Progressive Springs

[Longtooth]

I'm an engineer... and I've asked John Olsen several times --- on this site a couple years back, and in e-mails to his website ---- to provide the force displacement curves for his progressive springs for the W113's.  The force/displacement curve shows what "progressive" means in real terms.... whether sharply "progressive" or linearly "progressive" is the difference between an effective step change in stiffness and a gradual change in stiffness... but it's only with the force vs displacement curve that anybody can know the nature of the specific "progressive" nature of a given so called "progressive" spring.

The force vs displacement curves should also show the standard specified springs curve on the same chart.  Why does anybody pay big bucks for something that isn't quantitatively described as in "progressive"... then spend the labor to install them, not knowing until the springs are operational on the car whether they're the right type or degree of "progressive" desired or expected?

John Olsen never answers the question.


Longtooth
67 250SL US #113-043-10-002163
The 6% Club - Best of the Best
'02 SL500 Sport

[mdsalemi]

quote:Originally posted by Longtooth

I'm an engineer... and I've asked John Olsen several times --- on this site a couple years back, and in e-mails to his website ---- to provide the force displacement curves for his progressive springs for the W113's.

John Olsen never answers the question.

Longtooth,

[Obviously]John himself does not wind the springs. Making a "force displacement curve" entails a bit of testing using relatively expensive equipment, don't you think?  If you thought that the springs are expensive now (at least Jeff did in 2003), think about adding that testing to them.  Also, offering that information is giving away the trade secrets, so to speak.  Armed with known data such as the diameter, the size, where the flats are, with the information you want for free you could go have them made for quite a bit less, taking advantage of knowledge John obtained by trial and error and at some expense.  One of the largest performance spring manufacturers in the world, Eibach, does not provide this information except to its special designated partners--which don't include customers.  While engineers like to know these things, it isn't information generally shared.  Note also that you indicate that the stock springs should be tested as well.  Well, which ones?  My Technical Data Book indicates that there are two different springs available for the W113's, and each spring came in 3 different varieties: short, medium and tall.  Which springs should be tested?  All of them?  That's a pretty hefty expense to do for what amounts to custom springs.

Think about it another way.  Let's say you choose to install some kind--any kind--of mod or device that "increases horsepower".  If you want the real specifications, first you have to put your car on a dyno and get a test report.  Then you make your mod or add your device.  If you want to see if it actually did anything, back to the dyno.  Around these parts, you've just added ($180.00 x 2) about $360.00 to your costs.

In praise of John, [who posted on this topic here in 2005] he spent a good deal of time on the project.  I've driven a car in superb condition with his springs, and compared it to mine which had new factory springs and otherwise similar condition suspension parts.  His springs provided the results that were claimed: reduced nose-diving on braking (see that video posted on this site recently to see, from outside the car, just how severe it is; also read all the old test reports which note the same thing) and reduced body roll on cornering.  He identified an issue; devised a solution; makes a claim; makes a product for it, and sells it at a price he considers fair.  Those that don't agree with any part of his methodology or price, I'd say don't buy them.  Listen to Raymond: John is way out there on the leading edge of the curve in both experience and knowledge on springs.  He's well known nationally and internationally, for many many years now and has earned the respect he generally receives.  On top of that he's a heck of a nice guy.

Some discussions were posted on this site in 2005 because some owners in pursuit of doing it by themselves for a fun project and or to save some money, or both--bought progressive springs from a stock spring house and cut them to fit, and made things work with spring pads.  John cautioned against cutting a spring.  So does Eibach.  The consensus among the spring makers--and I lay no claim to any truth here--is that your spring must be made to specification and size; you don't take a "close enough" spring and cut to fit.  Don't argue with me on that topic--I'm just the messenger.


Michael Salemi
1969 280SL
Signal Red 568G w/Black Leather (Restored)
President, International Stars Section
Mercedes-Benz Club of America

[Longtooth]

Micheal,
The design Olson uses for the Progressive Springs on the W113's are constant for that vehicle.... excepting the differences between front end weight with and without air conditioning &/or power steering.

