FX4 Tire Pressure - Revisited

[sbacpo]

Wow. Thanks HenryMac/John. I may have to resort to that. Makes a lot of sense.

Rob - just to throw more crap in the game, here's an interesting article- https://www.tirereview.com/determining-the-right-psi/
My primary takeaway from the article is how the factory determines the recommended pressures. There is some opinion in the process.

I just lifted and put new/bigger tires on the truck. Went form 265-65/17 to 285-70/17. Here's what I did.
1. I used the TRA charts similar to what someone linked to in another thread to determine what the minimum safe pressure was for the new tires based on the load requirements for the truck. This, IMO, is the minimum pressure for safe operation of the vehicle.
2. I drove the vehicle to determine if I liked the ride and the handling. If the ride was too harsh (it wasn't) then I would have had to live with it because I would not deflate below the minimums. Same with handling. I ended up adding 4lbs above what was indicated on the charts.

I did not do the chalk test. It does not determine what I determined in Step 2. It's certainly not the only way to determine optimal tire pressure. I have never owned a car where I had the tires inflated to the factory recommended pressures but I have never gone below them. YMMV.

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[MT19RANGER]

We all know on a truck the weight ratio, front to rear, is pretty dramatic when the truck isn't loaded.

I've always wondered why the sticker doesn't show an "Empty Truck" tire pressure and a "Loaded Truck" tire pressure?

Seems like that would be ideal, the correct pressure based on the actual loading.

Pretty amazing the variance of pressures based on tire sizes... here's a photo of the door sticker for my Ranger:

I noticed your tire/rim is R17C what is that compared to R17's?

 

[HenryMac]

I noticed your tire/rim is R17C what is that compared to R17's?

I have no idea. I know the sticker has R17C... but there is no "C" on the tire.

 

[HenryMac]

I notice that your wheels are shown as LT265's and the previous photo above yours shows just 265's.

That would account for the 38psi vs 30psi variance.

Not sure about that SN13. My spare isn't an LT tire (I verified that on the truck spare), yet the sticker on the door frame shows the same pressure, LT vs non-LT, @ 38 PSI.

And I checked the "factory air" in the spare tire... it has 38 PSI in it.

The other thing I'm noticing... on my truck the spare has a higher load capacity (112T), than the LT tires (109T)? And I think that's true of most trucks, the spare has a higher load capacity.

 

[VAMike]

Not sure about that SN13. My spare isn't an LT tire (I verified that on the truck spare), yet the sticker on the door frame shows the same pressure, LT vs non-LT, @ 38 PSI.

LTs always have a higher pressure than non-LT for a given load rating. The spare is probably defined as the same because having one tire running almost 10PSI/25% lower could lead to squirrely handling.

 

[gasmanjohn]

I've been running 35 front, 32 rear like a lot of you (FX4, P265/65-17). I'm going to be taking a 4500 mile road trip, all highway. Would you experts recommend upping the pressure a few psi for better highway fuel economy?. I've always done this in the past on my cars, but this is my 1st truck and didn't know if the same methods apply.

Thanks guys.

 

[CO2Ranger]

But you all haven't even accounted for altitude yet!

https://m.tirerack.com/tires/tiretech/techpage.jsp?techid=167

 

[runner69]

We all know on a truck the weight ratio, front to rear, is pretty dramatic when the truck isn't loaded.

I've always wondered why the sticker doesn't show an "Empty Truck" tire pressure and a "Loaded Truck" tire pressure?

Seems like that would be ideal, the correct pressure based on the actual loading.

Pretty amazing the variance of pressures based on tire sizes... here's a photo of the door sticker for my Ranger:

its not the tire size its the load ratting, you have the LT tires, 10 ply rated, the nonLT are 4 ply rated that's why the difference in pressure

 

[Dhass68]

I have no idea. I know the sticker has R17C... but there is no "C" on the tire.

A "C" denotes a 6 ply tire a "D" is an 8 ply tire and an "E" is a 10 ply

 

[HenryMac]

A "C" denotes a 6 ply tire a "D" is an 8 ply tire and an "E" is a 10 ply

Ugh... OK... Great...

So when the tire doesn't have a C.... or a D.... or an E... yet it has LT.... what say ye then?

 

[CO2Ranger]

Ugh... OK... Great...

So when the tire doesn't have a C.... or a D.... or an E... yet it has LT.... what say ye then?

According to Hankooks website you've got a 6-ply (as do I)

https://m.hankooktire.com/us/tire/passenger-cars/hankook-dynapro-at-m-rf10.html

 

[Waltztj]

What about the tire manufactures PSI rating on the tire? My factory FX4 tire say 51 cold and the door says 30 PSI

 

[Tim H.]

What about the tire manufactures PSI rating on the tire? My factory FX4 tire say 51 cold and the door says 30 PSI

You’re supposed to add the 2 and inflate to 81. ?

 

[Joeiconic]

Not sure why I didn’t think of this sooner. 34-35 front, 32 rear. Firms the front up nicely (more than you think it would) and the rear is still compliant. I am really happy with the feel now. Way less movement in the front. Perfect, and costs nothing to try.

Added: sticker says 30 front, 30 rear. I tried everything up to 35 front and rear then finally let some out of the rear to 32 and it seems to balance the truck out very well. It’s surprisingly how little it takes to change the feel.

You may like the feel, but your tires will likely wear poorly and unevenly at that psi.

 

[Joeiconic]

What about the tire manufactures PSI rating on the tire? My factory FX4 tire say 51 cold and the door says 30 PSI

The number on the tire is MAX inflation, not optimal inflation.

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