Wheels list 65 max PSI

[James4]

Mike T: Just for kicks I tried the 50 psi all around and it was way too soft and the low tire pressure light came on. I did get the van re-weighed at a truck stop that had a Cat Scale. Weight without the wife was 4100 front and 4140 rear. On the drive back I used 60 psi all around, and today I changed that to 70 around...one off of the 69 psi that JoeH figured for me with the formula he mentioned, and the ride is the best that I have had since owning the van. Thanks, again, JoeH!

James

[MountainBikeRoamer]

Haha! Hey well so much for the charts. Math and specs are a great foundation to build from, but the proof is in the actual rubber-hits-the-road pudding. At least based on those charts you know "how low you could go" and still be safely within spec.

I know that in my own case the lower (more chart-correct) psi yielded immeasurably better ride quality and stability. But as they say...YMMV

Glad you found a comfortable pressure setting!


PS: as another worthwhile FYI:
>> your dashboard tire pressure warning light will kick on based upon the **original Ford factory tire size/weight specs**, so it won't be an accurate measure of correct PSI after you've changed to a different tire size. A lot of guys ended up having to get that reprogrammed to "play nice" with the lower PSI settings that are correct for larger tires than OEM.

[James4]

Mike T,

Good morning! Yes...safely within specs until one can make it to the nearest air pump, unless they have such means onboard! I cannot imagine anyone running such low pressure as a norm for the weight and tires I have. This said, it has been a rewarding experience.

I'm thinking 65 to 70 psi will be very good for me.

What are your axle weights and tire specs?

James

[MountainBikeRoamer]

Originally Posted by James4

Mike T,
....

What are your axle weights and tire specs?

James

Ok, here ya go:

CAT SCALE RESULTS
Front axle: 3500 pounds
Rear axle: 3500 pounds
(Seriously, they read within 50 pounds of each other.)

Notable as-weighed-with-the-van contents:
Me, 1/2 tank of gas, half of usual provisions.

Tire size, Make, Model:
285/70R17 BFG KO2

Rim Size / Rim make&model:
17x9 American Racing Baja

Calculated (as weighed) load to be carried per tire:
3500/2 = 1750 pounds per tire

Recommended tire pressures from that same Toyo / Tire & Rim Manufacturer-originated chart I posted the link to earlier:

35 PSI -- 2105 Pounds
40 PSI -- 2315 Pounds
45 PSI -- 2510 Pounds
50 PSI -- 2755 Pounds
55 PSI -- 2900 Pounds
60 PSI -- 3050 Pounds

And....after all of that....
....the actual **on-road** tire pressures that I am
currently choosing to run (though I'm still (perpetually) experimenting...)

Fronts: 40 pounds
Rears: between 40 and 45 pounds (varies depending upon how much additional gear is loaded in the inside rear storage areas and exterior rear racks for a trip.)

You might argue....
....that at 40-45 pounds, I'm guilty of ignoring my own advice to "read the charts"...that it appears I am running too high a tire pressure for what those charts advise....and you'd be halfway right! But in my case I'm so "over-tired" with the big 285's that I can't effectively "dip out" of the safe load window. For this van's weight, I'm safely covered no matter how low on the chart I dip.

Even if I ran 35 pounds (the lowest safety-rated PSI range even shown within the charts indications), I'd still have an overabundance of safe load-carrying capacity.

So in my case, since that official load/PSI table had essentially given me the confident all-clear "foundation" of what PSI range is truly approved and safe (in my case it was essentially without any restrictions....)....then it came down, ultimately, to choosing a PSI setting based on personal tire ride/handling preferences.

Again, the chart says I could run 35. And I might end up doing that. But 40 is the lowest I've ever run as it is, and it rides great. Any lower than 40 and I'll probably want to pick up one of those IR tire thermometers that 86Scotty recommended, just to confirm *one more way* that things are running cool.

