BC racing coilovers, not too low please

[perttu]

The BCR shocks allow adjusting to the stock ride height.

Thanks for comments! I guess I'm one more step closer to pulling the trigger now

[plenty]

I am running close to stock height in BCs. In fact I could run significantly higher than stock if wanted...haven't measured but from memory at least 20mm higher than stock front and rear is available should you want it.

BCs on the default 6F/10R springs, or any decent aftermarket setup for that matter, are a massive improvement over OEM regardless of condition, as OEM spring rates are far too hard at the rear and too soft at the front. I would actually suggest opting for 7 or 8 kgs springs at the front as IMO 6 kgs are still a tad soft.

[perttu]

I am running close to stock height in BCs. In fact I coild run significantly higher than stock if wanted...haven't measured but guess at least 20mm higher than stock front and rear is available should you want it.

BCs on the default 6F/10R springs, or any decent aftermarket setup in fact, are a massive improvement over OEM regardless of condition, as OEM spring rates are far too hard at the rear and too soft at the front. I would actually suggest opting for 7 or 8 kgs springs at the front as IMO 6 kgs are still a tad soft.

Thanks, it's good to have first hand comments since there is quite much conflicting information about this. One dealer says this, another says that and the internet says something in between or both at the same time .

I'm currently looking at 7kg/mm / front, 10kg/mm / rear. What has been your experience on different stiffness settings? Mostly what I'm hearing is that softest setting is close to stock and stiff is really hard.

[maupineda]

Rears need to be stiffer due to placement within the upper control arm, the effective rate due to where it sits relative to the wheel is about 0.5 (0.45) of the rate and about 0.9 (0.91) for the front

i.e a front spring effective rate would be rate x 0.9, and the rear would be rate x 0.5

You need the rear to be stiffer for the rear tires to even the fronts after a bump at speed

In my case, my spring rates are 225 and 600 which gives me a wheel rate of 202.5 and 270 respectively. Not ideal, if I wanted a 14% delta front to rear for a fast road/ GT setup I would need to have a 500#/in spring at the rear. The reason I have 600 at the rear is that I calculated to a 250 front, but then back down the fronts. Eventually, I will go to 500 at the rear.

So, the thought that the car is off from the factory is incorrect. The issue is the damping. the rates are on the firm side, but not extreme. Also, keep in mind that we seat closer to the rear axle, so the need of a stiffer spring and more aggressive damping are exacerbated by this, and we cannot do much about it, is the car's architecture trait. That is why the Z will never ride very well if you want a sporty suspension.

The reason why the Z has even stiffer rear springs relative to the fronts VS the E46 is due to the shorter wheelbase, this requires the rear wheel to recover quicker from a bump to keep up with the front.

[plenty]

Even taking into consideration the positioning of the springs, the OEM wheel rate is too stiff at the rear and too soft at the front.

On a front-engined car you want harder suspension at the front as there is more weight at the front, especially with the heavy iron S54 block on the Z4M. Furthermore, the seating position on the E8x is so close to the rear axle that you want as much compliance at the rear as possible.

The OEM suspension is a strange combination of the front end being too soft, contributing to poor turn-in, a general feeling of vagueness, lift under hard acceleration and dive under braking, but also a jittery ride and a back end that hops and skips over bumps rather than absorbing them, due to the lack of compliance at the rear. The end result is a car that does not reward being pushed hard and has the sensation of the front and rear being disconnected, as if you are driving halves of two different cars that have been spliced together.

Most aftermarket suspension including BC and KW fixes this with wheel rates that are higher at the front than the rear, making for a more planted, confidence-inspiring and cohesive drive.

The Caterham is another example of a car which is front-engined with the seating position close to the rear axle. Most Caterhams run wheel rates at a delta of roughly 2F:1R. The only cars which have stiffer wheel rates at the rear are mid- and rear-engined.

[plenty]

I'm currently looking at 7kg/mm / front, 10kg/mm / rear. What has been your experience on different stiffness settings? Mostly what I'm hearing is that softest setting is close to stock and stiff is really hard.

