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Thread: Effective spring rates

  1. #1
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    Effective spring rates

    I have been changing my springs around for a couple years to see how different springs effect my car. I have ended up with 600 front and 750 rear.

    I run 255/40 17 extreme performance tires. I started with Star Specs 4 years ago, then Hankook RS3s for 2.5 years and now Rivals a few months ago.

    I have found that with the spring I run the car has great grip on concrete, but not as good on asphalt. When I ran with the same 4 guys for a few years in the Wash D.C. region I was usually first on concrete and usually 3rd or fourth on asphalt.

    So here in Florida almost all our events are on concrete and it is really good and my car sticks very well. But we have some events on asphalt and I want to be fast there also.

    So I have done some searching and made this chart using data from Gustave's web site. Also if you checked Vorshlags site when they sold AST shocks for our cars they recommended 3 sets of springs, 500f 550r, 550f 650r and 600f 750r. So I was running their stiffest spring recommendations, which happens to agree reasonably well with this chart.

    At the next asphalt event I think I will run 550 front and 700 rear, because I have those springs handy, maybe order some more soft springs after that. I am ditching the 5.5 springs in the rear and making some delrin adapters so I can run 6 inch springs front and rear.

    14001019498_8293f1bebb_b.jpg
    Last edited by jbrannon7; 05-14-2014 at 06:38 PM.

  2. #2
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    Errr, you are using wheel rate for the front, but suspension ratio for the rear. Rear wheel rate is 0.45


    http://e30m3project.com/e30m3perform.../eff_rate2.htm


    /.randy

  3. #3
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    Joe -- Both Sunzout and I have noticed the same thing about my spring rates (was 575/700 and now trying 500/600 both with no rear bar) relative to his vis a vis concrete vs. asphalt. Years ago, I noticed that I began chasing my tail when I tried to keep changing setups from the different surfaces and just decided to settle on concrete as my local events are typically on concrete and most Tour and Nat's are on smooth concrete. With my recent change to lesser rates, I'm going to try bumping compression a bit and seeing if it can work on both surfaces with maybe reconnecting the rear bar for concrete. I too have several pairs of springs (6) and access to another library of springs at varying lengths/rates. I've also noticed that it's very tire dependent with surface. This year I finishing off some old Dunlop ZII's but have focused on Toyo R1R's as they are great for events where you only have 3 runs to get in a strong time or Pro Solo's but have run RS3's, Rivals, AD08R, RE11A, you name it. RS3's have a pretty forgiving sidewall and accept more spring rate as they don't fall off the cliff if you push past their happy state on slip angle. Toyos and Dunlops really punish you if you use big slip angles. I think their side walls contribute to resulting motion/spring rate and want less rate especially on asphalt where grip levels tend to be lower.
    Now in E92 M3 ZCP -- Absolute beast

  4. #4
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    Ok, Here is another chart with the rear spring wheel rate changed to .45. The earlier chart seemed to fit better with what people are running but this chart says you need to run nearly double the spring rate in the rear as the front.

    Randy, you have posted stuff about spring frequency, which I know nothing about, what do you think about what this chart says.

    14188979092_28b11637a8_b.jpg
    Last edited by jbrannon7; 05-15-2014 at 09:25 AM.

  5. #5
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    This is a great conversation guys.
    Could you dumb it down for the rest of us?

    I'm experimenting with my new MCS set-up. It uses Hyperco springs, not beehive type progressive springs.
    I found the higher rates to be too harsh for a DD. It came with 450f/600r.
    I went down to 450r and found that a bit too soft but it did allow me to increase damper and rebound.
    The 450f are to harsh with road imperfections.
    I've ordered 400f/500r which i think will be the right combination to bring it together and allow better use of the adjustable rebound/damper.

  6. #6
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    With the 600 front and 750 rear, I felt the front was very stiff, jarring over unexpected bumps in the road, but able to compress enough that it scarred my inner liner. I feel the rear is good, I can feel the rear compress some when I go over the small bump at then end of my driveway.

    With the AST 4100s on asphalt I have them at full soft. I turned them 2 clicks from full soft on asphalt and got really loose. No rear sway bar. I have not played with them on concrete but will have a chance to turn them a little tighter this weekend and see what happens. I am thinking the second chart may be closer to what we need. Instead of a 150 split front to rear maybe a 200 or higher split. Don't know, the math says one thing but results say something else.
    Last edited by jbrannon7; 05-15-2014 at 11:16 AM.

