Hi All,


Silly question but, my tire sidewall shows a max of 51 PSI. My door sticker shows 36 PSI cold. I've googled the difference and get mixed answers. I have them at 36 PSI now per the door sticker. What is right (understanding that 51 PSI is way too high)?


Thanks.


JDH

 

The tire pressure is the maximum for the tire. If you have different size than OEM, I usually split the difference. For example, the LT tires I have, the sidewall states 85 PSI max. My door sticker says 32. I run them about 50 PSI.

 

Well, I bought a tire compressor mostly for my snowblower and figured I should top up my D's tires while I was out there. The Goodyears read 51 PSI max which seems really high to me so I was aiming around 44 PSI until I caught sight of the door sticker which read 36 PSI cold. That seems more like every tire I've had so I ended up deflating the 3 from 44 while my 4th hit 36. I'm sure there's a proper explanation out there outside of splitting the diff but I haven't found it yet. I've been to Kal Tire and Tire Rack but I haven't really tried that hard since I figured the forum would know best.

 

The PSI numbers of the door sticker is to ensure the correct tire contact patch (surface area) for optimal handling characteristics, as determined by the engineers. If you have the stock tire size on the vehicle, use the pressures listed on the door sticker. PSI is Pounds per Square Inch. So if we assume the vehicle weighs 5600 lbs and that is evenly distributed over all 4 tires, each tire is supporting 1400 lbs. At a tire pressure of 36 PSI, each tire then is making contact over 38.9 square inches (1400/36 = 38.888888). For the same size tire, that calculation will remain regardless of the sidewall Max PSI rating. There's no reason to alter the tire pressure just because the sidewall lists a different number.

If you go with a different tire size you could reverse the calculations to determine what tire pressure would be appropriate to get the same contact patch. However the geometry of that contact patch will be slightly different depending on if the tire is wider, narrower, stiffer sidewall, etc.

-Rod

 

I've always run mine higher than a car manufacturer recommends. I run 40psi on my D with 20" wheels.

Even at work (on a 445/50R22.5 tire at 120psi) I've gotten better wear and longer life than the 100psi our company recommends. I tend to lean towards what the tire manufacturer recommends, but clearly not to their "max".

roog

 

the 51 psi is the maximum allowed cold pressure by the tire-maker, and is given on sidewall only for Standard load wich have an AT-pressure of 35 psi in USA system and 36psi in European system with exeptions to lower.
Also for XL/reinforced/Extraload with AT- pressure of USA 41 psi and EUR 42 with exeptions 41 and 44psi this max of 51 is given.
From C-load ( USA ) with at pressure of 50 psi ( EUR 6PR for plyrating 55 psi) they give AT -presssure on sidewall and maximum allowed cold pressure can be 1.4 times At pressure.

This AT pressure is the cold pressure for wich the maximum load is calculated up to maximum speed of tire, or if lower 99m/160km/h.
Also called maxloadpressure or in the formula I got hold of European ETRTO reference-pressure.
This AT-pressure is also cold, so when inside tire temp is outside tire temp and about 65 to 70 degr F outside.

The 35 psi you give, is not coincidentially the AT - pressure of a Standard load P-tire, this is nowadays often given for absolute savety.
But I will give text I used for other topics and saved, with info what you need to calculate ( or let me do it) an advice pressure.

Tirepressure advice is all about load on tire and speed ( and sometimes about alighnment - camber angle).

So if you can give details of car and tires , I can calculate an advice pressure with some reserve for things like, pressure-loss in time, unequall loading R/L, incidental extra load, misreadings of pressure scales,and misyudging of weight, etc.

This is from tires next and can be read from sidewall:
Maximum load or loadindex.
Kind of tire to determine the AT-pressure/pressure needed for the maximum load up to maximum speed of tire, or if lower 160km/99m/h/reference-pressure, wich is not the maximum pressure of tire.
Maximum speed of tire, most given as letter ( Q=160km/99m/h,N=140km/86m/h fi)
If you have offroad or tires looking like that , with large profile blocs that cover a part of sidewall, also mention, they are allowed lesser deflection then a normal road tire, then the tire maker used to determine the maximum load (to my conclusion the case for the Bridgestone tires on Ford Explorer in the Ford/Firestone affaire).
If you cant find all of it give sises of tire and Loadkind, then I will google for it.

From car next and mostly can be found on same plate as the original pressure advices:
GAWR and GVWR ( Gross Axle/Vehicle Weight Rating)
But best would be to determine the real weights in your use on seperate tires or estimate it as acurate as possible, by weighing per wheel(pair) or axle.
Maximum speed , you dont go over for even a minute in your use, eventually different for different situations, for instance when towing or fully loaded.This apart from trafic regulations, if you drive faster then allowed give that speed. Nature punnisches with tire-failure, police only with a penalty.
Give all that and I will calculate and give a picture of one of my filled in spreadsheets in my answer.
If other then original tires, indead as is already answered other advice is needed, a stiffer tire ( fi C-load instead of P-tire) needs a higher pressure for the same load, or the other way around, has lower loadcapacity for the same pressure.

Greatings from a Dutch pigheaded self-declared tire-pressure-specialist.

 

I've always gone with whatever the door sticker says. It's always been just fine.