Another Bilstein Escort Cup Spring Question
 

I've posted a couple of threads before about this and still having trouble deciding on what to use. So here are the basics:

86 951 Bilstein escort cup struts & shocks with the firmer track valving were bought with no springs so need springs for them. For the fronts I am using 2.5" springs and want a street friendly spring but ok to be on the stiff side as I like no lean in my cars. I was thinking around 375 but am open for suggestions. The main question I'm not sure about is spring length. I believe that 9" is the size to use but guess what? Most 2.5" ID springs don't come in a 9" length; hypercoil makes an 8 and a 10 but no 9 and other brands have limited 9" selection.

So which is better for a 375# spring, 8 or 10? I will not be lowering much further than stock, maybe 1/2" or 1" maximum. I read on Hypercoil's site that the way to chose a spring is to double the travel of the shock. i measured the strut's travel and came up with 4.5" so 9 is right on target. Furthermore, my adjuster has 12" of total length for the spring so I'm afraid a 10" spring might not allow the car to go low enough but then afraid that an 8" might fully compress into coil bind.

Any thoughts??????

Many thanks as I need to get these on my car considering they've been in my ex's closet for two years now!

Use an 8" spring if you choose 375 pound springs. 10" would be too tall and raise the car up.

Thanks. what do you think of a 375# spring?

Also, I wish I knew more about all of this from an engineering point of view as I'm sure it's all easy enough to calculate. I figured that with total shock/strut travel at 4-5" the car will compress the spring a little less than 2" when sitting still with a 375# spring. Then I assume an 8" spring will have about 4" of compression travel before binding although I'm not sure how to accurately estimate this. So with an 8" spring on this strut, the shock should bottom out before the spring runs out of travel which I assume is what is wanted since once a spring binds the rate will go to infinity which will cause some nasty handling---Am I correct with all of my assuming?

Of course maybe with I am overthinking all of this and coil bind isn't really a worry as with a stiffer spring, maybe the car doesn't have enough mass to fully compress any of these springs....?

I think 375# spring is going to be stiff on the street but nice on the track. It's a good choice if you plan to use the car primarily on the track.

The math is easy since these cars have nearly 50/50 weight distribution. For example, a 3000 pound car has 1500 pounds on the front and 1500 pounds on the rear, and 750 pounds on each tire. 750 pounds on a 375# spring will compress it 2", but the front motion ratio is .92, so it'll compress the spring slightly more than 2". If you go on the Eibach website you can look up specs on every coilover spring, including travel to coil bind. The barrell type springs tend to have a little more travel for a given rate and length.

thanks, Dave.

So I installed one of my fronts (yup, just one) with an old 8" spring of unknown rate but I think it's around 300# or so. I set the ride height maybe slightly less than stock, maybe 1/2". I have to say that it feels way too soft; it actually feels about the same as stock even hitting bumps it isn't much stiffer. It does feel different but not necessarily stiffer if that makes sense. Also, the car is slightly jouncy where the frequency of spring bounce is higher than stock so the car feels a bit like it bounces. is this just a factor of a stiffer spring or maybe even a shorter spring or is it due to shock dampening? I can't believe that these shocks would allow a 300# spring to jounce.

Anyways, going to try a 400# spring as I think maybe I want stiffer spring rates than what I've heard recommended.

And I finally ordered some rear 2.25 perches from Lindsey for my rear shocks so I'm going to fit some rear springs in addition to the torsion bars. I've been told 225# but I might try a bit stiffer depending on what I like for the front.

But my question for the rear spring is what length? Will an 8" fit or do I need shorter?

Hmmmm, not sure why getting info on these shocks is so difficult on here as lots of folks seem to have them.

Also, installed a 400# spring in the front today and it doesn't feel that stiff. Ok, it's not soft and cushioned but it isn't so stiff that I wouldn't use it. It rides pretty good on slight irregularities and feels great until there is a dip in the road and then it can be awkward, especially when you hit a bump and dip simultaneously. I think I need a bit more ride height as it runs out of travel pretty quickly and also the car does jounce quite a bit which I really don't like but maybe that's just a function of stiff springs. Do stiff springs always rebound super fast and uncomfortably? I thought that's what the damper was supposed to control but maybe there's only so much it can do. I like the way these shocks feel and how they control the smaller motions but bigger movements are uncomfortable.

That being said, the car still doesn't feel like the lean is gone. I put 400# springs on my scirocco and that car feels like a go kart! I was hoping for a similar feel to the 951. Do I need a stiffer spring for that? If so, how stiff?

So a couple of questions I wish someone can answer:

1) Can I use an 8" spring on the rear or is this too long? (275# or similar) (This is with stock turbo torsion bar and slightly lower than stock but not much as I want more suspension travel.)

2) What spring rate do those who track their cars use? I realize there is probably a big range for this but just looking for a general range. And is there any lean or do they have a go kart type feel meaning that they don't lose speed as the car leans into a corner but instead just seem to lose no energy in the corner and just grip and go.

Many thanks and more to come, not that anyone seems that interested but that won't stop me from finding a super sticky 951. :)

If you're buying parts from Lindsay, maybe they can offer some advice?

