Help Support Bigcoupe.com

Which Bilstein struts?

Post in this forum for topics relating to suspension, steering, and brakes

Moderators: ron, bfons, GRNSHRK

Post Reply
User avatar
smtguy
Posts: 77
Joined: Sat Apr 29, 2017 3:38 pm
Location: Southern California

Which Bilstein struts?

Post by smtguy » Thu Jul 04, 2019 3:29 pm

My '83 e24 needs new struts, and I am thinking Bilstein., but the question is which ones? I see they have Touring, Heavy Duty, Performance, and SP (whatever that is). I use my car strictly as a street car; no track or performance use. My car is stock, and I am running the stock rims/tire size. I like a nicely controlled ride, but don't want harshness; especially considering the really crummy roads we have here locally in S. Cal.

Any suggestions?
1983 Bronzit 633CSi 5 speed
2001 Jaguar XJR
2004 Audi TT

Scott

User avatar
jps635
Bigcoupe supporter
Posts: 695
Joined: Sat Feb 27, 2010 10:50 pm
Location: NZ

Re: Which Bilstein struts?

Post by jps635 » Fri Jul 05, 2019 9:29 am

If you don't want a harsh ride stay away from the B8's. Can't speak about the others
'85 635csi JPS (RA2-66)

bpoliakoff
Bigcoupe supporter
Posts: 2726
Joined: Thu Sep 28, 2006 9:28 pm
Location: scottsdale, arizona
Contact:

Re: Which Bilstein struts?

Post by bpoliakoff » Sat Jul 06, 2019 12:20 am

B6 Heavy duty. B8s are for lowering springs. The B6 will give you a firm sporty ride Touring is just a plain cushy factory type feel.
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.

User avatar
smtguy
Posts: 77
Joined: Sat Apr 29, 2017 3:38 pm
Location: Southern California

Re: Which Bilstein struts?

Post by smtguy » Sat Jul 06, 2019 1:58 am

I appreciate the advice. Thank you gentlemen!
1983 Bronzit 633CSi 5 speed
2001 Jaguar XJR
2004 Audi TT

Scott

Ronnie Wilson
Bigcoupe supporter
Posts: 129
Joined: Fri Nov 18, 2016 11:40 pm
Location: Liverpool uk

Re: Which Bilstein struts?

Post by Ronnie Wilson » Sun Jul 07, 2019 12:39 pm

Hi

Bilstein B4’s are the standard replacement for the factory fitted ones.

Thanks
Ronnie
Liverpool uk.
1986 635csi

User avatar
Masked Man
Bigcoupe supporter
Posts: 1290
Joined: Sat Jun 28, 2008 5:46 pm
Location: Los Angeles, CA

Re: Which Bilstein struts?

Post by Masked Man » Tue Jul 09, 2019 2:29 pm

Hey smtguy!

As someone who had decorative stock shocks (for far too long) on Grace, I'm here to tell you that I went with the B4 (touring) and they are anything but cushy. They give a firm ride that (depending upon whether you're running a 16, 17 or God forbid, an 18" wheel) will provide you with a solid comfortable ride and that I've flung quite happily through twisties here in the Los Angeles area, specifically Angeles Crest highway, and they performed safely, predictably and did I mention that they are substantially less expensive than the other shock absorber/struts mentioned previously? The touring is going to give you all you might need for confident driving.
And that's my two cents.

Keep the shiny side up

Phillip

Masked Man
Image


85 635CSi Euro
Big Brake Upgrade
Ireland stainless exhaust
Upper & lower control arms
New tie rod kit

User avatar
Brucey
6 Series Guru
Posts: 10039
Joined: Fri Apr 09, 2004 7:17 am
Location: Cambridge, UK

Re: Which Bilstein struts?

Post by Brucey » Thu Sep 05, 2019 12:07 pm

last time l looked (IIRC) B4 are twintube shocks (like the OEM boge units) and valving is similar (they may be identical; IIRC boge was taken over by Bilstein's parent company...?). These shocks use external bump stops front and rear. If you change knackered shocks for these it will feel like a new car.

B6 (HD) and B8 (sports) are classic Bilstein monotube (yellow, gas pressure) shocks. They have a bumpstop integral to the front insert, hidden in the base. The rear shocks use a standard BMW external bumpstop. The internal valving between B6 and B8 shocks is very similar (but not quite identical) but the bumpstops are different at the front and the shock stroke/ perch adjustment is different at the back.

This means that B8s work with Mtech springs *perfectly* and (with revised perches to allow the larger diameter coils to be fitted at the rear) the M635CSi springs are again a perfect match for these shocks. Note that the ride height is only ~20mm lower than stock with either spring setup.