  7. #7
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    Quote Originally Posted by jbrannon7 View Post
    this chart says you need to run nearly double the spring rate in the rear as the front.
    Yep. It's hard to accept, but the numbers don't lie. All else being equal, you'd predict double the spring rate in the rear to be a good baseline on these cars.

  8. #8
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    Quote Originally Posted by dcrothers View Post
    This is a great conversation guys.
    Could you dumb it down for the rest of us?

    I'm experimenting with my new MCS set-up. It uses Hyperco springs, not beehive type progressive springs.
    I found the higher rates to be too harsh for a DD. It came with 450f/600r.
    I went down to 450r and found that a bit too soft but it did allow me to increase damper and rebound.
    The 450f are to harsh with road imperfections.
    I've ordered 400f/500r which i think will be the right combination to bring it together and allow better use of the adjustable rebound/damper.
    Layman's terms -- the suspension's ability to absorb imperfections is a combination of spring rates, shocks (ability to control spring compression down/rebound back up), sway bars (which boost wheel rate on the side compressed in a corner), and ultimately tires (which depending on wheel diameter, sidewall stiffness and aspect ratio offers less or more acceptance to imperfection. I was pointing out how the stiffness of sidewall of some tires adds more rate and tolerates less translated rate from the rest of the suspension whereas a tire with a softer sidewall but very sticky compound may accept or need more spring rate. If you've ever seen me make a critical post of someone using 18" or worse yet 19" wheels on their car, it's because the wheels are heavy, tires are heavier, everything costs more, but more than anything its because in order to fit a tire in our wheel well, you need to go to a smaller aspect for each increasing inch of diameter wheel, and the smaller aspect absorbs less and less of the imperfections adversely affecting ride and performance. The line is you want to keep a tire in a "happy place" so it can give you all it can give.

    Your situation is a conundrum in that I would have expected the MCS single adjustables which I understand have double digressive valves to be valved to make much higher spring rates and still be very street compliant. It may be that you are not adjusting the units to adequately dampen the reaction to imperfections translated by the springs. If I were nearby, I almost certainly could sort your car out pretty easily.

    - - - Updated - - -

    Quote Originally Posted by BenFenner View Post
    Yep. It's hard to accept, but the numbers don't lie. All else being equal, you'd predict double the spring rate in the rear to be a good baseline on these cars.
    Based on the chart and wheel rate numbers, that would be the assumed answer if you want exactly the same wheel rate front to rear but according to Sam Strano of Strano Motorsports, it would wreck havoc on the handling characteristics of our cars. On concrete, I don't think it is unrealistic to think that 50% higher spring rate for the rears may be beneficial but it's never proven successful. Yes I've tried it out. Either my shocks weren't ready for the valving or I was too impatient to try all the combinations to make it work. Car became hella instable in the rear on rough surfaces.
    Now in E92 M3 ZCP -- Absolute beast

  9. #9
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    It seems the data used front and back is from the E30. Do we have similar data for the front of an E36? It makes sense to assume it's close to the E30, but maybe not as close as typically thought?

  10. #10
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    That's the problem, correlating theory with reality. If anyone has done it, they aren't talking. The math says the common spring choices will induce lots of understeer. And people seem to spend a lot of effort dialing out the understeer with other adjustments.


    /.randy

  11. #11
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    Quote Originally Posted by BenFenner View Post
    It seems the data used front and back is from the E30. Do we have similar data for the front of an E36? It makes sense to assume it's close to the E30, but maybe not as close as typically thought?
    I thought about that, the spring / wheel rate ratios are from Gustaves website are for a E30 M3. So the rear ratio is the same. Then I searched on E36 front lower control arm geometry and discovered that Turner sells the same part number control arm for E30s and E36s (unless I read it wrong). I also discovered a couple threads talking about E36 front spring rate ratios and their numbers were the same.

    There is a reason Vorshlag and Elephant Motorsports recommend what the springs they do, however they are much stiffer than what Koni people recommend. I am just searching for a way to go a little faster.

    Joe
    Last edited by jbrannon7; 05-15-2014 at 01:06 PM.

  12. #12
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    Quote Originally Posted by rf900rkw View Post
    That's the problem, correlating theory with reality. If anyone has done it, they aren't talking. The math says the common spring choices will induce lots of understeer. And people seem to spend a lot of effort dialing out the understeer with other adjustments.
    This understeer everyone talks about. I'd assumed the previous owner's upgrade to TCK's entry-level Sport setup (Koni/H&R) had basically removed it. The H&R springs are progressive, and I tried to look up the rates but am not finding anything meaningful. I'm guessing they are similar rates front-to-back. Maybe a tad stiffer in the rear. Which would again be a recipe for understeer similar to stock we'd all agree?

