What leaf spring capacity do I need?

[bowfisher8967]

I dont trust my old leaf springs since they came out of a junk yard off an old model pickup. I plan on buying some new boat trailer leaf springs and welding on new brackets/hangers. How do I know what capacity to get though? If I get springs with a "capacity" that EXACTLY matches the weight of my boat, then hitting a bump on the highway would break them, right? I figure that if my boat weighs 500 lbs, I need springs with a total cap. of 1000lbs? There has to be a more mathematically correct answer... Also, I dont know how much of the trailer's weight I should factor in-- Weight of the trailer minus the wheels, hubs, and axle?, or the total combined weight?

 

[90stingray]

Re: What leaf spring capacity do I need?

Well what does your boat weigh or what is it? Is this a home-made trailer... or is it a factory built setup? What are the hubs rated for... do you know your bearing sizes? I would get springs that are as heavy as your hubs. Also, each spring has a capacity... just like a hub. So my hubs are rated for 1750 lbs each... thus a 3500 lb trailer. And if my trailer weighs 500 lbs, i can haul a 3000 lb boat.

 

[H20Rat]

Re: What leaf spring capacity do I need?

There is somewhat of a small margin built in, springs won't instantly break if you put 501 pounds on a 500 pound spring. If you go overboard and put 1500 pound springs on a 500 pound load, you are pretty much defeating the purpose of having the spring, you might as well just weld up the axle solid at that point, because the spring isn't going to move. Going overboard will drastically affect the ride quality.

So you don't always need to match the hub/axle rating... The trailer under my boat currently has a 3500 pound axle, but the boat weighs roughly 1600 pounds. There is no way I'm running springs rated for 3500, they are 2000# springs.

 

[Silvertip]

Re: What leaf spring capacity do I need?

Here is how this works:
What is the capacity of the axle. For an axle to carry its rated weight, it needs hubs, wheels, springs and tires each of which is capable of carrying "at least" 1/2 the axles rated capacity. There are two of these so each side carries 1/2 the total capacity. So if the axle is rated at 1500# then each side of the trailer needs a 750# hub, an appropriate wheel (8, 10, 12, 13, or larger) and appropriate tire capacity. It also requires 750# springs. However, if the total GVW (gross vehicle weight) which is the boat, the trailer, and everything in or on the boat (gas, engine, supplies, and gear) is only 750 pounds then everything can be derated. But if you do that you then need to change things again if buy a newer and heavier boat. So start with the axle and work up to its carrying capacity. Iit is very common for "estimates" of boat weight to be very wrong -- and very wrong on the light side. Most folks forget about the engine and everything that goes into or on it. The reason I mention this is suppose the axle is rated for 1000# and you put appropriate springs, hubs, tires, etc., on it. Then it turns out your boat and all the gear actually weighs more than that. You now have an overloaded trailer. Putting larger tires on does not solve the issue because you still have overloaded springs and axle. So the entire system needs to be rated to carry the total weight (GVW) "minimum"

 

[bowfisher8967]

Re: What leaf spring capacity do I need?

Well what does your boat weigh or what is it? Is this a home-made trailer... or is it a factory built setup? What are the hubs rated for... do you know your bearing sizes? I would get springs that are as heavy as your hubs. Also, each spring has a capacity... just like a hub. So my hubs are rated for 1750 lbs each... thus a 3500 lb trailer. And if my trailer weighs 500 lbs, i can haul a 3000 lb boat.

Its a 14' jon boat x 48" across. Pretty light weight (riveted not welded). My gear is another story though. Including the motor i'd say the gear total is somewhere in the area of 350 lbs, give or take 100 lbs depending on what i'm doing. As for the trailer, it looks like the whole thing was built by hand, welded (i'm the 3rd owner i believe). I believe the axle and hubs are from an old model pickup truck. The axle is square steel tubing, 1/4" thick, and 2" wide on each side. It must be rated for 10 times the weight of my lil jon boat. The trailer frame itself though is quite heavy (200lbs?). Anyways, because it was homemade and not manufactured, I have no way of ordering a "correct" leaf spring set. Dont know what the hubs or bearings are rated for but assume that of a small or mid-sized pickup.

 

[bowfisher8967]

Re: What leaf spring capacity do I need?

