Another Question on Front Coil Springs

[Son_of_Norway]

I last posted a question about replacing the front coil springs on my HR, which is on an '89 P30 chassis. It was recommended that I contact Supersteer, so I went to the website. I weighed the coach on a CAT scale and there was 4100 pounds on the front axle. ( Although I guess I need to fill the coach with food, water etc. to get a more accurate weight.) So let's say that I put another 500 pounds on the front axle once I fill the coach, for a total of 4600 pounds. Supersteer will sell me a set of springs rated for 4600 pounds.

My problem is this: According to AC Delco, the original OEM springs on that chassis were rated at 3289 pounds per spring, for a total of about 6600 pounds. It would seem like the original springs were way too stiff to begin with and the coach should ride like a tank.

The Supersteer rating and the OEM rating don't agree. They have a 2000 pound difference. What's up? I tried to talk with the rep at Supersteer about it but she really didn't have an answer. Did Holiday Rambler replace the original springs with a lighter set during manufacture?

My more basic question whether I should pay $360 for the Supersteer coils or just buy an OEM set for $106. But I don't want the coach to ride like a tank.

Thanks for your wisdom on this one.

[enblethen]

Racer-x- that is good explanation of springs, however many P-30 chassis have airbags installed for more capacity. The airbags go bad. Small rockes get trapped between sprongs and airbags causing punctures. Replace with variable rate springs eliminate air bag requirements.

[Racer-X-]

I guess I'm late on this discussion. I just joined the forums here for other issues.

For future readers who might find this thread in a search or want more information, I thought I'd share some details.

Short answer, if OE springs are still available, like from GM or Ford or whoever, use your VIN to look up what was installed, and use a replacement for the original. That's the easiest solution. If you want to "do something different," then you should understand a bit more about how springs work and how y our suspension works.

Springs have two ratings that are important. One is the load capacity of the spring. This is how much weight can be put on the spring without damaging the spring (permanently deforming it or breaking it). For safety reasons, you need a spring that exceeds 1/2 of the GAWR for the axle that it's installed on. The reason for this is fairly obvious.

The other rating for the spring is the spring rate, expressed in "pounds per inch." This is how many pounds of weight must be applied to the spring to compress it one inch. The stiffer the spring, the higher this rate will be. Also note that for most suspension designs, the "wheel rate" in pounds per inch is different, often lower than the spring rate of the spring itself. This is because the suspension usually has leverage on the spring. For a dual wishbone type suspension, the wheel rate is the spring rate times the ratio of the distance from the spring center to the control arm pivot point to the distance from the lower ball joint to the control arm pivot point.

For a simpler explanation, if the center of the spring is half way between the control arm pivot (the bushings) and the lower ball joint, then the wheel rate will be half of the spring rate. That's because the wheel has 2:1 leverage on the spring.

[olfarmer]

All I can say is that I weighed the front end and bought the super steer springs rated for that weight. The motor home rides and drives better than it ever did. So far I am very satisfied and I got rid of those blasted air bags!

[enblethen]

Did you have a dealer run your VIN number to see what front end you have?
GM made several different vehicle ratings with different weight front ends.

[twodownzero]

Springs are not rated for a certain amount of total weight. They are rated in pounds per inch of travel. It might be said that a pair of leaf springs can support "5000" pounds, but that doesn't mean one more pound would put them on the bumpstops or that would be useless. You do want to know the weight per spring corner so you have a ballpark of the proper spring rate, but spring capacity really doesn't tell you anything.

[MountainAir05]

Oem is Oem. Did HR change them, I suspect not, My friend and the one we owned were rated for 6000 lbs or so. We were close when loaded up. HR could have order the front different than Chevy standard. Our Ford is rated at 7000. I would think you have gotten there life out of them. Only you can decided what stiffness or firm ride you want. On my 7000 front axle I decided it was too soft, so air bags were install and that way very well worth it. On the P30 I just air up the bags to make thing better.