I seem to have a bad habit of buying cars from people who put on strange tire sizes. No good explanation why they do it, or why I do it

I just bought a 1994 E150 conversion van. The previous owner took off the stock 15 inch tires, and put on P245/75R16 109Ts.

My door sticker calls for 41 psi (seems high to me but I believe Ford). What pressure should I use with the larger tires.


Thanks all!

Les

 

Hi Les, my 1992 E350 specifies LT245/75x16 tyres, and these are what my van has fitted. Sticker inside the door says front 55 psi cold, rear 80 psi cold! But she is a heavy van, it is a camper conversion, about 1900kgs on rear axle and 1300kgs front axle. (I do run these pressures BTW!) Your van will be much lighter, so you could probably run a bit less than this.

 

If the van is fully loaded, then go the the highest pressure listed. If not, then you can reduce that by 5-10 psi, depending on the load rating of the tire and the number the "plys" the tires are (4, 6, 8, 10 etc)

 

I am able to calculate a pressure if you give me more details of car and tires. Tires of Lesh are already given , they carry 1030 kg/2271 lbs AT 35 psi/2.4bar up to 99m/160km/h.
So because your speed wont be above that and you wont go over the GAWR's , more then 35 psi is not needed, and front most likely even lower.
this will give more comfort and gripp, and still save for the tires.

Will give copy of text I used in other fora so I dont have to write it 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.

 

What's the max pressure rating of the tires? If it's a conversion, shouldn't it have a tire pressure chart with the conversion house's name rather than Ford's?

Sixto
93 E150 Chateau 5.8 191K miles

 

@tabijan
Lesh11 s tires are P tires and have AT pressure of 35 psi in American system.
This is called mostly max pressure rating but is not the maximum pressure of tire.
His tires a P tires and for higher speed the 35 psi has to be added with a system.

Conrod has probably E-load tires with AT-pressure of 80 psi , and I ausume they are the original tires because plate on car gives 80 psi behind, wich is often done nowadays.
this is to cover overloading wich often happens behind, though by law its not permitted.
1400kg/3086lbs /Loadindex 120 I found with google if its realy E-load.
Then if Conrods Axle weights are realy 1900 kg rear and 1300kg front, wich is the most dangerous part in this all that estimating.
Then front roughly calculated 1300kg/( 2 x 1400kg)x 80 psi = 38 psi enaugh.
Taking maximum reserve with already slight bumping add 20%= 1300x1.2=1560/2800x80 psi=45 psi max needed.

Rear same system 1900x1.2=2280 kg/2800kg x 80 psi=66 psi.

But again , estimating the weight is verry dangerous, practice prooves its always more then you think.
Weighing , is the best way.

 

Friend of mine has a 1994 E150 conversion van. Door stickers (both Ford and manufacturer) state 41 psi cold for the stock tyres.

 

Wow, what a wealth of information.
The tires are labeled as follows:
P245/75R16 109T
Standard load
Max load 1030kg / 2271lb @ 51psi
plys 2 steel, 2 poly, 2 nylon
sidewall 2 poly
DOT T79L

I would not be exceeding 80mph in any instance.

The van was converted by Glaval, but the only door jamb sticker is from Ford as an "Incomplete vehicle".



Thanks

 

You're going to find the ride a bit rough at 51 psi. That would be the fully loaded psi

 

EDIT: Reading back I see that the original tires where XL, and you gave standard load for the new ones.
So will make new picture wich will give lower pressures because standard load = AT-pressure of 35 psi. Will give that in next post.

Seeing the plate you gave I see I made one mistake in my second post.
I assumed P tires only to be in normal car tire, but XL// is called also P-tire.
So the 35 psi I mentioned should be 41 psi.
At 41 psi at the bottom could also be meanth for the rimms, but think its for the tires.
On P-tires they only give maximum allowed cold pressure of yours 51 psi, but the AT-pressure we use for pressure advice up to 99m/h is that 41 psi in american system ( EUR 42 psi with exeptions) for XL/reinforced/Extraload as given on your plate.
Rimms also are given maximum cold pressure , so putting for instance E-load tires on the rimms might not be allowed. mostly this maximum cold pressure allowed for the rimm is written on the inside , so you have to get the wheel of the car to see it.

But OK , I filled in my motorhome calculator in LBS ,because American forum I assume, and with conversion you mean built as motorhome I think.
But correct me if wrong somewhere.

