Tire pressure

[Home Cookin']

Re: Tire pressure

"you have instantly massively reduced road surface" No, you haven't, if there is no load on the tire, even if it's a tyre. The question is not about running a full load, but a light load. The effects you describe from over-inflating will occur with a max inflated tire and a light load. It's all about balance.

Good point, though, about road surface. When I drove through your outback on the corduroy roads*, we just kept the "5 tonne" landcruiser at 70 and floated right over it!

*dirt/gravel roads with even ruts perpendicular to your line of travel--their interstates can be one lane roads!

 

[Silvertip]

Re: Tire pressure

I think all of you tire "experts" need to have a look at this link. Pay particular attention to the discussion about how a tire sidewall loads and unloads during its rotation and the affect of inflation pressure. My 3500# cargo trailer tires have a very rounded tread profile. Because the cargo is shock sensitive, in an attempt to soften the ride I tried running the tires at 35# rather than 50# since weight is not an issue. Ride is not significantly improved and even at reduced pressure the outer edges of the tires do not contact the road.

Tire Tech Information - Checking Tire Inflation Pressure

 

[bigdee]

Re: Tire pressure

Because the cargo is shock sensitive, in an attempt to soften the ride I tried running the tires at 35# rather than 50# since weight is not an issue. Ride is not significantly improved and even at reduced pressure the outer edges of the tires do not contact the road.

Monroe RV & Trailer Shocks/Kits This is the only solution to reduce bounce. The type of tow vehicle also has an effect on how the trailer rides. A SUV with a soft suspension will allow the trailer to ride better than a truck with a stiff suspension. Playing with air pressure is barking up the wrong tree.

 

[san dimas]

Re: Tire pressure

I talked to my trailers manufacturer and he said max pressure regardless of load.

 

[MH Hawker]

Re: Tire pressure

Well what little I know is I set mine to what ever the tire is rated at and run them. IN 25 plus years I have never had one wear out its all ways age that gets them.

 

[Hoobz]

Re: Tire pressure

After a long hot day of working outside doing carpentry yesterday, I let off a bit of steam last night in this thread. Plus I haven't got a boat at the moment, which makes me more irate maybe?

I tow a work tradesman's trailer everyday, and have found that adjusting the pressure of the tires to suit the load has reduced transport wear and tear (from road surface vibrations and sharp road hits) of many items in the trailer over the last 20 years.

Having said that a lot of light boats cop a hiding from water surface anyway. Plenty of vibes going on there too. So what's a ten minute drive with vibrations on a trailer gunna do?

"you have instantly massively reduced road surface" No, you haven't, if there is no load on the tire, even if it's a tyre. The question is not about running a full load, but a light load. The effects you describe from over-inflating will occur with a max inflated tire and a light load. It's all about balance.

Good point, though, about road surface. When I drove through your outback on the corduroy roads*, we just kept the "5 tonne" landcruiser at 70 and floated right over it!

*dirt/gravel roads with even ruts perpendicular to your line of travel--their interstates can be one lane roads!

I kind of exaggerated a bit.

I might try and chill out today. It's Friday.

It's interesting to read everyone's thoughts on the topic.

Even though quite a few have no idea

 

[dingbat]

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.

You can throw your friction formula out the window when it comes to tires because of the dynamics involved.

COEFFICIENT OF FRICTION
The coefficient of friction is defined as a unit less ratio of friction force to normal force. It is generally considered true that the resulting friction force is not proportional to the surface area of contact. However, this is far from the truth when a rubber tire is considered. This dissimilar behavior is due to the viscoelastic nature of rubber. Thus, as force is applied, deformation occurs both elastically and plastically in a non-linear fashion due to the mechanical behavior of polymer chains (Ref 6). Viscoelasticity also explains why the coefficient of friction of a tire is load dependent. As a tire is loaded, the surface area grows larger increasing the total friction force but lowering the coefficient of friction (Ref 1). Since a tire does not follow Newton’s laws of friction, a coefficient of friction above unity can be obtained. For example, given a 500 lb normal load on a tire, it would not be uncommon for a tire to produce 800 lb of force giving a coefficient of friction of 1.6. Under ideal conditions, this would make the vehicle capable of pulling 1.6 g’s (Ref 2). However, ideal conditions are rarely achieved because the coefficient of friction depends on many transients.