    Well, I spent the first two years trying to find this supposed understeer and I couldn't find it. Maybe it has to do with my understeer-limiting driving style coming from a FWD car, but I couldn't find any at all. At Atlanta Motorsports Park I was gelling so well with the car at the limit it was the first time I'd felt I was "dancing" with the car. Now I understand that metaphor. It was the definition of neutral.
    It wasn't until my first day at Barber Motorsports Park in Birmingham, Alabama that I ever experienced anything I'd call understeer in the car. Turn 2 climbs high and turn 3 dives down in elevation, and it's all sort of on-camber. For whatever reason this seemed to be the only thing to cause the car to understeer so far. The car would push wide ever so slightly and the tell-tale skip-howling noise from the front tires could be heard. It was only toward the end of the day with hot temps and I'm sure overworked front tires.

    I've completely changed the setup now, and am curious how it will work at Nelson Ledges (Ohio) in June.


    Edit: I always forget, I more than likely have the H&R springs meant for an E36 in the rear since the previous owner seems to have slapped on an E36 kit, too tall shocks and all (which I replaced soon after purchase). I wonder how that changes things. Taller? Stiffer?
    Last edited by BenFenner; 05-29-2014 at 01:55 PM.

  13. #13
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    As of right now i am at 450f/450r. I am going to dial them pretty far up today for my usual work commute ( my baseline ) and see how the car responds to that. I had been running them at pretty low settings, so we will see what happens if i let the shock do more of the work.

    Am i the first Z to use MCS ?????

  14. #14
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    Adding links to other posts on this topic. One is to a thread started by Ben about a year ago and the other is to a thread linked to by Msilva. Both basically say we do need much stiffer rear springs in the rear.

    However another thread I read says not to be "balanced" at wheel spring rate front to rear because rear wheel drive cars need to be a little softer in the rear.

    http://forums.bimmerforums.com/forum...normal-chassis

    http://forums.bimmerforums.com/forum...s-for-drifting

  15. #15
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    What really matters is the suspension frequency, both absolute and comparitive. For our particular cars with that almost perfect 50/50 weight, comparing wheel rates will get you the same thing, not so on less well balanced cars.
    From a ride stand point, you do not want the same frequency at both ends, as this will lead to a very uncopmfortable pitching motion over bumps. Really good suspension tuners (BMW is one of the best) will choose frequencies such that a disturbance will quickly decay to a purely vertical movement as motion is arrested. These are the cars that jujst feel planted. From a traction perspective, yes, it usually (always?) works out that a rear drive wants a softer rear to be able to put the power down smoothly on corner exit.

    There are many tuning tools to control the car balance. Some have more effect on transitions, others on steady state. There are many adjustment combinations that can be found that give reasonable balance, with verying compromises. This includes driving style. As you say, there are some that seem to run higher rear springs. Others claim the lower ones work best. The math says we need more rear spring and less front than what is commonly run. This isn't to say there is some strange feature of the car that requires the common setup. For me the question isn't only what works, but WHY? If these cars really do require the soft springs and you can figure out why, then you are on the way to addressing that "weirdness" and may be able to find the bit of extra speed you are after.

    One other thought to help avoid conflicting info. Unlike track events, autocrossing puts very little weight on steady state cornering power. Autocrossing is about the transient handling, which is mostly in the realm of shocks and roll center axis and driver.


    /.randy

  16. #16
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    Randy -- you make many very salient points. It was much more concise than the meandering PM I sent to Joe much the same thing. I have tried a lot of different setups and am discovering the "why" and am running through the weirdness issue. Certainly, I hear you in the major distinction between setting up a car for track vs. autocross as last year I was doing several times events for both.
    Now in E92 M3 ZCP -- Absolute beast

  17. #17
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    Went to an event today at Hernando County airport on an old concrete runway. It is high grip and is smooth. Put some zip ties on my shock struts and pulled the bump stops down a little.

    With 750ib springs in the rear you can see I have about 1/8 to 3/16 inch motion remaining. AST 4100 single adjustable shock with rebound set full soft. Don't think I can go any softer at this venue or I will bottom out the shocks. I have been told by a certified AST technician not to trim the bump stops. When I go to a dirty asphalt lot I may go with softer springs but the asphalt lot for our next 2 events has humps, so I am sure I will hit the stops there. (edit) When you add the gap at the top of the bump stop and the width of the zip tie, I have a bout 1/4 inch motion remaining.


