Stretch, what's the better springs/shocks setup?

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I thought others would be interested too, so i figured I'd ask it publicly.

Stretch, I've read a lot of your posts in the last couple days and I highly respect your opinion and knowledge. I'm confused about a few things and I'm hoping you can clarify it for me, or at least let me know what you think about it.

I've heard a lot of good things about autoexe (ie. they are reputable and do a lot of testing on their products), and you say RPM's new springs will be one of the best, but I notice the spring rates on the two brands are very different (rear, anyway). RPM's firm set is 380 front and 290 rear. Autoexe is 370 front and 225 rear. I don't autocross (although I might later) and I'm fairly tolerant when it comes to ride quality, and if the handling is going to be that much better, and price isn't a huge issue when the difference is $100-$200. Do you think RPM or autoexe took natural frequency into consideration? and if one of them did, would you suspect it was autoexe? Which one in your opinion is the better one terms of performance?

Koni's are great shocks, but in a link you posted (http://www.wincom.net/trog/autocross_secrets6.html) this guy says bilstein is better if you don't need adjustability... and if you do want to adjust shocks, you should do it on a shock dyno (which I have no idea how to get access to anyways). Also, if you were to adjust them, you would just set them to 65% critical dampening and leave it at that (according to the article). I would expect the non-adjustable bilstein's to be set up at a good dampening by default. As a plus, the bilsteins are cheaper than the konis. Which one would you recommend?

If parts of my post don't make sense, I apologize, I'm still new to this.

Cheers and TIA.

[Stretch]

I'm going to try to answer this question a little vaguely so that this may help everyone regardless of which two specific springs or shocks they're looking at.


On shocks:

Dampers (shocks) are valved for a specific natural frequency of the vehicle. Since the Mazdaspeed6 is a heavier vehicle than the normal '6, and adding weight lowers the natural frequency of the vehicle, the Bilsteins will be able to handle firmer springs on a Mazdaspeed6 than on a normal Mazda6. Similarly, springs designed to feel stiff on a normal '6 will feel softer on a Mazdaspeed6. Take that into account when reading reviews of suspension products, most of which were designed for a 600lb lighter Euro or JDM 4cyl Mazda6.

Now, to get to your question: the Bilsteins would likely be the better product if you could revalve them yourself to match your springs. Unless you have the means to take apart the shocks, rebuild the shim stacks, and then pressurize the assembly again, then I'd be a little cautious with buying Bilsteins. We don't know what they're valved for- maybe Bilstein will tell us what natural frequency they targeted. However, it's a pretty safe bet that the Bilsteins would be underdamped on the K-Spec springs.

The Koni's don't have that problem since they can be adjusted to match whatever spring rates you wish. The valving is excellent (like the Bilsteins), but the problem with Koni's (as stated in that article) is the difficulty in being able to adjust the left and right shocks to equal stiffness. The adjustments are very sensitive and hard to make precisely. This is a problem with nearly all adjustable shocks, even Bilstein's own adjustable parts (actually more so). That article does go on to call Koni's a fantastic value, etc- they're still an incredible product. And for the Mazda6, they're kind of the only game in town if you like to pick your own spring rates (which requires adjustability).

Believe it or not, shock adjustability is not usually desirable. I've read this several places: you want your shocks to 65-70% critically dampen your springs, that's it. This is the "perfect" setting for both daily drivers and track cars, so there's never a reason to adjust your shocks. They just need to be matched perfectly to your springs. Bilstein non-adjustable shocks would therefore work great if only we knew what springs (er- natural frequency) they were tuned for so people could run ONLY that EXACT rate. However, in the absence of knowing this value or having fancy accelerometer data logs, your best bet is going to be Koni's stiffened to your own preference (likely close to full soft, but not quite).

One comment I will add is that I think it is extremely common for those with adjustable shocks to make them too stiff. Again, your Koni's should be set close to full soft on most aftermarket springs. Shocks determine your ride quality more than any other part, so if you're uncomfortable, chances are you're suspension is overdamped. Soften your shocks. Going too stiff only decreases your performance!


