Tire PSI Rting Qestion.

[kyle f]

I know this may border on duh... but I have three different tires out here, on three different vehicles, nd they all have a max load rating at 50PSI.

Does that mean I should run them at 50PSI, or just that I could?

These Three tires are on:

Boat trailor
84 Bronco
00 F250 Diesel

All different sizes, all different load rating etc.

 

[bjcsc]

Re: Tire PSI Rting Qestion.

It means that they will carry their max load of whatever they say at that max PSI. You should inflate them to whatever your vehicle manuals call for (typically less)...but that could change depending on what you're doing.

Ex. In my CJ-7, running BFG MTs, I run them at ~40-45PSI on the road and ~20-25PSI on the dirt.

 

[kyle f]

Re: Tire PSI Rting Qestion.

OK, no stickers or manulas for the 84 or the Boat trailor... I think the Door Jam stickers are still on the F-250, but they are not OE Tires.

 

[JB]

Re: Tire PSI Rting Qestion.

Run the tires on the boat trailer at 50psi.

On the others do what the manual says to do.

 

[jeeperman]

Re: Tire PSI Rting Qestion.

Dang that must be a rough ride with 50 psi in the Bronco tires.

Which are not o.e.m. size or types or ply rating are they?

Running tires per the manual when your not running the same tires as it came with can be dangerous.

 

[kyle f]

Re: Tire PSI Rting Qestion.

Currently the Bronco is ran at 35Psi. Its an OK ride... afterall it is an 84 Model. F250 is Running at 45Psi as it was that way when I picked it up from the dealer.(means very little to me)

Boat Checked in at 35Psi, but it has been sitting on my concrete slab over winter and I am just workign on getting everythign ready for the first trip. WOuld rather take care of it slowly overtime instead of tryign to rush it all done the night before we head out.... never a good idea IMO.

 

[Gary H NC]

Re: Tire PSI Rting Qestion.

What JB said,The trailer tires do need to be 50 psi,the others are probably fine.

 

[hankll]

Re: Tire PSI Rting Qestion.

I have Carlisle trailer tires, and w/ 50 psi in them, aren't I looking at a blow out more likely than if I ran them at say 35psi? I have 19'6' ProCraft which is pretty heavy, with all gear, I'm guessing it to be 2400 lb.

 

[Mkos1980]

Re: Tire PSI Rting Qestion.

I have Carlisle trailer tires, and w/ 50 psi in them, aren't I looking at a blow out more likely than if I ran them at say 35psi? I have 19'6' ProCraft which is pretty heavy, with all gear, I'm guessing it to be 2400 lb.

Heavy boat + low psi = alot of heat buildup. Run them at max psi.

 

[kenmyfam]

Re: Tire PSI Rting Qestion.

Trailer tires at max inflation without a doubt otherwise excessive heat build up = tire failure.

 

[4poco]

Re: Tire PSI Rting Qestion.

personally, I run my boat trailer 5 psi over max.(55psi) because tires are wearing on outsides.Have not had any issues. As far as truck and cars, I run psi about 10 psi less then max for little better ride. I am sure everyone has an opinion, this is just my preference.

 

[edzzed]

Re: Tire PSI Rting Qestion.

when you measure the psi do it with the tires cold. don't drive 5 miles to a gas station to check the pressure. air expands with heat and 50 cold could be 65 or more hot. then you'd be letting 15 out and running even hotter wheels in the end. just go with what is on the tire sideawall. they must know what the designed specs are. Ed

 

[Andrew Leigh]

Re: Tire PSI Rting Qestion.

Hi

In order to make an informed decision you are missing some information, the max load rating for the tyre, the tyre profile and the speed of towing (although it must be said that you will never exceed the speed rating of a normal passanger tyre when towing). The tyre profile is important, if you are using a low profile you dont have much latitude when it comes to deflation.

Generally the load rating of tyres well exceeds the requirement of a car / truck. With a two wheel trailer things get more interesting.

I recently discovered this on refurbing my boat trailer. It was fitted with 13" rims and 6.1" tyres with a normal profile of 3.15" (all conversions from metric). This tyre has a load rating of 963 lbs per tyre, my boat weighs 3000lbs loaded ....... yup i'm in trouble.

The bottom line is that I cannot get tyres for 13" rims that will take the load I have so I now need to upgrade to 14" rims with new tyres. Here there are also choices, one can stick with a passenger tyre or one can move to the higher load bearing crossply tyres normally used on light delivery vehicles. Apart from the load and speed rating the only other difference I can see is road noise.

So after that boring interlude I concur with JB, the load a boat places on the trailer tyres is fairly constant (same fuel fishing gear etc.) one normally will tow at safe speeds here we are allowed to tow at speeds up to 75mph. Normally the trailer designer will design the trailer at meet to max load, therefore run at max pressure. I would not overinflate, that will lead to excessive bounce.

My camper that I tow has the maximum 50PSI printed on the wheel arch.

On passenger vehicles the manufacturer has calculated the best pressures for a variety of load scenarios, follow those. If you drive fast then it is wise to overinflate, my tyre guy once told me that that traveling at 100mph vs 60mph is a doubling of downforce on your car.


Cheers
Andrew

 

[JMRuth72]

Re: Tire PSI Rting Qestion.

