Why two axles????

[Francesca Knowles]

Originally Posted by Jim Bennett

Tire pressure is totally independent from the weight carried. Whether I have a trailer with the tires at 80 lbs with the 4,000 lb load, or with a 14,000 lb load, the tire pressure is pretty much the same. If you carry heavy loads, you want to have your tires near maximum pressure.

It's my understanding that tire pressure is based on the weight of the load. That's why the number on a car door, for example, is usually below the tire's actual maximum capacity.Any particular tire has a range within which it can be used on many different vehicles, each at a particular (under the max) pressure determined by the vehicle manufacturer.

And here's a chart for trailer tires that more or less illustrates the same thing:




Francesca

[MC1]

Originally Posted by Francesca Knowles

It's my understanding that tire pressure is based on the weight of the load.

Francesca

Agree.

[Thomas G.]

Originally Posted by Jared J

Wheel bearings never used to be tapered, and still took the side loads. ............

I'm 60 years old and remember packing tapered wheel bearings as a kid. When was never to you?

[Jim Bennett]

Originally Posted by Jared J

Wheel bearings never used to be tapered, and still took the side loads.

As for tire pressure, he meant with less load, you can run less tire pressure.

A dual wheel single axle won't track as well as a double axle will.

Never knew that, but I am just a Whipper Snapper according to Francesca.

Gotcha

Absolutely agree. Having towed hundreds of different trailers I can't think of one that had a single dual axle. Tandem duals I have used though.

Originally Posted by Francesca Knowles

It's my understanding that tire pressure is based on the weight of the load.

My thinking is that it is based on the limit of the load, the max the trailer can handle. Even the chart you show is based on limits, not necessarily the amount carried. While one can lessen the pressure lower than maximum as the weight decreases, it is not necessary. Reace from Escape told me he recommends running at or near maximum pressure, as I have done with almost every trailer I have owned, including lots of construction and holiday ones.

One is not expected to change pressure for different loading for a give trailer with its specific tires. I would go crazy trying to pressure up and down trailer tires many times a day, if you used a tire pressure based on the weight of the load. Trailers get loaded and unloaded frequently. I know that this is to a much lesser degree with our travel trailers, but it still holds true.

[Francesca Knowles]

No one, least of all me, suggested changing tire pressure every time a trailer gets a couple of gallons of water etc. Most of us know within a couple of hundred pounds what our loaded trailers weigh, so it's easy to set an optimally high-end pressure and keep it there unless conditions dictate otherwise.

I actually learned this in this very forum, and had to "unlearn" always running the tires at the max...and I'm more than satisfied with the resulting improvement in the ride.

Francesca

[Brian B-P]

Originally Posted by Jared J

Wheel bearings never used to be tapered, and still took the side loads.

Yes, ball bearings handle axial loads as well. You could even use plain bushings, but there would be a thrust washer or other axial bearing surface (check out a kid's wagon or your lawn care equipment for an example). A wheel/hub bearing must handle both radial and axial loads to transmit a vehicle's sideways force, and it does handle both. Tapered roller bearings do very well for both, but are relatively expensive, so they are used where both directions of load are important.

Whatever the bearing type, side loads are carried through a chain of components, and like any chain each link carries the full load. The chain in this case includes tire tread, tire sidewalls, wheels, hubs, bearings, suspension components (such as leaf springs + bushings + brackets, or torsion axle arms + rubber + tube + brackets), and the frame. I offer no opinion here on which is likely to fail or how any of them are affected by the choice of single versus multiple axles.

[ruscal]

I wonder if this whole tire pressure thing could be just gauged by your eye and never to exceed the manufacturer’s weight limit? Say if you knew a tire could carry maximum weight at a certain maximum pressure while traveling at freeway speed because the manufacturer formulates these ratings at normal traveling speeds. Then you load your trailer to the maximum tire pressure rating, but you are 10 PSI under the recommended setting. You notice the tire will be deformed and squatting. Will the tire blow out or fail while parked? I don't think so. Its strength is not likely in question. It is at speed that the havoc happens. It is likely caused by all that deformation and puckering of the sidewall which has to straighten and re-pucker with each revolution of the tire. That causes friction within the composition of rubber and cords of the tire. Friction causes what? Heat. Heat can cause what? Meltdown. Blooey!
So why not just use our eyes to determine how much air is needed as we load our trailers? Eliminate excessive pucker without exceeding the tires recommended maximum? If it doesn't flex much it won't heat much. A lightly loaded trailer surely does not need maximum tire pressure.
Russ

[Francesca Knowles]

I keep a close eye on everything having to do with my tires, but for pressure readings I insist on using an old-fashioned mechanical gauge. I've had a slow leak a time or two, and mightn't have known it in time to prevent disaster otherwise.

