Tire pressure

[san dimas]

Hello everyone. I have a 14' tin boat that weighs about 250lbs with motor. My tires say 60 psi max. I was reading on another forum that guys with these lite boats run the tire pressure down to 35psi so that the trailer doesn't bounce so much. I have heard that if the tire says 60psi max then run it at 60psi. What's right?

 

[Oshkosh1]

Re: Tire pressure

Deflate em or it'll be bouncing all over the road
60 PSI is the MAX pressure, but they can be deflated to compensate for lighter loads.

 

[roscoe]

Re: Tire pressure

Trailer tire manufacturers tell you to run the tires at max pressure.
They require the pressure to maintain sidewall integrity.
An under inflated tire will flex and cause heat buildup. Heat kills tires.
Under inflating will also cause tire wear problems.

Hit a severe pothole, curb, or road debris with an under inflated tire, and you can cause serious damage.


From tire dealer site:
The trailer tire should state what load range it is on the side wall. Trailer tires should be inflated to their max psi rating listed on the tire sidewall for best performance and longevity.



From trailer manufacturer site:

Trailer tires should be run at their maximum inflation pressure. Consult the maximum pressure rating on the sidewall of the tire, and inflate your tires to this amount when the tires are cold. The pressure will rise as the tire heats up, so it is important to check them before you leave and not bleed off the pressure when they get hot. Most tire failures result from too low of pressure, overloading or excessive speed. These factors or a combination causes the tire to become hot and may result in a catastrophic tire failure.


From West Marine site:
Trailer tire safety tips:
Maintain pressure at the maximum PSI recommended on the tire’s sidewall for cool running, load-carrying ability and lowest rolling resistance.

When the manufacturers and dealers all say the same thing, there is a reason.

My new tires even came with a label, instructing to inflate to max pressure regardless of load.

 

[Oshkosh1]

Re: Tire pressure

I run about 45 PSI on my similar 14' Mirrocraft and have pulled it all over the country for decades without issue. Would I do the same with my "heavy" trailers(4 place sled/industrial size smoker/Wellcraft etc...)? No...but a 300lb tinny? Sure.

OEM's/dealers etc...say ALOT of things for legal/liability reasons.

 

[Bamaman1]

Re: Tire pressure

35 psi is okay for such a lightly loaded boat. If you were hauling a load that was 100% of the axle's weight capacity, you'd want to be on the high end of psi's.

 

[H20Rat]

Re: Tire pressure

Trailer tire manufacturers tell you to run the tires at max pressure.
They require the pressure to maintain sidewall integrity.
An under inflated tire will flex and cause heat buildup. Heat kills tires.
Under inflating will also cause tire wear problems.

So that is half of the story... Running a tire at max psi when you are running less than half the rated load is just as bad, ESPECIALLY if its a bias tire. So your comment about sidewall integrity is exactly correct. The tire manufacturer designed the sidewall to have a certain amount of deflection at max load/max psi. If you are running at half the load but max psi, your sidewall deflection is far out of spec in the opposite way.

Also, especially with a bias ply tire but even a radial, the load/psi directly contribute to how much tread is on the ground. Max load/max psi puts the entire tread in contact, but if you are at half load/max psi, the contact patch of the tire drops dramatically, even to an unsafe level. Want a good example? Watch the pattern your empty boat trailer leaves on the concrete after you unload... Only the very center strip will be touching, that is maybe 1/2 an inch on a tire that has 6 inches of tread! (and that doesn't show you the longitudinal loss of contact patch, its only one dimension of the story, it gets worse!)

Finally, your tire is going to wear on the center only, the outside treads aren't taking any load. This shortens the useful life of the tire, vs having the entire tread width take the load.


Long story short, adjust your PSI for the load within reason, and always error on the side of caution by using too much air. Manufacturers will always tell you max psi because it covers them when you screw up and overload a trailer. They have no liability if your tires wear out faster, or your trailer slides sideways because of lack of traction from too much air. Their only legal responsibility is to keep a tire from blowing out due to overheating.

(and one more 'finally' before I forget... Rims also have a max psi, and I've seen more than one ocassion where the rim psi was lower than the tire. NEVER, EVER exceed the rim psi!!! You risk having the thing rip you apart while you are filling it...)

 

[WIMUSKY]

Re: Tire pressure

Here's a link that provides a little trailer tire 101. Didn't watch the vid yet. Wife, who is sitting behind me, is in a meeting with her boss.. FWIW, I always maxed mine out........ I'm guessing you're running 4.80x8 load range B?

