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Last Post 04 Feb 2015 01:28 PM by  SpeedingBolt
How can I determine what Bilstein shock valving to use?
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SpeedingBolt
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17 Apr 2014 11:09 AM

        I have come to the conclusion that I want to get more durable shocks for my 96 STS miata since my old Advance Design shocks seem to need a rebuild every year.  I have decided that I want to use Bilstein's but to get FCM elites it runs about 1900$.

        I'm a cheap bast*rd and decided I'd see if I might be able to go a different route by geting some Bilstein ASN shocks and the coilover componets to adapt them.  This way I can order valving that would be close to what should work get an aluminum shock body spherical ends and a rebuildable shock that has a reputation for durability and being pretty easy to work on that will continue to have support in the future for less.

       For the length I think 5" shocks will work for me I'll use the FM top hats in the rear and make some mounts for the front from NB top hats so that I can use the spherical end on top this will give me another .5" of travel in front and back I will loose .25" of bump travel in back but I can live with that at least for awhile.  And I know that I want to use digressive valving so that just leaves the valving.

        The big question that I still have is what valving should I get.  I have tried to use the autocross to win site's dynamic calculator to figure out what valving I should order in the four number format that you can order the ASN shocks in.  After putting in the values that I can remember and using the example values for the values I was unfamiliar with (the roll center heights and digression knee values) I got whats shown below.  

      So does this mean I should order digressive 5530 for the front and digressive 2535 for the rear or am I missing something?

    SpeedingBolt
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    17 Apr 2014 01:43 PM

    Also for reference these were my inputs I also just set the tire rate to get the ideal spring rates to mach what I have and the values are rough estimates for the unsprung weights.

     

    kyoo
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    18 Apr 2014 01:40 PM
    it may be worth doing the consultation fee w/ FCM even if you're not going to go with their suspension entirely. Just FYI, I went with the full thing damper-wise with FCM, and I really love the setup. Totally understand the cost thing though.
    SpeedingBolt
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    20 Apr 2014 04:51 AM

    Well I found out that bilsteins are rated in newton meters at nearly 20in/s so if you extrappolate from the dyno curves for the popular setups then convert to newton meters you can find comparable results. For compression afco's were 1000 Fr 700 Rr xida 1500Fr 1200Rr the numbers for rebound were a littie less consistent since they were ajustable. The afcos ranged from 3300-3900 Fr and from 2800-3200 Rr.  A friend that has the xida setup said he used 7-8 Fr 6-7 Rr the dyno charts appear to only show the odd numbered settings so I looked at 7 for both which were about 4500 for both.  In light of this I think 4013Fr and 4010Rr valving should work fairly well for a first attempt if it will get me close to the other systems.  Can anyone with more experience with bilsteins let me know if anything is incorrect in the above assumptions?

     

    ion_four
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    28 Jul 2014 12:36 PM

    Hi!

    I found your thread during a search as I'm considering doing almost exactly the same thing, for my RX-8.

    Thanks for spelling out some of your findings.  How're things progressing?

    Also, do you have a reference for these dampers being spec'd at 20in/sec?  I see the SL series are spec'd at 10in/sec, but I don't see a decoder for other series.  Either way, it's funny they spec them at this velocity, since most shock dynos for commercially available coil over packages don't go to 10in/sec, and none I have found go to 20in/sec.  It's likely, this is the range where the differences in ride quality and road-holding come into play.  My limited research indicates "coil over" manufacturers don't like to release the magic numbers because it's either their secret sauce, or the skeleton in the closet, depending on the make...

    Also, have you seen Bilstein offers an adjustable shaft for their 46mm dampers?  It can be single or double (simultaneous) adjustable, or independently double adjustable if you go with an external reservoir with compression adjustment.  No clue on price...probably expensive.

    Hope it's working out!

     

    SpeedingBolt
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    28 Jul 2014 09:33 PM
    Well it took over two months for me to get them after dealing with the lack of knowledge the personnel at Bilstein had about their own product. Long story short it is very difficult to get anyone that really knows what they are talking about when it comes to valving although they did ask if I wanted to use another clients valving so apparently they can do that for you. The valving manual on the bilstein website contains digressive valvings that are in the kilograms of force at .5m/s which is approximately 20in/s. After some confusion the valving that I ended up getting was for 520/200 lbs@10 in/sec for the rear and 560/200 for the front. The low speed rates were not as high as i wanted and the shapes of the graphs were off in that the shocks for the front were shaped like they were for the rear and vise versa. I still have not fabed the upper top hats. So it would be better to have someone that knows what they are doing do your valving for you.
    SpeedingBolt
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    28 Jul 2014 09:46 PM



    SpeedingBolt
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    28 Jul 2014 09:48 PM
    ion_four
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    28 Jul 2014 11:24 PM

    Thanks for the update.  I take it you went with the ASN and will be doing inverted up front and non-inverted in the rear?  I'm sure I'm just "ignant", but why do you think the fronts look like they are valved for the rear and vice versa?  Is it because of what looks like double knees on the dyno at ~5 and 7in/s?

    SpeedingBolt
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    30 Jul 2014 12:01 AM
    The 520/200 has a higher slope near 0 inches per second than the 560/200.  Most of the time you want a lower slope near 0 for the rear shock since this means that they will generate less resistance and allow the tire to follow the contour of the road and there by give you better traction for a rear wheel drive car. I'm gonna try to mount them inverted in the rear as well if my measurements were correct then moving the mounting points a quarter of an inch rearward should give me enough clearance between a 2.25" spring and the halfshafts, and will let me use concentric spring mounts.
    flikert
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    31 Jul 2014 09:53 AM
    We have an aluminum top hat made for the ASNs.

    www.twosixmotorsports.com
    ion_four
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    17 Sep 2014 01:42 PM

    Just following up, again, to see if you got everything together?  Hope it's going well!

     

    I have my shocks and springs...just need to get some time to mock them up and make some new upper mounts and clevis adapter (the RX8 mounting points are different from the miata...lucky dog!), then of course, revalve them!

    ion_four
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    12 Jan 2015 07:55 PM
    I hope your project is going well...I've been doing a lot of learning and have accumulated some parts...let us (me?) know how it goes with you, when you have a chance!
    SpeedingBolt
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    04 Feb 2015 01:28 PM
    I decided to leave the inverted mounts for the next reworking of the shock mounts and have used the stock NA upper mounts for the rear already and will likely do the same for the front after getting some longer shock bodies so that I can clear the stock upper control arm since ideally I would replace the stock lower control arm with some V8 roadster control arms for the increased weight savings and adjust-ability, which would make inverting the shocks more difficult due to clearance issues between the stock upper control arm and the spring and spring perches.
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