Modifying Bilstein Shocks

[Dihudaxia]

Hi Kostamojen, or other gurus here.

I have a question on the B14 with a spring swap.
If I were to get a shorter spring, say 7", instead if stock 8", without adjusting the spring perch seat, will the overall height be shorter by 1"?

And will that still maintain the damper stroke? Cos lowering the stock spring usually results in a worse off ride, and was hoping shorter spring could have the same effect without sacrificing damper stroke

[Shankenstein]

Originally Posted by Dihudaxia

Hi Kostamojen, or other gurus here.

I have a question on the B14 with a spring swap.
If I were to get a shorter spring, say 7", instead if stock 8", without adjusting the spring perch seat, will the overall height be shorter by 1"?

And will that still maintain the damper stroke? Cos lowering the stock spring usually results in a worse off ride, and was hoping shorter spring could have the same effect without sacrificing damper stroke

It depends on the spring rate you choose. The original progressive springs from Bilstein go from 2.5 - 4.5 kg/mm front and 3.0 - 7.0 kg/mm rear. Source

A shorter spring with a comparable rate will lower the car. A shorter spring with significantly higher rate might raise the car.

Regarding damper stroke, the goal is to have the piston about half way up it's stroke when the vehicle is static. Compression damping is often weaker than rebound, and if you want to stay off of the bump stops, it's not a bad thing to have slightly more compression travel. For street cars, potholes and road imperfections will require some more rebound travel to keep you stable and happy. It's up to your needs.

If you don't have enough travel, bumping up the spring rate can help (at the expense of comfort and stability, if the damper can't keep up). If weight transfer and roll are a problem, sway bar size/leverage can be adjusted to help reduce this (at the expense of ultimate grip).

[strat61caster]

Originally Posted by JoeHK

So if i convert to linear springs, lets say same specs as the ones you have installed, will my car raise 12mm (0,5inch)??
Cause honestly i like the way it looks how it sits now, but if it raises 1cm with different springs i can't lower it any more to compensate...

Any tips on what i could do lol?
(i'm an absolute noob when it comes to coilovers so that's why i prefer asking here instead of impulse buying different parts or just switching my coilovers to lets say KW V1's )

Greetz

The big advantage to B14's is that you can change the spring length and move the spring perch to preserve your desired ride height.

I assume you're slammed as low as you can go on the Bilstein ~8.7" length springs. If you use 8" springs like @kostamojan you would move the spring perches up to compensate and keep a similar ride height to what you have now, or potentially go even lower (which I couldn't even fathom). @Shankenstein is posting similar information in the post above mine as well.

[JoeHK]

Front is "slammed" yes
I definitely don't want/need to go lower, it sits perfect (and functional, which is very important for my daily driving) as it is right now. I bought these coilovers knowing they wouldn't slam the frame to the floor since that is absolutely not what i want.
That means in the front no more/half a thread left and in the rear 3-5 threads left...
So i'd need the 8" springs like @kostamojan used with a not to high spring rate if i understand correctly, question though, how do the spring perches move up if the springs are shorter? (Or is that how it goes with inverted shocks? As i stated, full noob here)
Thanks in advance guys, i'm glad i'm learning new things about how these coilovers work


Sent from my Potato using Tomato

[JoeHK]

So you have an idea how it sits now


Sent from my Potato using Tomato

[strat61caster]

Originally Posted by JoeHK

So i'd need the 8" springs like @kostamojan used with a not to high spring rate if i understand correctly, question though, how do the spring perches move up if the springs are shorter? (Or is that how it goes with inverted shocks? As i stated, full noob here)
Thanks in advance guys, i'm glad i'm learning new things about how these coilovers work


Sent from my Potato using Tomato

Look at his post again.
For convenience:
http://www.ft86club.com/forums/showp...4&postcount=87

Note the height of the spring perch in the before picture, now look at the after. You can actually see where the perch used to be in the after picture because the threads are cleaner there.
And if you re-read his entire post he reccommends keeping the spring perch in the same location, because the spring is stiffer than the Bilstein spring it doesn't compress as much under the car's weight meaning if you move the spring perch up to compensate for the length 1:1 you would raise the car up, again as described by @Shankenstein earlier. If you use a softer spring you may have to move the perch up higher to keep the car from dropping.

I realize it's one of those adjustments that seems obvious to people with experience but can take some monkeying for it to click with someone who hasn't seen it before.

