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Old 12-20-2010, 05:20 PM   #1
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m030 spring rates

I want to upgrade my stock springs, and must use other stock springs for racing class. how do I find out which springs are the stiffest, and what hieght they will be? does anyone have ROW m030 springs? what are the color codes on them? are they the same as USA mo3o color codes? USA is yellow/white front, but two different part #s for -02 and 03-. the rear gets really complicated, as it makes a difference which transmission and which engine. the rears seem to be:
base, 5speed:
-02 red brown
03- yellow brown
base, automatic:
-02 red white
03- yellow white
3.2 6speed:
-02 orange brown
03- orange brown(different part #)
3.2 auto:
-02 orange white
03- orange white(different part #)
and they list another 3.2 no trans specified 03- violet white
I want to end up with the stiffest possible rear springs and stock ride hieght. and have the front springs be about 20-30% softer. is there any way to find the specs on all these springs from porsche?
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Old 12-23-2010, 06:09 PM   #2
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I just got my 986 kit today from Design 911 and I don't know which is front and rear but one pair shows red/red on one end with green on the other while the other pair shows red/yellow on one end with blue on the narrow end. Hope this helps.

Steve
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Old 05-04-2011, 06:27 AM   #3
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Spring Rates & Adjustable Dampers

A little late to help the posters above, but I think this issue needs some clarification.

I've have seen too many people at the track all but bragging about how stiff their springs are (ie "which springs are the stiffest?"). I've also heard people say adjustable shocks are the bee's knees because you can stiffen them up for the track and soften them for the street.

Thinking about your suspension in these terms is completely ridiculous.

Let's start with the springs. As a suspension moves, its geometry changes. Modifications to the suspension for track use should therefore focus on "correcting" these movements. For example, in bounce, MacPherson struts generally add positive camber -- not what the tire contact patch needs for maximum grip. Likewise, the inside wheel adds negative camber. If your car is set up with, say 2 degrees of negative camber, then the inside front tire might go to 3 or 4 degrees, based on the rate of change in camber (in degrees/g) as the suspension compresses.

The issue here is the ROLL RATE (deg/g), not how stiff the springs are (which contributes to roll rate, to be sure). As a 4-wheel vehicle turns, weight is distributed from 50/50 right to left to some amount where the outside is greater than the inside. In addition, differences in front and rear roll rates cause the weight to shift from front to back (or vice versa). Hence, a vehicle with a static 50/50 weight distribution might go to 60/40 in a turn.

This happens because the front roll rate is generally in excess of the rear roll rate (well, this is vastly simplified, since the height of the roll center and other variables need to be taken into effect, but let's think in these terms for now). The following is counter-intuitive, but imagine a board placed across two springs, one 50 lb/in and one 100 lb/in. In total, the spring rate is 75 lb/in, so if a 150 lb person gets on the board, the springs sag 2 inches. But in fact the stiffer spring must take more load because the softer spring compresses less in order to keep everything level. You might say, no, the board is now tilted, but Shazam! The weight must move towards the 100 lb/in spring-- hence the stiffer spring takes more of the load relative to the static weight distribution!

As you stiffen the rear suspension roll rate, say by installing a stiffer anti roll bar, then we all know the car will tend away from understeer ("US") and towards oversteer ("OS"). In our example, the person on the board moves back, towards the 75 lb spring. Shazam! again.

So if the car has 50/50 front to back and 50/50 right to left weight distribution, then in a turn, perhaps 60% of the weight is on the outside, and because the front is stiffer than the rear, of the 60%, maybe 35% is on the front outside and 25% on the rear outside.

As the front outside tire gets more load, it grips better (the friction force is proportional to the weight on the contact patch times the coefficient of friction, mu), but the nature of tires is that the additional grip is not linearly proportional to the weight on the tire (mu changes). As a result, the front tires together as a combined system do grip more due to the weight transfer to the front, but not proportionally more than the rear -- in fact, it is proportionally LESS than the rear. Hence, the REARS grip more relative to the fronts -- and the car starts to US.

