[stretch]

Well, I've become quite familiar with coil bind after selecting my own springs from Ground Control. It's been a learning experience that hopefully others can learn from. Coil bind can actually be a very difficult problem to avoid in coilovers and I'd like to create a thread dedicated to it.

Summary:

I'm worried that most coilover systems can experience bind especially near the stock ride height. 8" springs seem to be popular but they are quite frequently insufficient.

If you missed the thread on lowering springs hitting coil bind, that may be helpful reading: Another major problem found with certain lowering springs- coil bind.




Full Text:

As I said earlier, I'm worried that most coilover systems can experience bind. Luckily, coilover springs are VERY easy to replace so long as you can identify which ones need replacing!

So, what's the problem? Even good 8" springs may not allow enough stroke. Even some 9" springs might not have enough stroke on certain long-travel coilovers. I'm finding that for my own setup, I have to run 9" springs to not experience coil bind. I don't hear any coil bind in driving (just feels "firm" on some big bumps) but I know it is happening; my springs are too short. By replacing my springs I will gain more bump stroke, which is critical for improving comfort and performance! It's one of those rare win-win situations.


Why does this problem exist?

Why would coilover manufacturers do this? I don't think they're stupid. No, I bet they use shorter springs because they are required to lower the car to "show car" levels. This sells. They don't think you'll notice coil bind at taller ride heights because it's rare enough. Coil springs become progressive at the end of their travel (usually a bad thing) which softens the blow a bit.


Examples:

Here are some examples using 850lbs of load on each front spring. (I got that figure by estimating a 3425lb vehicle weight with driver, 58% on the front axle is roughly 995lbs per front tire. Subtract 95lbs of unsprung weigh and another ~50lbs from the gas pressure in the shock.) Anyway, allow me to demonstrate:

An 8", 300lb/in Eibach spring up front will coil bind 2.05 inches into its bump stroke. At stock ride height, even the stock shocks have more than 2" of bump stroke. Thus, if you run a 2" bump stop like I do, you basically have to lower your car onto its bump stops to prevent coil bind. Riding on the bump stops sucks too.

An 8", 400lb/in Eibach spring will coil bind 2.64 inches into its bump stroke, a bit better. Firmer springs support the car's ride height sooner into their stroke which is why they have more stroke before coil bind despite having a longer solid length. 2.64 inches still might not be sufficient to support a stock ride height on a shortened strut, however. Ground Control coilovers (with plates) and Whiteline coilovers both allow more travel than that, and I'm sure others do too. Basically, this may not yet be sufficient for those running a 14-14.5" hub-to-fender ride height.

An 8", 500lb/in Eibach spring will coil bind 2.85 inches into its bump stroke, better still. This is approaching the range we want to be in for most coilovers, I think. One could set their ride height 1 inch above a 2" bump stop safely. I suspect that's enough for most coilovers. However, Ground Control coilovers (when used with Ground Control camber plates) have close to four inches of bump travel at a stock ride height (3.5" at typical mildly lowered height), so even this spring isn't sufficient for long travel coilovers. Longer springs are mandatory.

Keep in mind that Eibach springs have more travel then most! Odds are the springs bundled with your coilovers do not have as much stroke at the same rate.

Whiteline coilovers used 280lb/in (soft), 8" springs. Want to bet they had coil bind? I'm sure it was rare since it took a bit of stroke to reach bind, but it had to have happened. Whiteline claimed to have 3" of bump stroke in the strut but there couldn't have been more than 2" of remaining stroke in the spring. Using 2" of stroke happens for most people every time they hit a speed bump. Over time, this destroys the spring and makes the problem more frequent. I'd bet that Whiteline owners would be very happy with longer springs. Ideally you don't even want to run close to coil bind; parts of the spring will collapse earlier than others and this ruins the performance of the spring.

Other coilovers may have the same problem. I'm only able to pick on Whiteline because they listed their specs, in detail, online. For other makes, you're going to have to take your own measurements because the manufacturer has not supplied them. It's worth checking because you might be able to gain some ride quality with longer stroke replacement springs. Replacement springs might be a cheap way to improve your coilovers.

Personally, I'm in the process of doing just that. My Ground Control (Eibach) springs are too short for my setup.


Which replacement springs?
I found Eibach has all their racing springs online. No guessing at solid lengths, Eibach tells you exactly what they are:
http://eibach.com/cgi-bin/htmlos.exe...75112100032549

Swift has similar documentation up here:
http://www.swiftsprings.com/file/Swi...Racingmain.pdf

I know from experience that Eibach and Swift both have more stroke in their springs for a given length and rate than most of their competitors, perhaps Hypercoil excluded. Between Eibach and Swift, Swift's springs seem to have a quarter inch more stroke on average. However, both have substantially more stroke than AFCO, QA-1, and many JDM bundled coilover springs.


How to pick new springs:


Step 1:

Measure your current springs. Use my calculator to figure out how much of the spring's stroke is used to reach your ride height. The figure you need is on the first worksheet- the spring rate calculator- called "droop travel to unload spring". Then, subtract that value from the spring's total stroke to see how much bump travel you really have left in your spring:
Weight transfer, spring frequency, damper, body roll calculator... and more!


Step 2:

Can you adjust your spring perch lower than it currently is? If so, you can run a longer or firmer spring and gain some bump stroke. Pick one out from the Swift catalog and repeat the above measurements:
http://www.swiftsprings.com/file/Swi...Racingmain.pdf


Step 3:

Call Turn-In Concepts and inquire about Swift springs; they can get them and Swift seems to be the leaders of spring stroke. Swift also makes a rare 9" length. As an added bonus, the Swift springs seem to be the most linear springs out there, too, and this has additional handling benefits. Tell them Stretch sent ya and maybe they'll throw a second model airplane in the box.