Here is a paper on the subject
http://www.engr.colostate.edu/pts/Job/Understanding Parameters Influencing Tire Modeling.pdf

 

[bigdee]

Re: Tire pressure

Back to the OP question about trying to soften the trailer ride. What size tires are on your trailer? I am assuming for that size trailer they are probably 4.80x12 and if that is the case you most definitely do not want to lower the pressure. If your goal is to improve ride there are a few things you could do that may help. Make sure your tongue is level or slightly downhill. Move the boat to get 10 to 15% of weight on the hitch. Strap the boat securely. Unless a trailer has shocks it will ride rough,period. Softer tires or springs may cushion the shock of hitting bumps somewhat but will do nothing for bounce. You can only attenuate bounce with shocks not more springiness.

 

[Frank Acampora]

Re: Tire pressure

Thank you, Dingbat!

According to the reference cited by Uncle Willie, a fully loaded 18 wheeler should be able to stop in the same distance as a Corvette--and we all know that is just not true. I just didn't know how to counter the argument.

 

[san dimas]

Re: Tire pressure

Yes bigdee, my tires are 4.80X12. It actually says iflate to 90 psi but I'm afraid I'll blow the side of the rim off

 

[san dimas]

Re: Tire pressure

Forgot to say I've been running them at 60 psi.

 

[UncleWillie]

Re: Tire pressure

Yes bigdee, my tires are 4.80X12. It actually says inflate to 90 psi but I'm afraid I'll blow the side of the rim off

Forgot to say I've been running them at 60 psi.

4.8x12 Load range "C" Tires;
YEP! 90psi. At 60psi you are way under inflated.

 

[UncleWillie]

Re: Tire pressure

Thank you, Dingbat!

According to the reference cited by Uncle Willie, a fully loaded 18 wheeler should be able to stop in the same distance as a Corvette--and we all know that is just not true. I just didn't know how to counter the argument.

There are a lot of variables in the real world that are hard to control.
The composition of the tire and the road make huge differences.
Debris/Impurities between the two materials effect the traction.

On sand, Decreasing the tire pressure increases traction because the surface can not support the load.
On a wet puddled surface, Increasing the pressure increases the traction at speed because the water can not support the higher load pressure and hydroplaning is delayed.

The Tires on the Corvette were chosen for increased traction and maneuverability at the cost of longevity.
Like motorcycle tires, the rubber compound is soft to allow extra compliance in turns and high acceleration maneuvers.

18 Wheel Truck tires are composed of much harder rubber compounds; longevity is of higher concern than maneuverability.
Shipping companies would go out of business if their tires only lasted 50,000 miles.
They would have to replace tires 2 or 3 times a year.

All thing being equal; there is no reason that an 18 wheeler and a Corvette would not be able to stop in the same distance.
If (Big IF)they were both on the same road surface, With tires composed of the same rubber composition, traveling in a straight line, at the same speed, with all tires locked up in a skid;
They would both stop in the same distance.

The weight of the vehicles and the amount of rubber on the road will not effect the outcome.
The coefficient of friction is the controlling variable.

The wild card in this experiment is trying to get tires for the truck and the Corvette manufactured out of the same batch of rubber.

In the real world the Corvette with it's sticky tires will win every time.
However, changing the pressure in the tires of the Corvette will affect tire squirm and how it performs in turns, but it will not produce any difference in the locked wheel, straight line, stopping ability.

ST Trailer tires come as close to ideal conditions are you will likely get.
They are designed for minimal flex and squirm and react almost as if they were solid rubber.
Lowering the pressure to get a larger footprint on the road will only get you a tire that runs hotter and does not last as long.

