Ideal tire PSI for me

[srileo]

All,
I have a Nissan Titan Pro4X with an FWC Hawk on it fulltime. I have airbags and E rated tires and stock suspension. I am trying to understand what a good tire pressure should be for me given my stock suspension, Airbags, and MPG. I currently have:

43 psi up front
55 psi in the back
30 in the airbags.

With this combo I get about 13 MPG but the ride is a bit rough. I can feel it on concrete or expansion joints. For maximum ride comfort and MPG,

1) Should I keep front and back PSI the same?
2) For comfort, should i lower the rear tire pressure to 50 or so, and increase the pressure in airbags?
3) In general, what is the absolute lowest I should go on E rated tires? Is 40 too low?

Thanks for your advise,
Shridhar

 

[MarkBC]

...For maximum ride comfort and MPG...

Since these trend in opposite directions with tire pressure, seems like it's a personal/subjective judgement -- how rough is too rough for you vs. how poor MPG are you willing to tolerate.
One approach would be to measure MPG as a function of different tire pressures and decide based on that. For example, "45 psi in back = 13.5 mpg but butter smooth"

3) In general, what is the absolute lowest I should go on E rated tires? Is 40 too low?

I think proper inflation pressure depends a lot on how much weight the tires are supporting, e.g., E rated tires on a Tacoma will likely call for less pressure than E rated tires on an F350 with camper.
What does your truck+camper weigh?

I normally run 65+ psi in the E tires on my F250 with FWC Hawk, and I've aired down to less than 40 for driving on rocky dirt and sand.

 

[JHanson]

The best way to determine correct tire pressure for your own vehicle and load is chalking, although I think paint works better than chalk. Get some white paint and paint a line all the way across the tread on each tire. Then go for a drive somewhere where you don't have to make a lot of sharp turns. Inspect the paint frequently. Ideally it should wear off evenly across the tread. Excess wear in the center indicates overinflation; excess wear on the sides, underinflation. Once correctly adjusted, that figure should be a good compromise between comfort, safe handling, economy, and optimized tire life.

 

[Foy]

IMHO, the factors leading to a determination of ideal tire pressure have a pecking order in which fuel economy and comfort are next to last and last, respectively.

As Mark suggested, it's likely a Tacoma with a camper has more leeway than a Titan with a camper and an F350SRW with a camper has the least, assuming each of the 3 has E-rated tires sized within the normal range for the particular truck. My own understanding is that tires are capable of carrying their maximum rated load when, and only when, inflated to their max PSI, as shown on the sidewall. Ideally, I'd get a good read, at a scale, on the overall weight and the front and rear axle loads stated separately with the truck fully loaded in the fashion I'd be driving down the highway on a trip. If the rear axle on my F350 shows 5,800 lbs at the scale and my E-rated tires show 3,100 lbs max load at 80 PSI (and I'm making up all of the figures above other than my Michelins' max PSI), I'm bumping close to where I need to run the max PSI simply to carry the load. That being the case, fuel economy and personal comfort play no part in the decision of what PSI to run.

Likely somewhere in the tire manufacturer's literature for each tire is a scale or chart showing how much the load weight capacity declines with reduced pressure. If I see I can run between 55 and 80 PSI and still carry my load, I feel free to consider other factors in selecting operating pressure. IMHO, that's the range where JHanson's excellent tire-marking suggestions come into play.

Foy

 

[RicoV]

FWIW, I run my Titey with spartan Grandby shell on Michelin LTX E-load tires, 52 psi in front, 58 psi in rear (axle weights are roughly 3000 lbs and 3500 lbs, respectively). So far so good, but I'm certainly no expert. My instincts suggest that 43 in front might be a bit low for day-to-day. Best of luck getting it dialed in; let us know what you eventually decide to go with for the long term.
Rico.

 

[veryactivelife]

Foy is on the right track here, your inflation will depend on the tire type (E in your case, which is good), tire size, and the expected load. Once you know what these are for your rig you need to consult tire load and inflation tables to determine the recomended PSI to match the tire and load. If you are unhappy with the ride consider making changes to the tires or suspension, not the PSI. IMHO.

These links (orothers) may help further:

http://toyotires.com/tires-101/tire-load-and-inflation-tables

http://toyotires.com/sites/default/files/page-files/LoadInflation_Table_P-LT_102913.pdf

http://overlandexpo.squarespace.com/storage/downloads/Discount%20Tire%20inflation.pdf

Dean

 

[srileo]

Foy, Jonathan, Travelmore,
My apologies for the delayed reply. Thank you very very much for the wisdom. You guys have given me a pretty good plan of action

1) start with getting the truck weighed at a scale
2) figure out how much weight is on each axle (and what the damn payload is!!)
3) consult available literature for the tire's capacity by axle.
4) Pick a suitable PSI
4) Then apply JHanson's method of painting/chalking the tires front and back to see how less i can get away with between MPG and riding comfort.

Thank you all very much. You guys are really knowledgeable. I promise to report back with the numbers.

Shridhar