There has been a lot of threads dealing with tire pressure used in our SD trucks and how the ride is affected. I decided to experiment a little with the pressures and post the results. I ran between 55 and 80 PSI in 5 pound increments to see what happens.

My truck is A 2007 Super Cab short bed 4x4 with a 5.4L. The tires are 265/70/17 BFG Rugged Trail T/A AT Load Range E tires with 25,000 miles on them. I still have the stock steering damper. Truck was tested unloaded. Factory door sticker calls for 75 PSI front and rear.

55 PSI - Ride is smooth on even pavement. Bumps produce a hard oscillation in the steering wheel (death wobble?) that continues for 3-5 seconds after the bump. Handling seems somewhat mushy, like rear suspension is held on with bungee cords. Back end feels like it wants to swap with front on moderate corners.

60 PSI - Ride still smooth. Steering oscillation over bumps still bad. Handling still mushy, but at least rear doesn't seem to want to swap places as badly.

65 PSI - Ride firmer. Oscillation over bumps damping a bit. Truck seems more responsive to steering input. Back of truck feels more connected.

70 PSI - Ride firmer yet, but not bouncy. Oscillation over bumps all but gone. Steering response good, rear end feels solidly behind me during steering input.

75 PSI - Ride firm, detecting a little bounce. Hard braking over severe bumps activates the ABS. Steering response quick.

80 PSI - Ride bouncy. Braking over moderate bumps activates ABS. Rear end starting to feel like there are no shocks.

Based on my testing, I will run 70-72 PSI all the way around, it seems to suit my truck, tires and driving style.

I found it very interesting that the low tire pressure induced a steering oscillation after a bump. That oscillation was strong enough to jerk the steering wheel from my hands.

 

I haven't heard of death wobble from low air before, especially 60#. Good find!

 

Actually the TSB for the "death wobble" fix, the first thing to check is that the tires are filled to the proper pressure as indicated on the B-pillar sitcker. Low tire pressure has been found to make the steering wheel oscillation worse.


"VEHICLE INSPECTION - TIRE PRESSURE

Set tire pressures as indicated on the vehicle label (located on driver's door label).
NOTE: SETTING TIRE PRESSURE TO DOOR SPECIFICATION IS ONE OF THE SINGLE MOST IMPORTANT MEASURES IN RESOLVING THIS ISSUE. LOWERING TIRE PRESSURE WILL MAKE THIS ISSUE WORSE." TSB 06-22-14
http://www.ford-trucks.com/tsb/fullt...p?tsb=06-22-14

But i do agree at first glance it seems counterintuitive.

 

Thanks for the info............ I'd just lowered my tires to 55 PSI and thought I had a big issue {death wobble at 65} I'll replace the air and save the money .!!! THANKS AGAIN!!!

 

I hope it works for you Randy. I always assumed lowering tire pressure would cure the wobble, not induce it.

Blackhat, good point.

 

Thanks Redford for the testing and feedback. The 265/70/17 BFG Rugged Trail T/A AT Load Range E tires are stock?

I have the same truck (4.10 gear) and believe the same tires. Truck is sitting in the garage during the week. The door sticker recommends 75 psi all around. So, looks like a 5 psi drop and it rides like a Lincoln Town car.

Noticed the same results as you at 75 psi. Any data on the amount of weight the tires can handle at 70 psi?

My truck is rated 9200 GVWR and get close to that when hauling the horse.

 

265/70R17 are rated at 3005 lbs per tire @ 70 psi.

 

HoresyHauler,

No, I'm still looking for a tire inflation chart for these. If you fid one, post a link to it. All I know is the tires go to 75 when towing...and yes, those are stock....drove the truck off of the lot 11/06.

I thought with 4.10s you were rated at 11,000 pounds. Mine is rated at 9200 with 3.73 gears (and yes, I have towed very close to that and was pleased with the performance).

 

Load/Inflation table for LT265/70R17...

35 psi - 1890 lbs.
40 psi - 2075 lbs.
45 psi - 2255 lbs.
50 psi - 2470 lbs.
55 psi - 2595 lbs.
60 psi - 2760 lbs.
65 psi - 2910 lbs.
70 psi - 3005 lbs.
75 psi - 3100 lbs.
80 psi - 3195 lbs.

 

i run 75 psi in frt and back i love the ride and i am also getting get 19.4 mpg which is not to bad for a full svc body vehicle or at least i think it is good my truck is an 08 5.4l and 3.73 ratio reg cab

 

I am with you on this, at first glance and thought, increasing tire air pressure seems counterintuitive to reducing steering oscillation over bumps etc., and I was skeptical of FMC's reasoning to increase tire pressure when the TSB first came out. I have setup a few autocross and road race cars and tire pressure plays a large role in performance & handling, my first thoughts on reducing steering wheel oscillation was to lower tire pressure. Looks like FMC got this one correct.

Thanks for all your testing and posting the results.

 

Do you only have Load/Inflation table data on this size tire, or is there a place that we can go to locate Load/Inflation tables for passenger & Light truck tires?
Seems the only Load/Inflation tables i can find are for Heavy truck tires or race tires.

 

Anyone running the All Terrains? I'm running 285/70-17's and I just installed them. I haven't had a chance to find the "right" tire pressure...

 

I am not sure of anyplace that offers this type of information online. Like you said it is not readily available.

If you have a specific size(s) you are interested in, just let me know and I will check to book I have and see if it is listed. Unfortunately the book I have is a couple of years old and does not have some of the recently introduced sizes.

 

Okay look up 275/70R18 E Light truck tires.

Thanks for the help