Anyone have a knowledge resource that isn't littered with brotato ricearoni stancetards regarding the basics of DIY coilovers (eBay and the like)? I've got a set of struts, and instead of drop springs, I thought it might be better to go with a coil over kit. Ideally someone could point me toward a link or another education resource.
There's not much to know, really. They're just threaded sleeves that slip over your strut, then standard race-size springs - usually 2.5".
Basics: you'll have to figure out the correct spring length for your application and probably a way to keep the spring centered in your strut top. Also, make sure the sleeve is a relatively good fit to the strut body, although I have to admit I've seen a fairly well-known manufacturer use rubber o-rings inside the sleeve to keep it centered.
^ what he said.
For my challenge car ('87 shelby charger) I found a set (springs and threaded sleeves) locally on CL for $30 that was originally for a Mitsubishi eclipse. The kit included hex screws to fit the perches to the struts and orings if there was any play. In my setup there was no play. Once I ground off the stock strut spring perches on my $1.95 Rockauto struts the sleeves fit on very snug.
The main thing to think about is what length spring you need. I had 10" coils available in my shop but they are really too long so I plan to go to 8" or maybe even 6" if the suspension will take the drop. Ebay and the classifieds here are both good places to watch for springs.
In reply to Keith Tanner:
I wondered what that bag of O-rings was for when I bought a set 
Some of the pics on the Miata cheapo ebay thread on m .net is useful in visualizing how the setup could be put together. The cheapo ebay setup on this thread is rather ghetto but something to refer to. http://forum.miata.net/vb/showthread.php?t=289656
Ground Control has some good parts to help enable better setups: http://www.ground-control-store.com/products/index.php
Thanks for the input guys. Let's say for a moment that the top hat/centering the springs isn't an issue, how does one go about calculating spring rate/length? I understand that tuning is often a trial/error scenario, but I'd like to shorten the learning curve a bit if possible...
What car?
4cylndrfury wrote: Thanks for the input guys. Let's say for a moment that the top hat/centering the springs isn't an issue, how does one go about calculating spring rate/length? I understand that tuning is often a trial/error scenario, but I'd like to shorten the learning curve a bit if possible...
You go to a race track and ask the winner what he is running :)
I usually buy AFCO sleeves, collars and seats from Summit or Speedway for "homemade" stuff where I'll be welding and trimming things to fit as they are not too expensive and known not to suck.
I'm also a big fan of Ground Control for when I'm looking for advise on spring rate and so on. They have always treated me well with regard to prices too when I called and said:
They have made me some really nice custom things by assembling parts bin stuff to fit my clearly "different" applications twice now too. Like an E30 with inverted 944 fat tube Koni coilover rears... I like to support that sort of "hey I got an idea... what if we... " imaginative service.
Giant Purple Snorklewacker wrote: I usually buy AFCO sleeves, collars and seats from Summit or Speedway for "homemade" stuff where I'll be welding and trimming things to fit as they are not too expensive and known not to suck. I'm also a big fan of Ground Control for when I'm looking for advise on spring rate and so on. They have always treated me well with regard to prices too when I called and said: - Am a racer - Am a return customer - I'll put some stickers on the car if you send them in the box They have made me some really nice custom things by assembling parts bin stuff to fit my clearly "different" applications twice now too. Like an E30 with inverted 944 fat tube Koni coilover rears... I like to support that sort of "hey I got an idea... what if we... " imaginative service.
Ahh...the old direct approach huh? Call the manufacturer? Innovative idea lol. Thats good advise, I will give em a call
I was sorta hoping for some kind of calculator though that might provide a range of spring diameters/lengths and rates that could work. Brian Crower and K-Sport are popular off the shelf offerings for my car. I suppose I could always start there as well...
amg_rx7 wrote: What car?
1999 Infiniti G20
Here's my advice, if this is a straightforward install for a production car, and you plan on ever running a high-end coilover setup, save yourself a lot of money, time and stress and jump straight to that, get a good set from a good company.
If you don't, you'll just be continually exposing the weak point of your setup by breaking it, having trouble fixing it, then building on your pile of hacks with another hack to fix that weak point which you can't get an easy off-the-shelf solution for...if I could go back in time and get a nice set of ISCs or KWs for my 'rolla I'd do it. I would've had to take out a loan but it would've been worth it.
Edit: Huh second time today I've been able to advise people to avoid the biggest mistakes I ran into myself, after Toyman's locker thread.
AAFCO sleeves are awesome, but spendy. Lately I have been making due with the cheapo ebay stuff with no problems. Main thing you will need to make sure of is that the spring perch sits higher than the tire. Ideally you want to measure the compressed height of your stock spring and the weight of the car on that wheel and go from there.
4cylndrfury wrote: I was sorta hoping for some kind of calculator though that might provide a range of spring diameters/lengths and rates that could work. Brian Crower and K-Sport are popular off the shelf offerings for my car. I suppose I could always start there as well...
For spring rates, depends on the weight of the car and what you want to do with it...You say it's a G20 so that's half the info.
