Perfromance, real, not so real, balance in the middle?

[MINIz guy]

http://performance-suspension.eibach..._spring-system

It is under the Eibach Main and Helper system. I'm sure Ground Control could order them for you since they supply Eibach springs with all their kits.

I'm not looking to drop weight on my car. And I don't think I'll need to go super stiff if I keep my ride height similar to stock, and I keep the same roll center. Plus, I'm pretty sure my dampers cannot handle too much spring without getting them revalved. I'll keep looking at what height would be idea for me. I first have to figure out what ride heights my current lowering springs are getting me and see if I like it first.

[JFMBMW318i]

Originally Posted by 03whitegsr

Link to the integrated helper springs? I'm not an Eibach fan at all, but that feature would almost make me reconsider. The droop travel is something I am trying to address now on my car as yeah, with a high spring rate, you have very little travel in the rear before the spring goes loose. I have added internal spacers on my shocks to limit droop travel but you could also do it with more typical steel cable travel limiters.

I've been playing with the idea of basically gluing a helper spring to a 4" spring to get the added travel. 3M makes some pretty serious adhesives for metal so it may or may not work. I came across a post from one of the guys from GC and he mentioned that the original BMW race springs were two springs welded together to pull off this same feat. You'd have to re-heat treat the springs though IMO for this to work out.

Welded Eibach Spring

Another option I have considered is possibly trying out some of the J-stock rear springs as they are basically a 900 pound spring with a built in helper. I'm not sure it will get the car down to the ride height I want though.

Depending on the rate and desired ride height, you may need a 5" spring. Here is my car with the Ireland Engineering E30 spring perch, urethane isolator, and 950 lb/in springs on a car that is ~300 pounds lighter then stock. The adjuster is all the way down and is basically just a spacer at this point.


The urethane pad is about 3/8" thick and the adjuster is about 1/2" thick so they add ~7/8" to the spring height. If you dropped to the ~700 pound spring most people use and the car is full weight, a 6" spring with 1/8" isolators top and bottom would put you about the same height as my car is. A 600 pound spring and 1/4" isolators would be about the same too.

I like that look, what size tires and rims do you have? How is the ride? Is
it comfortable over bumps?

[03whitegsr]

Those eibach springs are two separate springs and you use a spacer with them. They are not a one-piece spring. Hyperco, swift and most other spring companies offer similar springs. Some body at Ground Control said using the two-piece springs like that is a bad idea on the E30 rear trailing arm as the springs will separate and pop out. I'm not 100% convinced that to be the case if you limit droop travel enough but I could definitely see how it is possible since you are putting the springs in bending. Not sure I want to chance it though.

I'm not a fan of the wheel/tire selection. They are 215/45/17s on the 17x8.5 Kosei K4R rims. Needs more tire but the larger RS-3s where on back order when I bought them.
There is nothing comfortable about 680/950 spring rates.

[MINIz guy]

Oh, I wasn't aware they were two separate springs.

What would be the con's about welding a helper spring onto the main coil? What is the purpose of heat treating them after welding?

Sent from my SAMSUNG-SGH-I537 using Tapatalk

[03whitegsr]

Springs are heat treated initially to remove internal stress from the winding operation as well as tempering to reduce material hardness. When you weld metal, you effectively harden the metal in the heat affected zone. Hardened metal is likely to crack. If you weld the springs without heat treating after, I have to assume you would create a hardness boundary layer that would lead to a weld failure.

This is why I am considering bonding them as there are some adhesives with very high peel and shear strengths.

[spidertri]

I'm using TC Kline non-shorty rear springs and fine tuning the height with different thickness spring pads. The TCK springs are nice because one end is designed to fit snugly onto the stock bmw rubber cone pad so if the rear droops too much it won't fall out.

I have 450f/600r, 28mm front bar/no rear bar. I did testing with and without the stock rear bar and found that I was almost a second faster w/o the rear bar at autox. With the bar in place I had to wait longer to get on the power otherwise the rear would step out.

[03whitegsr]

Bump to an older thread...

So I've had about a year of driving on the suspension now and can offer some 318ti specific opinions on this topic.