It should be intuitively obvious, then, that simply bolting up the stiffest springs and anti roll bars will modify the roll rate with no clear idea of what happens to the weight transfer. This could make a car handle worse than stock.

If you want maximum performance from your car, all this must be balanced. You cannot solve roll stiffness by anti roll bars alone, since at some point the combination of springs and anti roll bars starts to act "funny". Likewise, bolting the stiffest springs you can find and keeping stock ARBs means the car rides like a truck -- and more importantly, when the car isn't turning, the ability of the car to maintain traction is compromised, especially in the wet or at bumpy apexes.

So in fact we want the softest springs possible while maintaining minimal geometry changes in the suspension from roll. When I tuned my 944 Turbo, I used photos of the car on the track, measured the roll and the lateral acceleration as well as the change in camber, and then determined what I wanted out of the suspension in terms of roll rate, etc.

Moving on to dampers, they, the springs, and the unsprung mass of the vehicle comprises a total mechanical system. Underdamping the vehicle means that when it hits a bump, it oscillates as the chassis moves up and down relative to the vehicle. Ideally, it should move down (relative to the wheel, which is really the only thing that's moving as the road shocks move it up and down -- the chassis stands still), then up past equilibrium, and then back to equilibrium. If too firmly damped, the body goes "down" then back to equilibrium. This contributes to a harsh ride because HIGHER frequency vibrations are transmitted into the chassis. In other words, firming the damper increases the resonant frequency of the suspension. Softening the damper reduces the natural frequency of the system, which means as you tool down the road and hit minor undulations (ie low frequency inputs), where the stiff suspension wouldn't really notice them, the soft suspension wallows around -- which is also a degradation of "ride quality". Softening your dampers for street use will make your car handle like a Lincoln Continental -- if you want to do that to your Porsche, so be it.

So what's the deal about dampers? Well, the key is they act like springs when the suspension is MOVING. Springs act like springs when the suspension is STATIC (including steady state turns). If the car AT TURN IN is understeering, then from above we know the front roll rate is too stiff. As the damper compresses, it is adding to the roll rate, so we need to soften the front damper. You get the idea.

Softening the damper for street use and firming it for track use results in a car that has bad ride on the street. And mindlessly dialling up the dampers to "9 or 10" on your PSS9s is not the way to tune your car's handling.

One final word: Porsche race suspensions are softer than you think. The 968 Turbo RS front springs were 225 lb/in vs the stock 160 lb/in (fronts). NOT 400 LBS. NOT 500 LBS. NOT 1,000 LBS. At those levels, the suspension begins to be nearly solid, which means the tire starts acting like the primary spring in the suspension. While the suspension geometry changes are vastly reduced, traction is severely compromised. Stiffer springs also means the vehicle's weight transfer reacts faster to steering inputs, which makes it harder to control, especially in the wet, as the weight distribution changes rapidly.

Hope this helps.
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Old 05-04-2011, 07:42 AM   #4
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all very good information. on interjection: you can't compare spring rates on one type of car to spring rates on another. the WHEEL rate is what matters; that's the effective spring rate at the tire. that's based on spring rate, suspension geometry, tire make / model / size, and tire pressure. springs that are stiff on one type of car may be soft on another simply because there is mechanical leverage at the spring actuator (by design).
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Old 05-04-2011, 10:16 AM   #5
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Thanks for the beautiful write up. Is accurate to say that we want roll bars to control roll as much as possibile while controlling bump and rebound with damper changes and springs giving us the foundation and ride hide? What I take from this us to use roll bar adjustments as a primary set-up adjustment while playing with dampers where the surface is undulating or choppy? This of course is with no fiddling with tire pressures which would contribute greatly to wheel rate and perhaps damping.
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Old 05-20-2011, 12:17 PM   #6
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Insite,

You're dead right on that. The 944 Turbo has a front spring rate of around 160 lb/in, but the wheel rate due to the MacPherson strut geometry is more like 125 lb/in.