It may be that I'm hypervigilant, but in my own defense I'll say there's nothing like a front end blowout at freeway speeds to teach one to be that way. (Non-towing incident, and the last time I let my husband tell me "there's plenty of life left" in tires that I was pretty sure were shot.)

Per the trailer weight charts:

Certainly, just as with a car, one should listen first to the trailer manufacturer per tire pressure. It's their design, and who knows what part pressure plays in the performance of the product itself.

And in the case cited by Jim, (fifty pounds for his Escape19), if his trailer has 3500 pound axles and load range "c" tires, fifty pounds of pressure is probably right about where he'd find himself in the chart anyway!

Francesca

[Jared J]

Originally Posted by Thomas G.

I'm 60 years old and remember packing tapered wheel bearings as a kid. When was never to you?

I'm 30, and have done many vehicles with ball bearings. My '57 had them.

[Jared J]

Originally Posted by ruscal

I wonder if this whole tire pressure thing could be just gauged by your eye and never to exceed the manufacturer’s weight limit? Say if you knew a tire could carry maximum weight at a certain maximum pressure while traveling at freeway speed because the manufacturer formulates these ratings at normal traveling speeds. Then you load your trailer to the maximum tire pressure rating, but you are 10 PSI under the recommended setting. You notice the tire will be deformed and squatting. Will the tire blow out or fail while parked? I don't think so. Its strength is not likely in question. It is at speed that the havoc happens. It is likely caused by all that deformation and puckering of the sidewall which has to straighten and re-pucker with each revolution of the tire. That causes friction within the composition of rubber and cords of the tire. Friction causes what? Heat. Heat can cause what? Meltdown. Blooey!
So why not just use our eyes to determine how much air is needed as we load our trailers? Eliminate excessive pucker without exceeding the tires recommended maximum? If it doesn't flex much it won't heat much. A lightly loaded trailer surely does not need maximum tire pressure.
Russ

No, not even close. As an easy example, it's quite hard to tell the difference between 20 and 60 psi on my pickup tires.

To be honest, I always max out my trailer tires so I don't have to worry about it. I also tow faster than most here, so it gives the needed safety margin. When my camper is done and weighed, I might consider running them a bit under max, we'll see how it rides. Usually I just leave them at 80 psi.

[Jim Bennett]

Originally Posted by Jared J

I'm 30, and have done many vehicles with ball bearings. My '57 had them.

Man, I am 55, and labeled a Whipper Snapper. Kinda curious as to what Francesca would label you.

BTW, '57 was a very good year.

[ruscal]

Originally Posted by Jared J

No, not even close. As an easy example, it's quite hard to tell the difference between 20 and 60 psi on my pickup tires.

To be honest, I always max out my trailer tires so I don't have to worry about it. I also tow faster than most here, so it gives the needed safety margin. When my camper is done and weighed, I might consider running them a bit under max, we'll see how it rides. Usually I just leave them at 80 psi.

Jared,
You are right about being hard to see the difference on an unloaded pickup. It is easier to see the difference when loaded. There are various ways to fine tune your pressures such as infrared thermometers and watching tire wear patterns etc. Eyeballing is just what it says. Mine says if it don't distort it won't distruct. Putting 80 psi in an unloaded vehicle will make the trip less than pleasant. You'll get good mileage though!
Russ

[ruscal]

