If you're running tender coils, don't forget to add they're compressed length into those calcs. They'll also open up a wider range of spring rates that will work with your desired lift height, depending on your needs. (go-fast people will need stiffer rates than crawler-biased guys....)
coil overs vs. air shocks
- Thread starter LT.
- Start date
LT.
Well-Known Member
- Location
- Los Alamos, New Mexico
Cool! I will get back to you after I figure it all out. What is the inside dia. of the springs?
LT.
LT.
Well-Known Member
- Location
- Los Alamos, New Mexico
Nothing that I've ever read. Here's how I do it:
Build all your links and set the axle at full compression. Make your shock mounts so that the shocks are at full compression (or maybe just a tiny bit of shaft showing) when the axle is at full compression. Install the shocks, and put any spring of a known spring rate on. You can do this with just one spring, with the adjuster spun way down. Put the weight of the vehicle on the shock. Measure the spring before you put weight on it (generally 14" if you're using a 14" shock), and after you put weight on it. This will allow you to calculate how much weight you are putting on each shock.
For example, if you put a 14" 300 pound spring on, and it measures 11" long after the weight is on it, you know there is 900 pounds of weight on that spring.
Now, measure the shaft of the shock at full extension. 14" shocks usually have about 14.5" of shaft showing at full extension, but measure yours to be sure. Now set your axle at whatever you want ride height to be, and measure how much shaft is showing. Lets say you measure 6.5" of shaft at ride height. That means you compressed the shock 8" (14.5 - 6.5 = 8)
So, if you have 900 pounds of weight to work with, and you want it to compress the springs 8" to give you the correct ride height, that means you need 112.5 pounds per inch total spring rate.
900/8=112.5
This formula gives you your total combined spring rate:
(S1*S2)/(S1+S2)=Rate
S1 is your top spring and S2 is your bottom spring.
You can also use this calculator
http://www.swayaway.com/calculators/swayawayCalc.php#step7
BUT you already have that 300 pound spring you used to test with, so ideally you'd like to use that for your bottom spring. I changed the formula a bit to figure your second spring rate if you already know your total spring rate (112.5 in this case) and your first spring rate (300 in this case). Here is that formula:
S2=(S1*rate)/(rate-S1)
Plugging in our hypothetical numbers...
S2 = (300*112.5)/(112.5-300)
S2 = 33750/187.5
S2 = -180
Take the absolute value of that, so to get our desired spring rate of 112.5, using the 300 pound spring we already have, requires us to buy a 180 pound per inch spring. I like to get a spring that is just a little softer than "perfect" so I have to put a little bit of compression on the springs to achieve my desired ride height. This keeps the springs in compression even with the shock at full extension, so the springs stay seated, and I don't need a tender. So in this example I would look for a spring that is 175 pounds per inch or so.
Here are all of the 14" long 2.5" ID (you'll need 3" ID if you go with a 2.5" FOA shock) coilover springs Summit Racing has:
http://store.summitracing.com/egnsearch.asp?N=700+4294925130+4294846689+4294787535+115+4294791373
...and here's the 175 pound spring we are looking for.
http://store.summitracing.com/partd...846689+4294787535+4294791373+115&autoview=sku
Done!
Thanks for all your help! It looks like I have more information than I even thought that I would need.
LT.
Last edited by a moderator:
RockMonkey
Suddenly Enthusiastic
You may want to check out the price of springs before you decide on your shocks too. I was looking at FOA shocks until I looked at springs. The cheapest I could find for 3" ID springs is $75 each. You can get a wide selection of 2.5" ID coils from Summit Racing for under 40 bucks, and used 14" 2.5" ID coils are widely available and cheap. 2.5" coilovers are a bit easier to fit too. I went with 2.5" Sway-A-Ways instead of the FOAs because FOA doesn't make a 2.5" coilover.
RockMonkey
Suddenly Enthusiastic
You may want to check out the price of springs before you decide on your shocks too. I was looking at FOA shocks until I looked at springs. The cheapest I could find for 3" ID springs is $75 each. You can get a wide selection of 2.5" ID coils from Summit Racing for under 40 bucks, and used 14" 2.5" ID coils are widely available and cheap. 2.5" coilovers are a bit easier to fit too. I went with 2.5" Sway-A-Ways instead of the FOAs because FOA doesn't make a 2.5" coilover.
CONFUSING!
2.5" ID coils are for use with 2.0" shocks. 3" ID coils for 2.5" shocks, like the FOA's. Rockmonkey went with 2" SAW's because FOA doesn't make a 2", only a 2.5". (too many 2.5's in the above post...)
