Calling E85/E86 rear suspension gurus..

[B21]

So my Ohlins Road n Track for my E89 is under sprung on the rear ..in part due to carrying a full size spare…always hooning with roof in boot and wishing to have a reasonable ride height for bumpy Scottish roads…

The E89 rear suspension is essentially a copy of the E85/E86 albeit with minor differences.

The chances of any E89 guys here proffering a learned opinion here must be slim…however I know the E85/E86 fiddle much more in this area..

So…the 7 inc rear Ohlins spring is rated at 70nm / mm

Ohlins don’t do many options…the next one is 110nm..

I’ve found a company that does a 96 nm/ mm version

My question is that a too radical increase in spring rate or not?

 

[enuff_zed]

So that’s what, just under 30% stiffer? Seems a fair bit. But given the limited choice and how easy rear springs are to swap then I think i would at least try the 96 first.

 

[plenty]

I'm probably missing something, but the screenshot seems to be for a 7" front coilover spring? Not the shorter barrel spring used the rear? Or is the Ohlins a true coilover at the rear?

 

[B21]

I'm probably missing something, but the screenshot seems to be for a 7" front coilover spring? Not the shorter barrel spring used the rear?

The spec and pics apart from spring rate looks identical to the Ohlins spring..which is not barrel shaped

 

[plenty]

Is the Ohlins a true coilover, or a separate inboard spring as per OEM?

 

[B21]

Is the Ohlins a true coilover, or a separate inboard spring as per OEM?

The rear is as per standard E85/E89 design…seperate damper and seperate spring…caused great confusion to us when delivered ..front is thru coilover

 

[enuff_zed]

Firstly, I'm no expert in suspension tuning...................
However, given how high you have wound up the adjuster on your current spring, is if feasible to go up to an 8 inch? Would this give you more scope with regards to spring rates?

 

[john-e89]

Why is your ride height adjuster on the swinging arm Peter..?

I put my KWV3 ones the other way round. Having had a look lots seem to be how I’ve installed them but there are a few your way. I don’t suppose it matters too much, just curious.

 

[B21]

Why is your ride height adjuster on the swinging arm Peter..?

I put my KWV3 ones the other way round. Having had a look lots seem to be how I’ve installed them but there are a few your way. I don’t suppose it matters too much, just curious.

That’s how Ohlins states it should be fitted

 

[B21]

Firstly, I'm no expert in suspension tuning...................
However, given how high you have wound up the adjuster on your current spring, is if feasible to go up to an 8 inch? Would this give you more scope with regards to spring rates?

Not sure..frankly a bit disappointed with Ohlins on this one..I know they prefer soft springing ..but…one kit for the whole e89 range with such big weight variations 18i to 35is..

Given the faff and cost I wanted to try and do it in one hit…just thought identical spring with higher spring rate maybe the fix?

 

[plenty]

Interesting that Ohlins opted for a straight inboard spring - most use a barrel type. I don't think you need to replicate the exact spring type, which would open up more options if needed. If 62mm ID fits on your adjusters then there are many springs available, or else you could procure a set of adjusters e.g. from BC Racing that will accommodate a 62mm ID spring.

To address the original question, I'm running 10 kgs/mm or 98 n/mm rear rate on a Z4MR and I reckon 8-9 kgs would be perfect, so 96 n/mm is probably about right for a heavier E89. Any stiffer than that and the dampers probably wouldn't cope.

 

[Rsipad]

I'd be weary of straying too far from what you currently have. Spring rate and damping of your shock-spring setup have to somewhat match. If you go too high or low without adjusting damping, the ride and handling becomes significantly worse.

When I got my BCs, I recall them telling me to only go a max of 2 kg/mm spring rate away from what was originally ordered as they tune their shock's damping to be optimal for the spring rate you order, and otherwise my setup will be underdamped or overdamped.

Also I don't know if this would help, but iirc the e85 prefers either 2 or 0 kg/mm softer front springs compared to the rear as opposed to the opposite in most other cars.

 

[B21]

Interesting that Ohlins opted for a straight inboard spring - most use a barrel type. I don't think you need to replicate the exact spring type, which would open up more options if needed. If 62mm ID fits on your adjusters then there are many springs available, or else you could procure a set of adjusters e.g. from BC Racing that will accommodate a 62mm ID spring.

To address the original question, I'm running 10 kgs/mm or 98 n/mm rear rate on a Z4MR and I reckon 8-9 kgs would be perfect, so 96 n/mm is probably about right for a heavier E89. Any stiffer than that and the dampers probably wouldn't cope.

Thnx..I’ve bitten the bullet on the ones I highlighted and I’ll see how it goes..good to know on your suggestions ..

 

[B21]

I'd be weary of straying too far from what you currently have. Spring rate and damping of your shock-spring setup have to somewhat match. If you go too high or low without adjusting damping, the ride and handling becomes significantly worse.

When I got my BCs, I recall them telling me to only go a max of 2 kg/mm spring rate away from what was originally ordered as they tune their shock's damping to be optimal for the spring rate you order, and otherwise my setup will be underdamped or overdamped.

Also I don't know if this would help, but iirc the e85 prefers either 2 or 0 kg/mm softer front springs compared to the rear as opposed to the opposite in most other cars.

Thnx…as stated I’ve ordered the higher rated springs…the Ohlins have a wide range of damping ..position 10 is standard ..by the time you get to 6 or 7 it’s very damped..