Electric brake testing on old trailer

Diamondpilot · Mar 5, 2011

CurlyDave said:
Coming anywhere close to the real weight of the vehicle was just plain luck.

The air pressure in tires does not directly support the vehicle, it stiffens the sidewalls which are what really supports the vehicle.

There are two ways to demonstrate this for yourself.

1. Draw a force diagram on the steel wheel at the center of the tire. Air pressure is uniform completely around the wheel, and can not sustain an upward force.

2. Reduce the air pressure in the tires to about 5 psi. The area in contact with the ground increases, but it does not become 6 times greater than the contact area of the same tire at 30 psi.

It may have been just dumb luck but it worked pretty close.

Chris

sailorman · Mar 5, 2011

CurlyDave said:
Coming anywhere close to the real weight of the vehicle was just plain luck.

The air pressure in tires does not directly support the vehicle, it stiffens the sidewalls which are what really supports the vehicle.

There are two ways to demonstrate this for yourself.

1. Draw a force diagram on the steel wheel at the center of the tire. Air pressure is uniform completely around the wheel, and can not sustain an upward force.

2. Reduce the air pressure in the tires to about 5 psi. The area in contact with the ground increases, but it does not become 6 times greater than the contact area of the same tire at 30 psi.

Just some thoughts

. If pressure ( say 30 psi ) is uniformly distributed, then it is 30 psi in all directions including up and down.

Does not air offer support along with the tire walls ? Imagine the old hard solid rubber tires. The whole tire offered support. Pneumatic tires are simply solid tires with interior supporting rubber removed and interior supporting air substituted.

If pressure is dropped to extreme ( 5 psi ), the area of the tire can not increase enough due to the tire material properties ( elasticity, rigidity ) and the un-inflated tire has a finite volume. The same would probably happen if taken to high pressure extreme. Tire simply could not expand enough to reduce area.

I believe tires matched to a vehicle at a reasonable recommended pressure would yield a reasonable ball park figure. I doubt Diamondpilot 's teacher had mismatched or poorly inflated tires.

Interestingly, this experiment is performed in many schools through out the country. I don 't think so many Physics teachers would do it if it were not feasible. When I get my vehicle to a scale, I 'll let ya 'll know how I did

.

Here 's a link for anyone wanting to try it for fun.
Exploratorium: Science Snacks: Tired Weight

Summary : Extreme conditions will not be accurate.
Controlled conditions may yield ball park figure.

Reg · Mar 5, 2011

It is an interesting diversion to the O/Ps interest in weighing his trailer - for the PURPOSE of knowing how his tow vehicle will handle it.
For THAT purpose it is probably "good enough", but so is the 85% of the tires' rated max load rule of thumb, e.g. it is almost certainly not OVERtired or dangerously UNDERtired.

The fun thing with the contact patch "experiment" is that goofy teens are MUCH more likely to believe their equally goofy classmates who claim that wide tires "put more rubber on the road".
Well, sure they do if you lower the pressure enough to get the contact patch profile to the proper shape, but then the sidewalls are going to flex and that leads to heating and the carcass deteriorates from that,,,,,, and oh, lets talk about hydroplaning instead (-:

sailorman · Mar 11, 2011

What do ya 'll think of this complete kit if I determine it will fit my axle ? I have a 2 14" dia. axle which I believe indicates a 3500# capacity.
Add Brakes to trailer Complete kit 3500 DEXTER 5x4.5 - eBay (item 270280159948 end time Mar-15-11 06:26:08 PDT)

Diamondpilot · Mar 11, 2011

sailorman said:
What do ya 'll think of this complete kit if I determine it will fit my axle ? I have a 2 14" dia. axle which I believe indicates a 3500# capacity.
Add Brakes to trailer Complete kit 3500 DEXTER 5x4.5 - eBay (item 270280159948 end time Mar-15-11 06:26:08 PDT)

I have used many of these kits from R and P. Good kit but I doubt you will find drums to fit them old wheels. My guess is you will end up buying new wheels also. Getting real expensive real quick.

Chris

sailorman · Mar 11, 2011

Diamondpilot said:
I have used many of these kits from R and P. Good kit but I doubt you will find drums to fit them old wheels. My guess is you will end up buying new wheels also. Getting real expensive real quick.

Chris

Correct. I plan on getting new 5 bolt rims ( cheap enough ) for the tires to match the kit drums. I 'm not likin' 4 stinkin' little bolts anyway. I like the idea of kit with all I need including break away stuff. Expensive true, but I can 't afford new while payin' off my beautiful tractor :thumbsup:. I 'm also enjoyin' the leisure project requiring no dead line. Soon as I get interior more completed, I might do a little tractor/trailer campin' on my back property to shake ' er down.

Do ya think I should discontinue this thread and make all further comments on my "projects " thread ?

Diamondpilot · Mar 11, 2011

Not at all. Keep both going.

If I remember right you had 13" wheels. Make sure modern wheels will fit the brake drums and also make sure you can get them in 5 lug. Most I see are 4 lug.

Chris

sailorman · Mar 11, 2011

Diamondpilot said:
Not at all. Keep both going.

If I remember right you had 13" wheels. Make sure modern wheels will fit the brake drums and also make sure you can get them in 5 lug. Most I see are 4 lug.

Chris

are you saying most 13" modern wheels a 4 lugs ? Shouldn 't I be able to get 13" modern wheels that fit the Dexter 5 bolt drums ?

Diamondpilot · Mar 12, 2011

sailorman said:
are you saying most 13" modern wheels a 4 lugs ? Shouldn 't I be able to get 13" modern wheels that fit the Dexter 5 bolt drums ?

I am not sure. Most 13" wheels I see are 4 lug. Nothing wrong with that. I have only seen 13" wheels with disc brakes on boat trailers and with that I have only seen 2 boat trailers with 13" wheels and brakes period.

I know that 7" brakes are usually used on smaller trailers like pop up campers, ect. I have 14" wheels on one of my trailers and it has standard 3,500# Dexter Axles and 10" drum brakes and the wheel to brake drum clearance is very tight.

You need to do some more checking.

Chris

sailorman · Mar 12, 2011

Diamondpilot said:
I am not sure. Most 13" wheels I see are 4 lug. Nothing wrong with that. I have only seen 13" wheels with disc brakes on boat trailers and with that I have only seen 2 boat trailers with 13" wheels and brakes period.

I know that 7" brakes are usually used on smaller trailers like pop up campers, ect. I have 14" wheels on one of my trailers and it has standard 3,500# Dexter Axles and 10" drum brakes and the wheel to brake drum clearance is very tight.

You need to do some more checking.

Chris

I 've found many places on net that sell 13" 5 lug rims. The original brakes ( Fayette Dayton ) have 10 " drums with 2 1/4 " width brake shoes. What am I missing about sizing them to a 10" 5 lug dexter brake drum ? Bolt pattern differences ?

I 'm also very concerned about spindle sizes and how that plays into it.

btw, today I pull back plate off one side to see if I had unfrozen the nuts. Worked liked a dream since I had soaked the with liquid wrench fro 2 weeks. Put hub, wheel, a tire back on. Got a number off of outside bearing to see if it matches the number given somewhere on the R & P carriage site. Didn 't want to remove inside seal and bearing at this point.