[PLF69]

I am installing my Ohlins kit with custom spring rates, here is my question.

Normal spring rate for onlins is 90nm front and 190nm rear. I have 70nm front and 140nm rear.

Is there a way to calculate how much more preload I need to end up at the same ride height than with the original spring rates ?

Per instructions at the rear I need 40mm of space between top spring lock nut and body seat.

In the front it's really 5mm of preload


- Also why is the onlins rear shock lenght instructions so short, they say they need to be at 500mm and the OEM shock is like 600mm, that's like 4.5 inches less of full droop ??

thank you

[Ghostriderf80]

Well this is a very good question. How does it ride on Ohlins, I am about to get a set myself.
I suppose there are two versions of it. One track focused and another for road. So I suspect you may have the road version. As far as preload etc, I take my cars to a specialist that corner balances and aligns my car. It's for the best.

[PLF69]

Originally Posted by Ghostriderf80

Well this is a very good question. How does it ride on Ohlins, I am about to get a set myself.
I suppose there are two versions of it. One track focused and another for road. So I suspect you may have the road version. As far as preload etc, I take my cars to a specialist that corner balances and aligns my car. It's for the best.

There is only one version but you can order with different spring rates. I've read the shocks can take a difference of 25 or 35% before needing to be revalved.

I'll report back on the ride

[David.m]

Originally Posted by PLF69

There is only one version but you can order with different spring rates. I've read the shocks can take a difference of 25 or 35% before needing to be revalved.

I'll report back on the ride

Wondering if you've installed your Ohlins as yet and if so what you did re the spring height settings?

I'm planning to install mine tomorrow, I have springs in between, 78Nm front & 160Nm rear. I'd like to stay stock height or maybe 5mm lower, want to keep compression travel especially in the rear.

[FaRKle!]

The preload's function is to make sure the spring stays seated under full droop and doesn't come loose. I'd imagine 5mm with the different spring rates is still fine.

If you're really worried about it you can calculate how much force the stock spring rates make at 5mm of compression and then calculate how much compression you need from the new springs to make the same force and set that as your preload.

For the rear, the spacing they recommend is to give the damper piston sufficient margin for travel under driving conditions so it doesn't hit either end.

To compare ride height differences between the springs you'll need the corner weights of the car. You already have the spring rates.

[PLF69]

Alright guys, I got some time to work on the car and here is what I've been trough.

First of all what I did not realise from the start is that the 140nm swift rear springs that Ohlins sent me were 230mm long instead of the 190nm 200mm ones that come in the original kit and that the instructions are based on. This is basically the same difference between the original M3/M4 kit and M2 kit wich explains the preload difference (40mm vs 10mm)

I realised this after dropping the car at 40mm preload, the rear was like 1.5inch higher than stock specs I then proceeded to drop the preload to 10mm wich required unbolting shock and control arm. This gave me a ride height around 10mm lower than the instructions and even lower than the front. I then managed to lower the adjuster (more prelaod) 5mm without unbolting everything wich is NOT easy because of the lack of space and the tedency for the seat to spin.

I have to go out now to find some flat places to re-measure the ride and decide were I want to finalise my adjustments. This could be made much easier and a lot faster on an alignment plaform and I DO own a lift.. (my floor is sadly not flat)


Surprisingly following the instructions the front ended up exaclty 10mm lower than stock. I have not decided but may remove a max of 5mm of height wich I will try to do with the spring preload to not lose any travel.

I have found the best method to measure height and make adjustment is the oem one. See picture attached, this helped me because my car was not stock and had Dinan HAS already installed and I had no idea of my stock ride height. Here is also the OEM specs:

AFAIK, F87 M2 OEM stock ride height (OEM suspension, wheels, tires, tire-pressure and of course without shipping blocks):

front wheels: 612mm ("series") and 622mm ("bad-road package") (see here);
rear wheels: 615mm ("series" + "bad-road package") (see here).

[PLF69]

Originally Posted by David.m

Wondering if you've installed your Ohlins as yet and if so what you did re the spring height settings?

I'm planning to install mine tomorrow, I have springs in between, 78Nm front & 160Nm rear. I'd like to stay stock height or maybe 5mm lower, want to keep compression travel especially in the rear.

If your 160Nm springs are 200mm long I would maybe add a 5mm to the 40 from the instructions and see from there. If you have to readjust you can lube the threads to make it easier and clean the lube with brake cleaner afterwards so everthing does not stick on them.

See my above post for the fronts, I set everything up per instructions and ended up 10mm lower like they supposed to.

[M2C AW]

Before finishing up.....suggest you check your rear shock travel and make sure your not on the bump stop (pinch the bellows to check the space between the shock body and top of the bump stop).
The rear shock body on the R&Ts may be a bit too long for the F8x chassis, and can be problematic if car is lowered too much.

[David.m]

Originally Posted by PLF69

If your 160Nm springs are 200mm long I would maybe add a 5mm to the 40 from the instructions and see from there. If you have to readjust you can lube the threads to make it easier and clean the lube with brake cleaner afterwards so everthing does not stick on them.

See my above post for the fronts, I set everything up per instructions and ended up 10mm lower like they supposed to.

My 160Nm springs are 200mm, I decided to set the spring adjuster gap at 50mm, haven't completely finished yet but using a jack to lift the wheel ride height is roughly 5mm lower than stock.

[David.m]

Originally Posted by M2MGM

Before finishing up.....suggest you check your rear shock travel and make sure your not on the bump stop (pinch the bellows to check the space between the shock body and top of the bump stop).
The rear shock body on the R&Ts may be a bit too long for the F8x chassis, and can be problematic if car is lowered too much.