Step 4:

Take a marker and write on your coilovers, "Engineered by {your name here}." This is the most important step! Gloat at your next autocross.

[stretch]

No sooner do I create this thread than Duncan posts here:

Originally Posted by DuncanG

I used 10" (well 250mm) springs without helpers in my ASTs to gain more bump travel, in addition to longer stops. That alleviated the coil-bind....

I believe 200mm (8") is stock. Anyway, just an example of this problem in real life. Apparently, some have already taken it upon themselves to improve things.

[mgsm666]

another excellent thread...thanks for taking the time stretch! *subscribed*

Jesse

[RainMaker]

This is going to continue to be a challange for anyone running coilovers without dual height adjustability and stiff (450/350+) springs.

Another thing to note is that spring quality specifically becomes an issue here. From what I could tell, there was no difference between the $45 QA1 7" 500lb/in spring and the $60 Eibach 7" 500 lb spring other than compressed length. The Eibach was 1/2" shorter, added clearance before coil bind.

That being said, if you run stiffer springs, even on dual height adjustable coilovers, you often DO trade bump travel for droop. With 5mm preload, a 600lb spring on the front of a GDB has about 1.5" of droop travel... since thats all you've compressed the spring to begin with. Helper springs can rescue you here, but often at the cost of tire clearance, since with stiffer springs even coilover perches can be moved above tires if you choose a shorter spring (knowing that you are limiting your bump travel potentially).

Its all a give and take. A non-dual height adjustable coilover makes lowering a car a significant planning and calculation challenge.

[psuLemon]

Subscribing.... I love these kinds of threads.

edit: quick question, how do you know you are having coil bind as opposed to bouncing off the bumpstops if your paint on the springs isn't flaking yet?

[stretch]

Originally Posted by psuLemon

Subscribing.... I love these kinds of threads.

edit: quick question, how do you know you are having coil bind as opposed to bouncing off the bumpstops if your paint on the springs isn't flaking yet?

You have to measure both the available stroke of the strut and spring. The stroke of the spring should about match that of the strut without the bump stop. This means that with the bump stop, the spring will not be able to reach its solid length.

Perhaps you could ask the manufacturer of your coilovers to give you the measurements; they should have them already. If you get them, it'd be nice of you to share the measurements here for others.

The paint on a binding coil will flake eventually, but it can take a long time.

Originally Posted by RainMaker

This is going to continue to be a challange for anyone running coilovers without dual height adjustability and stiff (450/350+) springs.

Agreed, it is a big challenge. Long springs prevent you from being able to slam the car but short springs eliminate a key advantage of keeping a conservative ride height. Unfortunately it seems coilover manufacturers tend to prioritize lowering over travel. That might make sense on a car that takes well to lowering, but the STI does not!

I suspect many people will see an improvement from longer-stroke Swift springs, especially if they can run a 9" or greater length. I look forward to hearing from those who make the swap.

You're also right that greater than 8" springs will push the lower spring mount down to the height of the tire which can impair the fitment of 265mm or wider tires, but I bet running tires that wide are also running stiff enough rates to use an 8" spring.

Another thing to note is that spring quality specifically becomes an issue here. From what I could tell, there was no difference between the $45 QA1 7" 500lb/in spring and the $60 Eibach 7" 500 lb spring other than compressed length. The Eibach was 1/2" shorter, added clearance before coil bind.

I have 10" long QA1 300lb/in springs that have only 4.75 inches of stroke. It's pathetic. Eibach's 8" springs have more, and Swift's springs more yet. I'll never buy another off-brand spring.

[twiSTies]

Interesting. I'll have to measure the BC springs. Thanks stretch.

[RainMaker]

Originally Posted by psuLemon

Subscribing.... I love these kinds of threads.

edit: quick question, how do you know you are having coil bind as opposed to bouncing off the bumpstops if your paint on the springs isn't flaking yet?

I end up measuring tire clearance alot, so I started looking at coil bind the same way... basically jack the whole car up using one corner or use a jack and stands to put the weight of the car onto one corner. If you coil-bind or run out of clearance, note why. Generally speaking if you can do it with a jack, you can do it on a track or on the road. If I can't get it to coil bind or run out of strut using this or a little hill I can back a corner onto that teeters the whole car on that corner and the opposite, I wont run out of clearance on the road or the track.

[lackskill]

subscribed.

[boondocksaint]

Originally Posted by psuLemon

Subscribing.... I love these kinds of threads.

edit: quick question, how do you know you are having coil bind as opposed to bouncing off the bumpstops if your paint on the springs isn't flaking yet?

I guess you could do a quick ghetto check for coil binding. Put some tire chalk on top of a spring coil or two. Drive around. If the chalk is then visible on the bottom of the spring coil above the one you marked...

I dunno if this will work.

[lackskill]

tie a string around a couple single coils. If it breaks, you have contact.

[boondocksaint]

Originally Posted by lackskill

tie a string around a couple single coils. If it breaks, you have contact.

Yeah, both methods should tell you. To be precise, though, you'll have to do the math in stretch's method. I suck at math (and I'm lazy), hence the attempt at an alternative.

[crand002]

Seems like the moral of the story is if you plan on lowering your car a lot with coilovers or springs research the spring that has the fewest coils or the largest gap between coils. Obviously wire strength would also play into factor.

[lackskill]

Originally Posted by boondocksaint

I suck at math (and I'm lazy), hence the attempt at an alternative.

[waktasz]

Interesting...time to call mark and change my springs AGAIN!