When I set the tire pressure on a vehicle I never go less than the door stickers recomendation and more than the tires max psi rating. Other than that I play with the pressures until I feel like I am getting the best ride, and handling. Example I had a 06 nissan 350Z for a while. The tires were inflated to 35psi, but I noticed the max for the tires was a little over 50psi. Believe it or not when I upped the pressure to 50psi the car actually rode better, even my wife noticed the difference. The only thing that I can figure is that it allowed the suspension to do its job with out have essentially a double spring ( the suspension spring + tire acting like a spring ). All I do know is that it made a massive difference. I have also just put better tires on my truck that are rated at much higher psi than the truck says. I am currently running 50 and it is much better than it was. Play with the numbers until YOU like the feel and then leave it there. Just don't go below minimum (generally 35psi) or over max for the tire and you will be good. By the way you might just reduce the rolling resistance and gain a little mpg. I know that I did, it is not much but something is better than nothing.

 

[donnymac]

Re: Tire PSI Rting Qestion.

When I set the tire pressure on a vehicle I never go less than the door stickers recomendation and more than the tires max psi rating. Other than that I play with the pressures until I feel like I am getting the best ride, and handling. Example I had a 06 nissan 350Z for a while. The tires were inflated to 35psi, but I noticed the max for the tires was a little over 50psi. Believe it or not when I upped the pressure to 50psi the car actually rode better, even my wife noticed the difference. The only thing that I can figure is that it allowed the suspension to do its job with out have essentially a double spring ( the suspension spring + tire acting like a spring ). All I do know is that it made a massive difference. I have also just put better tires on my truck that are rated at much higher psi than the truck says. I am currently running 50 and it is much better than it was. Play with the numbers until YOU like the feel and then leave it there. Just don't go below minimum (generally 35psi) or over max for the tire and you will be good. By the way you might just reduce the rolling resistance and gain a little mpg. I know that I did, it is not much but something is better than nothing.

Another story for thought. I bought a 1990 Pathfinder off the show room floor in well 1990. It came with P235/75 15's. Max sidewall pressure said 35psi. The door sticker said to inflate to 32psi all around. After many questions to various tire shops I was told that the suspension was designed to work best with the 32psi. So I did. 5 years later I got a deal on some LT235/75 15's
Max sidewall said 80psi. When they were being installed I asked the guy what pressure he was going to put in them. He said 32psi all round cause that is what the door sticker says to run So we disscussed for a while and I left with 32psi. Well the first puddle on the hiway I felt I was water skiing So I went to 40psi. Still hyroplaned. 50psi, no hydoplaning. The handling was more abrupt, but I felt more confidant with the LT's when off-roading on rocky terrain. I did go to 80psi, but I lost 2 fillings in my teeth and it was just way to rough of a ride. At 50psi tire wear was normal and I got
75000km's out of them. No opinion, just food for thought. Oh and I always run sidewall pressure on the trailer tires.
D.

 

[ocb_dave_ocb]

Re: Tire PSI Rting Qestion.

Trailer tires probably 45 - 50 psi
Bronco 32 - 36 psi
F-250 34-38 psi

That IMO.

I worked in a garage for 2 years, when we inflated the tires its was at what the door called for, if the door didn't have a sticker they were filled to 35psi

 

[JMRuth72]

Re: Tire PSI Rting Qestion.

That sounds about right. I would have to say that the reason you hydroplaned is that your tires were wider than designed to be because of the lower than required (for them and your truck) air pressure. By increasing the air pressure you stood the sidewall more upright essentially narrowing the tire to its designed width. Therefore cutting through the water instead of floating over it. Wider is not always better. There are a lot of things that effect what tire pressure to use and I am not going to pretend to be an expert. I have just learned by playing with my own vehicles. That is why I start at the door sticker and work my way up to the tires listed max until I am happy that I am getting the best ride and handling. The differences between P-metric tires and LT tires throws that out the window and I start with a higher pressure than the door sticker. My limited experience with them shows a good starting point of 10psi higher than the door sticker is a good starting point. It seems that the higher the max pressure then the higher that you have to start. I think that my new truck tires have a max rating of 55psi, but I can't remember for sure and I am happy at 50psi. My truck rides a lot better, it doesn't feel like it bucks, but it also doesn't feel mushy, wobbly and bouncy. It feels more competently confident. Kind of hard to describe what it used to feel like. I just know that I didn't like it. When it feels like the suspension is doing its job with out being drastically effected by the tires it is about right. However let me see if I can explain what I read about springs in a book about automotive mathematics.
If you take 2 springs designed to compress 1 inch with a load of 250lbs and put them parellal (side by side) it will take 500lbs to compress them 1 inch. However if you take those same springs and put them in series (on top of each other) it will take only 125lbs to compress them 1 inch. Does this make since to anyone yet? Well essentially what you are doing in a car suspension is putting 2 springs in series and you are damping only one of them (the suspension spring is dampened by the shock). Therefore if you fill the tire with higher pressure air it acts less like a spring and makes the shocks do their job of damping the dynamic load. Depending on your use and load changing your tire pressure to match is a really good idea.

 

[donnymac]

Re: Tire PSI Rting Qestion.

Both sets of tires were metric sized. 235=width, 75=%of 235 is the height.
The "P" stands for passenger and the "LT" stands for light truck.
But I know you knew that The difference in weight of the 2 tires when I held 1 in each hand was quite noticable. The LT's had more belts on the tread and sidewalls. And the load capabilities, well I could have stacked 2 Pathfinders and still been within load range