[Kostamojen]

Originally Posted by strat61caster

The big advantage to B14's is that you can change the spring length and move the spring perch to preserve your desired ride height.

I assume you're slammed as low as you can go on the Bilstein ~8.7" length springs. If you use 8" springs like @kostamojan you would move the spring perches up to compensate and keep a similar ride height to what you have now, or potentially go even lower (which I couldn't even fathom). @Shankenstein is posting similar information in the post above mine as well.

Actually with these 8" springs I'm higher than I was with the stock springs. 7" springs might actually work better if the bumpstops are removed.

If I were to lower the spring perch all the way to the bottom, I would be MAYBE lowered 1" from stock with these 8" springs, just for reference. Right now I have the spring perches lower than I had with the stock springs and I'm still quite a bit higher than before.


As of right now, I'm trying to decide If I want to take the risky option or the expensive option... Risky being modifying the stock bumpstops to get a little more travel, or the expensive option is to run a camber plate like the Racecomp camber plates which lower the suspension a lot and would allow me to raise the spring perches and get more suspension travel.

Not sure what to do...

[strat61caster]

Originally Posted by Kostamojen

Actually with these 8" springs I'm higher than I was with the stock springs. 7" springs might actually work better if the bumpstops are removed.

If I were to lower the spring perch all the way to the bottom, I would be MAYBE lowered 1" from stock with these 8" springs, just for reference. Right now I have the spring perches lower than I had with the stock springs and I'm still quite a bit higher than before.


As of right now, I'm trying to decide If I want to take the risky option or the expensive option... Risky being modifying the stock bumpstops to get a little more travel, or the expensive option is to run a camber plate like the Racecomp camber plates which lower the suspension a lot and would allow me to raise the spring perches and get more suspension travel.

Not sure what to do...

If you jack the car up are the springs loose at your current adjustment?

If the 7" spring is the same rate as the 8" spring and the perch is shifted to compensate for the spring length difference you'd get very nearly the same ride height. Wouldn't a 7" spring be pretty loose on the strut at full droop?

In any case, most spring manufacturers don't make a 7" but rather an 8" or 6" from what I've seen.

As for your decision it depends on how handy and mechanically experienced you feel taking apart the strut. IMO if you use hand tools and take your time the risk should be low.

[Kostamojen]

For reference, where I have the spring perch now versus the ride height with the 8" springs and having them on for a couple weeks so that they've settled. Its about where I want it ride height wise, but the travel seems to be an issue.

Originally Posted by strat61caster

If you jack the car up are the springs loose at your current adjustment?

If the 7" spring is the same rate as the 8" spring and the perch is shifted to compensate for the spring length difference you'd get very nearly the same ride height. Wouldn't a 7" spring be pretty loose on the strut at full droop?

In any case, most spring manufacturers don't make a 7" but rather an 8" or 6" from what I've seen.

As for your decision it depends on how handy and mechanically experienced you feel taking apart the strut. IMO if you use hand tools and take your time the risk should be low.

The springs are not loose when jacked up.

I don't know if a 7" spring will be loose.

I'm experienced enough, but I'm still concerned. I might experiment more with the strut after May if its an issue.

[Racecomp Engineering]

With a 7 inch spring I'd recommend a helper spring.

- Andrew

[Kostamojen]

Originally Posted by Racecomp Engineering

With a 7 inch spring I'd recommend a helper spring.

- Andrew

I'd almost say it would be required for a 7" spring.

RCE, what do you think I should do... Lowering camber plates, shortening the bump stop, or both?

[Shankenstein]

Originally Posted by Kostamojen

I'd almost say it would be required for a 7" spring.

RCE, what do you think I should do... Lowering camber plates, shortening the bump stop, or both?

The earlier comment about running without bump stops is not a great option. It'll be fine until things go horribly wrong.

There are plenty of inexpensive options to consider (<$100):
- puck-type or donut-type (polyurethane)


- short bump stops (foam)


- trim the existing stops (the easy and effective option)

[Kostamojen]

Originally Posted by Shankenstein

The earlier comment about running without bump stops is not a great option. It'll be fine until things go horribly wrong.

Who said anything about running WITHOUT bumpstops???

[Shankenstein]

Originally Posted by Kostamojen

7" springs might actually work better if the bumpstops are removed.