Here is how this works:
What is the capacity of the axle. For an axle to carry its rated weight, it needs hubs, wheels, springs and tires each of which is capable of carrying "at least" 1/2 the axles rated capacity. There are two of these so each side carries 1/2 the total capacity. So if the axle is rated at 1500# then each side of the trailer needs a 750# hub, an appropriate wheel (8, 10, 12, 13, or larger) and appropriate tire capacity. It also requires 750# springs. However, if the total GVW (gross vehicle weight) which is the boat, the trailer, and everything in or on the boat (gas, engine, supplies, and gear) is only 750 pounds then everything can be derated. But if you do that you then need to change things again if buy a newer and heavier boat. So start with the axle and work up to its carrying capacity. Iit is very common for "estimates" of boat weight to be very wrong -- and very wrong on the light side. Most folks forget about the engine and everything that goes into or on it. The reason I mention this is suppose the axle is rated for 1000# and you put appropriate springs, hubs, tires, etc., on it. Then it turns out your boat and all the gear actually weighs more than that. You now have an overloaded trailer. Putting larger tires on does not solve the issue because you still have overloaded springs and axle. So the entire system needs to be rated to carry the total weight (GVW) "minimum"

So silvertip, would you reccomend I go to a truck weigh station to weigh the whole deal? Considering i'm unaware of the axle capacity (I mentioned the axle dimentions in my previous post/response). And assuming I find out the exact weight of the boat+trailer+gear, I'm still confused as to what capacity springs I would buy....

 

[Bondo]

Re: What leaf spring capacity do I need?

There has to be a more mathematically correct answer...
Dont know what the hubs or bearings are rated for but assume that of a small or mid-sized pickup.

Ayuh,.... Pull a hub, 'n measure the diameter of the quill,...
Both the inner bearing, 'n outer bearing diameters can be checked in the sticky at the top of this forum, for it's poundage rating...
Match the rating you come up with for the axle, with the springs ya need....

 

[Cheetah 210es]

Re: What leaf spring capacity do I need?

If your springs are from an old model truck why not just get a pair from a later model truck?

 

[Silvertip]

Re: What leaf spring capacity do I need?

What wheels and tires are on this thing? Meaning are these truck wheels, car wheels, or trailer wheels. Trailer wheels can be identified by the "zero offset" of the center (where the wheel bolts to the hub). That surface is set in the exact center of the wheel - horizontally. If you were able to look straight down through the middle of the tire and wheel, the hub would be positioned on that exact centerline. Front drive wheels have the offset toward the outside of the wheel and rear drive wheels have the offset toward the inside of the wheel. If what you say about construction is true, then you can put most any capacity springs you want on this rig up to the capacity of the tires. It appears this is a heavy trailer and again - your weights are "estimated" so the only way to know what you have is to weigh it. I would guess however, that 2000# springs are sufficient. One other check is to pull one wheel and hub. Measure the spindle diameter where the bearings rest. If the front and rear bearings are the same diameter are the same you have 1500/2000# spindles. If they are 1-1/16 outer and 1-3/8 inch inner you have 3500# spindles (per pair). Tire capacity is the other factor. The maximum weight for the trailer and load is the LESSER of the capacity of the tires, hubs, spindles, springs and axle.

 

[bowfisher8967]

Re: What leaf spring capacity do I need?

What wheels and tires are on this thing?.

The tires are trailer tires (it says that on them), and pretty big ones at that. Maybe RV trailer tires or something. So I would think the wheels would be too. I havnt taken them off yet but from what i can see the offset is neutral (centered). Thanks for the advice silvertip, I will measure the hub and bearing/spindle diameters.

 

[bowfisher8967]

Re: What leaf spring capacity do I need?

Just to quickly revisit this topic, I havnt checked the axle/hub capacities yet, but after installing most of my gear/outboard, the leaf springs almost have a NEGATIVE camber. I maybe wrongly assumed they were from a pickup, but they are about 4 feet long eye to eye and very thin. Anyways, there is work to be done, and I will follow the above suggestions. A good resource I found for calculating leaf spring capacities and understanding spring-related "rate" definitions.... http://www.therangerstation.com/tech_library/leafspringrate.htm