BoatUS - 11 Things You Need To Know About Boat Trailer Tires - BoatUS Trailering Magazine

 

[UncleWillie]

Re: Tire pressure

...They have no liability if your tires wear out faster, or your trailer slides sideways because of lack of traction from too much air...

Under and over inflating will have an effect on the wear pattern on the tread and how much the sidewalls flex and bounce the load but it will have no effect on the amount of traction/friction between the tire and the road.

The Force of Friction/Traction is independent of the area of contact.
The amount of traction is dependent on the coefficient of friction between the tire and the road and the weight of the trailer (Force).

The trailer will skid sideways in a sharp turn at the same speed whether the boat is on the trailer or the trailer is empty.

 

[fishrdan]

Re: Tire pressure

I run my 14'er under inflated. The 14' tinny trailer has 12" tires rated for 990#, but each tire only has 250# sitting on it (bathroom scaled it). At 60PSI the tires are seriously overinflated as in SC's pic and the trailer rides like a hay wagon. I've been running them at 32PSI for the past 4-5 years without issue, most of the time at "interstate speeds".... If I had left them at 60PSI the center of the tires would probably be worn out by now.

On my 18'ers trailer, I always max out the tire air pressure as they are running well into their load rating.

 

[Frank Acampora]

Re: Tire pressure

Uh---Willie---You are reading what you want to see and misinterpreting. While it is true that the coefficient of friction between the rubber and the road remains relatively constant (for a given road surface) The total frictional force is dependent upon the area of rubber in contact. THUS: Under inflation and over inflation reduce the optimal contact patch and the optimal friction developed.

Don't believe me? Why do dragsters run skinny tires up front and MASSIVE slicks on the rear? Bigger tire contact patch means more traction and, more rubber because there is no tread, means more traction.

 

[oregoncruiser]

Re: Tire pressure

:sleeping:

Do a search and you'll find that this is a highly debated topic, and you'll never get consensus. My $.02 worth is run them at the 35-45 mark. That trailer and boat will probably catch air running at 60 psi.

 

[NYBo]

Re: Tire pressure

It's going to be a long winter...

 

[KD4UPL]

Re: Tire pressure

I totally agree you should do what the manufacture says. However, I seriously doubt that what they really want is a 60 psi tire carrying that small load.
The fact is that any reputable tire manufacture will publish a load inflation table. This basically gives you a reference for how much weight a tire will carry at a certain pressure. You need to weight you trailer, then look up the table for your tires. It will be very easy to find the appropriate pressure. If your tire manufacturer doesn't provide such a table for some reason then you could find a similar tire from an other manufacturer, use their table, and apply to your tires.

 

[F14CRAZY]

Re: Tire pressure

I've had enough trailer tires wear a 3/4'' line in the center to say that max PSI is not always the best. I would be using less than max with a 14'' tin boat. I personally would use common sense and set them to something that has just a little "mush" then monitor wear and adjust from there.

 

[bigdee]

Re: Tire pressure

Trailer tire manufacturers tell you to run the tires at max pressure.
They require the pressure to maintain sidewall integrity.
An under inflated tire will flex and cause heat buildup. Heat kills tires.
Under inflating will also cause tire wear problems.

Hit a severe pothole, curb, or road debris with an under inflated tire, and you can cause serious damage.


From tire dealer site:
The trailer tire should state what load range it is on the side wall. Trailer tires should be inflated to their max psi rating listed on the tire sidewall for best performance and longevity.



From trailer manufacturer site:

Trailer tires should be run at their maximum inflation pressure. Consult the maximum pressure rating on the sidewall of the tire, and inflate your tires to this amount when the tires are cold. The pressure will rise as the tire heats up, so it is important to check them before you leave and not bleed off the pressure when they get hot. Most tire failures result from too low of pressure, overloading or excessive speed. These factors or a combination causes the tire to become hot and may result in a catastrophic tire failure.


From West Marine site:
Trailer tire safety tips:
Maintain pressure at the maximum PSI recommended on the tire?s sidewall for cool running, load-carrying ability and lowest rolling resistance.

When the manufacturers and dealers all say the same thing, there is a reason.

My new tires even came with a label, instructing to inflate to max pressure regardless of load.

Roscoe is dead on. Why are people so stubborn on this issue...life is simple just inflate to max and forget it! If anyone is dead set on running soft tires why not run passenger cars tires,they are designed for sidewall flex.
The other myth is that softer tires bounce less. The ONLY way to keep a trailer from bouncing is to install shock absorbers on it. Softer tires will cushion the shock but it has little effect on how much the load bounces up and down.
Just remember this fact...trailer tires will fail if the sidewalls are allowed to flex.

