Quote:
Originally Posted by MPaulHolmes
To carry more weight, do you just replace the springs with larger diameter ones, or longer ones?
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First so it doesn't get lost in the bloviating -
Ben, have you considered checking the electro-metro's axle weights on a truck scale (local grain elevator will have one) and comparing them with stock metro specifications?
Aside from additional springs (inside current spring, around shock, other), there are four basic possibilities: heavier, longer, tighter windings, variable rate. (You could also have combos like longer and heavier, but we'll kind of ignore that.)
Two times longer fixed rate spring will carry twice as much weight, but good luck fitting it into available space.
Two times heavier (not 2x increase in spring stock diameter, maybe ~1.3x ???) will carry 2x the weight, but will ride like a lumber wagon.
Twice as many windings with same size spring stock won't carry 2x the weight (sagging stress failure) and will ride like a lumber wagon.
A variable rate spring could be made from the same spring stock and it would not carry 2x the weight, nor as much weight as a 2x as many windings spring, but it would not ride like a lumber wagon. Using a slightly heavier spring stock and variable rate windings you can get a spring that is the same length, carries 2x the weight and doesn't ride like a lumber wagon. (Ok, that's an exageration. If it's carrying 2x the weight, it's still going to ride like a lumber wagon, but it will ride better than all the other alternatives.)
For anyone that isn't sure what is meant by variable rate spring, here a picture of a variable rate (top) and a fixed rate (bottom) spring.
Lets assume the springs in the picture are made from the same diameter spring stock. (They appear to be close.)
If 140 lbs will compress that fixed rate spring 1", 280 lbs will compress it 2"; 420 lbs - 3"; 560 lbs - 4" ... The numbers for the variable rate spring would be something more like: 140 lbs compresses spring 7/8" (less than the fixed rate spring as even the loosest windings are tighter), 280 lbs - 1 5/8"; 420 lbs - 2 1/4"; 560 lbs - 2 11/16" ...