Tandem axles are analogous to building a child’s wagon without a pivoting front axle for steering. If you built such a wagon you couldn’t turn unless you overcame the friction of the tires to the pavement, or failed a wheel or wheel bearing or the connection between the wheels and frame. The wheel bearings are likely not the weakest link, but probably the tire will most likely skid. Trailers are just like big kids wagons. The tires “scuff” when the trailer is required to change directions. Here again the tire to pavement connection is the weak link and the trailer turns. Are the tires going to wear faster than a single axle setup? Yep. Are the wheel bearings going to wear faster than a single axle setup? Maybe, as thrust loads are increased, but weight is shared with the other axle. Tandem axles do have advantages though. What if the resistance to turning is a good thing for stability? A dually axle with one wheel mounted inside the other (like trucks use) would carry the weight equally, but not scuff during a turn, so be no more stable than a single axle with only 2 wheels. It would turn easily and carry the weight but maybe not add the stability a tandem does. Also the inner outer wheel arrangement of a dually would take up valuable interior floor space in a travel trailer. The Wheel bearings would not have the mechanical advantage of a trucks rear axle either, as it is supported at the wheel and differential. These reasons may be why we don’t see this configuration used.
Russ

[Francesca Knowles]

Originally Posted by Jim Bennett

Man, I am 55, and labeled a Whipper Snapper. Kinda curious as to what Francesca would label you.

....

I'm thinking...

[Jared J]

Originally Posted by ruscal

Jared,
You are right about being hard to see the difference on an unloaded pickup. It is easier to see the difference when loaded. There are various ways to fine tune your pressures such as infrared thermometers and watching tire wear patterns etc. Eyeballing is just what it says. Mine says if it don't distort it won't distruct. Putting 80 psi in an unloaded vehicle will make the trip less than pleasant. You'll get good mileage though!
Russ

One of my trailers has a 35 and 80psi tire, I can't tell a difference in how they squat with a 5000 lb pickup on it.

[ruscal]

Originally Posted by Jared J

One of my trailers has a 35 and 80psi tire, I can't tell a difference in how they squat with a 5000 lb pickup on it.

You will need to gauge those tires. The construction must be pretty rigid. My Scamp tires visually show me they are low by 5 PSI. More squat. I use a gauge to top them off.
Russ

[Francesca Knowles]

Originally Posted by Jared J

One of my trailers has a 35 and 80psi tire .

A passenger car tire and-what-an LT?

You've got nerves of steel, Jared!


Francesca

[Jared J]

Originally Posted by Francesca Knowles

A passenger car tire and-what-an LT?

You've got nerves of steel, Jared!

Francesca

The lt is 35 psi, st's are 80 psi.

[Night Sailor]

Originally Posted by MC1

In a tight turn there is a lot of side load pressure on dual axle trailer bearings but the wheel bearings seem to handle it well. Torsion axles are designed to "give" a little in a tight turn. This is normal.

This is exactly what I was talking about. Thanks for posting that picture.

I was climbing a hill on a state road in North Carolina heading towards Mt Mitchell when I noticed smoke coming from a bearing. I pulled over to check on it and found myself on soft shoulder and could not pull forward. I was very afraid to back up even though there was no traffic. Backing up was my only option because I did not have four wheel drive on my tow vehicle. I was able to back up and get going again but it was a frightening experience as I was worried someone would fly down the mountain and cause a wreck. Backing up put additional stress on the wheel bearing. I could not safely service it there so I proceeded on.

Wheel bearings are adjusted to be fairly tight. There is no flex in wheel bearings. And yes thry do carry high loads--the entire weight of the trailer. A tandem axle set up, if heavily loaded with tires under high pressure means there has to be give somewhere because both axles can't turn at the same rate like a single axle can.

I watched one tire roll past me down the freeway after I cleared the pass over the mountain. I was able to continue on only because I had tandem axles, even though that was the cause of the failure. The tight turns I made backing up were the main reason this bearing failed so early. Since then I have avoided sharp turns with tandem axle trailers and watched my tires in my rear view mirror.

Dually wheels on a single axle would have scrubbed in this situation but held up IMHO. Narrow tires on a single axle trailer do the best.

While "dry" sailing in San Francisco, at the Brickyard, we stored our 30' boats on trailers. There were two types of trailers in use, single and tandem axle trailers. We would push these to the hoist to launch our boats. People helped each other so it was quite obvious which trailers were easy to turn and which were not. Tires and springs would flex, but not enough to eliminate loads on the bearings and spindles.

There is a trade off between single and double axle trailers. It is a complex trade off and a function of axle location--farther from the tow ball the better, axle width, and axle spacing.

[Thomas G.]

Originally Posted by Night Sailor

......... The tight turns I made backing up were the main reason this bearing failed so early...........

No offense, but I don't think that this is correct.