Coil-over Spring Isolators - which to use ?

[Jason5driver]

I was wondering which spring isolator is better to use ?
Between poly (by Energy Suspension) or rubber ?
This is on an inline-6 E39 , and I am installing Fortune coil-overs ...
My car is mainly a daily driver , but I do like performance , and the ability to adjust camber / alignment , to help with tire longevity .
The attached pictures are of the front, and the other picture is of the rear .
On the rear , I thought about using a rubber isolator between the rear mount and chassis , to help ride and NVH ...

Please let me know .

Thank you !

I added another picture , and a picture of Ground Control’s rear mounts , which looks like it has a poly isolator ..

https://www.suspension.com/blog/durometer/

[circuit.heart]

I was wondering which spring isolator is better to use ?
Between poly (by Energy Suspension) or rubber ?
This is on an inline-6 E39 , and I am installing Fortune coil-overs ...
My car is mainly a daily driver , but I do like performance , and the ability to adjust camber / alignment , to help with tire longevity .
The attached pictures are of the front, and the other picture is of the rear .
On the rear , I thought about using a rubber isolator between the rear mount and chassis , to help ride and NVH ...

Please let me know .

Thank you !

Fortune Auto already gave you the isolators you need, you circled them. It wouldn't be easy to find rubber versions of that, considering how thin the piece is you'd just wind up tearing it.

FWIW, by choosing FA you've already locked yourself into a world of NVH. Spring isolators be damned, FA valves their dampers pretty aggressively to give you sharper handling on track. Kinda feels like Bilstein B8's, which are just... harsh.

[Jason5driver]

Fortune Auto already gave you the isolators you need, you circled them. It wouldn't be easy to find rubber versions of that, considering how thin the piece is you'd just wind up tearing it.

FWIW, by choosing FA you've already locked yourself into a world of NVH. Spring isolators be damned, FA valves their dampers pretty aggressively to give you sharper handling on track. Kinda feels like Bilstein B8's, which are just... harsh.

Wow ! Thank you much for the reply !
211 views , and NO response ... ? Mind-boggling . lol

The 1st picture is of the rear shock top mount , with a rubber spring isolator on top .
The idea is prevent metal to metal contact , and isolate anything from getting into the car .
At least that’s the concept / idea .

The 2nd picture is of the front top mount, with a poly isolator between the spring and blue Koyo bearing .

The 3rd picture is of the rear Ground Control shock mounts , and what looks to be poly isolators ...

The 4th picture is of the rear shock top mount again .

Fortune doesn’t really care about ride quality .
They only care about “race car” .
So, what was with the coil-overs doesn’t really apply imo .
I was hoping they ride similar to BC’s ?
I’ve driven on those and was pretty impressed .

What suspension do you recommend then ?

Thank you ,
Jason

[circuit.heart]

Fortune doesn’t really care about ride quality .
They only care about “race car” .
So, what was with the coil-overs doesn’t really apply imo .
I was hoping they ride similar to BC’s ?
I’ve driven on those and was pretty impressed .

What suspension do you recommend then ?

Correct... Fortune Auto is a grassroots motorsport company, they are not in the business of making your boat comfortable. Every single one of my dual street/track cars runs BC Racing, with tricks:

1) Custom order the damper to be valved 2kg/mm lower than your intended spring rate. If you want to run 6k front 7k rear, order the dampers valved for 4k/5k.
2) When the box arrives, toss the BC springs in the garbage and order 1" shorter, 65mm Swift springs in the rates you intended.
3) Ignore every instruction manual and thread about setting preload on coilovers. Set the spring perch to the point where, at full damper extension, the spring is just barely loose. For your rears (divorced spring/damper) you'll have to do this adjustment as you fix the ride height.
4) Install into car, and set the ride height only using the lower collar of the front strut. In the rear (divorced setup) you need to first adjust the spring perch for actual ride height, then adjust the damper length until, like the front, full extension leaves the spring just barely loose, not about to fall out but not bound up either.
5) Start the dampers off at the softest adjustment. Ignore other tutorials.
6) During the test drive, you should have so little damping that the car is bouncing around. Slowly stiffen the front dampers 2 clicks at a time until it stops oscillating, then do the same for the rears. If you can't tell which end is the one that's bouncing, have a friend drive and you sit in the back seat.