JayKay,

Thanks for the kind words. Controlling roll "as much as possible" isn't necessarily the right way to go about it -- decreasing roll means increasing the roll stiffness which requires stiffer springs. You could have a car with 0 degree of roll per almost infinite g loading, but traction would suffer, since the suspension would be solid and any bump you'd encounter would make the car just skip along. Not that softer is necessarily better either -- that's the trick of tuning these cars. Indeed, you can get your car to skip around by dialling up infinite damping, too, as the rear suspension becomes solid during bumps.

Let me try to clarify again: the three components are springs, dampers, and anti roll bars. The trick to all this is managing where the load of the vehicle moves when the vehicle is no longer static (that is, at a constant 60 mph in a straight line, the load is static, but if you accelerate, brake, or turn, then the load moves around from front to rear, side to side, etc.).

Springs manage the weight distribution during changes in pitch (nose up or nose down under acceleration or braking) and roll (left side up or down depending on direction of turn) AND when there are no changes in pitch or roll (steady state cornering). That is, stiffening the front springs will not only change steady state weight distribution in a turn but also how quickly the weight moves from static to dynamic distribution.

(Stiffer means the load moves FAST. This is the "go kart handling" people talk about, since go karts don't have springs other than in the tires, so the load moves extremely quickly. It's not necessarily desirable, by the way--undulations in the road surface make the weight move around, too, and a stiff suspension will make it move around quickly, making the car very darty and more work to control.)

Anti roll bars do the same ONLY for changes in roll. They do not affect pitch behavior. (There are also things called Z-bars that act opposite to anti roll bars--when one wheel goes up, the bar transmits the upward force to the opposite wheel which also rises. Myself, I've never seen one).

So if your car works fine with springs only with respect to pitch behavior but not with roll, then maybe you need to adjust anti roll bars. This is in steady state as well as transient handling maneuvers.

Dampers only work during transitions, when weight is in the process of moving around (force is proportional to velocity, while springs: force is proportional to distance, and mass: force is proportional to gravity. The equation is F = mg + cv + kx, where m is mass, g is gravity, c is damping factor in N per m/s, v is velocity in m/s, k is the spring rate in N per m, and x is the spring compression or extension in m. The force is what's transmitted to the chassis through the suspension. This doesn't take into account the tire's contribution to all these variables as well as the differentiation between sprung and unsprung weight, blah blah blah).

At steady state, the weight isn't moving -- it's already where it's going (of course, nothing is ever perfectly steady state, but you get the idea). So the dampers are contributing no force to the system (v = 0). If the car understeers when turning in -- not after its turned in and at steady state, but DURING turn in, or v > or < 0 -- then the dampers are making the front roll rate too high and are thus too stiff. Stiffening the rears has the same effect of softening the fronts, which would allow you to dial in more rotation during turn in.

This is a gross simplification, but ideally you'd set the car up with springs and dampers alone and see if you can get it to handle "properly" (maybe you like understeer or maybe you want neutral steer, etc., and the difference front to rear in spring rate contributes to pitch control -- you don't want the car to porpoise along after hitting a bump). If the geometry of the suspension isn't cooperating (too much roll = suboptimal contact patch, based on tire temperatures inside, outside and middle of tread), then add the anti roll bars and adjust the springs to restore the balance. Of course, adjusting camber will be a necessary step in here, too.

To control the spring & mass system, you need dampers. Install them, tune them so they're not too stiff (over damped meaning the car doesn't move when you hit a bump) and not too soft (car floats up and down repeated when you hit a bump). Then tune them, too, so that during transitions the car behaves the way you want (maybe you like lots of turn in oversteer, maybe you aren't so daring).