Therefore, there's only one set of tests that need to be run for the "25% - 30%" firmer condition he advertises for his progressive rate springs. ... that is to say, one test that applies to all springs sold for his advertised W113 progressive rate spring... actually two tests ... one for rear spring, one for front.

These tests (force - displacement) are not complicated or "high tech" in the least, and there are standard mechanical testing labs that run them for a fee... I'd guess $500 - $1000 on a one time set-up in a standard mechanical testing facility for high loads (say a 2 ton compression tester).

Moreover, a force-displacement curve does not give away the spring's design to achieve it's results.  In my field, hard disk drive development, the spec's for the drive's performance characteristic's don't define for the competition how those characteristics are achieved... indeed, even with reverse engineering, which is common in the tech industry, it's extremely difficult to duplicate results... co's spend billions trying to however.

Just by the way, I'll bet a dollar to a donut (or equivalent) that the spring mfg'er Olson uses to mfg'er his spring has a compression tester in their facility that they use for every single 'custom' design request for any customer's request for a given spring... and that the co. also uses the tester routinely to check their spring mfg'ing processes & metal processing / or metal suppliers.  

I therefore must respectfully reject your argument in favor of Olson not providing the spec's.  

I also see in one of the other messages on this thread that the straight road driving characteristics are "a little stiffer"... meaning that the springs Olson provides are already stiffer than standard springs even before invoking any "progressive" feature. One should therefore question whether and to what degree there's even a "progressive" stiffening under hard breaking, cornering loads.  

There is also very likely a mis-interpretation by some who read about the stiffening characteristics which confuse the terms "spring-rate" and "stiffness" with the perception and feel of a "stiffer" suspension in handling.  

Without undue technical jargon, "spring rate" and "stiffness" have the same measure and mean precisely the same thing.  The measure is in Unit Mass in Load per Unit Displacement (in Compression in the case of automobile springs) of the Spring (i.e. lbs/inch, or kg's/meter for example).

With any non-progressive standard spring the displacement increases linearly with load.  i.e. for example 1" displacement under 400 lbs load will produce an additional inch of displacement under 800 lbs, etc. Therefore if the starting load... say at curb weight, is already stiffer than the normal MB provided springs, then it will be displaced less under loads as well.  For example, assume the standard MB spring has a spring rate of 1"/400lbs load and a stiffer spring has a spring rate of 0.5"/400 lbs load.  Then, at 800 lbs the MB spring displaces 2", while the stiffer spring displaces only 1"... obvously less "nose diving" occurs with the stiffer spring.... and so too is the normal driving bumps a bit bumpier)... though the bumpyness one feels on the freeways and highways is more a feature of the shocks than the springs. I don't know how a novice non-professional race driver would tell the difference in performance characteristics between a stiffer linear spring and one advertised as "progressive" when the "progressive" spring is already stiffer than the MB provided spring. In short, how would you know whether you were using a higher spring rate (stiffer) spring or a progressive spring with a stiffer than normal starting spring rate?

I read another comment on this or another of the threads related to progressive rate springs on this forum that at some point in hard cornering conditions using Olson's progressive rate springs in the rear there was a relatively sudden shift... the writer believing that the progressive spring (the one on the outside of the turn)had 'bottomed' or 'stepped' to the next progressive level of stiffness under this condition.  I showed a diagram on the difference in force-displacement curves for stepped vs continous progressive rate springs and standard springs (see the other message from me on this thread dated 17 Apr '08).

From that diagram you'll note that under any given cornering condition the force on the outside wheel (spring) is the same no matter what spring's on the car... the difference is only in how much the spring compresses.... a progressive or stiffer spring (pick either) will displace less under that condition than the standard MB provided spring.  The behavior of the vehicle's "feel" when the spring's stiffness reaches a given level will be noticably "marked" and the same no matter whether the spring's a stepped progressive or continuous progressive or just a stiffer linear spring.

Without the spring's spec's, there is no way to tell whether the spring's progressive or just plain stiffer.. or if progressive then at what points in load or displacement the stiffness changes to the next higher stiffness (spring rate).