1. Semi-trailing arms suspensions suck.
Sorry, but the rear suspension that makes the E30 and 318ti fun to drive...also makes it slow. The issue is 2 fold. Lots of camber change, lots of toe change. The camber change is less of an issue then the toe change, IMO. High spring rates "help" with these issues as you can "lock down" the range a bit and camber/toe stays within a manageable range. The issue with this method though is it's highly dependent on the tire being able to generate the body roll needed to get the tire straight with the ground to offset the required static camber.

How does this play out in the real world?
If the tire has the grip, it's great. The car isn't sensitive to bumps because toe isn't going all over the place. If the tire doesn't have the grip (wet roads, cold roads, dirty roads) the car simply can't generate the body roll you need to make the tire happy. The results is less grip because you are on the inside edge of the tire from the static camber.

In comparison to softer rear spring rates...
On the stock suspension with the same tires, I would say grip was more consistent. The soft springs meant you got deep into the camber curve with body roll, so you need less static camber to make the tire happy. The car wasn't that bothered by rain and cold either because as the body roll varied due to grip levels, camber angle matched appropriately. However, if you hit a bump mid-corner, it would get a little unruly due to the high toe change. It made the car more twitchy and more difficult to drive in high grip conditions.

2. I'm not sure why people recommend ~1.5* rear spring then front on these cars. For one, it still doesn't make the rear have a higher natural frequency then the front anyway. With the motion ratios, you would need to be about 2.0* higher in the rear then the front to match frequencies.

Beyond that, at 1.4* higher rear the car has TONS of oversteer. A stiffer spring in the rear is just going to make it more oversteer prone.

3. A wheel rate of 580lb/in is too high for street tires. I was pretty sure it would be going into this, but I had the springs so I figured why not try it. That much spring is for one reason and one reason only, control body roll. Unfortunately, it's on the same order of magnitude as the tire stiffness. With the small and stretched RS3 tires, if they are aired up to 40psi, the tire stiffness is high enough it's no longer a problem. But toss on the 15" winter tires and the tire is the softest item in the suspension....it's also undamped. BOUNCE...

With the RS3s in the air pressure range they want to be, the tire is stiffer than the wheel rate, but you definitely get some undamped motion out of them relative to the suspension. I'm dropping the front to a wheel rate around 450lb/in in hopes it helps offset this issue a bit. With some 245 wide Hoosier A6s, the 580 wheel rate would probably be fine and you'd want ti there to control body roll, but it's too much for the RS3s.

I also think it's above the level that the chassis can really deal with anyway. The 318ti chassis isn't that stiff.

4. Droop travel SUCKS on these cars. If you want to keep the spring captive, you have VERY little droop travel because of the independent spring and damper. It's garbage and I'd definitely rather have coilovers with tender springs in the rear. That just takes more work. The constant tripoding is annoying as hell. Trying to keep the rear inside tire on the ground requires a completely different driving style then I'm use to and is greatly slowing the car at this point.


Anyway, I picked up some front springs. Deciding if I want to build a brace for the rear and convert my setup to coilovers with helpers in the rear.

[raamaudio]

You are taking this to a far higher level than most even comprehend. I have been messing with this stuff for decades and made some pretty fast cars that were lame to begin with and you make me have to think, something I prefer to do less of as I get older....

For what you are after coilovers are probably the way to go, As noted you will have to stiffen up the upper mounts, not a bad idea to have a cross brace which can be aluminum to save weight, and stiffen he lower arms and mounts.

----------------

I am back to playing with a FWD, twist beam rear axle, I have had great results with them and kind of fun to beat up on AWD and FWD cars at times with an inferior platform but in the end, a well setup RWD is dang hard to beat when well done, if possible!

[BlackBMWs]

Rick, just a mention, thanks for starting what is an educational thread for me. I will have to reread it to have the concepts and math sit in, but I can appreciate learning in a thread. While I don't have deep knowledge here, I guess with my simple suspension configuration, I believe I have it more right than wrong overall.