7 kgs front would be a good all-around choice and you could even consider stiffer if you value front-end sharpness. Ride quality is much more influenced by the rear axle, so you can stiffen up the front considerably without significantly compromising ride.

And you can always swap out the springs later - you can go +/- 2 kgs without needing to revalve the dampers.

I've yet to really experiment with damping settings. On the smoother roads of Europe where I've done most of my Z4M miles I was able to run close to full hard on the front. I've haven't yet driven many miles in anger on bumpy UK lanes.

[peteslag]

Hello all,

I'm definitely going to buy BC racing coilovers but I don't want to lower the car. Before I pull the trigger on a purchase I was wondering if any body on here has BC coilovers set to their highest setting, if so I was hoping you could measure the ride height for me.

I contacted BC racing but they couldn't say with any certainty what the figure was.

Thanks in advance,

Pete

*EDIT* i have my answer, they are height adjustable to near standard height. Thanks for looking.*EDIT*

Came across this old thread while looking for an answer to exactly same question. Pete, if you ended up purchasing BCs, can you confirm if you're able to reach stock or close to stock height with the highest setting? Or maybe your EDIT comment was already based on your own experience after installing the coilovers? .

Long story short........I put the car up for sale because couldn't bond with it. I bought a VX220 turbo to fill the void. Recently I have started to unravel the peculiar way that the Z4m goes about its business and have found love for it. The VX220 is going up for sale tomorrow.

I know that others will probably disagree but in standard form I feel like there is a disconnect between the front and rear suspension. When the rear of the car breaks traction I can sense what is going on and fix it with corrective steering inputs. When the "drift" comes to an end and the rear tyres start to find traction and I find that it snaps back quite viscously. This might be down to the fact that the dampers are very tired but my personal thoughts are that decent coilovers and a good alignment will fix this.

There is a brutally honest review here, it kind of mirrors my views:

https://www.youtube.com/watch?v=tgATPu4zFOU

As soon as the VX220 sells I'll be fitting BC racing coilovers and I'll get back to you with some feedback. My understanding is that they can provide OEM ride height.

[plenty]

@peteslag I'm in the SE but if we can meet somewhere in the middle you are welcome to drive my Z4MR. My diagnosis was 100% the same as yours and I'm now very happy with how my car drives.

[maupineda]

Even taking into consideration the positioning of the springs, the OEM wheel rate is too stiff at the rear and too soft at the front.

On a front-engined car you want harder suspension at the front as there is more weight at the front, especially with the heavy iron S54 block on the Z4M. Furthermore, the seating position on the E8x is so close to the rear axle that you want as much compliance at the rear as possible.

The OEM suspension is a strange combination of the front end being too soft, contributing to poor turn-in, a general feeling of vagueness, lift under hard acceleration and dive under braking, but also a jittery ride and a back end that hops and skips over bumps rather than absorbing them, due to the lack of compliance at the rear. The end result is a car that does not reward being pushed hard and has the sensation of the front and rear being disconnected, as if you are driving halves of two different cars that have been spliced together.

Most aftermarket suspension including BC and KW fixes this with wheel rates that are higher at the front than the rear, making for a more planted, confidence-inspiring and cohesive drive.

The Caterham is another example of a car which is front-engined with the seating position close to the rear axle. Most Caterhams run wheel rates at a delta of roughly 2F:1R. The only cars which have stiffer wheel rates at the rear are mid- and rear-engined.

I love tech discussion, what data would you have to indicate the rates are off, either soft or stiff, you do realize that despite engine and drive positions, the Z4 is close to 50/50 weight distribution. I think is 52/48 and about 49 cross-car. so it is pretty balanced.

The rears can be a bit softer, yes, the OE rear springs are progressive and the rate ramps up quickly at the rear to be close to 700#/in. however, that can be remedied with different rate springs (preferably linear), but again, not by much. equal rates front and rear are incorrect, again, if you match them you now have a soft rear and the wheel will not settle after a bump, and the car will jack down, and ride the stops as a result which will make the ride even shittier. Have a look at videos from Fatcatmotorsports in youtube, he does a very good job in getting this message accross.