Considering a Coil Spring Specialties quote for progressive springs for the W113 was just over $400 for a set of 4 in '03 (jeffc280sl's post), and might be on the order of $500 now, and that this co. has also been confirmed by others (see other messages on this thread) to be the mfg'er for Olson's progressive srings at twice the price, it's a bit obvious that Olson's charging 2x the price for something nobody can define or even know for certain they're even getting progressive rate springs ... perhaps by observation after purchase and receipt, but not in an objective sense.... it is they're getting but Olson's name attached to it.  

I'm an engineer.  Olson's an author and marketing businessman.  I require facts and figures and comparisons to assess the value of something I intend to purchase.  Olson I'm sure requires the same for his investments before he makes the investment without recourse of a refund.  Yet, Olson has not chosen to be forthright in providing the facts and figures even at the most rudimentary level to those he's marketing his progressive rate springs to.

It should go without saying that I don't inherently trust glad-handers.  All the moreso when they're charging twice the going rate by virtue of their position in a niche (MB) enthusiast's market.    
 
Buyer Beware.            

   

[mdsalemi]

...and all of this is why I have the springs specified by Unlenhaut himself.  Stock.

Too many variables, too much money, too time consuming and expensive to do any kind of testing.  Installation isn't pretty, either...

[dixy2k]

Do you guys know what the stock spring rate is? 250lb/inch?

[Longtooth]

I've recalc'ed the spring rates once again, this time based on detailed spring data from the MB Technical Data manual, as opposed to pictures in the Service Manual and rough measurements made while coils are installed in the car.

Calculation inputs are from the Technical Data manual.  Calculation formula is the standard formula available on any spring rate / and most spring mfg'ing co's web sites (formula shown below).  The calculated spring ratesw are 1% - 2% less than the reported (MB Tech. Data manual) spring rates.

The design values are shown for front and rear springs respectively for the 250SL/280SL versions
 
Active Coils = 9.75 & 5.5 compressed to Curb Wt
Wire Diam = 0.614" & 0.622"
Coil OD is 4.94" & 5.35"
Mean Coil Diam. = 4.33" & 4.72"

Parenthetically, Free Ht of springs are 15.26" & 11.40"
Compressed Ht of springs are 9.96" & 8.43" at 672 & 550 lbs load/spring respectively.*

*Note that the loads at curb weights with and without the hard-top do not match the above stated compressed spring loads for the compressed spring heights given.  The sum of the front and rear spring loads at the compressed heights given above are 18.3% less than the curb wts given for the roadster without the hard-top, and 21% less than the roadster with hard-top installed.  Therefore, the additional spring compression will occur over and above the compressed heights given above for the standard 250SL/280SL at curb weights with and without the hardtop installed. 

At Curb Wt, without hardtop the spring loads are 792 lbs & 704 lbs/spring (front & rear respectively).  Therefore, an additional compression at curb weight, without hard-top installed, of 0.475" & 0.424" are expected.  This would put the compressed spring heights at curb weight without the hard-top at 9.5" and 8.0" (front & rear respectively).
 
The hardtop weighs 45 kg = 99 lbs (230SL/250SL/280SL) based on subtractions of the car's weights given with and without the hardtop in the Technical Data manual.   The distribution of curb weights to front and rear axels with the hardtop installed are not provided.  The distribution without the hardtop is 53%/47% for the 250SL/280SL, & 53.7%/46.3% for the 230SL. 

Assuming the commonly used modulus for coil spring steel,
Calculated (see formula below) Spring rates as installed are:
Front: 252.7 lbs/inch (255.7 MB Reported).... Calculated is 1.2% less than Reported... equivalent to 0.12 less active coils.
Rear:  363.0 lbs/inch (370.8 MB Reported).... Calculated is 2.1% less than Reported ... 0.12 less active coils.