You're right about tire pressures: There is only one optimal tire pressure. It's the one that ensures the tire isn't over inflated (middle of tread tire temperature higher than average of inside and outside edge) or under inflated. It's really that simple. Yes, a stiffer tire increases spring rate and changes the damping, too, and you can use this as a stop-gap measure to adjust handling (in the rain, take out rear tire pressure to add understeer and soften the rear suspension for better traction). But deliberately running too high tire pressures is obviously wrong given the negative effect on tire wear.

If you can't get your tires to the manufacturer's suggested operating temperatures (where grip is maximized), then you have too much tire for the car (the contact patch is underworked).

You bring up ride height, which I didn't address much. Lowering the car is sexy, but mostly it reduces the vehicle's center of gravity. The force transmitted to the outside springs depends upon the mass of the vehicle, the height of the CG, the track, and the cornering Gs. Lower CG = lower weight transfer = more even weight distribution side to side despite cornering.

But lowering the car also has a pronounced effect on this weight transfer stuff, since lower ride height = stiffer springs. It also could affect geometry of the suspension -- excessively lowered 944s often suffer ball joint wear due to extreme angles of the tie rods. On my 944 Turbo, I lowered it 20 mm which is what the 968 Turbo RS's setup called for. I think that's the max drop with the rest of world M030 for the Boxster as well. Note that in this case, Porsche drops the front 20 mm and the rear 10 mm. All things being equal, this makes it harder for the front to roll (lowers the CG relative to the front roll center more than the rear roll center) -- increasing roll stiffness. Interesting, isn't it, that the ROW and USA M030 use the same anti roll bars? This illustrates the complexity of all this -- Porsche could have simply ordered up a larger front ARB instead of dropping the ride height to get the same effect, but for some reason they didn't.

I find it interesting that the Bilstein PSS9 setup doesn't suggest new anti roll bars (at least I haven't found anything suggesting it does). If we assume it gets to the same roll control as the ROW 030 setup, then the PSS9 must be much stiffer in pitch than the factory setup. Driving down the street, the PSS9 should bob up and down much more than the 030. Maybe you like that sort of thing, maybe you don't. Bear in mind that race tracks in Europe are smoother than ones in the US (generally), so the PSS9 might work really well in Europe but not as well in the US. I don't mean to rag on the PSS9, since I'm sure it's excellent in its own right, but one just needs to understand what it is they're handing over their Benjamins for.

My 944 Turbo had Koni coil overs front and just heavier rear torsion bars. If I wanted to adjust front/rear springing, I could swap out the front spring. It had Koni shocks all around, so if I wanted to adjust transient behavior, no problem. And I stuck to M030 anti roll bars. So with camber adjustments, I limited the variables to 5: single adjustable (bounce) dampers front and rear, front springs, camber, and rear anti roll bar soft, medium, firm. For the Boxster, it's ROW M030, period. No muss, no fuss.

Most importantly, while this is all complicated, if you give it careful thought and planning, noodling around with setting up your suspension can be a lot of fun. Change one variable at a time, see what happens, and if you likey, good. If you don't, then do the opposite. I'm not suggesting you not do it, just that your mileage will definitely vary and if you're not careful you can make a dog's dinner out of the whole thing.

Here's an idea: remove your car's anti roll bars and take it for a drive. Then put the rear bar back on and see how it handles (massive oversteer). This will give you a taste for what's in store for you if you want to go down this path. Maybe you'll love experimenting, maybe you'll say it's not your cup of tea.

If you want to learn more, try Fundamentals of Vehicle Dynamics (Gillespie) (not as much detail), How to Make Your Car Handle (Puhn) (a little hokey and definitely grass roots stuff), and the granddaddy of them all Race Car Vehicle Dynamics (Milliken & Milliken). The latter is THE authoritative tome on how to set up your car. It is 900 pages long, extremely complex, and gives all the answers but does not concern itself too much with ride comfort.

