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Proper PSI / what is cold tire pressure

39K views 15 replies 14 participants last post by  kklebicki 
#1 ·
My tire and loading information sticker says my front tire cold tire pressure should be 49 psi, while my rear tire cold tire pressure should be 74 psi.

If I am out and about during the day, should I presume my tires are warm and fill to the 84 psi inscribed on my Continental VancoFourSeason 235/65R 16 C tires for front and rear?
 
#2 ·
howmanyds,

Inflate to what the factory sticker says, not what is on the tires. Mine says 49 /74 psi also.

Semper Fi
 
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#16 ·
I would agree.
I have a t350 with 10K miles and 2 tires seems worn on top. I'm thinking it's from the 74psi pressure I've kept as per recommendations. Given I'm rarely loaded over 1,000 pounds, I seriously doubt I need such high pressure. I think I'll go with 54 front and 64 rear from now on. Unless, of course, I see compelling evidence fir different numbers.
 
#6 · (Edited)
That has always been my take. Over the years I have used all kinds of tires on my trucks that were not nearly the same as the factory ones they came up with the figures for.

For instance, if the door sticker is not for E rated tires and you upgrade to them, you might be way off.

Also, as Orton indicates there is a difference between running empty and running loaded. I would rather see a recommended psi range for unloaded to loaded - minimum/maximum.
 
#7 ·
Found your question when searching for tire/tyre-pressure , wich I do every day. registered to give an answer.

Live and was born in Holland ( Europe) and once got hold of the officially used formula for calculating pressure for a sertain load, and went running with it.
Got much wiser in time about it and tires by the internet, but also by nagging tiremakers and others specialists on internet about it.
Even nowadays dare to call myself tire-pressure specialist ( but sertainly no tire-specialist).
Dont own a Ford Transit so dont think its usefull to introduce myself in a seperate topic.

Tire pressure advice is all about to give the tire for the speed used , a not to high temperature at any spot of the rubber so it hardens. Then if this damage is done , the tire crackes at those spots when the rubber bends, because the tire deflects.
Mind that every segment of an average tire deflects and flexes back about 10 times a second when driving 50m/80km/h.

To give the tire a deflection in cold condition that wont give to much heatproduction for the speed , there has to be a sertain pressure for the weight resting on it.

In time I constructed my own universal formula , of wich the European officiall formula can be made by putting the right power (P) in it, and the ( babtised by me) construction load,( Lc). but also an alternative one I found described by an American IR J.C.Daws, in his article where he compares it with the formula used in Europe and America.

To make it short I will copy text I saved , so I dont have to write it all over again.

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.
 
#8 ·
Googled the Continental tires, but could not find the AT- and maximum cold pressure .
But Continental is probably the only tire-maker who often gives and AT-pressure ( yours found 74 psi) and maximum allowed cold pressure by them, of 84 psi as you give.
This is 10 psi higher as for instance others also give for instance for ST tires.
There for 65m/h the AT pressure is given of for instance D-load 65 psi and for 75m/h , 10 psi extra is adviced so 75 psi.

Michelin also gives maximum pressure on their Camper tires of 80 psi but only that and dont give the 70 psi AT-pressure for that 8 plyrated tire , wich can be compared to D-load.

So also read from sidewall of tire , if both are given and 74/84 psi is right.

Continental also often gives an additional Loadindex Single and sometimes also Dual for other speed on their C( omercial)- tyres ( American LT for Lighttruck). For instance 115Q and aditional 117N or 113S.
See if you can find that too on sidewall of your tires.
 
#10 ·
howmanyds,


Since you've still got the original equipment manufacturer (OEM) tires on your Transit you'll want to make sure your tire pressure matches your door information sticker of 49 psi front / 74 psi rear.

As to your question of assuming your tires are "warm" and inflating them to the maximum PSI given by the tire manufacturer I would not do this. Over-inflating your tires will lead to uneven wear and a different/even unsafe ride than Ford's intended tune of your vehicle's suspension and tires. You're correct that you should inflate a little bit more than what is on your door sticker as your tires are "warm" after lots of driving, however since it is winter time your tires will not actually be very warm depending on the weather which means just make sure they're inflated to at least what is on your door sticker or a few PSI higher.
 
#12 · (Edited)
Vehicle manufacturers must spec tire pressure at full rated load, otherwise some guy will load the van to the max running less pressure and when a tire blows he'll want to sue them.

Some tire companies publish charts of the pressure that should be set at specified weights.
Interestingly the tire load rating has no bearing on pressure, in other words a 235/80-16 tire load range C specs the exact same pressure as a load range E of the same size, until the C rated tires maximum rated capacity is reached.
IOW at say, 2600 lbs the C, D and E rated 235/80-16 all spec exactly the same pressure 50psi. Once the weight goes beyond 2600 lbs the C rated tire can no longer be used but then at say 3000 lbs the D and E tire spec the same pressure 65psi.

And to answer the OP's question NO you cannot accurately set tire pressure while hot.

Here is a chart that may make more sense than I can-
http://www.maxxis.com/trailer/trailer-tire-loadinflation-chart
and another-
http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf
 
#14 ·
Good piece of reference. I use my van for mainly transporting my dirt bike or fishing stuff, estimate I've not yet load more than 500 pounds in the van so far. I've set the tire pressure to 42 psi/ front and 38 psi/ rear. The ride and handling is much better after taking it to a dirt road for a quick check. I'll install a set of TST TPMS to monitor the temperature for next trip.
Thanks for the info.
 
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