There are several coil spring calculators on-line.  I used http://www.auto-chat.net/help/math22.shtml

The formula is (applies only for vertical springs... any off-vertical mounting angle requires an adjustment which is significant):

Spring Rate (lbs/inch) = TM x WD^4 / 8 x NC x CD^3
  Where:
    TM is torsional modulus of spring material (11.25e^6 psi **);
    WD = Wire Diameter (inches)
    NC = Number of free coils
    CD = Mean Diameter of Coil Spring = OD - WD

** Modulus shown is commonly used in all coil spring rate calculators... I have no knowledge of whether or to what degree this modulus applies to the MB springs or any other for that matter, but with the calculated values within 1% - 2% of the reported values there's no reason to believe the modulus is any different than the commonly used modulus.

Assume the estimated spring rates are approx. correct, then the questions as they relates to any progressive spring are

 1) how much does the static spring rate change;
 2) at what load/displacement does the spring rate increase;
 3) to what spring rate does it increase;
 4) is there another stage or more and at what displacements/loads does the other stage(s) occur, and what are the spring rates.

[Longtooth]

I've modified the content of this message to reflect the changes I made in estimated coil calculated spring rates (361 lbs/inch with 10 active coils --- see my other entry below this one).
 
I've seen several references in threads on this forum related to Olson's progressive springs where either the comments were that the car was a little stiffer in normal driving conditions (harder bumps, etc), or that the car sat higher after installing the progressive springs (technical manual, Suspension/Springs)  

Both of these observations indicate Olson's progressive springs are stiffer than standard springs in the static (curb wt) condition.... i.e. before the progressive feature increases stiffness under hard cornering or braking.

If the standard and new springs are the same height before installing in the car, and the change in curb height and curb weight are known after installing a new set of springs, and the spring rate before installing the new springs is known, then the stiffness (spring rate) of the new springs at curb conditions is also known, since:

Curb Wt / Spring Rate (lbs/inch)  = Inches Compression at Curb Wt
therefore
New Spring Rate  = Curb Wt / New Inches Compression at Curb Wt

Using the curb wt of the 250SL and estimated (calculated) spring rate of the standard springs (361 lbs/inch - see my other message today), the standard spring compresses by 1.99 inches under curb wt conditions.  If installing Olson's progressive springs increases the height of the car by 0.5", then the progressive spring stiffness before any progressive increase in stiffness occurs is already increased in the range of approx. 20% - 30%!  from 361 lbs/inch with standard springs to ~425 - 482 lbs/inch.  If the change in curb height was 0.375" (3/8"), then the increase in stiffness with the new springs at curb conditions (before any progressive feature at all) is 10% - 25% (to ~396 - 445 lbs/inch).

I'm not proposing that the estimated calculated spring rate for the standard springs is correct ... or incorrect for that matter... but only that a small change in ride height after installing the new springs, all other things equal, indicates a significantly stiffer spring at curb conditions - before any "progrssive" feature occurs at all.  The possibility therefore exists that any improvements felt in cornering or reductions in nose-dive on breaking could as easily be do just to the fact that the springs are just plain stiffer without any progressive or significant progressive features claimed.

And how would you know whether or not the progressive aspects were significant over and above the fact that the springs were stiffer before the progressive feature began?  For example, assume the static spring rate for the "progressive springs" were 22% stiffer than standard springs to begin with... and that the progressive stage increased the stiffness by 25% over the standard spring stiffness... i.e. the progressive feature would actually be miniscule and imperceptible in the scope of performance improvement due to the "progressive" feature.

Without the comparision of force-displacement curves for both the standard spring and the Progressive spring, how could one tell whether they were paying simply for greater stiffness springs or for a significant progressive feature induced increase in spring stiffness?

At over a grand for a 4 spring set of Olson's "progressive" springs, plus installation costs if you're not doing it yourself (somewhere in the $500 - $800 range), compared to perhaps half or less for just plain stiffer springs by the same amount at curb conditions, it might be important if value for your dollar is also important.

Hence, my pre-requisite condition that the force - displacement curves be shown and published for Olson's progressive rate springs in direct comparison to the stock W113 springs used on US imports.... over the load ranges that include hard cornering and braking.