Budget coilovers are never designed for ride quality in mind - you're going to have to put effort into it. If that bothers you, a nice set of Koni FSD's and lowering springs is head and shoulders above what you're going to get from an out-of-the-box China/Taiwan/Japan coilover.

[Jason5driver]

Correct... Fortune Auto is a grassroots motorsport company, they are not in the business of making your boat comfortable. Every single one of my dual street/track cars runs BC Racing, with tricks:

1) Custom order the damper to be valved 2kg/mm lower than your intended spring rate. If you want to run 6k front 7k rear, order the dampers valved for 4k/5k.
2) When the box arrives, toss the BC springs in the garbage and order 1" shorter, 65mm Swift springs in the rates you intended.
3) Ignore every instruction manual and thread about setting preload on coilovers. Set the spring perch to the point where, at full damper extension, the spring is just barely loose. For your rears (divorced spring/damper) you'll have to do this adjustment as you fix the ride height.
4) Install into car, and set the ride height only using the lower collar of the front strut. In the rear (divorced setup) you need to first adjust the spring perch for actual ride height, then adjust the damper length until, like the front, full extension leaves the spring just barely loose, not about to fall out but not bound up either.
5) Start the dampers off at the softest adjustment. Ignore other tutorials.
6) During the test drive, you should have so little damping that the car is bouncing around. Slowly stiffen the front dampers 2 clicks at a time until it stops oscillating, then do the same for the rears. If you can't tell which end is the one that's bouncing, have a friend drive and you sit in the back seat.

Budget coilovers are never designed for ride quality in mind - you're going to have to put effort into it. If that bothers you, a nice set of Koni FSD's and lowering springs is head and shoulders above what you're going to get from an out-of-the-box China/Taiwan/Japan coilover.

By using a damper that is under valved , won’t you blow the damper ?

Also , why would you use a 1” shorter spring ?
You will not be able to utilize the full stroke by using too short of a spring , correct ?

The E39 has true coil-overs on the front and rear .
No divorced springs .

Fortune’s preload is snug on the fronts , and 1/4” on the rears .

Another reason I was asking about poly or rubber isolators , is because I have 65mm springs for the front , but the coil-overs are meant for 60mm springs .
Really , the perches are 58.7mm .

The poly or rubber isolators are also to adapt the 65mm spring to the 60mm perches .

[circuit.heart]

And this is why I hate the internet, nothing but misinformation even on forums.

By using a damper that is under valved , won’t you blow the damper ?

BC's come horribly overvalved for what they "tell" you it's valved for. I'm giving you the correct offset factor so that you end up with a balanced spring/damping force combination.

Also , why would you use a 1” shorter spring ?
You will not be able to utilize the full stroke by using too short of a spring , correct ?

1) Swifts have much thinner coils than BC springs, you will not lose any travel.
2) You're going to a stiffer spring rate overall - it's going to push the car higher when sitting on the ground, possibly outside of the height adjustment range you originally bargained for. Use a shorter spring and simply push the spring perch up higher if you need to.
3) Unless you are going stupid low and using 4" springs, the spring almost always has more travel than the BC damper assembly. So this is moot.
4) The "preload" setting I recommend is to maximize your usage of both the damper's up-travel and down-travel, because the damper travel is limited, you can't afford to waste any of it.

The E39 has true coil-overs on the front and rear. No divorced springs.

Sweet, must be a sedan thing, sorry. I only own an E39 Touring and my SLS spring is divorced.

Fortune’s preload is snug on the fronts , and 1/4” on the rears.

See note earlier about preload.

Another reason I was asking about poly or rubber isolators , is because I have 65mm springs for the front , but the coil-overs are meant for 60mm springs .
Really , the perches are 58.7mm. The poly or rubber isolators are also to adapt the 65mm spring to the 60mm perches .

Doesn't matter as long as you have a thrust (aka torrington) bearing in the system. I freely run 65mm ID springs on my 62mm BC plastic "isolators", in the past I'd even take them out if I needed to drop my ride height 1/8" real quick. It doesn't affect ride quality or NVH in the slightest.

The biggest culprit to coilover NVH is not the spring isolator, it's the fact that spring AND damping loads eventually end up going into the chassis via a pillow ball, and pillow balls can loosen up => NVH. If you don't like that, you can replace the pillow balls every so often, or, find a way to keep using stock rubber top hats and a comfort-minded damper like a Koni FSD.