I started out with Ksports (under the D2 brand), they're the cheapest coilovers you can get with specs that look legit (fully threaded, independent height adjustment, adjustable shocks, camber plates and slotted bolt holes on most models...sounds great right?)...but they're known to be fragile (cracked the camber plates on mine, have big problems with rusty threads, my mechanic has seen the strut bodies crack on this brand), the shock valving sucks hard, and the customer support sucks even harder (I'm running modded T3 camber plates and a buddy put Bilstein inserts in his after giving up on getting them rebuilt). They'll get the job done but they'll make you wish you spent more later.
My whole reason behind wanting to go DIY is that I already own a set of new GR2s for my chassis (I know, not adjustable). Im not looking for Hoosier blistering corner stickyness, this will still be my daily. But I would be interested in driving to an autox, and running for fun.
I understand that GR2s are not much better than stock replacements. I understand it will be very easy to overwhelm the shock damping if spring rates get too high.
My other option here is a simple set of drop springs and offset tophats. That could be fine, but I figure COs are a break from the norm and could provide a neat project and a learning experience. Its also an option that might save me some money (in the short run, thanks Gamboy 
). Like I said, Brian Crower and K-Sport are quite popular with the G20 community. But entry price will be about 5X what I have already spent on these new struts.
OK well for a setup like that, a set of sleeves could make sense. For your uses on a vehicle of that weight you probably want spring rates in the 300-400lb/in ballpark.
Would you happen to know the stock spring rates or those used on any coilover sets intended for the car? Those can give you some ideas on what proportion of rates to use front vs. rear.
Ive been searching G20.net and SR20-Forum.com, and have not yet struck that golden nugget, but I am still looking...
The "safe" setup is to proportion the spring rates to match the weight distribution, but if you could copy the proportion of an aftermarket setup that would be better.
For autocross, disproportionately super-hard springs in the rear often make for a faster setup. It will make the back too loose for a good track setup but it will be a decent bit faster through the cones. A good track setup (usually somewhere near the proportion of weight distribution, or 50:50 at most) will still be very nearly as quick in autocross though, and nicer on the street.
4cylndrfury wrote: Ive been searching G20.net and SR20-Forum.com, and have not yet struck that golden nugget, but I am still looking...
Just find someone that sells the KSports, the spring rates will be listed.
Is this helpful? http://www.ridetech.com/info/spring-rate-calculator/
Here's another: http://www.hypercoils.com/spring-rate-calculator/
Swank Force One wrote:4cylndrfury wrote: Ive been searching G20.net and SR20-Forum.com, and have not yet struck that golden nugget, but I am still looking...Just find someone that sells the KSports, the spring rates will be listed.
Looks like the Ksport website says 9.8k Front / 6.2k rear. A little bit of maths equals 548.3lb/in front, 346.9 lb/in rear
Sounds like as good a place to start as any. Once again, the GRM braintrust proves successful!
Thanks Guys!
That might be harder than you want for a mostly-street vehicle, you might want to scale those to at most 80% of what they are now...especially for use with the GR2s.
I was thinking maybe go 450/300 based on the numbers above...My statement about "a good place to start" was probably not very clear that I would use those numbers as a starting point for what a race setup would be, and back off a little for street use with stock-ish struts.
Still, youve been very helpful Gameboy (and the rest of you). I am still very much open to ideas and opinions, this is uncharted territory for me.
If you want some science to get you started on spring rates, you could use the frequency. You can calculate it from sprung and unsprung weight as well as motion ratios. Autospeed also has a clever and easy way to do it, although you will have to figure out what your current rates are in order to make use of the information. You can figure that with a bit of measuring, the calculators were posted earlier.
http://www.autospeed.com/cms/A_113057/article.html
Copying other stuff on the market isn't always a good choice. For example, I know that our springs for the NC Miata are quite a bit different in their balance than others on the market - but they also work better.
Also, if you're lowering the car, you'll need more spring rate to keep the car off the bumpstops. A higher spring rate can actually be more comfortable than a soft one.
Length is easy enough. Find out what the free length of your springs are and what their length is when the car's at rest. By looking at your spring rate and that number, you can tell how much weight is on the spring. Now you just pick a spring that, when it has that much weight on it, compresses to a length that fits between your upper and lower perches. If it's too short, you won't be able to raise that new adjustable perch high enough to get your ride height. If it's too long, you won't be able to lower the perch enough. The higher the spring rate, the shorter the spring will need to be, all else kept equal. That's the because the stiffer spring won't compress as much. If you have a choice of a range of lengths, go with the longest to avoid coil bind. Coil bind is what happens when you compress a spring all the way and it becomes a solid metal tube. Then stuff breaks.
Note that your struts exist to control your springs. So you'll need to ask the strut manufacturer what the maximum rate you can run on that shock. If you're using OE struts, stick within 15% of the original.
Not much info out there on stock spring rates, but they appear to be in the ~120 lb/in front and ~200 lb/in rear range...My guess is that 450/300 will still be substantially higher than the GR2 dampers are designed to cope with. By using the stock replacement shocks as your base, you're ideally relegated to building more of a 'lowering spring' rate system that simply preserves the limited wheel travel availability by not lowering the car as much.
Stock these cars actually have a higher rear spring rate than front, as would most lowering springs for them. This is probably to make sure that the rear suspension doesn't ride on the bumpstops with people and/or cargo in the rear, as well as to provide more of a 'flat ride'. The front sway bar and twist beam rear are then tuned to still provide understeer. For the 'lowering spring' rate type setup, I would probably consider following suit.
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