Buyer Beware.

[JimVillers]

Coil Springs Specialties in St Mary's KS manufactures John's springs. His specifications are of course proprietary.

I had them make two different sets of progressive springs for my 190SL as I experimented with both progressive and stiffer springs. The design of progressive springs is VERY touchy and after three sets of different specifications, I came to the conclusion that stiffer springs work just as well as a progressive spring (yes, I understand the technical benefits of a progressive spring but I don't believe that our cars have enough spring travel to correctly incorporate the progressive capabilities).

My recommendation is to try a stiffer spring and then decide if your want it stiffer or softer. I would start with an Eibach EIB 1500.500.0300, (They were $49/ea a couple of years ago at www.cvproducts.com). They are 15 inch tall, 5.00 inches in diameter and 300 lb/in. They are stiffer than the standard spring and for $100, you can afford to experiment.

From the Technical Data Manual, my 230SL front spring is 255 lb/in; the other special option 113 spring is 307 lb/in. (my TDM is dated 1966 so it does not cover 250SL or 280SL).

[dixy2k]

Would it be safe to assume that 280's require more than 300 lb/in?

[Longtooth]

I contacted Coil Spring Specialties and inquired whether they have their own in - house coil spring tester.  They do... as I suspected they must if they mfg'er coil springs.  There is therefore no good reason Olson doesn't provide the spring constants for his Progrssive springs... or show the comparison in force -displacement curves of standard springs with his progressive springs.... I mention this since the cost of testing was given as one argument for why Olson wouldn't provide the specs.

As I suggested in my note below, it's very possible and even likely that his spring's are probably significantly stiffer before even running into the progressive stage(s), and it's even likely, imo, that the progressive feature's added stiffness is insignificant in a technical sense, but provides for better marketing and much, much higher pricing.

Jim Villar's note suggests in a practical sense that simply purchasing stiffer springs may provide the same performance improvements as Olson's Progressives --- which, supports my contention (see my analysis below).

[mdsalemi]

quote:Originally posted by Longtooth

I contacted Coil Spring Specialties and inquired whether they have their own in - house coil spring tester.  They do... as I suspected they must if they mfg'er coil springs.  There is therefore no good reason Olson doesn't provide the spring constants for his Progrssive springs... or show the comparison in force -displacement curves of standard springs with his progressive springs.

Longtooth,

I have the utmost respect for you; your analysis of springs, and also for John Olson.  I think you've done your homework as an engineer.

But you are asking for data specifically so you, or anyone else, can have the identical "Olson Springs" made elsewhere for less money.  I do not understand why anybody would think that is a proper thing to ask for.

Am I missing something here people?

What you MIGHT do, with all your knowledge and calculations, is actually improve upon his idea.  You can "run the numbers"; have a bunch of springs made, test them all; and then test them in your car.  If you get results worthy of applying to other cars, you can keep the calculations and specifications to yourself and sell the springs!  Maybe there are some other changes you can incorporate into the whole improved suspension idea.

I might buy them someday, but I'd never ask you to "open source" all your research.

[JimVillers]

I agree with Michael that it is not appropriate to ask for proprietary specifications.

On the other hand, MB freely sells this information for $35 or so.  Just buy a Technical Data Manual for 1970 or so and look up their W113 standard and optional spring specifications.  This includes free length, length under normal load, normal load, maximum load, spring travel in mm per 100 kp of load, wire diameter, mean winding diameter and number of windings.

With that information, it is reasonably easy to design a reasonable spring for your car.  

The two significant issues are: how stiff do you want it? and getting the ride height correct (which is very touchy).

The real fun is finding out what you want.  You won't know exactly what you want until you make it too stiff and then soften it up until you are satisfied.  

Much more fun that buying a set of springs that you "force yourself to like". I went through about six sets of springs on my 190SL and was never really satisfied for the long term.  I thought that I wanted stiffer springs until I drove on them for a year or so.  I am back to my stock springs now.

