[stevekat]

Wanted to confirm the stock front spring rate for an M030. I cannot determine from reading around if it is different from a 951 Turbo S, though the 968 M030 shocks seem to have stiffer valving. The Turbo S spring rate seems to be 160 - 175, with 175 perhaps being the '89 Turbo S. Also the 968 has the 100 Coil Spring Rate, 60 Effective Rate coilover spring in the rear that the 951 does not. So the additional rear rate would seem to change the balance of the 968 M030 unless the front wheel width increase (plus .5" or sways made up the difference.)



Also, want to get my recenlty acquired 1993 M030 set up for DE. Was thinking of:



400lb up front and;

25.5 (175lb) stock torsion with 375lb Coil Spring Rate (211lb Effective Rate rear) = 386lb rear.



...initially using stock M030 wheel sizes and stock M030 sways.



Aiming for car to be relatively neutral, with tendency if any toward understeer. Seeing different opinions about whether the car should be biased spring rate wise to slightly stiffer front or stiffer rear to accomplish this (wheels and sway bars beeing stock.)



Also have Koni stock M030's rear that need rebuilding. Have to make a decision to rebuild, revalve, and perhaps add double adjustable capability to rear Koni's, (and perhaps rebuild, revalve fronts and upgrade them to double adjustable at same time though they are servicable) or think about other dampers since they Koni's would be out of the car and incurring expense.



Primary interest right now is DE.



Would welcome any tweaking from those with experience.

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[flash]

the stock rates for the standard car are 160 front and 175 rear, the bias is to the rear, and the car still understeers - remember, in stock trim the car is 66# tail heavy



the manual shows the same spring rate, alebeit a progressive spring, but the wire sizes make me wonder - the rears got an additional helper spring, which if the front rate is the same 28nm would make the bias even more to the rear



i am going through this right now - i also started with softer springs in the back than the front - mistake - little by little i have been increasing the rear rates - curently i am at 300 front and 450 rear (no torsion bars) - still not enough rear - likely going with 400 front and 600 rear - so, interestingly, i am just about to do the same thing - i would go stiffer in the rear, and try to acheive the same ratio (which would ask for a 625), but my shocks won't handle more than 600 well, and i don't want to change them



by the way, everything i have been able to find puts the effective rear spring ratio at .65 and NOT .56 (contrary to the paragon website) - when i first started on this, i contacted eibach, who did the math with me using actual measurements of the car, karl at racer's edge, who confirmed it with porsche information, and did actual compression testing of the spring in the car - all showed .65 - i talked to chuck at paragon who said at the time that he had no idea where the information came from - this part has been very frustrating - i am doing another set of measurements this week to determine what the actual per inch rate is on my car, and see if we made a mistake somewhere



the good news here is that makes the rear suspension a bit stiffer than you think, which is good - the difference would be 25# more in choice of rear spring to achieve the stock front to rear ratio, versus nearly 100# needed

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[333pg333]

Here is an excerpt of what Karl said in view of my upcoming system. I have a turbo S:





"But believe me, my numbers correct (or close to it - see the following explanation). The info on Paragons site is stuff they got from me a few years ago. In any case, the 47% is a number that I have calculated By taking measurements. I am now pulling out one of Porsches own Motorsport sheets that shows all the rates of their Turbo and "Cup" cars back when they ran competitively. Porsche lists the 25.5 mm bar as 31 N/mm which is 177 lbs/in. They also then give the variable rate coilover helper spring rates at 34-65 N/mm which is 194 lb/in - 371 lb/in. They then give the total Rate at the wheel(T-bar plus coilover) as 45.4 - 58.5. Back out the rate at the wheel due to torsion bar which they list as 31 and you have 14.4 - 27.5 at the wheel due to the coil over. So take your pick, 14.4 / 34 is approx 42% or 27.5/65 is 42%.



Bob is right about them being inboard but his numbers are off. Actually they are correct I think in that the motion ratio is about 65%. But when calculating wheel rates from spring rates it is the motion ratio squared that is used. So 0.65 ^2 is , guess what,... 42.25% which is the number that Porsches own sheet claims as I outlined above. So your torsion bar is 177 at the wheel, and your helper spring rate is a 285 which is 119.7 lb/in at the wheel. So working backwards 177 plus 119.7 is 296.7 pounds per inch at the wheel. Divide this by .42 and that is your equivalent coilover, or 706 lb/in coilover (initially I had 661 lb/in which is attributable to my measurement error - I had 47% and Porsche lists it at 42%).



So it may be a bit stiffer in the rear than I might run but with the ability to tune sway bars etc... you should be Fine. Your setup is actually much stiffer in the front than the Porsche cup setup which ran progressive front springs (200 - 371 lb/in) with the rear setup I described above which is not that far from what you have( yours is 296 at the wheel and theirs was 259 - 334 lbs/in at the wheel).