 

[UncleWillie]

Re: Tire pressure

Uh---Willie---You are reading what you want to see and misinterpreting. While it is true that the coefficient of friction between the rubber and the road remains relatively constant (for a given road surface) The total frictional force is dependent upon the area of rubber in contact. THUS: Under inflation and over inflation reduce the optimal contact patch and the optimal friction developed.

Don't believe me? Why do dragsters run skinny tires up front and MASSIVE slicks on the rear? Bigger tire contact patch means more traction and, more rubber because there is no tread, means more traction.

If you ever walk across the launch zone of a drag strip you will immediately notice that it is nothing like a public road.
It is so sticky you will almost walk out of your shoes.
The amount of traction IS dependent of the area of contact when Glue is involved.

The friction Formula

F= u x N

Where:
F = Force of Friction
u = Coefficient of Friction
N = Force Normal to the surface. (Weight/Load)

Notice that area is not part of the equation.

There 3 laws of friction are:
1. The force of friction is directly proportional to the applied load. (Amonton's 1st Law)
2. The force of friction is independent of the apparent area of contact. (Amonton's 2nd Law)
3. Kinetic friction is independent of the sliding velocity. (Coulomb's Law)

Friction is counter intuitive. Watch This!
A brick, a block of wood, or even a sheet of plywood will have the same amount of friction no matter which edge or face you place on the bottom and drag across the driveway.

Yes, an empty trailer will be easier to drag with locked brakes than a loaded trailer.
Not because the tires are flattened less, but because it weights less.

 

[bigdee]

Re: Tire pressure

The friction Formula

F= u x N

Where:
F = Force of Friction
u = Coefficient of Friction
N = Force Normal to the surface. (Weight/Load)

Notice that area is not part of the equation.

There 3 laws of friction are:
1. The force of friction is directly proportional to the applied load. (Amonton's 1st Law)
2. The force of friction is independent of the apparent area of contact. (Amonton's 2nd Law)
3. Kinetic friction is independent of the sliding velocity. (Coulomb's Law)

Friction is counter intuitive. Watch This!
A brick, a block of wood, or even a sheet of plywood will have the same amount of friction no matter which edge or face you place on the bottom and drag across the driveway.

Good data UncleWillie. Besides, who cares about traction on a trailer anyway?

 

[maproy99]

Re: Tire pressure

If you ever walk across the launch zone of a drag strip you will immediately notice that it is nothing like a public road.
It is so sticky you will almost walk out of your shoes.
The amount of traction IS dependent of the area of contact when Glue is involved.

The friction Formula

F= u x N

Where:
F = Force of Friction
u = Coefficient of Friction
N = Force Normal to the surface. (Weight/Load)

Notice that area is not part of the equation.

There 3 laws of friction are:
1. The force of friction is directly proportional to the applied load. (Amonton's 1st Law)
2. The force of friction is independent of the apparent area of contact. (Amonton's 2nd Law)
3. Kinetic friction is independent of the sliding velocity. (Coulomb's Law)

Friction is counter intuitive. Watch This!
A brick, a block of wood, or even a sheet of plywood will have the same amount of friction no matter which edge or face you place on the bottom and drag across the driveway.

Yes, an empty trailer will be easier to drag with locked brakes than a loaded trailer.
Not because the tires are flattened less, but because it weights less.

Willie you are 100% correct on this issue. Too bad you beat me with the well explained response. There are some other factors that become involved when you get off the pavement, like on sand..., but lets not go there.

 

[roscoe]

Re: Tire pressure

Well, you all have fun with this one, and get back to me when you want to discuss crimping vs soldering. Or Petrol vs synth.


For those of you that haven't yet had a tire failure, or popped one off the rim when you hit something, while running them at low air pressure, your day will come. Been there, done that. And that was with a 500# capacity trailer, 80# load.

And when you find a commercial hauler that drops his tire pressure down by 50%, because he is only loaded with 2 pallets of pillows, let me know.

 

[EddiePetty]

Re: Tire pressure

And when you find a commercial hauler that drops his tire pressure down by 50%, because he is only loaded with 2 pallets of pillows, let me know.

Now Roscoe, that got me to thinking. Talked to a couple of OTR truckers about your statement. They looked at me like I had two heads when I asked if they ever reduced trailer tire pressures with light or empty loads! Both confirmed that the majority of their tire failures were either run-flats, puncture damage or age of re-cap. FWIW.