IME reports of 'a jiggly ride' inevitably result from any given shock being fitted with the wrong length springs. The shocks are designed so that the bump stops are not significantly in the first 10-20mm of bump travel. This gives a plush ride on normal roads. However when you fit lowering springs to shocks without fitting/modifying the bump stops accordingly the bump stop is always in the travel and since it adds significantly to the spring stiffness it soon makes the ride feel terrible. IME this is the #1 fault with most peoples efforts at lowering on this car.

So with B4s or B6s you should stick with stock ride height and expect the ride to deteriorate significantly (with standard bump stops) if you go even 20mm lower.

With B8s you should fit springs that give a 20mm reduction in ride height from stock if you want the ride to be OK. If you go 40mm lower (-20 in the case of M6 or M635CSi) the ride will be a fair bit worse. If you lower any more than that it will be bloody awful.

It is really very easy to get a setup that allows the car to be 'driven very enthusiastically' on the road and TBH you need look no further than the Bilstein B8 shocks plus M-tech/M6/M635CSi springs.

However there are innumerable variations on ways you can screw it up totally, and between the folk that post here, we have seen most examples of how this is possible. Topping out, bottoming out, wrong bumpstops, no bumpstops ( :shock: :shock: ) its all been seen before.

In a nutshell;

If you must lower further (than 20mm on standard models or at all on M6/M635CSi ) then you should modify/fit shorter bump stops accordingly, and if you don't do this the ride will become increasingly bad on normal roads.

With B4s you MUST fit new OEM bump stops.
WIth B6/B8 you MUST fit the correct length OEM type bumpstop at the rear (there are two types).

Used bilstein front inserts almost invariably need new (internal) bumpstops fitted; they don't last for ever and any oil leakage soon rots them.

If you fit springs that are a different length then you need to modify/ fit different bumpstops according to the new ride height, else put up with a terrible ride quality.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

CSGuy
Bigcoupe Contributor
Posts: 31
Joined: Fri Mar 09, 2018 2:40 am
Location: SoCal

Re: Which Bilstein struts?

Post by CSGuy » Fri Sep 06, 2019 9:03 pm

Does anyone know the difference in ride height between a standard suspension 1985E24 and an M or sport suspension.

I thought I read once that it was 15mm but I can't remember where I read that or find it now to verify

I'm thinking of new H&R springs and see they are about 1.25 inches lower than stock but don't know how that compares to the sport suspension

Thanks in advance

User avatar
Brucey
6 Series Guru
Posts: 10039
Joined: Fri Apr 09, 2004 7:17 am
Location: Cambridge, UK

Re: Which Bilstein struts?

Post by Brucey » Fri Sep 06, 2019 9:37 pm

as noted above the M6/M635CSi suspension is no more than 20mm lower than stock. Sometimes it is a bit higher than that so 15mm is close too.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

CSGuy
Bigcoupe Contributor
Posts: 31
Joined: Fri Mar 09, 2018 2:40 am
Location: SoCal

Re: Which Bilstein struts?

Post by CSGuy » Sat Sep 07, 2019 8:33 pm

Thanks for the confirm

User avatar
Brucey
6 Series Guru
Posts: 10039
Joined: Fri Apr 09, 2004 7:17 am
Location: Cambridge, UK

Re: Which Bilstein struts?

Post by Brucey » Sat Sep 07, 2019 10:04 pm

BTW one thing I forgot to mention; spring rates.

Standard BMW springs are rising rate springs i.e. they are pretty soft initially (about 200 lb/in) but the end coils soon become coilbound at the end two turns, leaving fewer 'active turns' and thus are ~20-30% stiffer than you might expect when compressed. During hard cornering this results in the springs on the outside of the turn being stiff and the inside of the turn being softer. [NB This effect is further exaggerated by the effect of the bump stops; whenever the suspension is compressed more than ~20mm past the static height the bump stops contribute increasingly to both the spring rate and the compression damping.]

M-tech and M6/M635CSi springs are only about 10% stiffer in initial rate than stock springs.

Most aftermarket springs are single rate springs, i.e. they are (moreso than stock BMW springs) about the same spring rate until all the coils go coilbound at about the same time.

So you might think a set of aftermarket springs at ~250lb/in are going to be a lot different than stock (or Mtech springs). Well they are and they aren't; they will give no benefit when cornering (the rising rate BMW springs will be about as stiff as the aftermarket ones are, on the hard-working springs on the outside of the turn), but the aftermarket springs will be stiffer in the middle of the travel thus making driving in a straight line a bit more (needlessly ) uncomfortable.

Remember that in order to fit correctly at the front, (i.e. without the top hat sitting at completely the wrong angle) the springs need to have a whole number of turns. Any aftermarket front springs that have (say) 5-1/2 turns or something are automatically condemned into my 'utter crap' category.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Post Reply

Who is online

Users browsing this forum: No registered users and 2 guests