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Should new Bilstein sports feel this still.

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  • #31
    You have a legitimate concern about irreversible modifications. Unmodified struts are hard to come by as they are unique to the M3. A new set is expensive, if they are even available.


    • #32
      Bilstien B8 dampers

      Springs 150lb/in Front and 450lb/in rear

      Front - 9 5/8" long 100lb/in for the 1st inch, 150 there after.

      Rear - 7 1/8" long 265lb/in for the 1st in and 450 there after.

      Uprated sway bars 24mm front 18mm rear
      Sport Evo No.47

      My Sport Evo Restoration


      • #33
        If running bilstein sports, you should trim the internal stop to keep travel especially in the front. If have the insert strut in hand it's a simple process. The bottom silver plate can be tapped off with a srewdriver and hammer. The shaft will stick out and reveal the stop on it. Trim up to two knuckles of the three off with a razor knife. Stick the cap back on and tap the bottom.

        I run HR race and bilstein sports. Vorshlag front plates. No spring pads up front, and stock ones in the rear. No rear bumpstops (never bottoms in the back). BW spec e30 bars. Completely streetable to me and sees track time. Sure there are other suspensions, but IMO only gain about %10 improvement over a HR race setup. The only real setups with more than a %10 advantage are if like mentioned, caged out, and true coil over beyond a moton like a MCS triple comes to mind.

        I like the GC kit myself and ran it on previous cars, but the HR race is plenty without any setup hassles really. It's one of the areas people question me all the time at the track "what coil-overs you running". They are surprised to find off the shelf HR race on there.


        • #34
          Happy this discussion is going on. I'm in the process of planning a pretty comprehensive restoration of my M3, and I don't want to cut the struts.

          Likely going with H&R Race springs and want a street friendly shock. Peoples comments on the Bilsteins are scaring me a bit. Wonder if Konis are more street compliant?

          Car could possibly see an HPDE day but will be 99% street.


          • #35
            The Bilsteins are fine. I still blow through all the travel (that makes for a harsh ride) over potholes and railroad crossings. It was worse with the Konis. I guess another 150# of spring rate front and rear (from the H&R race springs) would be ideal. My suspension geometry is pretty darn close to correct and I still don't have enough spring rate to keep the car off the bump stops over many road imperfections. (Its a lot better than it was however.)

            '69 Datsun 2000 Roadster vintage race car (Street driven on a regular basis :taz
            '59 Alfa Romeo 101 Sprint (HUGE project :uhoh
            '88 M3


            • #36
              Well just reworked the struts on another 91 318is which is very similar sharing the same as the M3. I've my old M3 springs on this car which work great btw. Anyways popped off the front struts cause I never trimmed the stops on it. It's new maybe 500 miles before parking and we are building an engine for it (go M42 pwr). The bilstein bumpstop had the first segment crushed in pieces inside where it was slamming the stops. Trimmed off the two knuckles like I've done on the M3 using HR race springs. It's simply too long a stop for application.

              This should be part of the instructions for use of bilstein sports with short springs IMO. I've been trimming the stops since learning that's what specE30 does. They run HR race for the class. It works and track proven.

              Just another note in here but the HR sport springs are barely stiffer than the stock M3 spring. Only real higher rate stock spring is the HR race. Group N's would be cool if can find any but need custom bilsteins to handle the rates. I use a GC true coil over kit on a E21 that the rates above 400 lb springs will eat a bilstein sport strut without revalving. With the .63? rear ratio of the stock e30 spring location just keeps within limit.


              • #37
                I had a set of H&R Sport Springs tested. Much stiffer front than stock, and softer rear than stock. I believe these springs were disigned for the 6cyl cars, and sold for the M3.
                Sport Evo No.47

                My Sport Evo Restoration


                • #38
                  I have been researching suspension options for some time now and I will share my thought/findings.

                  The stock E30 M3 Spring rates are 100lb/in Front and 300 lb/in Rear based on what an ex user here discovered after having had a set tested. It would seem that the rear is much stiffer than the front, but
                  The springs are not mounted on the same plane as the centre of the wheel. In the case of the front, as the spring is inboard of the wheel for every 1” of wheel travel we only get 0.926” of spring compression due to the relative positions of the pivot points and the spring. At the rear, as the spring is mounted much further inboard towards the chassis mounting point, for every 1” of rear wheel travel we only compress the spring 0.67” The motion ratio also effects the force acting on the wheel required to compress the spring. This is calculated by using the following formula;

                  MR*MR*Spring rate=Wheel Rate

                  Where MR=Motion ratio

                  Front- 0.926*0.926*100=85.75lb/in
                  Rear- 0.67 * 0.67*300 = 134.67lb/in

                  When you take in to account the motion ratio of the suspension system, the difference is not so great, a ratio of 1.57:1 Rear:Front.

                  Note: For those with coil over rear springs the motion ratio is 1.06; this will be important when it comes to dampers.

