B12 kit question

[thecremeegg]

So I've just got an M Roadster with a bilstein B12 kit fitted, supposedly around 3000 miles ago.
It rides and handles very nicely until I hit any kind of mildy sunken drain or pothole and it makes a huge bang.

Is this a quirk of the B12 kit or does it sound like something is amiss?

Thanks!

[maupineda]

For some stupid reason B6 dampers ride on the bump stops, that combined with a shorter ride height and too much gas pressure make them pretty bad for secondary ride quality.

You need to:

Raise the car
Shorten the bump stops

[Ed Doe]

For some stupid reason B6 dampers ride on the bump stops, that combined with a shorter ride height and too much gas pressure make them pretty bad for secondary ride quality.

You need to:

Raise the car
Shorten the bump stops

Bilsteins have internal bump stops so you shouldn't be running them externally at all!!

[thecremeegg]

As far as I'm aware the B12 kit doesn't allow for height adjust, is it possible that I need longer springs?

[GumbyOTM]

I have an M Coupe and installed the Bilsteins with HR Springs (B12 as a kit was not available and suspension needed replacement).

The so called crashiness that people (and yourself) describe) was like that when I first made the installation to the point I thought I had made a horrible mistake. After about 5000 more miles or so (Can't remember exactly when) the ride significantly smoothed out as the suspension settled. I avoid potholes at all costs, but it no longer feels like I broke the car.

We all know these cars are a shockingly stiff ride, I guess the message is that it the kit does get better with mileage and time.

[99ron]

Same B12 kit, same issue.
Good to hear it gets better with miles and I have heard that said before so I'm persevering at the moment, which is getting harder as our roads are getting worse year on year. I'll see how this year goes and plan B is keeping the shocks but changing the springs back to standard. Others have reported this to be a good compromise.

[thecremeegg]

Interesting to hear, I guess I'll persevere too and see how I get on!

[maupineda]

As far as I'm aware the B12 kit doesn't allow for height adjust, is it possible that I need longer springs?

I know, put back the stock springs.

[maupineda]

For some stupid reason B6 dampers ride on the bump stops, that combined with a shorter ride height and too much gas pressure make them pretty bad for secondary ride quality.

You need to:

Raise the car
Shorten the bump stops

Bilsteins have internal bump stops so you shouldn't be running them externally at all!!

Who talked about running external bump stops. Is already well known B6 have the stops inside the strut housing, you need to take the insert out and then shorten the bump stop.

Until people start approaching these maters objectively and avoid marketing gimmicks, they will be sold short on their expectations.

[Ed Doe]

For some stupid reason B6 dampers ride on the bump stops, that combined with a shorter ride height and too much gas pressure make them pretty bad for secondary ride quality.

You need to:

Raise the car
Shorten the bump stops

Bilsteins have internal bump stops so you shouldn't be running them externally at all!!

Who talked about running external bump stops. Is already well known B6 have the stops inside the strut housing, you need to take the insert out and then shorten the bump stop.

Until people start approaching these maters objectively and avoid marketing gimmicks, they will be sold short on their expectations.

And which crisp packet did you read that last sentence off?

Firstly the B6 are very unlikely to run on the bump stop purely as the B8 is basically the same damper but shortened. It doesn't take a genius to work out if the damper was on the bump stop there'd be no further damper travel

Secondly, how can you expect your average hobbyist to know to disassemble the damper and modify the bump stop?

And thirdly for that matter please pray tell how you increase the ride height of a fixed height damper (per your first reply to this thread)? Given the context of your reply on the bump stops I'm already imagining its 'simple - just angle grind the spring perch off and weld it back on higher up'.

[maupineda]

Bilsteins have internal bump stops so you shouldn't be running them externally at all!!

Who talked about running external bump stops. Is already well known B6 have the stops inside the strut housing, you need to take the insert out and then shorten the bump stop.

Until people start approaching these maters objectively and avoid marketing gimmicks, they will be sold short on their expectations.

And which crisp packet did you read that last sentence off?

Firstly the B6 are very unlikely to run on the bump stop purely as the B8 is basically the same damper but shortened. It doesn't take a genius to work out if the damper was on the bump stop there'd be no further damper travel

Secondly, how can you expect your average hobbyist to know to disassemble the damper and modify the bump stop?

And thirdly for that matter please pray tell how you increase the ride height of a fixed height damper (per your first reply to this thread)? Given the context of your reply on the bump stops I'm already imagining its 'simple - just angle grind the spring perch off and weld it back on higher up'.

you write as someone who knows, but everyday is a day at school. there is no B8 dampers for our cars (///M). And agree, it does not take a genius to figure out the car is riding on the stops, but again, as you said, the average person will not deduct this naturally, but that is the very reason these cars ride so bad with Bilstein shocks, and even more so when lowered. let me share some numbers.

