Coilover lenght???

I'm going to use coilovers on the rear of my 47 int. pickup project. I can use 12" springs or 14" spings. Since I am building the mounts either will work. I am thinking that I will go with the longer 14. Longer is better?

14" comp.-ext. 6.25"
12" comp.-ext. 5.4

 

Does it make any difference?

 

Long as you don't run out of shock travel, it shouldn't matter. IMO, the only
advantage between long or short is, which one fits your set-up best.

 

My experience says that the spring rate is the #1 factor. You need a stiff enough spring so you dont bottom out. Coilovers tend to bottom out easy so more spring less travel and a stiffer ride.

 

Does the spring rate increase as it compresses or remain constant?

 

It 'X' lbs per inch. A 200# spring will compress 200#'s in one inch, 2" will support 400#'s. I look at the shock travel and size the spring so that the shock will be in the middle of its' travel when setting normally. Kinda need to know jow heavy the vehicle is on the rear, then divide by 2 (# of springs) that'll tell you how much each spring supports, then 1/2 of the total shock travel.

 

When setting up a coilover suspension, the thing you need to keep in mind is that every coilover has a design "ride height" center to center distance, which is usually compressed one third of total travel from fully extended. Confirm this with the coilover supplier and build your mounts at ride height using this dimension. Select the spring that will support your vehicle at that height. If you have adjustable collars I would start with the spring that gives you design ride height with the collars in the middle of the threaded length, that way you could go one rate higher or lower to stiffen or soften ride.

 

also remember that if your installing the coilovers at an angle than you will have to increase the spring rate accordingly. There is a formula to figure this out for different angles.Most coilovers have a three inch stroke so whae you compress it 1 inch you only have 2 inches left for bump.Try to find a shock with a longer stroke like pro shocks, they have some with a 5 inch stroke...used them on my roadster, work great no bottoming out

 

Ch***isWorks says at least 5" travel for a drag car, so more probably wouldn't hurt on a car that sees real world roads.
They also recommend 60/40 extension for drag racing, 40/60 for road cars.
Some coil over springs are wound for single spring rate, so progressive (gets stouter as the spring compresses).
Larry T

 

Thanks Guys, this is exactly the information I needed. What a great place!

 

Shocks should have about 60% of their travel left at ride height with a normally loaded vehicle - driver + full tank of gas. That way you have 60% compression and 40% rebound. Make sure you have enough shock travel. I like to figure out shock length and travel first, within my desired ride height parameters and then determine spring length and rate accordingly.

Your best bet is to talk to a shock manufacturer as sometimes published data can be way off - such as the correction factor chart in the Speedway catalog. According to the Speedway chart I needed a 350 lb spring but when I spoke to the shock manufacturer they said 525-550 lbs - guess who was right.