Cheers,
Mike

What anti-roll bars (sway bars) are you running? Alignment specs and corner weights?

As to your "no lean" comment, there is a lot more to it than spring. You need to choose the correct tire and THEN set up the suspension and steering to make optimal use of the tire. Body roll is a function of spring and anti roll bar stiffness, suspension geometry, roll centers and center of gravity. You are trying to select a spring rate and ask for advice with no other info. Example, how much gas will my car burn in 25 miles? Lots of missing info to make an educated guess.

Ummm, you're overthinking this. First of all and as already stated, I am not racing this car but it is a street car. The reason I asked about tracking is because most people tend to be very conservative when suggesting spring rates for the street and I like stiff and borderline race suspensions. But if you must know the details, the car has a 26.8mm front bar and stock 951 rear with Michelin PS2 17" tires. Nothing much to tell really.

That being said and after some testing of my own, I can say that a 400# front spring with the Bilstein Cups is about where to start. I think if you like softer riding cars or have bad streets, maybe you could go softer but I like the 400's and think I could tolerate a bit stiffer. The car handles pretty nicely and definitely is much flatter when cornering but still not a go kart. I think maybe 500# would get that feel as I'm close right now but not sure I want it that stiff.

Furthermore, the Bilstein shocks are nice. They dampen the springs quite well once I raised the car back up to stock ride height. The only place they aren't very nice is on multiple small road imperfections as when a road has been patched and patched over and over again so that there are many small bumps and imperfections. In this case, the shocks don't seem to handle the high frequency small oscillations and are just too stiff. But when hitting bumps during braking or cornering, they are very nice especially considering how stiff they are. I definitely like the feel of them. Also, an added bonus is that the brakes now feel so much better with hardly any dive and better initial bite since no energy is wasted on compressing the front springs before the braking begins.

Damn, I love stiff linear springs! It's always how a car should feel to me once I put them on. Sure the ride isn't for everyone but for how much better the car feels and handles, it's a small price to pay.



oh, and Dave Lindsey said he didn't think an 8" spring would work on the rear shocks and suggested a 6" which is the shortest I've heard for this set up. I'm sure he knows what he's talking about but it's always good to hear from those who actually have these springs on their car....

You asked...

Was this after raising just the front or the front and rear?

Do you know your front and rear frequencies? Tuning around suspension frequencies is just as important for ride quality on the street as it is for performance at the track. It sounds like you either have to high a frequency in the front relative to the rear frequency or you have to high a spring rate for the dampeners.

Huh?????

Just the front.


No, I don't know the frequencies. And my car is sort of in a testing mode right now as I haven't bought the proper springs yet. So as of now I have all 4 Bilsteins on but the rears just have the stock torsion bars and no helper springs yet. Rear ride height is all the way down on the eccentrics which is too low; the rear jounces and feels like it may be hitting the bump stops too. It did this with the prior Koni yellows as well and it still does it with the Escort shocks. I will raise it back to near stock when I get the rear springs which right now I'm leaning towards around 250-300#.
In the front I currently have an unknown but what I believe is around a 300# spring on the right and a 400# on the left. I know this is a messed up set up but it's actually not as bad as it sounds. the fronts are close enough that I don't really notice any strangeness from right to left turns and the rear just needs more; it moves around too much and doesn't settle into the curve like the fronts but, again, not as bad as you would think. Now this is on the street so I'm not at the limit or anything crazy but was on Mulholland today so I definitely got some curves in.

I can't wait to get all 4 matched springs on!

Oh, and how do I check the frequencies for front and rear? I would think I'd need corner weights and then spring rates but doesn't shock valving have an effect in here? These shocks are so stiff that they must increase the overall spring rate or wheel rate I should say.

Just an idea: you could use 60mm ID springs which I believe is what the shocks were designed for.

All the info you need is in the photos here: http://www.ecstuning.com/Porsche-199...ers/ES1304117/

A 180/70 spring is 180mm long by 70N/mm rate. 70N/mm is about 400#.

Also check my other thread for spring perch bearings for 60mm springs.

Cheers,
Mike

Didn't you say that you wished you knew more about how to calculate the proper spring rate from an engineering standpoint? And then I mentioned the other values that are needed to calculate the proper spring rates, from an engineering stand point. You then said I was over thinking it, which I am not. I thought about giving you the actual equations, but if you thought I was over thinking it before, your obviously not interested. I hope you get it figured out and the car works out just as you would like it to.

You're correct in not worrying too much about the current state of the front until you get the right springs on the rear and the ride height set. Those are all variables in how the front suspension feels and works as well.

There are calculators on the web. Most want your corner weight, spring rate, and unsprung weight.

Your shocks do not push or pull the car like a spring, they actually work against the springs to slow them down, or dampen them. A monotube like a Bilstein is pressurized, but it only provides 10-15 lbs of static force.

Here's some good info on how frequencies come into play for suspension tuning for both comfort and performance. Check out the rest of Shaikh's suspension truth videos, he really does a great job of helping you visualize what's going on.