Will give the pressures first because having some problems lately producing pictures from my one-drive that belongs to my hotmail.com adress with same username as here ( so jadatis, combine yourselfes if you want to mail me, SPAMM machines cant this way).

Advice 1.
First filled in the GAWR's as given and tire data and gave F 32psi/ R41 psi.
This is highest needed pressure ( if device gives it right that is) with maximum reserve for things like , pressure loss in time, unequall loading R/L, expected overloading Rear, etc etc, but probably still no bumping.

Advice 2.
But also highened up the maximum load by 3 Loadindex steps to get the maximum load for up to 81m/130km/h ( a thing I figured out).
Then it gives F29psi/R37psi So this must be seen as minimum pressure with no damage done to tires up to your 80m/h. So if you measure that cold on the road, and are not able to fill up that moment, dont worry to much.

Advice 3
But also used my determined motorhome standard and that is next.
Substract Rear GAWR from GVWR to get probable weight on front axle.
7000-3800= 3200 lbs on front axle even when fully loaded or even when overloaded.
Left it at advice for 99m/h so maximum savety with probably no bumping, so pressure to fill if you check and are able to fill of 31/41.

The lower the front PSI the more comfort and gripp wich is for frontwheeldrive positive , but also for braking, and to give less nervous stearing. For comfort the front axle you experiënce most because you are sitting pretty close to front axle.
Rear weighing would comfirm that axle weight begins at GAWR for these light trucks, and overloading ,though not allowed , is more rule then exeption. If you then use a pressure yust enaugh for the gawr, nature will punishe with tire damage and mayby blowout, and axidents , and damage to motorhome or worse injured or death people.
so better to high pressure with some bumping, then to low with all the missery that can go with it.

Managed to insert a picture direct from my computer, so see if it works.
Is the first advice so highest needed.

 

OK then , here the correction with new picture.
Googled the 235/75R15 XL and apeared to be 108 LI , so not that much difference, but need 41 psi for that, because smaller .

Advice 1: 27/35 psi
Advice 2: 25/32 psi
Advice 3: 27/35 psi
And advice 3a is using my motorhome standard and 3 LI steps higher so lowest pressure with probably no tire damage for up to 81m/h.
Advice 3a: 24/32 psi.

And here the new picture of advice 1;

 

Okay so it seems we've drifted just a bit away from what I'd call better advice about tires, pressure etc----what the hell is the actual weight of your van as its driven daily? That along would/should be the main decision factor to selecting tires.

Door stickers assume one set of conditions that often vary considerably from the OEM configuration so info there might not be safely applied to your actual vehicle.

FWIW I run an extended body E250 loaded as a daily driver work van weighing just at 7,800# on Michelin LTX 245-R16/75's @ 70 PSI all around. This is what I found to work best in my situation yet it doesn't match the door sticker recommendations-----oddly enough that cites conditions where LT225-R16/75.

Injecting my own opinion most vans would greatly benefit from an LT rated tire over the P-rated due their more stout construction etc.

Just my $0.02 worth mind you, YMMV!

 

I agree that LT tires do better on a van, especially if it will be loaded down with passangers/cargo. Too many times there are threads about "scary handling" when loaded and tires are the culperate.

I run 225/75r16 LT tires on my E250. Sometimes it is just me in the van and sometimes it is full of passangers with a trailer. My door sticker says 58psi cold for the front and 80psi cold for the rear. Tires also say 80psi cold max. manual says to do 80psi all around when towing/loaded.I simply run 80psi cold all around all the time for lower rolling resistance. Gives me a mileage increase and I also see a reduction in my EGT. I am sure it affects my ride quality some, but it isn't terrible. Not sure if there are negative handling affects since I have not experienced any situation that calls for extreme maneuvers. ....and I hope in never do.

 

The ambulance I brought Uses the standard F-350 dually tires, 235-85-16 10 ply. GVWR 10,500 lbs. and I run 80 PSI front and rears using Nitrogen. As recommended by the body manufacture. It has air suspension in the rear, no springs all all. It's so you can drop the rear all the way down making loading patients easier. On board compressor inflates the bags in less than 2 minutes. So the ride is great, and I am sure if I put 65 psi in the tires she would smoothen out even more.

 

You're overcomplicating this. And a conversion van is not a motorhome. It's a dressed up "luxury" van. The first clue would have been the 15" tires it came with. These were common to "half ton" vehicles in the USA before the recent drive towards larger diameter wheels.