                  So, as stock the E30 M3 has rear wheel rate which are 57% stiffer than the front.

                  Something which effects the ride quality is the natural frequency of the suspension system. This is related to the sprung mass (Axel mass-un sprung mass) and the spring rate.

                  sqrt(wr/((m*0.5-um)/1000))/2/Pi= Frequency

                  sr=spring rate (N/mm)
                  m=weight on axle (kg)
                  um=unsprung mass for one corner (kg)
                  Lb/in / 5.7=Nmm

                  If we take our stock springs and some mass figures I pulled off the net:

                  Front axle weight 660Kg
                  Rear axle weight 630
                  Front un sprung mass 41.3
                  Rear un sprung mass 43.5
                  Front WR in Nmm 85.75/5.7=15Nmm
                  Rear WR in Nmm 134.67/5.7=23.6Nmm

                  To save me the long hand it comes out at

                  Front 1.19Hz
                  Rear 1.53Hz

                  The ratio between the two is 1.28:1 Rear:Front.

                  There is a good reason for the rear being of a higher frequency than the front. If the front axle hits the bump first (hopefully J), in order for the car to remain flat, the rear needs to catch up, so therefore it is normal for a road car to have a higher frequency.

                  I would suggest for a road car, we shouldn’t stray too far from these ratios. For a track/race car, what is best for lap time will dictate.

                  As it turns out, keeping the unsprung and sprung mass the same, the ratio front to rear and the ratio of frequency front to rear are interdependent; increase the spring rate by the same front and rear, the frequency increases by the same proportion.

                  My practical experience from using H&R Sport springs, it is worth mentioning at this stage that the part numbers for H&R sport springs differ in the US from those in Europe.

                  The USA H& web site lists the following for the E30 325i

                  50404-55 OE Sport lowers 1" Fr & Rr
                  50406 Sport lowers 1.3" Fr & Rr

                  For the E30 M3

                  50404-55 OE Sport lowers 0.25" Fr
                  50406 Sport lowers 1" Fr & 0.75" Rr

                  Same parts! I don't know what the weight distribution is Fr/Rr on the 325i, but with an engine that I guess is heavier and more of that engine in front of the front axle line, it would not be too much of a stretch to believe there would be a requirement for a stiffer front spring.

                  In Europe we have

                  29663-1 for 4 cyl models lowering 35mm or 1 3/8”
                  29664-1 for 6 cyl models lowering 35mm or 1 3/8”

                  Luckily, in Germany all aftermarket parts need to be approved with the TUV and have a certificate which is available for download.

                  The above springs share the same TUV certificate, on which certificate it states spring dimensions.

                  The rear springs are the same 204mm long 6.5 turns of 13.5mm wire. The front springs are 272mm long, 6 turns, but differ in the wire diameter, the 29663-1 being 12mm and the 29664-2 being 12.5mm. Presumably this is to account for the heavier 6 cyl engine.

                  Why in the US the same springs are cold for both I don’t know.

                  I had a set of 29664-1 fitted to my car and found the front ride height to be too high and the front ride to be very stiff and the rear to be very soft. I removed the springs and had them tested.

                  Fronts are 110lb/in-205 lb/in rising rate, hitting 205 at 5in compression

                  The installed length was approximately 145mm of 5.7in and the free length is 245 mm or 10in. If we take 5.7 off 10 we get 4.3in compression when installed, so nearly 205lb/in when installed.

                  Rears are 259lb/in linear-softer than stock which explains a lot.

                  If we plug this in to the spread sheet we get wheel rates of:

                  Front 176lb/in

                  Rear 116 lb/in

                  Ratio of 0.66:1 Rear:Front- substantially softer at the rear than the stock 1.57:1 Rear:Front

                  Natural Frequency ratio of 0.86:1 Rear:Front again very different to the stock of 1.28:1 Rear:Front

                  This would explain why the rear felt so soft on both road and track.

                  I suppose the question in relation to the OP is, what is the wire diameter, number of turns and free length of the 50406 springs and are they the same part under a different number to the 29664-1 sold in Europe?

                  Myself, I wasn't happy with the off the shelf springs available, so went for some custom wound springs of 155lb/in front and 435lb/in rear which gives wheel rates ratio of 1.47:1 rear:front and frequency ratio of 1.24:1 rear: front. The ride is much flatter than the H&Rs. I still believe the front reacts much more than the rear when hittin high speed compressions so I am going to look in to the dampers next.

                  I’ll come on to damper rates later.
                  Sport Evo No.47

                  My Sport Evo Restoration


                  • #39

                    As far as I understand there are the following dampers available in Europe from Bilstein for the E30.