Looks like I have too much compression travel. Doing the 2nd rear wheel I left the spring out and jacked the wheel up until the car started to lift off the jack stand. The oem shock measurement from bottom of rim to wheel arch is 560, with the Ohlins shock its 545 and the tyre (PS4s 285/35) is touching the guard lining around 10-11 O'clock. I actually set the Ohlins shock length at 510 instead of the recommended 500, I'll have to pull them out and lengthen to 515-520 to reduce travel to bump stop. Wish I had remembered to test this on the first wheel

[PLF69]

Originally Posted by David.m

Looks like I have too much compression travel. Doing the 2nd rear wheel I left the spring out and jacked the wheel up until the car started to lift off the jack stand. The oem shock measurement from bottom of rim to wheel arch is 560, with the Ohlins shock its 545 and the tyre (PS4s 285/35) is touching the guard lining around 10-11 O'clock. I actually set the Ohlins shock length at 510 instead of the recommended 500, I'll have to pull them out and lengthen to 515-520 to reduce travel to bump stop. Wish I had remembered to test this on the first wheel

Interesting, I did not touch the shock lenght adjustment, left them at 500mm but now you have me wondering..

[M2C AW]

Originally Posted by PLF69

Interesting, I did not touch the shock lenght adjustment, left them at 500mm but now you have me wondering..

I believe the 500mm per set-up instructions is where you want to be. My suggestion was to be careful in lowering rear ride height beyond Ohlins specs (using the spring perches...which is a separate issue altogether), to be sure you’re not on (or near) the shock bump stop.

[PLF69]

Originally Posted by David.m

Looks like I have too much compression travel. Doing the 2nd rear wheel I left the spring out and jacked the wheel up until the car started to lift off the jack stand. The oem shock measurement from bottom of rim to wheel arch is 560, with the Ohlins shock its 545 and the tyre (PS4s 285/35) is touching the guard lining around 10-11 O'clock. I actually set the Ohlins shock length at 510 instead of the recommended 500, I'll have to pull them out and lengthen to 515-520 to reduce travel to bump stop. Wish I had remembered to test this on the first wheel

I was thinking about what you here and don't you think that with the spring in place it will be fully compressed by the time the tire reaches the wheel well ?

[David.m]

Originally Posted by PLF69

I was thinking about what you here and don't you think that with the spring in place it will be fully compressed by the time the tire reaches the wheel well ?

I wouldn't think so. Assuming that at the recommended 500mm shock length, full compression onto the bump stop wouldn't (or at least shouldn't) fully compress the spring.

Using a piece of A3 paper between the tyre tread & guard lining (because you can't see in there) I worked out setting my shock length at 520 gives me 4-5mm clearance (ie the 285/35/19 PS4s touches the guard lining with shock at 515mm). I still have more compression travel than the oem shock allows and a lot more travel before initial contact with the bump stop compared with stock.

Had my alignment done today and went for a 1/2hr drive on roads I travel daily and the improvement in compliance (if that's the right term) is significant. It's still as stiff/firm as oem (maybe even firmer) but the dramatic rebound is gone, and whereas before a road with varying smaller undulations would have you bouncing around you now feel the bumps but pretty much stay in your seat. Very happy

[PLF69]

Originally Posted by David.m

I wouldn't think so. Assuming that at the recommended 500mm shock length, full compression onto the bump stop wouldn't (or at least shouldn't) fully compress the spring.

Using a piece of A3 paper between the tyre tread & guard lining (because you can't see in there) I worked out setting my shock length at 520 gives me 4-5mm clearance (ie the 285/35/19 PS4s touches the guard lining with shock at 515mm). I still have more compression travel than the oem shock allows and a lot more travel before initial contact with the bump stop compared with stock.

Had my alignment done today and went for a 1/2hr drive on roads I travel daily and the improvement in compliance (if that's the right term) is significant. It's still as stiff/firm as oem (maybe even firmer) but the dramatic rebound is gone, and whereas before a road with varying smaller undulations would have you bouncing around you now feel the bumps but pretty much stay in your seat. Very happy

I was also able to run the car for a few 100kms and I got pretty much the same impression, stiffer than OEM (spring rates) but more compliant in the sense that the suspension soaks up the bumps, joints and other irregularities better. The faster you the better it seems to get, I think it will be terrific at the track.

My alignment is still not done and I'm riding on beat up Cup2 tires wich have a very stiff carcass and seem to get noisier and maybe even stiffer as they have less thread on them but I have to keep in mind we have some of the worst roads, you wouldn't believe it.

I am hoping switching to brand new PS4s will improve the ride and lessen the metallic bang you ear/feel at the front with the camber plates.

As of now I tried setting the clicks to 15, 18, 20 and to like 30 wich did not make much difference from 20. What clicks have you tried ?

[David.m]

Originally Posted by PLF69

As of now I tried setting the clicks to 15, 18, 20 and to like 30 wich did not make much difference from 20. What clicks have you tried ?

So far only 18 clicks, corona 19 restrictions here means driving only to work or to shops for food. Pre install my main concern was it being too stiff as my wife has had spinal fusion and doesn't like riding in the M2 so I was hoping (though not expecting) a smoother ride on the soft setting. So I'm both surprised and very happy with the outcome, the poor surface on some local roads even caused M2 occupants to be thrown side to side, really not good for her back, but now you feel the bumps but don't get thrown around.