On Springs:

The natural spring frequency is how quickly it takes a spring to bob up and down one oscillation. Choosing springs is all about choosing your spring frequencies front and rear. Dennis Grant, the author of the article you linked to, says this regarding springs ( http://www.wincom.net/trog/autocross_secrets5.html ):

... Rule of thumb is rear [natural frequency]slightly higher than front (by a tenth of a Hz or two). Street car: 0.8 Hz. Occasional autocrosser: 1-1.5 Hz. Full-bore autocrosser: 2.2-2.5 Hz. Yes, it really is that simple.[/b]

The stock Mazda spring rates are a mystery to me in that I do not understand why Mazda continuously goes so soft in the rear. The choice of spring rates does not make sense to me. AutoEXE goes even further away from having equal natural frequencies front and rear, which I understand even less. The general rule of thumb (taught in most vehicle dynamics textbooks) is to have a firmer natural frequency in the rear, as Dennis says, so that the front and rear springs settle at the same time after a bump. If you haven't already, plug in the spring rates to my spring frequency calculator to see how far off from a "flat" ride even a standard '6 is:
http://forum.mazda6club.com/index.php?showtopic=75618

RPM's springs get us closer to an even front and rear natural frequency, even though they're still not really close. At least they're off by less. The result of this should be bumps having a closer-to-equal impact on the chassis front and rear. I'd love someone to experiment with firmer springs in the rear than front- that's what I think the car really needs (due to the motion ratios, your rear wheel rate (spring rate at the wheels) wouldn't necessarily be higher. I would very much like to try a Mazdaspeed6 on 900lb/in front, 1336lb/in rear spring rates, Koni's, and R-compound tires. But anyway, I'm digressing.

Let's just ignore all the theory on what an ideal natural frequency should be since Mazda clearly ignored convention when selecting the stock springs. I don't think too many will dispute that the Mazda6 understeers too much. One main reason this happens is due to excessive body roll, which makes the front tire go off camber. Camber is the angle of the tire in relation to the asphalt, and you want the tire to be perfectly perpendicular for best grip. If your car rolls three degrees in turns, odds are your tires are off two degrees from perpendicular, which reduces its grip. A stock '6 has no camber adjustment, so the best way to optimize your camber (and grip) up front is through an adjustable upper ball joint, which will allow you to add two degrees (or more) of negative camber.

In the absence of a way to adjust camber, the best way to minimize camber loss is by reducing body roll. Both AutoEXE and K-Spec springs reduce body roll by firming the spring rates, and this is extremely important for anyone who does not have adjustable upper ball joints (camber adjustment) installed. The reduction in body roll is generally minimal (even though from inside the car, it can feel significant) with lowering springs, but every little bit helps a lot.

However, AutoEXE increases the spring rates primarily up front, meaning it is increasing load transfer in the front of the car. Increasing load transfer reduces grip by putting too much weight on one tire, over-saturating it. So, in this case, increasing load transfer will cancel out some of the newfound front grip from reducing body roll. I find this undesirable, especially since the front of the car has an open differential. Any car with an open front differential will want as little weight transfer up front as possible to prevent the inside tire from spinning under throttle.

RPM increases the front spring rate too, but increases the rear spring rate proportionately more. This will reduce body roll even more than the AutoEXE springs, but also shifts some of the vehicle's load transfer from the front to the rear tires. The result is reduced understeer from reducing body roll and a further reduction in understeer from shifting load transfer from the front to the rear. Since the rear of the car has a limited slip differential, this should work great (and even in FWD Mazda6's, we're still helping the front tires).

Nearly everyone has had favorable comments on the behavior of the car after installing a larger Whiteline rear sway bar. The RPM springs get you that performance without the sway bar installation. Now, should you want even less understeer, RPM spring owners still have the option of installing the Whiteline sway bar. Since the Whiteline bar is the largest that will fit in the rear, AutoEXE spring owners have no further course of action for increasing roll stiffness in the rear. They're stuck with whatever handling bias they have.