RockMonkey
Suddenly Enthusiastic
ChestonScout
opinions are like Jeeps..
- Location
- Clinton, Ut
FYI
FOA is making a 2.0 coilover shock now. They are in testing now and will be available sometime in December.
He is trying to price them at 300 each.........INCLUDING SPRINGS!!!!
Freiken sweet
FOA is making a 2.0 coilover shock now. They are in testing now and will be available sometime in December.
He is trying to price them at 300 each.........INCLUDING SPRINGS!!!!
Freiken sweet
Seth
These go to 11
- Location
- 2 weeks from everywhere
LT.
Well-Known Member
- Location
- Los Alamos, New Mexico
LT.
Well-Known Member
- Location
- Los Alamos, New Mexico
I have also spoken to another shop owner and fabricator about the FOA shocks and if I was on the right track about ordering shocks with 18" travel. I was told that there was a posibility with the 18" travel shocks that the rods would bend too easy. Has anyone else heard of this? I would think that as long as the four link was properly engineered that there should be no problems. I figured that if I am going to do this I only want to do it one time. So, go big or go home, is what comes to mind. If there are no other ideas then it looks like the FOA's will get the go ahead. I am thinking about 18" travel, 2" shock and I am unsure of the spring weights still to this point. I will need to weigh the back end of the rig and subtract the weight of the wheels, tires, and rear axle. If I remember correctly then I will also have to subtract half of the weight of the link arms. Is there anything else that I am missing?
Again, thank y'all so much for all the help. I will be taking pictures of the whole thing. I will post them up when I get to hacking. Now, all I need to do is find someone who will be willing to finish the work after I start it. I am really good as starting projects and not finishing them.
LT.
Again, thank y'all so much for all the help. I will be taking pictures of the whole thing. I will post them up when I get to hacking. Now, all I need to do is find someone who will be willing to finish the work after I start it. I am really good as starting projects and not finishing them.
LT.
I wouldn't go with 18's, only because of the availability of 18" long coils in very many rates. Shorter coils are more available in more rates, and are cheaper.
The shaft bending would be due to the column load on them, so the longer they are the more likely they would be to bend. It's not necessarily your suspension or anything else.
The shaft bending would be due to the column load on them, so the longer they are the more likely they would be to bend. It's not necessarily your suspension or anything else.
LT.
Well-Known Member
- Location
- Los Alamos, New Mexico
I also noticed that the FOA's use a 3/4" shaft instead of the usual 7/8" shaft. So, then am I correct that I should be using the 16" travel vs. the 18" travel? I just thought that that I should go as big as I could because I have the real estate for them. I think that it would be cool to be able to flop over and still have three wheels on the ground. (Just kidding.) That and I do like to blast down through the desert at speed.
LT.
That and I do like to blast down through the desert at speed.LT.
RockMonkey
Suddenly Enthusiastic
Just weighing the back end of your truck and subtracting the axles, tires, and half of the drive shaft and control arms probably won't get you the perfect spring rate. It changes dramatically based on the angle the shocks are mounted at. Really, the chances of you getting it right the first time is nill. I'd get Seth's springs (or just his 250s, if he'll sell just those), and go from there.
LT.
Well-Known Member
- Location
- Los Alamos, New Mexico
Sounds like good advise. The only problem as of now is that FOA only has the 2.5" coil-overs in stock. The 2" will be coming out this December but, there is a long list already for them. I have the room so it looks like I will end up with the 2.5" versions. It will be closer to January when I have the cash in hand so I will see what FOA has available at that time. But, Seth, I will be giving you a ring if the 2" shocks are available in time.
LT.
I also noticed that the FOA's use a 3/4" shaft instead of the usual 7/8" shaft. So, then am I correct that I should be using the 16" travel vs. the 18" travel? I just thought that that I should go as big as I could because I have the real estate for them. I think that it would be cool to be able to flop over and still have three wheels on the ground. (Just kidding.)
LT.
The 3/4" shaft is only in the 2.0" shock, the non-coilover one. The rest use 7/8".
That was the problem that I ran into with the 18" coilovers. I could only find really heavy coils for them. This was in issue for me because of the fairly light buggy. But may not me much of an issue for you because you are quite a bit heavier than I am.
Last edited:
LT.
Well-Known Member
- Location
- Los Alamos, New Mexico
Y'all have been so helpful. Thanks for all the replies and I will let y'all know how it goes.
LT.
LT.