                    Front_______Rate___Wheel Rate___Application
                    34-003350_233/75.5___200/65____M3 sport/325i HD
                    34-236406_280/150___240/129____GpN Rally

                    Rear_______Rate___Wheel Rate___Application
                    24-020275_160/55____180/62____M3 sport/325i HD
                    24-060653_140_60____157/67____M3 sport/325i HD
                    24-233267_260/120___292/135____GpN Rally

                    I believe in the USA the B6 are known as HD and the B8s known as Sports, for use with lowered suspension.

                    As you can see the same dampers are used for the 6 cyl cars and the M3, only the application differs.

                    In the table I have converted the damper rates to damping rates at the wheel using the same formula as used for the spring rates;



                    mr=motion ratio
                    dr=damper rate

                    The motion ratio for the front damper is the same as the spring at 0.926 as the spring sits concentric with the damper. For the rear, the damper is separate from the spring and further from the pivot point than the wheel so the motion ratio is 1.06.

                    In view of the problem that the front seems too stiff, even in my case where the rear sprung wheel rate is higher than the front, there must be cause for this. My next step is to measure how much of the damper travel I am using when the car is static, then remove the insert, measure the full damper travel (the only data I can find is for 34-003350 Front B8- 597mm extended and 515mm compressed =82mm travel)and bump stop length and calculate how much travel is remaining before the bump stops come in to play. From what I can see on the web, the bump stops seem to be about 3-3.5” long, so I would hope I have at least 3” damper travel before I come in to contact with the bump stops.

                    When you look at the stock bump stops, they are about 1.5” long. When we consider the lower spring rates and damping rates of a stock car in comparison to one with Uprated springs and dampers, I can’t see any reason why we should need a longer than stock bump stop.
                    Sport Evo No.47

                    My Sport Evo Restoration


                    • #40
                      Great info Steve

                      As you know I've been looking into this a bit recently too. With regard to the US only 50406 H&R springs I've had confirmation from H&R reps in Europe that these are different to the EU offered parts and aren't available in Europe at all.

                      I also received the following info from H&R in Europe regarding spring rates:
                      29663: 33N/mm front and 50N/mm rear
                      50406: 33N/mm front and 60N/mm rear
                      29664: 33N/mm front and 50N/mm rear
                      29818-1: front 45N/mm, rear 56N/mm

                      29729-1: front 30N/mm, rear 55N/mm

                      Confused though as to why they state the same rate for 29664 and 663 as the wire diameters are different.....

                      If everything seems under control, then you're just not going fast enough...


                      • #41
                        In lb/in

                        H&R Sport 29663-1 - 188/285lb/in- -1 3/8” Euro Market All 4cyl. Not M3 Specific, so presumably the ride height drop is referenced from a non M3 4cyl model)
                        H&R Sport 29664-1 - 188/285lb/in- -1 3/8” Euro Market All 6cyl. I had a set measured at 200/285 which is consistent with the 12.5mm dia wire as opposed to 12.0mm of the 29663.

                        H&R 29818-1 - 256/319lb/in- -1 ¼” Euro Market All 4cyl Cabrio
                        H&R 29729-1 - 171/313lb/in- -1 ¼” Euro Market All 4cyl Touring

                        H&R Sport 50406 - 188/342 -1” front -0.75” rear USA Market M3 Specific

                        That is all good info
                        Sport Evo No.47

                        My Sport Evo Restoration


                        • #42
                          It does seem that manufacturers are unwilling to offer kits with a similar front to rear stiffness ratio as stock, especially in Europe. I guess it's playing it safe towards an understeer balance. The closest combination I've found, by requesting the rates from various manufactures, would be to use the following:

                          Front = Vogtland E30 4 cyl 951010VA (Front their 951017 kit) = 24N/mm (137lbf/in) - Free length is stated as 260mm on the TUV certificate
                          Rear = KW E30 Touring 22061 = 65.2N/mm (372lbf/in) - 200mm free length

                          I'm not entirely sure where these will end up regarding ride height yet, but sure it can be tweaked with spring pads. I don't want to go too low.

                          The TUV certs are here:
                          KW (ST) =
                          Vogtland =

                          Although from these numbers I don't see how the Vogtland supplied spring rates can work out. They seem almost identical to the H&R springs at ~188lbf/in....But two different people at Vogtland gave me similar numbers...
                          If everything seems under control, then you're just not going fast enough...


                          • #43
                            I've also had confirmation from Bilstein that the B6 34-003350 travel length before bump stop is 82mm.....will check how much of that I'm using tonight.
                            If everything seems under control, then you're just not going fast enough...


                            • #44
                              I suspect that almost all of the 82mm is used up. 82/0.926 MR is 88.5mm of wheel travel. If you measure your ride height from bottom of the wheel rim to the wheel arch with the car sat on flat ground, jack it up and repeat. I'd besurprised if it is less than 75mm.

                              I have a set of stock bump stops in the garage. I will measure them and report back.
                              Sport Evo No.47

                              My Sport Evo Restoration


                              • #45
                                Stock Bump Stops measure 52mm
                                Sport Evo No.47

                                My Sport Evo Restoration