[Jason5driver]

And this is why I hate the internet, nothing but misinformation even on forums.

BC's come horribly overvalved for what they "tell" you it's valved for. I'm giving you the correct offset factor so that you end up with a balanced spring/damping force combination.


1) Swifts have much thinner coils than BC springs, you will not lose any travel.
2) You're going to a stiffer spring rate overall - it's going to push the car higher when sitting on the ground, possibly outside of the height adjustment range you originally bargained for. Use a shorter spring and simply push the spring perch up higher if you need to.
3) Unless you are going stupid low and using 4" springs, the spring almost always has more travel than the BC damper assembly. So this is moot.
4) The "preload" setting I recommend is to maximize your usage of both the damper's up-travel and down-travel, because the damper travel is limited, you can't afford to waste any of it.


Sweet, must be a sedan thing, sorry. I only own an E39 Touring and my SLS spring is divorced.


See note earlier about preload.


Doesn't matter as long as you have a thrust (aka torrington) bearing in the system. I freely run 65mm ID springs on my 62mm BC plastic "isolators", in the past I'd even take them out if I needed to drop my ride height 1/8" real quick. It doesn't affect ride quality or NVH in the slightest.

The biggest culprit to coilover NVH is not the spring isolator, it's the fact that spring AND damping loads eventually end up going into the chassis via a pillow ball, and pillow balls can loosen up => NVH. If you don't like that, you can replace the pillow balls every so often, or, find a way to keep using stock rubber top hats and a comfort-minded damper like a Koni FSD.

Still, why would I need or want a shorter spring ?

I have TONS of height on the strut and shock.
Springs have a set range of travel, which correlates to the stroke of your damper .
The standard spring height is 7" tall for these coil-overs , and I think for the BC's as well .
I can adjust the height of the coil-over to whatever height I want ...
There is absolutely no need for a shorter spring imo .
Using a shorter 6" tall spring would be under / below the damper stroke range .
Why would you want that ?

What is the reason for running 65mm springs, if the coil-overs use 60mm springs ?
I am using front 65mm springs because I got a great deal on them, and I know they are FAR superior to the Fortune springs .
I don't understand why you would not some kind of adapter on the spring perches, because the 65m springs will slop around .

The spring isolator is in contact with the pillow-ball mounts (front) / rear mounts .
The point to the isolator is to absorb vibration and prevent metal to metal contact .

[circuit.heart]

Still, why would I need or want a shorter spring ?
I have TONS of height on the strut and shock.
Springs have a set range of travel, which correlates to the stroke of your damper .
The standard spring height is 7" tall for these coil-overs , and I think for the BC's as well .
I can adjust the height of the coil-over to whatever height I want ...
There is absolutely no need for a shorter spring imo .
Using a shorter 6" tall spring would be under / below the damper stroke range .
Why would you want that ?

If your original spring length is short enough that the tire tucks UNDER the spring perch, you can stay with the length they gave you. This move is to make sure you have tire clearance to the perch - when the tire flexes under cornering load I've seen far too many people carve their spring perch into their tire, with catastrophic results.

Springs don't "correlate" to the damper stroke, you use whatever you want that has a greater usable travel than the damper stroke. Which also means you can use the bare minimum, and since BC's have shit for travel, and you are probably using a decently stiff rate, you are never in need of travel. Shorter spring = less weight as well.

What is the reason for running 65mm springs, if the coil-overs use 60mm springs ?
I am using front 65mm springs because I got a great deal on them, and I know they are FAR superior to the Fortune springs .
I don't understand why you would not some kind of adapter on the spring perches, because the 65m springs will slop around .

It doesn't matter, because when the car's on the ground there's enough friction on the perches that the spring physically cannot "slop around". If you don't have torrington/thrust bearings, the force of compression or steering WILL cause intermittent slip, which you'll feel as clunking/creaking/groaning, but that is a separate discussion. The spring diameter is unimportant as long as it fully engages the perches and doesn't interfere with anything else. I also use 65mm Swift springs because they are usually the cheapest Swifts available.

The spring isolator is in contact with the pillow-ball mounts (front) / rear mounts .
The point to the isolator is to absorb vibration and prevent metal to metal contact .

Yeah it doesn't work like that. The spring is only partly responsible for NVH transfer - the other half is your damper, which has no isolator in a pillow-ball setup.