Hope this make sense, but believe me, what is above is 100% correct. I can fax you the Porsche motorsport sheet if you think it will help."





Karl Poeltl

Racer's Edge

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[flash]

that is almost the exact opposite of our conversation almost 2 years ago when i started out on this journey, wherein i ran down with karl the math i did with eibach - i would really like to get to the bottom of this and see the measurements and math porshe was using for the geometry - it isn't adding up from that point - i will send you an email with my fax number - i would love to see it - this has been very a frustrating and time consuming process, and i am very tired of swapping out springs - i am cntinuing to go stiffer back there, which seems to bear out those numbers more, but at this point, i want to know where the error occurred in the math



by the way, we did square the final number, so i am all the more interested in sorting this out and seeing that sheet



with my 450lb springs in the back, and there being two of them, at 100% it would take 900 lbs to compress the springs 1" - at 70% it would take 630 - at 65% it would take 585 - at 56% it would take 504 - at 42% it would take 378 - a 200 lb weight in the trunk should then compress them about .52"



i will verify this today, but the last time i did this, i confirmed the math which showed my effective rate to be about 70%



curiouser and curiouser

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[333pg333]

Bob, bear in mind this is an excerpt of an email from Karl to me so you will need to contact him directly to go through this. Keep me/us posted as it is indeed curiouser.

Patrick

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[flash]

i just had a very long and once again very nice conversation with karl - i will be going back and remeasuring everything and crunching numbers again



oh boy

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[stevekat]

Interesting stuff. Curious what agreement might eventually be on the Coil Spring Rate to Effective Rate constant. I was using a contstant of .6 meshing together an estimate incorporating a variety of things I had read. Sounds like this may be high.



In the meantime, just want to confirm I should be looking at a rear bias. I guess if I go with 400lb fronts, I can just change out the rears if initial attempt does not work out.



Flash, when you refer to your rear rates, are you referreing to the Coil Spring Rate or Effective Rate?

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[333pg333]

I am a novice at this sort of thing but I would imagine that apart from your spring rate you need to consider your shocks and how they work with what sort of valving, adjustment, and stem travel and then sway bars and bushings which will affect other parts of the total handling package. Plus tyre size, brand, and type. It's a lot of detail that goes into setting up your car correctly. The more I do this the more I respect the people who do this professionally or semi-pro. The bulk of it still goes over my head but the advantage you guys have in the 'States is that there is such a large market and history and so many people to get advice from and pay for their services. In Australia there are plenty of people in the race industry but virtually zilch on front engined water cooled P-cars. Pity.

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[stevekat]

Goal is to retain stock M030 sway bars (providing some adjustment at rear.) Regarding wheels, trying to determine desired size of wheel. Leaning toward 16". Would like advise on widths for what might be available in various factory forged and aftermarket. Obviously wheel widths shall effect set up. One interesting setup up might be a 16 x 9 Club Sport from 951 52.3 offset for the rear, and I believe there is a 16 x 8 Club Sport 16 x 8 52.3 offset, from a 928 GT, for the front. The 52.3 offset for the front is somewhat different than the stock 968 M030 wheels. Also considering all 8s or all 9's. I have had advise that there are S2's that like to run all 8's however the 968 has 20% more power so that experience may not be relevant. Have not had the car on the track yet, so trying to pick a rational and modest cost entry point for a set of track wheels.



I like the 928/931 dish wheels. They are made by Fuchs, are forged, and relatively inexpensive used. However max width on this style is 8.

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[flash]

steve - when i refer to rates they are the spring rates - it get too darned confusing, especially now, to refer to wheel rates or effective rates



333 - shocks do play a part in handling, but should not be used in calculations



i think i'll have time today to remeasure everything

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[333pg333]

Sure I know you don't include shocks to figure out your rates, more, that while figuring out your rates you need to take into account the other components of your suspension to understand the total package and how it's going to affect the car overall. Based on what Karl from Racers Edge has come up with in terms of my spring rates most would think they're too stiff for a car that is on the road (I think 615 f and 706 r) but with the technology of the shocks and their valving I'm hoping for it to be OK on the street and sublime on the track. I still haven't got mine yet but I've been in the Australian importers of KW suspension car with the same spring rates on the front and it felt fine on the street. Different car so I know it's not apples for apples, but a reasonable indicator nonetheless.

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[333pg333]

Just as a general update on this subject. I now have my new suspension installed and it has thus far proved to be fantastic. There is still work to be done on my car as my lsd is basically not working at all and there is an issue with 4th gear 'falling' into neutral at the end of the straights of 2 circuits I've driven on recently, but with this in mind I have taken 2.5secs off my previous best times on both tracks and this is due almost entirely to the suspension with the spring rates mentioned in above posts. So I've got nothing but glowing praise for KW's and their up to date technology as opposed to the 20 year old Mo30 stuff. Oh, and they also drive on the street with a BETTER ride quality which is a very nice bonus!

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