Oh wait! I forgot. Back when I first got these tires, when I was on a very-similar-to-yours intense drive to determine what was the correct tire pressure.....I also found yet another chart! And it agreed 100% with the numbers on that first .pdf link chart from earlier. This is an un-branded, direct-from-the-wheel-and-tire-manufacturer chart. For my 285/70R17 size tires, its all the exact-same indicated safe load/PSI ratings.



And yet....for my van, 40 is great! Seems like it's that "Goldilocks" tire pressure. Corners nice and stable, yet has comfortable bump compliance on the highway.

So sometimes you've got to damn the charts, lol.... (In the right instances.....)

But never should you air your tires up to a pressure BELOW what the charts recommend, except when doing slow travel off-road. When traveling rough/torn up fire roads, we've aired down happily to 30 pounds and that truly created a magic carpet ride.



Hey, before I forget --- I must ask --- apart from your tire pressure sensors going off, what was it in particular about the lower (50 pound) PSI setting on your van that made you feel it was "too low"? Did your tires actually look flat? Or was there a noticeably mushy/floaty quality to how your van handled? Unless a tire is truly underinflated to a level below it's safe PSI/load range....then typically a less-aired-up tire yields a better (smoother) ride. (Less abrupt feel of impact over bumps/freeway expansion joints). Curious for more understanding of how your ultimate PSI setting is felt to be "the best ride."

[James4]

Mike,

I had come across that same chart, myself. I don't know what the best answer might be as to why some folks use the info in the chart and why some people cannot use it, other than the kind of ride they get where a sense of responsive handling and safety are primary factors. For example, at 50 psi around, which is above the psi that the chart recommends, I got a very unresponsive drive. While the vehicle was tracking straight it was fine other than being way, way too soft. Suffice it to say that I would not want to make a defensive maneuver that required a sudden move in order to change lanes...scary thought, actually. One could tell by looking that the tires appeared to be somewhat low on air, and they drove that way. I don't know what tire pressure(s) that I might eventually settle on, but for this month, I'm at 70-around!



James

[86Scotty]

Mike, I think my biggest worry is killing my already bad fuel mileage. What do you get in your van? I haven't actually experimented with this but it just seems that lower tire pressure would eat in to the.........ahem........efficiency.

[MountainBikeRoamer]

Originally Posted by 86Scotty

Mike, I think my biggest worry is killing my already bad fuel mileage. What do you get in your van? I haven't actually experimented with this but it just seems that lower tire pressure would eat in to the.........ahem........efficiency.

Haha! Efficiency.

I like that optimistic descriptor.
And I'm an optimist at heart.

But....

My E250-based SMB was built with the second-to-last-production-year (1995) of the basic/reliable/crude-ish iron-block 351 Windsor (5.8L) before it was retired by Ford in favor of the more sophisticated modular V8's (4.6 and 5.4)....so I've never entertained any false delusions of getting mpg numbers that were much past the single digits.

And it's hard to get a solid read on any kind of relevant mpg, since when we're on a trip, we clock some seriously swift trap speeds to get to our destinations. (Averaging 75-80 mph while on the Freeways.) And then grinding along on fire roads/steep climbs once there. Not a formula for generating any kind of normal EPA numbers, lol....but:

* My best mpg, while still running the original 225/75r16tires: 13.5
* My mpg with the subsequent tire size increase to 245/75r16: 11.4
* My seeming mpg....now that the van has a 5" lift, re-geared rear axle (swapped to 4.10 vs the original 3.73 ratio) and 285/70r17 tires: 10-ish?

Still not totally sure though. I just realized the other day that the speedometer needed to be re-calibrated for the increased tire OD (despite the re-gearing which should have (in my original understanding) "balanced out" and delivered an identical final measured speedometer reading to stock/original....but it didn't...since the speed and odometer readings on these vans *aren't* taken from any sensors on the transmission, they're instead taken directly at the rear axle --- ***at the pumpkin tone-ring sensor.***

So the only thing that's truly measured is **the speed at which the rear axle is turning.** And that's dependent solely upon tire OD. Rear differential gearing has zero effect on what speed is measured by the speedometer.