- the OE dampers have ~125mm of total travel, the B6 dampers have the same amount of travel.
- the OE stops are 40mm in length
- when the car is on the ground, the shock compresses about 70mm, this leaves around 55mm of total travel; the math tells us there are only 15mm of free travel until the stop is engaged. I have no data on how much the stop can compress, but I think it can be compressed by half for another 20mm of travel until it becomes a solid block and the suspension bottoms out.

- the B6 stops are internal, and are 70mm in length
- assuming you leave the car height unaffected (stock springs), when the car is on the ground, you are now effectively seating on the stops and in fact they are already compressed some. this is offset a bit as we also know B6 make the car ride a bit higher, which is a combination of two factors, gas pressure (nitrogen filled) plus the stop, which is effectively an auxiliary spring with its own rate.

I know all of the above as I measured the suspension components and suspension travel when I got determined to make the car decent with Bilstein shocks.

That is why the B12 kit rides like s**t, as you are lowering a car that already has very little bump travel by design. Bilstein had to take this approach to allow for a lower stance and provide that tautness feeling they market and sell, and yes, if the road is smooth and transitions and bumps are low speed and ample they are not too bad.

Why they designed this kit so compromised? They had to as the car when lowered looses even more travel, and to avoid the suspension bottoming so easily they need to use stiffer spring rate to limit up/down travel by having the car riding on the stop, which effectively makes the overall spring rate much higher.

[XMetal]

maupineda, Do you have any instructions or know where to find some on shortening the internal bump stop? I'm about to pull the trigger on some B6 shocks/struts. So, if I read you correctly, when using the B6, we no longer need the "Additional shock absorber" (31307836823) for the front and "Auxiliary shock absorber" (33507838832) for the rear? Thanks.

[maupineda]

maupineda, Do you have any instructions or know where to find some on shortening the internal bump stop? I'm about to pull the trigger on some B6 shocks/struts. So, if I read you correctly, when using the B6, we no longer need the "Additional shock absorber" (31307836823) for the front and "Auxiliary shock absorber" (33507838832) for the rear? Thanks.

It is actually super easy, if you can remove a tire, you can do it.

https://youtu.be/RU-p0qTNVIY?si=UArHV5FMS9rAaWem

I cut mine to 38mm which is the size of the OE item, I have B6 inserts in H&R strut bodies so all my setup was done to ride at stock height or very close. I am at 600mm v 607mm stock.

I can adjust my ride height some to meet my OCD for matching all corners at the same height .

[XMetal]

It is actually super easy, if you can remove a tire, you can do it.

https://youtu.be/RU-p0qTNVIY?si=UArHV5FMS9rAaWem

I cut mine to 38mm which is the size of the OE item, I have B6 inserts in H&R strut bodies so all my setup was done to ride at stock height or very close. I am at 600mm v 607mm stock.

I can adjust my ride height some to meet my OCD for matching all corners at the same height .

Thanks - that was very helpful. Assuming that I don't want to modify the struts, does the front of the car actually sit higher than stock with the B6? I don't want to lower my car from the factory stance, but I definitely don't want to raise it either

[maupineda]

It is actually super easy, if you can remove a tire, you can do it.

https://youtu.be/RU-p0qTNVIY?si=UArHV5FMS9rAaWem

I cut mine to 38mm which is the size of the OE item, I have B6 inserts in H&R strut bodies so all my setup was done to ride at stock height or very close. I am at 600mm v 607mm stock.

I can adjust my ride height some to meet my OCD for matching all corners at the same height .

Thanks - that was very helpful. Assuming that I don't want to modify the struts, does the front of the car actually sit higher than stock with the B6? I don't want to lower my car from the factory stance, but I definitely don't want to raise it either

it very likely will due to the extra nitrogen gas fill. they will settle some after some miles and time. My car lost about 5-7mm in about a year and staid there.

I never used the Bilstein shocks with OE springs as I went the coil over route, so my numbers will be different some.

What I can tell you is that I chose a spring rate that was close to OE (225 lb/in). OE spring is (according to some forum data) 194 - 224 (progressive). However, I initially chose 250 in/lb spring and I was having trouble to meet OE height due to the Bilstein shocks (even though my math indicated otherwise). My rate was 10% higher, but the spring I chose was also shorter. I had to go down to 224 in/lb springs, and then the threaded body of the H&R strut allowed for the desired height.

If you want to compensate for any height gain with B6, you can add camber plates which have a lower height.

All this is a rabbit hole, I did it as I was already deep into it and wanted the car to be exactly what I wanted.