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DailyDriverSst · 07-10-2018, 09:53 PM

I am running into an issue with my stock suspension setup, hoping somebody here can have information I need.

I have talked to several people that run the same platform I am on in Stk/Sstk/Crate stock and they run a 18" 225 or 250# spring, but they are naturally aspirated and a regular cab. I will be procharged and have an extended cab.

Curtis @ Landrum thought a 250# spring would be fine till I threw this math at him - I am wanting to keep the ride height I am a now. He says they don't make a 275# 18" spring.

Calvert says they suggest a 200# split mono leaf in the back.

I don't have the truck in weight config yet (waiting for Sherman Racing Engines to have the bottom end and machine work sorted out), but final weight will end up around 4500 pounds.

I'm not too concerned about ride quality on the street.

What vendor offers an 18" long, 5.5" OD, 275# front spring, or alternatively, what are my options for putting a 1" spacer in the top of the spring bucket that will clear double adjustable shocks? I'm seen a couple threaded bucket spacers, they seem like they'd be weak though. Especially at close to 1200 pounds on each front corner.

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I didn't get a chance to measure the installed shock/spring angle, but from balljoint to lower control arm bolt is 17 inches, and the lower shock mount is 8 inches from the balljoint and 9 inches from the LCA bolt.

Using this calculator based on 1177 average corner weight and 55 pounds of unsprung weight, and a 9/17 motion ratio (0.529) and 85 degree install angle, RideTech says to use a 550-650 pound 12 inch spring with about 3.5" of travel.

Using the same inputs in this calculator with 3.5 inches of extension travel, comes up with a 600 pound spring rate with a 170 pound effective wheel rate.

So if they say that the ideal rate is 600 pounds over 3.5" of travel, that's 2100 pounds of spring force. Coincidentally, the 0.529 motion ratio * 2100 pounds of force = 1,110 pounds of wheel force. (Add in some trig and alot of rounding, gets back to the 1177)

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Taking a coil spring with an 18 inch free length, and compressing it to 10.5 inches at ride height is 7.5" of compression.

2100 pounds of spring force divided by 7.5 inches of compression = 280 pound-inches of spring rate (275 is probably next closest).

Using the 250# spring rate, max offered by most vendors, divided into the 2100 pounds of necessary spring force, yields a compression of 8.4 inches.

To maintain my current ride height, I need a 275# 18-inch spring of 5.5" OD or to place a 1" packer on top of an 18 inch 250# spring.

07-10-2018, 09:53 PM	#1
DailyDriverSst Junior Member Join Date: Dec 2017 Posts: 53 Likes: 0 Liked 4 Times in 4 Posts	Front Coil Springs I am running into an issue with my stock suspension setup, hoping somebody here can have information I need. I have talked to several people that run the same platform I am on in Stk/Sstk/Crate stock and they run a 18" 225 or 250# spring, but they are naturally aspirated and a regular cab. I will be procharged and have an extended cab. Curtis @ Landrum thought a 250# spring would be fine till I threw this math at him - I am wanting to keep the ride height I am a now. He says they don't make a 275# 18" spring. Calvert says they suggest a 200# split mono leaf in the back. I don't have the truck in weight config yet (waiting for Sherman Racing Engines to have the bottom end and machine work sorted out), but final weight will end up around 4500 pounds. I'm not too concerned about ride quality on the street. What vendor offers an 18" long, 5.5" OD, 275# front spring, or alternatively, what are my options for putting a 1" spacer in the top of the spring bucket that will clear double adjustable shocks? I'm seen a couple threaded bucket spacers, they seem like they'd be weak though. Especially at close to 1200 pounds on each front corner. --------------------- I didn't get a chance to measure the installed shock/spring angle, but from balljoint to lower control arm bolt is 17 inches, and the lower shock mount is 8 inches from the balljoint and 9 inches from the LCA bolt. Using this calculator based on 1177 average corner weight and 55 pounds of unsprung weight, and a 9/17 motion ratio (0.529) and 85 degree install angle, RideTech says to use a 550-650 pound 12 inch spring with about 3.5" of travel. Using the same inputs in this calculator with 3.5 inches of extension travel, comes up with a 600 pound spring rate with a 170 pound effective wheel rate. So if they say that the ideal rate is 600 pounds over 3.5" of travel, that's 2100 pounds of spring force. Coincidentally, the 0.529 motion ratio * 2100 pounds of force = 1,110 pounds of wheel force. (Add in some trig and alot of rounding, gets back to the 1177) ------------------ Taking a coil spring with an 18 inch free length, and compressing it to 10.5 inches at ride height is 7.5" of compression. 2100 pounds of spring force divided by 7.5 inches of compression = 280 pound-inches of spring rate (275 is probably next closest). Using the 250# spring rate, max offered by most vendors, divided into the 2100 pounds of necessary spring force, yields a compression of 8.4 inches. To maintain my current ride height, I need a 275# 18-inch spring of 5.5" OD or to place a 1" packer on top of an 18 inch 250# spring.