A front wheel drive car (or a front-biased AWD car) will almost always have understeer under throttle. This can't be tuned out, only reduced- it's the nature of putting down power through the front wheels of a car. If you don't think the stock Mazdaspeed6 has understeer, you'll probably think AutoEXE springs are nice. They'll stay closer to the stock handling bias. The RPM springs look to change that- a change I very much recommend. I don't think the change will be too drastic, but it'll surely a step in the right direction.

RPM's springs were also designed to retain some suspension travel (thus why the "normal" springs do not lower as much), which is so often ignored with lowering springs. Let's face it, looks sell. All the big lowering spring companies know this and prioritize looks over functionality to create that perfect dropped look. I know RPM and I had a few discussions over producing a lower (better looking) drop versus going with a minimal drop and ultimately better performance. Having sufficient bump travel in your shocks is absolutely paramount to ride quality and handling. Since Koni's add suspension travel, RPM's K-spec springs lower the car more because they can. The stock struts do not have bump travel to sacrifice to lowering, and so if you must keep them for cost reasons, less is definately more regarding lowering. RPM springs have, I believe, the most conservative drop on the Mazdaspeed6 much like Racing Beat is to the standard '6. Because of this, they are very likely your most comfortable spring option, too (though I'm sure opinions will vary).


On reputations:

I'll rant here, if you don't mind. I really like the article you linked to: Dennis Grant (Wikipedia link) ranting about shocks ( http://www.wincom.net/trog/autocross_secrets6.html ). I had the opportunity to talk to the author of that article on the STI forums, where he said this:

Don't let "race team XXX uses them" fool you either, especially in more expensive series like ALMS. Money brings along a reality distortion field with it; there are tons of teams who, because they have money, think that everything they touch is pure gold and they will cheerfully ignore evidence to the contrary. One of the biggest shocks I got during my racing career was discovering how insanely poor the engineering was at most pro race teams - not just SCCA, but ALMS, IRL, CART, NASCAR.... the number of real live pro race teams out there who take the engineering professionally is distressingly small.[/b]

How many autocrossers- even myself, and I know better(!!!)- set their shocks much too stiff on autocross day? That's a horrible idea! Now, Dennis made this comment regarding coilover selection, but there are an incredible number of examples of poorly engineered products that see widespread use in racing series. I don't know what the statistic is, but I'd wager 80% or more of all car purchases are made over aesthetics: how a part makes the car look or sound fast. The slang for these parts is more commonly known as "rice". Seeing as that's where the money is, I think that's why you see so many show (or under-engineered) parts in race series. Always follow the trail of money.

Most lowering springs put the car well onto its bump stops and should be considered for looks only. Look at what K-Sport was shipping as rear shocks with their coilover kits- they had NO bump damping at all! I mean, what the hell?! Look at all the cross-drilled rotors out there- garbage show car parts marketed as racing equipment. How about tornado fuel savers, fuel magnets, etc? Intercoolers with garbage end tanks, short ram intakes that draw in warm air, cold air intakes that throw important sensors out of calibration- the market is filled with all of these. How about strut bars on a car that doesn't even have struts? Long story short: I think most aftermarket part manufacturers are run by enthusiasts who know what looks good (and sells), not engineers who know what performs good. Look at the incredibly in-depth data Custom Performance Engineering just released on their front mount intercooler- how often do you see a company do that? Almost never. Most don't have that data to publish.

One of the things I always try to do when replying to questions like these is to state why I have the opinion I do. I could have just answered your question, "Koni, RPM", but then you wouldn't understand how I arrived at my conclusion and whether or not you should disagree with it. The bottom line is that you need to think for yourself and do your own research when selecting car parts. Demand data. If you can't get it or the data doesn't make sense (I've seen data that could only have been made up), don't buy the product. If the subject matter is too complex for you to understand (I often feel that way regarding ECU tuning), then you're unfortunately forced to roll the dice and go with someone else's recommendation. And, unfortunately, you can never really know if that someone else is trustworthy- not even me. (Some of my old recommendations were terrible!) So, with that said, I hope I made everything easy to understand so that you can make the best decision for you!

[mazda6club6]

This is very helpful. Now I'm wishing RPM had more of the prototype 1/2" drop springs.

[Japan8]

Glad I snapped up the last set of "mild" prototype springs...

