and look at the pattern left on the page. Adjust air until you get an even pattern across the paper.

Here is an inflation comparison.

315/70R17 Single 2535@35 2685@40 2915@45 3195@50 D
265/70R17 Single 1890@35 2075@40 2255@45 2470@50 C 2595@55 2760@60 2910@65 D 3005@70 3100@75 3195@80

Chris

 

[Kry226]

I've ran two sets of the 315 BFGs without issue. Always ran max 50 psi in front and no less than 45 in rear empty. Maxed the rears out at 50 psi too when loaded.

 

[lpennock]

Nothing wrong with running a D tire as long as you don't loose load rating. The load ratings are the same between it and the stock tire. It is only a problem when you loose load rating.

No reason to run max pressure. Use the load pressure tables that Snoking provided and the data tag on your door. Choose the pressure that matches the load on the stock tire at the data tag pressure.

I.e. If stock pressure is 65 which is 2910 on stock tire so you need 45 on the 315.

 

[Kry226]

Having run three sets of E rated and two sets of D rated tires, specifically the BFGs in question, I disagree with this. Capacity shouldn't be mistaken for ride stiffness as even with similar inflation per weight ratio (as in the above table), the ride characteristics will be drastically different. The inherent downfall of the BFGs on the heavy duty trucks was the bounciness which many times contributed to death wobble, even with folks who were running them at max pressure. I did the chalk test several times and my fronts ALWAYS gave a complete footprint across the tire at 50 psi. Unloaded in the rear it was between 40-45 psi.

All things being equal, I always had more "give" or "sway" with the D rated tires versus the E rated tires that I've run. Running higher pressures in the BFGs will mitigate some of the sidewall softness and provide a more stable, if even safer ride. YMMV.

 

[SnoKing]

Kry226, I was going to point out the different between sidewalls for LRE and LRD tires, however I thought it might fall of deaf ears. Your detailed posts might get through! I ran LT265/75R16D studded snow tires on my truck in the winter for many years and would never have wanted to haul a heavy load or towed the 5th wheel with them for the exact issue of soft sidewall that you noted.

Freeway Queen, well maybe! Or maybe for off roading! Truck that works, NOT!

SNOKING

 

[Regcabguy]

Nothing wrong with running a D tire as long as you don't loose load rating. The load ratings are the same between it and the stock tire. It is only a problem when you loose load rating.

No reason to run max pressure. Use the load pressure tables that Snoking provided and the data tag on your door. Choose the pressure that matches the load on the stock tire at the data tag pressure.

I.e. If stock pressure is 65 which is 2910 on stock tire so you need 45 on the 315.

A friend runs 315 BFG's on his 10,750# '05 3500 w/utility bed and Callen camper.
He max's them out @ 50 psi. Riding behind him the sidewalls are bulged way out and the truck squirms. I've driven it. He has a Kore 2.65 Bilstein kit revalved for the camper load and overloads. He has experienced sidewall failure in Baja aired down. Despite this history,the great price he gets on the tires keeps him running them.
I just think a 50 psi tire for towing heavy and carrying a big load is overwhelmed.
I've seen the new BFG KO's firsthand. If BFG offers an E-rated 315-70-17 with a high load capacity they'll sell everyone of them.

 

[lpennock]

I had the opposite experience of you. I went from a LT215/85-16 E to LT275/70-16 D. The 215 was a E115 tire which is rated for 2470@80PSI and the 275 is a D119 Tire which is rated for 3000@65. I carried a cab over camper and found the D119 tire beat the E115 in ever catagory. I agree that at the same size tire the E will have the firmer side wall but my experience shows that when you go up in size you can't always say the E on a smaller tire is more stable than the D on a bigger tire.

With that said as you go up in height if you don't change rim size to keep side wall size constant the tire will have less stability. Doesn't matter if you stay in E in both cases it is just the difference in Sidewall size.

 

[lpennock]

I've seen the new BFG KO's firsthand. If BFG offers an E-rated 315-70-17 with a high load capacity they'll sell everyone of them.

I doubt that will ever happen. TRA doesn't allow any new 17" tire designs to be over E121 (3195@80). They want to make sure you don't use a 17" where you should have had a 17.5"

 

[Prairie Dog]

Not only do the BFG's have a terrible rep for causing death wobble, their ratings don't hold up either. The E rating is just as important, or more so, than the actual pounds rating because of the soft sidewalls associated with D's.
The worst mistake I ever made with my trucks was putting D's on my last Dodge. It destroyed the trailer towing performance, caused sway at speed and required me to use a WDH system (which only helped some) even though I was only pulling 4400#.
It's best to leave the blingy soft tires for the show-off trucks and put real tires on a real truck. Or if you go big tires at least get LR E's.

 

[Regcabguy]

I doubt that will ever happen. TRA doesn't allow any new 17" tire designs to be over E121 (3195@80). They want to make sure you don't use a 17" where you should have had a 17.5"

The prototype BFG KO's I saw were 315-75-16 load range E with a 129 load capacity. They probably were not DOT approved and were scheduled to be used in the Baja 500 or similar. I don't recall which but no flats or structural defects were reported from the racers.
Nitto's Duragrappler 285-75-17's have a 129 rating.

 

[lpennock]

The prototype BFG KO's I saw were 315-75-16 load range E with a 129 low capacity. They probably were not DOT approved and were scheduled to be used in the Baja 500 or similar. I don't recall which but no flats or structural defects were reported from the racers.
Nitto's Duragrappler 285-75-17's have a 129 rating.

Toyo AT 285-75-17 had a E129 rating also. The new AT2 only have a E121 rating. I called Toyo and they told me it was because TRA is not allowing new 17" tires with more than a E121 rating. That limit is only on the 17" tires. A 315/75-16 in the TRA tables is available with a E127 rating of 3860@65 psi. The BFG prototype 315/75-16E129 isn't in the tables I have but might be in a later version as my copy is dated 2011.