Because that hadn't been recalibrated, my speedo-indicated speed was reading about 10-11% too low. And the odometer readings too. Subsequently I've figured out how to recalibrate the PSOM (Programmable Speedometer/Odometer Module) and it's reading pretty dead-on now, so I'm hoping to get more reliable mpg readings again soon. (Incidentally, that's a pretty cool bit of tech that can be tinkered with on these older vans! Some neat YouTube videos showing how to recalibrate the PSOM.)

But long/short....to your initial question.....I've personally never noticed any difference in mpg on this rig in respect to PSI. The brick-like aerodynamics of this thing (and it's heft...and it's surely-great driveline parasitic drag...and super-inefficient, primitively-fuel-injected 5.8L) just don't seem to have ever been "destined for MPG greatness" as an overall combination, no matter what minor tweaks I make to it.

Yep....she's thirsty. (That's why she's named that here in my SMB forum garage!) But honestly....it's not that bad. I wish that the gasoline/fuel costs were my biggest financial outlay/concern with this thing.



EDIT:
Hey....I know you've owned a same-vintage 4WD rig with the mighty old-school 460 in it....what kind of mpg did that return for ya??

Curious how people do for MPG in the newer 5.4L setups once they're lifted (or 4WD) as well.

[James4]

Mike T,

I have had the chance to do some more highway driving and experimentation with psi numbers. Right now I have 69 psi for the rear tires which correspond with the numbers JoeH gave me, and 60 psi in the front tires, and the ride and handling is great. The difference between front and rear is similar to the 10 pound diff that 86Scotty mentioned in one of his posts.

I'm hoping to make a trip this summer to Texas via San Diego and have the guys at Agile see what they can do to improve on the ride I have now.

James

[arctictraveller]

[QUOTE=

I just realized the other day that the speedometer needed to be re-calibrated for the increased tire OD (despite the re-gearing which should have (in my original understanding) "balanced out" and delivered an identical final measured speedometer reading to stock/original....but it didn't...since the speed and odometer readings on these vans *aren't* taken from any sensors on the transmission, they're instead taken directly at the rear axle --- ***at the pumpkin tone-ring sensor.***

[/QUOTE]

My van (2001 E250, 5.4) came with 32's and the speedo was way off. I re-geared to 410's, and the speedo error went away. It's now almost exact at 60mph. With 4wd, 32's, about a 4in lift, a mostly flush GTRV top and solar panels, I'm getting about a 10 to 11mpg average, but I normally drive somewhere just above the speed limit.

[MountainBikeRoamer]

Originally Posted by MountainBikeRoamer

I just realized the other day that the speedometer needed to be re-calibrated for the increased tire OD (despite the re-gearing which should have (in my original understanding) "balanced out" and delivered an identical final measured speedometer reading to stock/original....but it didn't...since the speed and odometer readings on these vans *aren't* taken from any sensors on the transmission, they're instead taken directly at the rear axle --- ***at the pumpkin tone-ring sensor.***

Curious how people do for MPG in the newer 5.4L setups once they're lifted (or 4WD) as well.

Originally Posted by arctictraveller

My van (2001 E250, 5.4) came with 32's and the speedo was way off. I re-geared to 410's, and the speedo error went away. It's now almost exact at 60mph. With 4wd, 32's, about a 4in lift, a mostly flush GTRV top and solar panels, I'm getting about a 10 to 11mpg average, but I normally drive somewhere just above the speed limit.

Interesting! If changing your tire size corrected the speedometer, then the newer vans like you have (anything after 1997) must have a more conventional means of reading speed. The 5.4's must incorporate some sort of speed sensor on the transmission itself, instead of relying on the input from the VSS sensor/tone ring at the axle (like the older 5.8L engines do).

Your mpg is also interesting. It seems that there's really no "free lunch" in terms of MPG (5.8 vs. 5.4 vs. 460 vs. 6.8L V10) with the Ford vans......that once you get into bigger tires and a lift, you're probably playing with 10-12 mpg, tops, no matter which engine you're running.....unless you take the plunge into one of the diesels.