Thanks again! Rich

[AnuketTi]

And here I was about to ask whether to go springs or Coilovers... this has been an education. I thought learning to fly was tough!

If anyone wants to chime in though - I am all ears. My car is a daily driver / commuter / long distance hauler / goofer, etc. I would like to lower it - more for aesthetics than for driving performance as I am not building a race car or a high spec 318 Ti... yet!

I already have A/M springs on it, but they do not really drop the car much - if any amount at all. I have the ability to acquire coilovers - or maybe just lowering springs.

If I go for springs, then I will need to get new struts like KONIs or similar (prefer them to Billies).

If I go with Coilovers, they come with struts / shocks and adjustable camber plates up front. Nothing exotic or fancy mind you. I can also pick my choice of spring rates for front and rear.

My goal is NOT to have a slammed to the ground car. I would like it visibly lowered. Even though it is said you can have almost infinite height adjustment with coilovers, I have noticed that they come with shorter strut assemblies so they start out by dropping the car's ride height before you even start playing with the adjustable height - even at the highest setting.

Any thoughts on this?

[raamaudio]

I would not go to low where you live especially, I have driven all over the SF area and you will not like it much if to low and besides, a little lowering looks great, a lot of lowering reduces handling, etc.......

All things work best in balance, that is the natural order of things, all of them

Rick

[AnuketTi]

Originally Posted by raamaudio

I would not go to low where you live especially, I have driven all over the SF area and you will not like it much if to low and besides, a little lowering looks great, a lot of lowering reduces handling, etc.......

All things work best in balance, that is the natural order of things, all of them

Rick

Rick -

I concur with you. I don't want a slammed car. Never been my personal style. I would like it lowered with a nice stance though.

Just wondering if going with coilovers would not be a realistic thing for me considering my expectations.

Michael

[raamaudio]

If you want to set the car up for maximum handling you will need camber plates up front and some toe and camber adjustment in the rear. You would get a set of coilovers but the rears would still be separate springs and shocks but have height adjusters on the springs. True coilovers cannot be used without making the shock towers stronger or you would end up damaging them over time as not designed to call the full load there. I would also recommend sway bar upgrade and bushings.

If you just want to lower the car and make it right good, handle better and sit a bit lower then some good shocks and springs will do that for much less cost and setup time, tuning, etc....Bilstiens and some Eibachs, etc....good to go

[AnuketTi]

Originally Posted by raamaudio

If you want to set the car up for maximum handling you will need camber plates up front and some toe and camber adjustment in the rear. You would get a set of coilovers but the rears would still be separate springs and shocks but have height adjusters on the springs. True coilovers cannot be used without making the shock towers stronger or you would end up damaging them over time as not designed to call the full load there. I would also recommend sway bar upgrade and bushings.

If you just want to lower the car and make it right good, handle better and sit a bit lower then some good shocks and springs will do that for much less cost and setup time, tuning, etc....Bilstiens and some Eibachs, etc....good to go

I can get a good set of coilovers that will come with front adjustable plates for around $700 - $800. As you mention though, I would need to get shock / strut tower braces to avoid the mushroom effect that happens to these cars when the towers get stressed.

Then of course, there will be the issue with the rear to deal with.

I do indeed just want to lower the and reap the benefits of better handling so many shock and springs is the way to go. Not sure it will be for much less though - I can see a full set cost about the same as coilovers.

[raamaudio]

Be careful, not many good coilovers on the market for that kind of price unless a much more expensive used set in great shape

I have had $1k and up to $8.5k coilovers, I went to Ground Control for my ti, custom setup, it was around $2200 but got a deal for around $1900.

I also have used BC racing on two cars now so not afraid to try lower cost, they made me a custom set of inverted ones for the Forester XT I built that I passed a full race STI on a road course in my very streetable car using them.

I had few choices for the Fiesta ST but a vendor on one of the forums has raced on them in another car for 3 years and now doing very well on them in his barely street/mostly track ST. He has them custom tuned and I bought the set for just $950 shipped.

I will run them and see how I like them, there are some $2.5k or so KW's coming out I may end up with, first I have an expensive turbo to buy next.