coil over springs

I have 35 dodge coupe mustang 2 front end and 4 link triangular rear suspention I have set ride height with coil overs in front and 12 inch bars in back to simulate shocks My question is when I put motor,body ,trans back in I should be able to adjust front shocks back to ride height but on the rear due the coilovers settle or do they stay at 12 inchs when installed thanks,Michael

 

You're thinking about it backward. The 12" is the ride height you set. Select a spring that will give you that 12" height with the rear weight on the axle.

 

Coilovers have an installed ride height. You install springs to match the weight. If the shock mounts are welded in at the wrong location, you can't make up for it with springs.

 

Are you talking about( compression rate )if so how do you go about determining what that will be also am I right about the front coil overs. lower control arms level now when weight put back on frame adjust til arms level again that will be ride height (correct ???)

 

Yes, front lower control arms should be level at ride height for best geometry. Hopefully, this fits in with the ride height you had in mind for the car...

As far as rear spring rate goes: You need a good guess (or actual scale #s) for the rear sprung weight of the completed vehicle. Keep in mind this does not include the rear end, wheels, tires, etc.

Let's say it's 600lb... 300 of that will be supported by each spring. Now, you need to find the installed height of the spring itself on the coilover. I always try to set the bottom of the spring about 1 1/2" above the bottom of the threads. Long explanation why, but that seems to work out well... So, if you set the shock eyes at 12", set the perch 1 1/2" up and measure to the spring top hat, you will have your spring installed height. I'm guessing around 7" for a 12" eye to eye...maybe less.

So, we have 300lb to hold up, at a 7" spring length. If you use a 10" long, 100lb/in. spring, it will compress 3" and give you your 7 inch installed height. So will an 8" long 300lb/in spring. So will a 9" long 150, etc... You tailor the spring free length and rate to give you the installed height and ride quality you are looking for.

That's why I hate kits that have a 500-1000lb weight range for the springs they include... It's never exactly right.

 

exwestracer, I am starting to get a grip on the coil over suspention years ago I worked on circle track late model sportsman cars that had coil springs with jack bolts when i found out coil overs were adjustable I just took for granite that meant ride height as well but now I am starting to understan the difference in front and rear coil overs as I will be able to raise front end back up since springs are stronger but not the rear when I decided to build this coupe I had wrong impression how the coil overs worked. thanks for your time ,Michael P,S hope I can call on you again if i get in a bind

 

Exwestracer has an excellent grasp on the coilover setup. Keep in mind that you can adjust ride height with coilovers but only AFTER you have the weight on them. Never "load" the spring before install, they should be almost loose on the shock. If you put weight on them and they collapse the spring, all you are doing is making for a heavier spring rate by pre-compressing the spring. I am currently putting together a spreadsheet for typical components unsprung weight, will make for a good tool when done. If anyone has scales and would like to contribute please let me know.

 

All depends on what you need the spring and shock to do. I have springs on the left side of my supermodified that we pre- compress 2+" to get the ride height we need.

And with a linear rate spring, you are not changing the rate, only the height. A good 300lb spring will take 300lb to compress the first inch, and 300lb to compress the last inch. It's all about how much static load that spring has to hold up.

 

If I may jump in with a question...Shock lenth on new build [street car]..I have room to use at ride height 12" [300# spring] or the longer 14" [225# spring] shocks ..If they are mounted at the same angle the longer shock will have a softer ride, yes? So either would be in its proper starting point [approx mid travel] but the shorter one would have a stiffer ride...To get the travel of the longer shock but the stiffer ride [i.e performance] of the higher spring rate short shock what is used? I am thinking that mounting the short shock at more angle and using the appropriate spring to get to the ride height [i.e. shock lenght at ride height] would accomplish this?

 

the length of the determines the travel leaning the shock softens the resistance and have more suspension travel for a lessor amount of shock travel and you also have to increase the spring rate depending on the angle from vertical used . I like to go with the lightest spring rate for the application like exwestracer said example I would go for the 100# spring compressed 3"" also the mounting height and how close to the wheels determines body roll. also the shocks have different compression and rebound rates

 

I always try to get the shock operating with as much stroke as possible, that way I can run softer springs, and I'm convinced the damping of the shocks works smoother with more shock stroke. I try to mount the coil overs on the axis of the roll center. On a solid rear axle, this is typically 10-15deg inboard.

If you want a stiffer spring on a longer shock, just start with a longer stiff spring... The spring rate is still what holds the car up. The shock length is irrelevant as long as you can start (ride height) in mid-travel.