Hope this helps and good luck.
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Old 04-02-2013, 08:36 PM   #7
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"I find it interesting that the Bilstein PSS9 setup doesn't suggest new anti roll bars (at least I haven't found anything suggesting it does). If we assume it gets to the same roll control as the ROW 030 setup, then the PSS9 must be much stiffer in pitch than the factory setup. Driving down the street, the PSS9 should bob up and down much more than the 030. Maybe you like that sort of thing, maybe you don't. Bear in mind that race tracks in Europe are smoother than ones in the US (generally), so the PSS9 might work really well in Europe but not as well in the US. I don't mean to rag on the PSS9, since I'm sure it's excellent in its own right, but one just needs to understand what it is they're handing over their Benjamins for.

My 944 Turbo had Koni coil overs front and just heavier rear torsion bars. If I wanted to adjust front/rear springing, I could swap out the front spring. It had Koni shocks all around, so if I wanted to adjust transient behavior, no problem. And I stuck to M030 anti roll bars. So with camber adjustments, I limited the variables to 5: single adjustable (bounce) dampers front and rear, front springs, camber, and rear anti roll bar soft, medium, firm. For the Boxster, it's ROW M030, period. No muss, no fuss."

Sorry just seeing your additional comments here now. You hit the nail on the head with the above. Is there significant anti roll rate incorporated in the PSS9 set-up and if so how much? Will I be loosing my fillings with it on my car ...street or track? What bars are a suitable match? I have been urged to go PSS9 but will be upset if I end up bobbing and weaving down the road. I am doing that now as my stock S dampers are done; too scary over surface changes at speed.

Are you suggesting to go with the ROW M030 bars AND coil overs for the optimum arrangement (Boxster)? Not sure they are going to be making this much longer and sooner later we will all need another set of components....
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Old 04-02-2013, 08:59 PM   #8
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No posts by hcj986s since June 2011 ... don't hold your breath on an answer.

I've recently installed the RoW M030 and I'm very pleased with the street improvement. The new struts absorb much more than the 71k miles struts did and on track I get better turn in than previously, so I can carry more speed through the turns.
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Old 04-03-2013, 04:21 AM   #9
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There's no reason the PS9's would inherently "bob up and down" or rattle your fillings. That's the beauty of coil-overs, you have a huge selection of spring rates to choose from, to deliver the ride/performance you desire. You could fit springs softer than stock, or as stiff as a rock. Do a search on PS9's, I think Insite had lots of information on spring rates in his thread. There is no ONE optimum solution, everything is a compromise, and heavily dependant on your personal desires and vehicle usage.

Correction: insite's thread was on KS coilovers, but the spring rate information should still be valid.
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Old 04-03-2013, 04:28 AM   #10
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jaykay -

much of the information in that post misapplies sound science to draw INCORRECT conclusions. bobbing up and down the road' (known as porpoising) has nothing to do w/ roll bars & everything to do with ride frequencies (long story). his deduction that PSS9 are 'stiffer in pitch' if they 'match the roll control' of M030 just doesn't make any sense. it is the ratio of front to rear wheel rates that determine bounce frequency & the ratio of single axle spring rate to (single axle spring rate + anti-roll bar rate) that determines sway frequency.

gobbledygook aside, EXPERIENCE tells me that PSS9 is a well engineered system that works well with any number of sway bars. for the street, i like M030 S front & M030 base rear. for the track, i like GT3 front w/ H&R rear on half-stiff.

the PSS9 does not 'bob up and down the road' with any of these setups, as roll-bars have little to do w/ porpoising.

FYI: it is the ratio of front wheel rate to rear wheel rate combined w/ wheelbase length that ulitimately determines whether a car will porpoise. imagine going over a speed bump: if the spring rates are the incorrect ratio w/ respect to one another, the rear of the car will pich up as the nose is diving. when the nose of the car comes back up, the rear will squat. basically, the nose & tail of the car would be doing opposite things at the same time. the result is a crappy ride.

a properly designed suspension will attempt to move front & rear suspensions in phase with one another. this results in the entire car moving up & down a bit, but not diving & pitching.

hard to explain; hope it makes some sense.
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Old 04-03-2013, 05:18 AM   #11
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Originally Posted by BerneseMtnDog View Post
I just got my 986 kit today from Design 911 and I don't know which is front and rear but one pair shows red/red on one end with green on the other while the other pair shows red/yellow on one end with blue on the narrow end. Hope this helps.