Nice write up stretch!

[Stretch]

Thanks guys. I hope it's helpful. I just went through and edited the post again to hopefully make it more straightforward. Let me know if any parts are still confusing.

Maybe I can just copy and paste that post when someone PM's me the exact same question later today.

[mick_estes]

Maybe I can just copy and paste that post when someone PM's me the exact same question later today. [/b]

So I guess I can delete that PM that's been sitting in my unsent box But seriously, thanks for the detailed and informative writeup. I've been pondering this question, reading (& rereading) every post/link on this topic that I can find and I'm glad encrypted started this thread.

Elsewhere I've read that its advisable to first get springs until you find the stiffness, ride quality etc that suits you and THEN get thicker swaybars, if needed. Do you agree?

I don't have plans to autox but I'm not really satisfied with the stock ride either. Aside from the understeer, my only other major complaint is in high speed sweeper curves (e.g. exchange ramps from one freeway to another) where the car seems to get a little floaty and just doesn't feel planted.

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Thanks Stretch. I appreciate the informative answers you give, and it's one of the reasons I respect your answers so much. In regards to the Konis vs Bilsteins, I will try to find someone with a shock dyno, but failing that, is it better to have 4 bilsteins that match (because they're suppose to match pretty good by default) or 4 konis that don't? or are you saying that setting the konis at close to full soft will make them all the same. How would you set them to "close to full soft"? - All the way to soft, then 1/8 turn toward hard? Or would I just drive around in them, take some corners, and adjust as I see fit?

[Stretch]

Elsewhere I've read that its advisable to first get springs until you find the stiffness, ride quality etc that suits you and THEN get thicker swaybars, if needed. Do you agree?[/b]

That's pretty common practice on a race car where sway bars are usually pretty small in comparison to the spring rates. Those guys use sway bars to fine-tune the handling bias of their vehicle (minor changes), and some don't run sway bars at all. As said earlier, an autocrosser will often set their spring frequencies at 2.2hz front, 2.5hz rear and be done with it. From there, they dial in over or understeer by adjusting their sway bars if needed.

On a street car, sway bars are necessary to limit body roll while maintaining good ride quality. Half of your roll resistance might come from the sway bars, making them the most important components for reducing body roll or dramatically reducing understeer. Because of this, sways can be a very, very effective first modification especially for someone who wants to maintain their stock ride quality.

I haven't tried all the various Mazdaspeed6 parts, so I'm not familiar with how drastic of a change each makes. On a standard '6, the RB rear sway bar was an easy recommendation for a first modification. You went from an 18mm rear bar to a 27mm rear bar, something like a 400% difference in resistance (which was very much welcomed). On the Speed6, going from stock to the Whiteline bar is only a 1mm difference which, IIRC, equates to a 30% bump in stiffness. That's tiny in comparison, so you will probably notice more improvement from springs.

It's up to you. I guess my only advice would be to do shocks and springs at the same time. The combination should definately give you the more planted feel you seek.

Thanks Stretch. I appreciate the informative answers you give, and it's one of the reasons I respect your answers so much. In regards to the Konis vs Bilsteins, I will try to find someone with a shock dyno, but failing that, is it better to have 4 bilsteins that match (because they're suppose to match pretty good by default) or 4 konis that don't?[/b]

Let's not make things too complicated- I don't think you need to. Heck, I don't know how to do the math (nor would I have nearly enough measurements) to predict the optimal spring rate to mate with a Bilstein shock by looking at a dyno. Sorry! You can expect both the Bilstein and Koni dynos to look very digressive in the bump valving, just like most people would want. They're both good companies.

Let's just wait for some user reviews to come in on the Bilsteins and hopefully, someone who knows what they're talking about will say whether they are overdamped or underdamped for the springs they're running. The important thing is that the shocks match the springs. Having shocks that match each other is irrelevant if they aren't paired with the right springs! (Of course, since your spring rates match left and right, so should the shocks.)