[Longtooth]

Micheal and others,

I'm not asking for the means by which Olson's springs achieve their "improved performance", rather only what the function is in normal, expected, objective terms.

A spring's function is dominated by it's spring constant and load limit (allowable stress limit).  A progressive spring is no different, it just has more than one spring constant.

The means by which this function is achieved may be proprietary... the material properties, wire diam, number of active coils, coil spacing, any taper to the wire diameter, coil diameter, whether spring is conical or cylindrical, and by how much, specific mfg'ing conditions (very critical to proprietary systems by the way).

The spring constant(s) is measured by a force-displacement curve... the slope of the curve (lbs force / inches displacement, normalized to 1" displacement) is the spring constant.  This is the function of any spring... it's reason d'etre in fact.    

Here's a diagram of a force displacment curve for two different progressive springs and the standard spring --- hypothetical.



In the example the 3 stage progressive spring has the same initial spring rate as the standard spring, but increases in spring rate at 2 points along the load/displacement.

The 2 stage progressive spring (labeled "1 STAGE") starts with a greater spring stiffness than either the standard or 3 stage spring, with an initial spring rate that remains constant until nearly the end of it's functional limit, at which point it becomes "progressive" by increasing it's spring constant.  In effect, the 2 stage spring, though technically progressive, is primarily just a stiffer linear spring until the very end of it's funcational range.  For 98% of practical purposes it's not functioning as a progressive spring.

I point these examples out only to show that there are a multitude of possible combinations of stiffness and stages of increasing stiffness, each having a different "performance" advantage depending on the "advantage" being sought by the user.

Marketing a spring with no specification regards the spring's objective function is the same as advertising a "higher resolution" TV with no spec on what the resolution is, and no means of viewing it in comparison with any other TV one may be considering.  It's the same as advertising a "higher performing engine" with no specification of torque v rpm or power v rpm.

I'm therefore only seeking that which is minimimally required in terms of the function implied (but not stated) by the advertisement.  Olson's marketing an "improved performance" spring, but explicitely omits the functional attributes of a spring. I can only surmise that he's using the same marketing methods as the gasoline additives marketed on the web that give "improved mileage" or "improved engine performance", and similar.    

I'd simply like to know what it is would be paying before I make a purchase.  This is, I believe, the minimally responsible requirement placed on any consumer.

BTW, the correct ride height can be achieved by ordering a spring that has the same compressed length at curb wt as the standard spring.... with the same rubber cushion thickness. A spring mfg'er that provides custom springs will be glad to measure this for you on your existing springs (front and rear) for no extra charge (or a nominal fee -- $5-$10 or so) and use the information to provide the new springs so that ride height is the same as it was before (or if you want it adjusted up or down, then adjusted to suit).  So why all the fuss over ride height issues with new springs?  

Also BTW, special "off road" or "emergency vehicle" springs for police, fire, etc, could be ordered from MB with the W113's.... the were stiffer, and also were noted to increase ride height (road clearance).

So, Micheal, please don't take offense to my response.  I am not acquainted with Mr. Olson, and if I were I'd be asking the same questions since I would not be parting with my dollar without knowing what it was I was parting with it for.... and especially if he's charging a huge premium for what he says he's providing.

[JimVillers]

Longtooth .... You clearly understand the technical issues of spring design but I doubt if you have experience is actually designing and installing a spring in a pagoda.  I would also challenge you to "blindly" drive a pagoda with stiffer or progressive springs and to correctly identify the installed spring.  

If you ever install a special spring in your pagoda, I would be very interested in the achieved ride height of your first try (distance from the center of the hub cap to the bottom of the fender).

[Longtooth]

Jim,

Longtooth .... I would also challenge you to "blindly" drive a pagoda with stiffer or progressive springs and to correctly identify the installed spring.

Likewise, Jim.  As I've pointed out before (see my Nov 4 post below), I challenged anybody to distinguish between Olson's progressive springs and a set of linear springs with the same initial spring rate as the stiffer progressives he markets.  How would one know whether or not Olson's springs were progressive or just plain stiffer linear springs based solely on driving with them?