Steve
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Search this document on internet 986_USA_KATALOG.pdf You will need to refer to the last section for model year codes and options.
It show that you probably have m030 Row springs Red/Red front Red/Yellow rear
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Old 04-03-2013, 05:32 AM   #12
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properly designed suspension will attempt to move front & rear suspensions in phase with one another. this results in the entire car moving up & down a bit, but not diving & pitching.
Thanks for jumping in insite! IIRC the rule of thumb is that the rear ride frequency should be 10% higher than the front to minimize pitching.

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Old 04-03-2013, 05:46 AM   #13
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jaykay -

much of the information in that post misapplies sound science to draw INCORRECT conclusions. bobbing up and down the road' (known as porpoising) has nothing to do w/ roll bars & everything to do with ride frequencies (long story). his deduction that PSS9 are 'stiffer in pitch' if they 'match the roll control' of M030 just doesn't make any sense. it is the ratio of front to rear wheel rates that determine bounce frequency & the ratio of single axle spring rate to (single axle spring rate + anti-roll bar rate) that determines sway frequency.

gobbledygook aside, EXPERIENCE tells me that PSS9 is a well engineered system that works well with any number of sway bars. for the street, i like M030 S front & M030 base rear. for the track, i like GT3 front w/ H&R rear on half-stiff.

the PSS9 does not 'bob up and down the road' with any of these setups, as roll-bars have little to do w/ porpoising.

FYI: it is the ratio of front wheel rate to rear wheel rate combined w/ wheelbase length that ulitimately determines whether a car will porpoise. imagine going over a speed bump: if the spring rates are the incorrect ratio w/ respect to one another, the rear of the car will pich up as the nose is diving. when the nose of the car comes back up, the rear will squat. basically, the nose & tail of the car would be doing opposite things at the same time. the result is a crappy ride.

a properly designed suspension will attempt to move front & rear suspensions in phase with one another. this results in the entire car moving up & down a bit, but not diving & pitching.

hard to explain; hope it makes some sense.
You explained it fine and it makes sense. I always like to hear what others have to say; I didn't necessarily agree with it. I think he assumed that a lot of roll control rate must be incorpated in the PSS9 spring rates giving a very stiff ride leading to proposing. The gentleman seems to have reversed his camber change assessment with what actually happens

Yes when it come to suspension, theory is not always supported by testing
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Old 04-03-2013, 05:56 AM   #14
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My PSS9 car is running stock PSS9 springs and does not pitch, nor is it overly uncomfortable on the street. I have been in other PSS9 equipped cars where they ran too much spring rate and were harsh and gave away grip on corner exit (excessive wheel spin). Getting the setup right is important with coilovers.

M030 is Porsche-tuned and you just bolt it on, align and go for 90% of PSS9 effectiveness. A lot of value for the $$.
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Old 04-16-2013, 08:59 AM   #15
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guys -

i found my reference sheet with spring rates from various setups (M030, PSS9, etc.)

i will post it when i get home. it has F/R rates & ratio to stock.
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Old 04-16-2013, 01:51 PM   #16
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here is my list of spring rates. for some reason, stock is not on here; i will look for it. the first column of percentages gives an idea of F/R ratio. this plays into ride frequency. the second column of percentages shows stiffness relative to M030.
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Old 04-16-2013, 01:52 PM   #17
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oh, and the first column is in lb/in and the second is in kg/mm
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Old 04-16-2013, 04:16 PM   #18
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Sorry, I did not realize that this was such an old thread. Insite, thanks for the spring values, I've been looking for those.
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