The thing is, I think the Mazda6 (and Speed6) will respond very well to having much firmer rear spring rates. If the Bilsteins are tuned to springs anywhere close to stock, then they're not going to be happy with springs that are much firmer in the rear. Ultimately, then, that means you're stuck with "understeer springs" if you chose Bilstein. On a regular Mazda6 with the optional huge RB rear sway bar, that's not the end of the world. On a Mazdaspeed6, it's a deal breaker (in my opinion).

or are you saying that setting the konis at close to full soft will make them all the same. How would you set them to "close to full soft"? - All the way to soft, then 1/8 turn toward hard? Or would I just drive around in them, take some corners, and adjust as I see fit?[/b]

Regarding adjustments, it's pretty simple-

If the car feels floaty, bouncy, or uncontrolled- stiffen the shocks.
If the car feels uncomfortable, momentarily feels light, or tends to skip over bumps- soften your shocks.

To adjust your left and right shocks equally, simply turn the knob equal amounts. That's all there is to it, at least for a road car. You're right- start at full soft, then count the amount of turns from there. Only make sure your left and right shocks are set equally, it's totally OK to see the front and rear to different stiffnesses. They're different parts.

Here's the part on rebound damping from Koni's guide:

... It should be noted that too much rebound on either end of the vehicle will cause an initial loss of lateral acceleration (cornering grip) a that end which will cause the vehicle to oversteer or understeer excessively when entering a turn. Too much rebound control in relation to spring rate will cause a condition known as "jacking down." This is a condition where, after hitting a bump and compressing the spring, the damper does not allow the spring to return to a neutral position before the next bump is encountered. This repeats with each subsequent bump until the car is actually lowered onto the bump stops. Contact with the bump stops causes a drastic increase in roll stiffness. If this condition occurs on the front, the car will understeer; if it occurs on the rear, the car will oversteer.

STEP 1: With rebound set on full soft and the bump control set from your earlier testing, drive the car one of two laps, paying particular attention to how the car rolls when entering a turn.

STEP 2: Increase rebound damping three sweeps (or 3/4 turn) on all four dampers and drive the car one or two laps. Repeat Step 2 until the car enters the turns smoothly (no drastic attitude changes) and without leaning excessively. An increase in the rebound stiffness beyond this point is unnecessary and may result in a loss of cornering power. Note: As with the bump settings, this point will probably be reached at one end of the car before the other.

However, individual drivers may find it desirable to have a car that assumes an oversteering or understeering attitude when entering a turn. This can be easily "dialed-in" using slightly excessive rebound settings at either end.[/b]

Changing the subject back to spring rates again- would you like to experiment? I have an idea.

I wonder if RPM would be able to obtain some D2 or K-Sport rear springs, which are 9kg/mm (roughly 504lb/in). They're pretty cheap, as I recall. I'd be very, very interested to see how they perform combined with RPM's existing K-spec front springs. Your final spring rates would be 380lb/in front, 504lb/in rear. Your spring frequencies would be 1.29 front, 1.36 rear (assuming 3800lb wet weight with driver)- still fairly soft overall and well below a stock STI or Evo. If I had a Mazdaspeed6, that's what I would try.

Even on my lightweight 6i, the 500lb/in rear springs were totally comfortable with Koni's set 1 turn from full soft. I ran that for a while. My spring frequency in the rear, since my car was 500lbs lighter than a Mazdaspeed6, was a much higher 1.5 in the rear. I ran 11kg/mm (615lb/in) front springs with them, which was understeer city. I bet using RPM's 380lb/in front springs would work far better.

For what it's worth, I currently run a spring frequency of 1.78 front, 1.93 rear with Koni's on my STI. I consider these daily driver spring rates- most people run much higher. Stock is roughly 1.59 front, 1.79 rear on an STI. A stock Mazda6 is roughly 1.0 front, 0.6 rear! Ew!

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RPM with Konis it is! Thanks a lot!

[Stretch]

No prob. Maybe you can change the title of this thread to, "Stretch's dissertation is spring and shock choices." I can't believe how late it is- I wasted half the day talking about this stuff!!!

In the spring frequency calculator thread, I posted some calculated spring frequencies for the base Mazda6 and Mazdaspeed6:
http://forum.mazda6club.com/index.php?s=&a...t&p=1017876