My Nov 4 Post excerpt:
"...how would you know whether or not the progressive aspects were significant over and above the fact that the springs were stiffer before the progressive feature began? For example, assume the static spring rate for the "progressive springs" were 22% stiffer than standard springs to begin with... and that the progressive stage increased the stiffness by 25% over the standard spring stiffness... i.e. the progressive feature would actually be miniscule and imperceptible in the scope of performance improvement due to the "progressive" feature.

Without the comparision of force-displacement curves for both the standard spring and the Progressive spring, how could one tell whether they were paying simply for greater stiffness springs or for a significant progressive feature induced increase in spring stiffness?"

[Longtooth]

250SL Standard Springs Spring Rates (Front and Rear)   

Stiffness, lbs/inch   
255.7   Front, PN 1133210404 (21.9 kp/100mm)
370.8   Rear,  PN 1133240404 (15.1 kp/100mm)

Reference: converted from stiffness provided as kp/100mm by Roy Spencer, OurSL.com.

FYI:
kp = kilopond = 9.80665 Newtons = 1 kg-force = 2.2046 lbs-force at earths mean sea level.

mm = 0.039370079 inches or 25.4 mm/inch

[JimVillers]

Longtooth .... My point is if you can't determine the characteristics of springs by driving, why are you so concerned with technical curves.  The curves may be intellectually interesting but I am more interested in the sharing of the practical experience of installing and evaluating the characteristics of actual springs in actual cars.

[dixy2k]

The rear springs are stiffer?
It seems to that the front ones should be since the engine needs lots of support during turns and brakes.

[Longtooth]

dixy2k,
The pictures of front and rear springs during installation or removal in my service manual are consistant with the rear springs being stiffer than front springs. The rear springs have fewer coils than the front springs (rear has 8 total coils, ~7 or so active at curb wt). While I say this however, the rear springs may have a slighly larger OD.... I can't tell from the pictures... and as the OD increases (but with same wire diam), the stiffness declines dramatically.  I therefore can't say for sure from the pictures whether they support or don't support the higher stated stiffness of the rear springs since I can't tell if the rear springs have same or larger OD than the front springs.  From the number of coils in each though, if rear coils don't have a slightly larger OD then the front springs should be considerably less stiff than the rear springs.

On the other hand, it's pretty obvious to me in driving the car over the speed-bumps that the rear is sprung stiffer than the front, but this may also be due to the addition of the compensating spring...  while the excessive nose diving we have on even slight braking would indicate relatively low standard front spring stiffness.

Relative to front/rear weight ratios: According to an article in '63 when the 230SL was reviewed by Auto, Motor, & Sport (a German auto mag), the front/rear wt ratio was described as 53%/47% (with curb weight also given for each axel), although the max allowable loads on the axels have ratio 47%/53% of max total allowable load according to the service manual... hence a higher allowable max load on the rear springs... which tends to reason since the trunk is designed as a load carrying part of the car, and sits directly over the rear axel... with most of it to the rear of the springs.

[Longtooth]

Jim Villars,
It is indeed the practical driving experience which is the ultimate objective sought in purchase & installation of performance or improvement products.  What you may consider academic attributes (measures of functional characteristics), I consider comparative characteristics... "how much" more/less than something else is a guage or measure one can use to assess whether the ultimately sought objective is / can be / will be / will not be achieved.   The ultimate issue is however, how much g' force can be withstood on curves without the back-end or front end breaking out, how much "over-steer" or "under-steer"... drift or "rotational acceleration" relative to steered trajectory...  occurs on various radius curves at various speeds,  and how much vertical acceleration is transmitted to the body over bumps of various sizes with the automobile at various speeds... these are functional measures of what you "feel".  Of course these dependant variables are a function of several independant variables, spring stiffness being only one of them.   