    14031002668_673fb28d63_o.jpg
    Last edited by jbrannon7; 05-18-2014 at 08:36 PM.

  18. #18
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    The ideal rate / height setup will get you into the bump stops, just, on the biggest disturbance encountered.


    /.randy

  19. #19
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    Quote Originally Posted by rf900rkw View Post
    The ideal rate / height setup will get you into the bump stops, just, on the biggest disturbance encountered.
    Cool, so I am close for that venue. I drive my car to and from events with my race setup and I did fully compress everything then.

    So for the next event I will try 550 front and 650 rear and see what happens. I am currently in first in my class.

    Joe

  20. #20
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    I had my worst result (16th out of 60 ~) in probably three years Saturday on some very spent/heat cycled out Dunlops, and came back Sunday with nearly spent Toyo R1R's (4000 street miles and 110 runs) to be 1.8 seconds faster on mean drivers and be 4th overall on index. The latter result is at best typical. This was on new lower spring rates of 500/600 no rear bar. Interestingly enough, a STX competitor who I normally beat by 1-1.5 seconds on index nudged me out on his 8th run yesterday on brand new Hankook R-S3 Ver. 2. He had nothing but raves about the tire and definitely reported them coming in faster after being scrubbed on Saturday. I may consider getting a set of those but am sitting on a set of sticker new 245/40-17 Toyo's which are in my office.
    Last edited by z3papa; 05-19-2014 at 08:26 AM.
    Now in E92 M3 ZCP -- Absolute beast

  21. #21
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    Quote Originally Posted by dcrothers View Post
    ....Am i the first Z to use MCS ?????
    No, I had Tony Coliccio at TC Design install a double adjustable set on my race car in January. That along with converting the rear to coil-over. I've now got 800lb spings on the front and 400lb on the rear with a rear motion ratio of ~1.1 at the rear now. This is for my RR-STU class car, build thread:

    http://forums.bimmerforums.com/forum...class-Z3-build

  22. #22
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    200CPM in the front? Wouldn't it have been easier to just stick a pine 2x4 in there?


    /.randy

  23. #23
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    Quote Originally Posted by rf900rkw View Post
    200CPM in the front? Wouldn't it have been easier to just stick a pine 2x4 in there?

    Pine 2x4's wouldn't be as consistantly stiff

    It make a lot of sense when you take what Clark has to say into consideration, because I'm running BF Goodrich R1's in 245-45/16's on the stock 16x7 rim. Very sticky tires and a pinched flexible sidewall. Check out my video from Saturday's Inde race. It's a very bumpy track and yet it seemed compliant enough, inspite of getting thrown around. But it's probably better suited spring rate from Thunderhill as it's a way smoother track. I'm investing in several spring rates, both higher and lower.

  24. #24
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    Quote Originally Posted by Z3racer701 View Post
    No, I had Tony Coliccio at TC Design install a double adjustable set on my race car in January. That along with converting the rear to coil-over. I've now got 800lb spings on the front and 400lb on the rear with a rear motion ratio of ~1.1 at the rear now. This is for my RR-STU class car, build thread:

    http://forums.bimmerforums.com/forum...class-Z3-build
    Because you have converted to true coil overs in the back your rear spring rate is much lower. I think it be 850 900 lb springs in the rear for me to be that stiff. I did speak with some people that used to race E30 M3s and they ran 1100F 1050R. Very stiff, but the more tire grip and aero grip you have the more spring you need. How many events have you run with the MCS setup. They seem to be the "hot" setup. At the national events I have been to most of the class leaders had MCS stickers and were talking them up, but that's the way it was when I bought my AST shocks, even Strano had them on his mustang.

    Joe
    Last edited by jbrannon7; 05-19-2014 at 04:15 PM.

  25. #25
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    Quote Originally Posted by Z3racer701 View Post
    No, I had Tony Coliccio at TC Design install a double adjustable set on my race car in January. That along with converting the rear to coil-over. I've now got 800lb spings on the front and 400lb on the rear with a rear motion ratio of ~1.1 at the rear now. This is for my RR-STU class car, build thread:

    http://forums.bimmerforums.com/forum...class-Z3-build

    Tony is installing my RF dual ear next month. I'll be asking him about spring rates for my car. As a daily driver i wont be doing 800lb up front that is for sure....We'll see what he thinks.

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