48 chevy truck

[jaybee]

Fenders won't clear the underside of the upper hood sides?

[kb426]

Correct. With the wheel at full lock, I have 3/4" of clearance to the lower side panel. I didn't intend to have fenders but I didn't expect the tires to through debris on the windshield.

[kb426]

About a month ago, I ordered 2 Ridetech shocks for the rear. True to O&S, I finally put them on today. I had 300 lb. springs on the rear and had the adjusters run up quite a ways to get the desired ride height. I read an article recently that made point is the spring was too soft and cranked up that the ride quality would suffer. In my collection was 2 500lb. springs. I installed them and will see how it works out.

[WZ JUNK]

I must be missing something here.  I did not think that the ride height adjustment would change the spring.  Explain.

[kb426]

As you raise the adjuster, you are increasing the base load. 300 lb spring raised 2 inches is not a 300 hundred lb load anymore. You are using the additional compression to raise the vehicle and have altered the base rate by the amount of compression on the spring. If you raise a spring 1 inch, you have added the rate + the rate as it was explained to me. When I was working on the rear of the gray 51, the Ridetech guru who had been there a long time asked for base rate and installed height. He added the numbers together to come up with a new spring rate. I may not have explained any of this to satisfaction. I could be incorrect also.

[jaybee]

Depending on your rear weight, that 500lb/in spring looks like a pretty good bet. The OEM GT Performance Package spring is 728lb/in, and some of the aftermarket springs are nearly 1,000lbs/in. Your coilovers have a more favorable motion ratio, so it should use a lighter spring. https://www.mustang6g.com/forums/threads/spring-rates-drops-all-in-one-thread.44925/

(Edited: I found the pics of what I wanted to see. Thanks for doing such a great job documenting this build!)

[jaybee]

I remember learning about spring preload when I was into motorcycles. Every bike had adjustable rear shock preload, and you could put spacers in the forks to preload them as well. The suspension is effectively solid until you have enough load to overcome the preload. A little of preload may as well be be none, because the vehicle is already heavy enough to push past it. Heavy preload can be very harsh on light impacts.

[kb426]

The link Jaybee posted has a simple explanation of fixed versus progressive. My mind is clearer in the morning than at the end of the day so I'm going to try and have a coherent stream of thought on common knowledge regarding springs as we use them. We have fixed and progressive rate springs, Installed height, ride height and desired ride quality. If you have measured valve springs, most are fixed rate. You multiply the rate by compression height to get pressure on the spring seat. Auto and motorcycle uses cover progressive more often than not in today's world. Most every cycle produced after 1970 has progressive springs either in the front or both front and rear. I'm sure you understand that as speed increases the dynamic load becomes greater and the spring requires more compression pressure to avoid bottoming out and lose suspension performance. Most modern 1/2 ton pickups are very tall in height. Once again the 1st couple of inches of travel are to absorb bumps with a minimum of impact on the vehicle and occupants. Once the vehicle is loading and lowers itself on the spring, the pressure rises to over a compliant ride and adequate load carrying capacity. I have built 4 trucks with coil overs on all 4 corners. 2 road like cadillacs and 2 didn't. I have used long travel and short travel shocks. The long travel should be the best but if you miss on spring rate, it won't be the desired result. The rear is directly affected by the front. The dynamics of the vehicle in the way it transfers the reaction of the front to the rear is something I haven't gotten a good handle on yet. In my exp., the ride height needs to be less than 50% of travel for I feel compression travel is more important than rebound. The last 2 projects use shocks with 4.1" of travel. The spindle has more travel than that because the shocks are angle mounted. A competent math person could list a formula explaining that. As I poorly tried to explain before, if the amount of preload to raise the vehicle to the desired ride height is extensive, you might have too light of a spring. Case in point: a 100 lb spring installed at 3" preload has added 100 lbs per inch of load. You have used up a significant portion of the springs travel just to start with. I believe that will make the spring under powered to do it's job properly. If you start out with a 300 lb spring you will have most of the springs travel to do it's job. Here's the part that I struggle with. Depending on the vehicle's road dynamics, the forces transferred to the rear will have different loading on the rear suspension so a static spring pressure might be too strong or not strong enough for the desired result. I'm not there on the 48 yet. Part of this is due to lack of adequate measuring available to me. You need 4 wheel scales to have an accurate starting point. I only have long scales to use. I have used different percentages for front to rear bias but I'm not ready to quit yet. After installing the Ridetechs and returning to 500lb. springs, it will need to be driven in a variety of conditions to formulate an opinion of what to do next. When I tried the 500's before I had a much higher rate on the front so the transfer dynamics were different. I know that spring and ride engineers would have an answer in a heart beat. Over here where we use cad and chalk drawings on the floor, it's more trial and error, mostly error. LOL.

[idrivejunk]

All I heard was "... it will need to be driven in a variety of conditions..."

Sounds good to me

[jaybee]

I don't think there's any question the setup decision get more trial and error without a full set of corner scales as well as all the measurements and calculations needed to plug into a suspension calculator...and even that just gets you into the ballpark. Even how you drive the car matters. The lever arm length of the sway bar matters. So driving the car has to be part of it, in the real world. Here are my thoughts on it. Your mileage may vary.

• I'd always use just enough shock to keep the suspension from feeling floaty or overextending on rebound. The shocks have to be softened as spring rate is softened.
• Does the car traverse bumps, dips, and drop aways like secondary road bridge approaches feeling like it's level? Using about the same amount of suspension travel on both ends? The spring rates are probably well matched. That doesn't mean both ends can't be over or under-sprung.
• If the car uses an abnormal amount of suspension travel on acceleration or braking, it's under-sprung
• If one end of the car or the other feels like the wheels are trying to skip at bumps in cornering, it's either too much shock or too much spring.
• We're way beyond the stone age of suspension tuning, in which we make a car handle by making the springs too stiff to let the suspension move.

[kb426]

Valid points, Jaybee.