I certainly cannot measure the difference in g-force capability on curves, or objectively define the amount of over or under steer, nor the change in transmitted vertical acceleration levels, unless of course I purchase an accelerometer to make the g-force and vertical / horizontal acceleration measurements .. eminantly possible, terribly in-expensive ( http://www.geeks.com/details.asp?InvtId=KAT-MATRIX&cm_mmc=GoogleProducts-_-ConsumerElectronics-_-AutomotiveAccessories-_-KAT-MATRIX&zmam=2003677&zmas=15&zmac=159&zmap=KAT-MATRIX, or http://www.drillspot.com/products/320108/Monarch_6480-031_Accelerometer, to name just 2 inexpensive versions), or you can go whole hog and spend a lot more (http://www.microstrain.com/g-link.aspx?gclid=CNrU8JD27pYCFQ8QagodGwxmsA) , but beyond my purposes and intent... I'm not seeking any competetive advantage on a race or road course.

I do however have nearly 40 years of direct experience in making assessments of changes in performance based on engineering specifications only ... or proposed changes to specifications.  As it turns out that based on my near 40 years experience in making these engineering assessments and then following up with actual part measurements that it's not all that difficult to define the range of changes one is interested in pursuing with actual mfg'ing and procurement, testing of parts... something that must be done eventually, but which must first be narrowed down "on paper" so that the expense and time involved is minimized.   

One could say that Olson has already done the "narrowing down" to the point of having precisely what everybody wants who's interested in a performance improvement in handling based on spring changes... and is therefore charging for his "narrowing down" effort.  If he were able to provide me with the information he used to make his "narrowing down" conclusions, I could make my own assessment of whether or not his objective and conclusions matched mine.  I have zero reason to trust Olson's capability in his "narrowing down" conclusions... he's given me no reason to trust him, provided no data what-so-ever to enable me to determine whether he's even used any objective criteria, and in short is advertising his credibility based on his name as an author as near as I can determine.

I'm an engineer at heart I guess, since I was a kid in high-school (not just in career)... I seek objective facts and figures, measures.... not somebody else's subjective judgement and especially when that someone else is not primarily an expert in what they're judging in the 1st place, and most especially  when they want to charge me for their non-expert judgement. 

You find the empirical method most inspiring... & there is nothing at all wrong with that.  It's ultimately required to reach the final result no matter what anyway... but it can be highly misleading, far more expensive, and very time consuming in many cases to start with that approach.  My experience in development of new products and technology prioritizes the engineering assessments (what you refer to as "academic" exercises) over the empirical as the 1st order of business.  Olson's not marketing to my type... he's marketing to yours.



       

[JimVillers]

Longtooth .... Don't sell my Analytical abilities short as I am a mechanical engineer and have played with cars for fifty years.   My point is that until you have tested several set of springs, you only have one data point and you do not have an objective function.  Your objective should be your driving feel (not my driving preferences).  Without installing and testing multiple springs in order to quantify your preferences, it is just talk.   

[Longtooth]

My apologies, Jim... I didn't realize from informaiton you've posted on this subject you had used your analytic skills in selection or narrowing down the spring characteristics you were interested in, so I assumed, wrongly as it turns out, your empirical approach with multiple purchases of different springs was your preferred method.  :-[ctually, though, we differ on what our objectives are... though the ultimate objective may include better 'feel', it's my objective to achieve better cornering performance primarily... ride comfort is a compromising factor.  Nose-diving is a terterary factor if any at all since braking distance (power) is the performance objective I seek.  I harbor the belief that a progressive spring design should be able to achieve standard normal non-aggressive driving road comfort without compromise, while providing performance advantages I see in cornering. The question is only to what level do I consider "standard, normal, non-agressive" inputs to the suspension system.

As I stated in my last note, the process of narrowing down what you want / don't want is an analytic exercise... an option I chose despite (perhaps even because of) the lack of spring rate data for Olson's versions.

[Longtooth]

I've updated the estimated spring rate calcs in my for the 250SL/280SL's front and rear springs based on new detailed spring data from the MB Technical Data Manual (which I received today).   

Suffice to say in summary, the new estimated calculated spring rates using the standard formula matches MB's stated spring rates within 1% - 2%.  See my Reply #30, Nov 4.