 

[Frank Acampora]

Re: Tire pressure

AND, If you (meaning everyone who read it) took the time to fully read the cited article by dingbat, near the end you will see that they DO claim that tire pressure (here as related to racing tires and vehicles) is set individually to vehicle, load, and expected use (within design pressure parameters). I was never arguing that, only that the video you cited was not applicable to tires.

In my case, all my trailers are at or very near their rated capacity so I set my tires to mximum pressure.

 

[Silver Eagle]

Re: Tire pressure

I just don't get it. What's the dealyou guy's sound like a bunch of old ladies. If the tire pressure says 60 lbs, do it. My 24 ft pontton boat trailer has 10 inch tires .They say 50 lbs. That's what I use and the trailer tows great. So where's the problem ladies. ?

 

[beardeddone]

Re: Tire pressure

There are a lot of variables in the real world that are hard to control.
The composition of the tire and the road make huge differences.
Debris/Impurities between the two materials effect the traction.

On sand, Decreasing the tire pressure increases traction because the surface can not support the load.
On a wet puddled surface, Increasing the pressure increases the traction at speed because the water can not support the higher load pressure and hydroplaning is delayed.

The Tires on the Corvette were chosen for increased traction and maneuverability at the cost of longevity.
Like motorcycle tires, the rubber compound is soft to allow extra compliance in turns and high acceleration maneuvers.

18 Wheel Truck tires are composed of much harder rubber compounds; longevity is of higher concern than maneuverability.
Shipping companies would go out of business if their tires only lasted 50,000 miles.
They would have to replace tires 2 or 3 times a year.

All thing being equal; there is no reason that an 18 wheeler and a Corvette would not be able to stop in the same distance.
If (Big IF)they were both on the same road surface, With tires composed of the same rubber composition, traveling in a straight line, at the same speed, with all tires locked up in a skid;
They would both stop in the same distance.

The weight of the vehicles and the amount of rubber on the road will not effect the outcome.
The coefficient of friction is the controlling variable.

The wild card in this experiment is trying to get tires for the truck and the Corvette manufactured out of the same batch of rubber.

In the real world the Corvette with it's sticky tires will win every time.
However, changing the pressure in the tires of the Corvette will affect tire squirm and how it performs in turns, but it will not produce any difference in the locked wheel, straight line, stopping ability.

ST Trailer tires come as close to ideal conditions are you will likely get.
They are designed for minimal flex and squirm and react almost as if they were solid rubber.
Lowering the pressure to get a larger footprint on the road will only get you a tire that runs hotter and does not last as long.

Can you clarify this for me and let me understand exactly what you wrote here, is it my understanding that your saying that a Corvette and a 18 Wheel Truck should be able to stop in the same distance?

Surely I mis-read this.

 

[bassman284]

Re: Tire pressure

Thanks UncleWillie for a very informative post. Great stuff. I have so much to say it's probably better I say nothing for now.

 

[bassman284]

Re: Tire pressure

Can you clarify this for me and let me understand exactly what you wrote here, is it my understanding that your saying that a Corvette and a 18 Wheel Truck should be able to stop in the same distance?

Surely I mis-read this.

What he's saying is that if the 18 Wheeler had the same kind of gummies on it that the Corvette has, they would stop in roughly the same distance. Ain't going to happen because if the truck ran that kind of rubber they would be replacing tires every 3 or 4 months. Or less.

For another example, look at Formula 1 cars. Very fast and handle very well, but their most impressive feature is how they stop. They routinely pull 5 Gs decelerating for the tight turns. At the Austin GP this year, some were approaching 6 Gs into turn 12.

 

[roscoe]

Re: Tire pressure

Let's talk more about friction grip and traction for tires that are mounted on non drive, non steer axles with no brakes, and little to no practical side force.


Ding ding ding !! Round 8.

 

[bigdee]

Re: Tire pressure

Let's talk more about friction grip and traction for tires that are mounted on non drive, non steer axles with no brakes, and little to no practical side force.


Ding ding ding !! Round 8.

I'm glad someone finally brought this up. Life with a trailer is simple. We do not need to worry about grip,traction,surface area or bounce.....just make sure inflation is correct.