[peteslag]

Interestingly, I loved the way my Z4 3.0 handled. Hopefully someone more informed than me can explain why I find the Z4m so woeful in comparison. My only gripe with the 3.0 was that it understeered a bit (fixed with a stiff rear ARB). I always chucked that car around a track with a massive smile on my face, in standard form I can't say the same of my Z4m. I can't wait to refresh the suspension and see what this beast can do. Here is a cheeky vid of my old 3.0 in action, the little car that could.

https://www.youtube.com/watch?v=TW7KSQ1ta8U&t=28s

[plenty]

I love tech discussion, what data would you have to indicate the rates are off, either soft or stiff, you do realize that despite engine and drive positions, the Z4 is close to 50/50 weight distribution. I think is 52/48 and about 49 cross-car. so it is pretty balanced.

I’m more interested in the outcomes than the technical details, and I’m no engineer but I do enjoy modifying my cars to make them handle better.

I’ve noticed a relative lack of discussion and evidence on topics such as spring rates and weight distribution for the Z4 compared with other makes I’ve owned, which I attribute to an ownership base which tends to be more GT than sports, and because these cars are rarely used on track. I’m not a track person either, but cars that are popular on track tend to have a much deeper knowledge base.

I’ve seen the 50/50 weight claim mentioned frequently. There’s not a lot of available evidence of this, but I have no reason to doubt it. But I note that weight distribution presumably cannot be the same for an S54-engined car whose engine is significantly heavier than say the N52. Meanwhile the impression from my driver’s seat is very much one of front-heaviness, exacerbated by a driving position far from the front axle which magnifies the pendulum feel.

Many road tests and indeed the OP of this thread have described the same symptoms I felt when I first acquired the car, of the disconnect between front and rear. A vague front which does not inspire confidence during hard turn-in, combined with a lack of compliance (and poor damping) at the rear which causes the car and driver to bounce all over the place on anything less than well-surfaced roads.

It therefore made sense to me to look into stiffening the front and softening the rear. And it’s perhaps not a coincidence that this is also the approach recommended by the likes of BC and KW with their default spring rates. I also suspect that BC and KW damping is better-matched to their springs compared with OEM.

if you match them you now have a soft rear and the wheel will not settle after a bump, and the car will jack down, and ride the stops as a result which will make the ride even shittier.

I can understand this concept, but my experience suggests that you would need massively softer rear wheel rates and massively harder front rates before it manifests.

Using your spring to wheel rate ratios of 0.9F and 0.45R as a guide, the stock BC setup offers a delta of 1.2F:1R and this feels substantially better than stock. In fact on stock 6 kg BC front springs turn-in is still not as precise as I would like, and I aim to experiment with 8 kg springs at some point which would give a 1.6 delta.

My hunch is you’ll need a delta of of >2:1 before the problem you describe actually occurs, and that a delta of between 1.5:1 and 2:1 is ideal for our cars.

[maupineda]

I have no reason to doubt it.

From a video on YT where they weighed the car

BMW-Z4MC-Weight.PNG (203.95 KiB) Viewed 462 times

For your turn-in dilemma, put the CSL front sway bar. I have it, + the CSL alignment settings and the car is very eager to turn it.

[Ed Doe]

viewtopic.php?t=102312&start=150

This thread may assist in the question of weight, and weight distribution...

[plenty]

For your turn-in dilemma, put the CSL front sway bar. I have it, + the CSL alignment settings and the car is very eager to turn it.

CSL geo already applied. Thicker front bar makes sense to me in theory, as I only require added stiffness in cornering and not in a straight line. Will look into it - thanks.

[TomK]

For your turn-in dilemma, put the CSL front sway bar. I have it, + the CSL alignment settings and the car is very eager to turn it.

Are you suggesting the CSL bar is stiifer? I ask, as whilst it is a little wider it is also hollow, given the mass decrease I'm not convinced it necessarily is. I also have one fitted, I can't find any info about the relative specs online.
Turn in for me was most obviously affected by toe adjustments at the rear. This is with quite aggressive front camber/neutral toe.