I arrived in Taiwan yesterday and started my 3-week coilover research and design "project". The goal of this project is to gain as much hands-on experience working with and designing dampers as possible at the source (yes, I said the source), to gain a better understanding of how dampers work, and what we want a good set of coilovers to do for our cars. Of course, we don't all drive the same car, so my goals are generalizations mostly, methods that can be universally applied. I don't have a ton of money or access to any sort of high-tech equipment, so my methods aren't particularly "scientific". I'll try and get as clsoe as possible though with what I have at my disposal. The biggest benefit I have here is access to all the cars I am concerned with, a lift, and a test track of sorts. With that, I am confident that I can come out of this with relatively accurate numbers and a good feel for how these numbers relate to the end product. Our goal is NOT to clear up misconceptions about Taiwan and the coilovers that come out here (excluding our own, of course), or dig into other peoples' business.
With that in mind, my agenda for the rest of this week is to get measurements on the WRX, Evo, and 92-95 Civic, 96-00 Civic, and 94-00 Integra. We'll be using these measurements to determine motion ratios, wheel rates, all that good stuff. Unfortunately, I wasn't able to get my hands on the Millikens' RCVD book, so I'm left with internet formulae and procedures, which, while not as in-depth as SAE stuff, is good enough for initial numbers. In the coming days and weeks, I'll be test fitting various springs (and therefore valving) on these cars to determine how these numbers actually affect driving feel and performance.
If you remember in my Wheel Travel thread, I was more concerned with how Total Wheel Travel plays into spring rate, but it looks ilke Suspension Frequency is a more solid starting point. Why? Seems like suspension frequency numbers, unlike wheel travel, can be generalized from application to application, whether its a Civic or a school bus, because it relates to the human body's preference and natural comfort levels, not the car's. And (hopefully) with that we can derive more accurate spring rates. We'll see about that though.
I will keep this thread updated over the coming weeks with pictures and findings. We definitely have some knowledgeable people here on H-T so I look forward to your feedback as well.

 

No pics, because I haven't brought the drivers for my card reader with me. But I have learned some interesting things in the past few days.
Most interesting is the matter of adjustable dampers, monotube to be specific. Actually getting precise clicks is difficult due to the way the adjustable cores are manufactured. Even if you don't use clicks, its common to see the same cores produce different levels of adjustment, eg. 12 levels of adjustment can be the spec, but you might come out with 13, 14, 9, 11, etc. This has been a major headache...
Another is the matter of macpherson suspensions, and how to properly determine their motion ratio. Theoretically the motion ratio is 1:1 but from what I've read that is hardly ever the case, but so far I can't find the proper way to determine a macpherson's suspension MR so I've been using 1:1 for all of them. I'm using the distance from the chassis pivot point to the outer ball joint as D1, thats easy. But for D2, I'm using the distance from the chassis pivot point to the lower shock mount. On independent suspensions, this is standard, but on the macpherson suspensions, its different, since you are only measuring an empty space, not an actual control arm like on the independent suspensions. Here is what I am talking about:

The results yield pretty much 1:1 motion ratios for both the WRX and Evo. So for the moment, we will be using 1:1 unless someone can suggest an alternate method for measure the D2. We've had the Evo8 and a WRX up and measured, I just haven't gotten the opportunity to do the measurements because its been a busy past week or so. We got tripped up with these two cars due to them being customers' cars, and so we couldn't remove the individual components to measure their weights; we were relegated to estimations, but I'm confident these estimations are close, or close enough that our calculations won't be terribly far off. The Hondas shouldn't have the same problems as they are our own cars.
I'm still up in the air about pillowball mounts and how necessary they are for any application...
The Taiwanese market is currently flooded with cheaply manufactured coilovers, thats no surprise. A quick glance through the local car mags confirms this, plus there are a lot of horror stories. There's still hope though, its just a matter of raising production and quality standards and instituting stricter tolerances. Also, there is a good amount of shops here that produce top-notch products, so its not like they don't exist. Its just that they are the exception and not the norm.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Noob4life &raquo;</TD></TR><TR><TD CLASS="quote">Another is the matter of macpherson suspensions, and how to properly determine their motion ratio. Theoretically the motion ratio is 1:1 but from what I've read that is hardly ever the case, but so far I can't find the proper way to determine a macpherson's suspension MR so I've been using 1:1 for all of them. </TD></TR></TABLE>
The motion ratio for a strut will never be 1:1, that is a common incorrect assumption. Remember that if you are comparing the damper motion to the wheel motion, it is the centerline of the wheel or the hub itself and not the outer ball joint. Most struts are closer to the .9 range, I don't think it could ever be 1:1 if a wheel and tire are actually installed unless some extremely convoluted design is used to regain some motion. You really should take an actual car, remove the spring and the wheel and tire and incrementally take it through the normal motion range and take real measurements. The is the best and really easiest wayto do it, you could plot it in a computer program but you would have to get so many other accurate measurements from the suspension that you may as well take the actual measurement that you need.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Noob4life &raquo;</TD></TR><TR><TD CLASS="quote">I'm still up in the air about pillowball mounts and how necessary they are for any application... </TD></TR></TABLE>
Not, unless your goal is to use a typically non-sealed bearing that can wear prematurely and that will allow no isolation of unneeded road and suspension energy directly to the chassis.

 

Sounds like a cool project.

Were you able to get Gillespie's book? If so, Chp 5: Ride gives pretty good methods of calculating front and rear frequencies as well as bounce and pitch frequencies. Don't let any of these get much above 2Hz or your passengers will be upset and so will your tires (which is more important).

I agree with CRX Lee about measuring the MR. Run three trials to see if the MR equation varies much =&gt; error in measurement.

 

TY for the info guys. I don't think I'll be able to get any more time with the Evo and WRX since I am leaving the for Taipei tomorrow morning (I'm like 5 hours away), and they were donor cars from customers. I'll see what I can do with the EG and my Integra though, as far as testing my MR #'s.
Unfortunately I'm having a hell of a time finding Gillespie's and Milliken's books here in Taiwan, that will also have to wait until I get back to the states. So this kind of sucks because my numbers and calculations won't be as thorough as I would have liked them to be.
BUT, I have managed to get some rough #'s from the EG and WRX we measured so far, and the results are interesting. Yes, weights were estimated, and yes, my MR's for both may be off, but I think both were slight. Or slight enough that it would not change the end results drastically, or affect our choice of springs. You'll see what I mean.
Using 120 CFM as my target suspension frequency, these are the numbers I came outwith:
EG (sedan)
Front Driver's Side Spring Rate: 9.17kg/mm (514lbs/in)
Front Passenger's Side Spring Rate: 9.5kg/mm (532lbs/in)
Rear Driver's Side Spring Rate: 4.8kg/mm (274lbs/in)
Rear Passenger's Side Spring Rate: 5.6kg/mm(318lbs/in)

WRX (sedan)
Front Driver's Side Spring Rate: 5.6kg/mm (317lbs/in)
Front Passenger's Side Spring Rate: 5.5kg/mm (312lbs/in)
Rear Driver's Side Spring Rate: 4.12kg/mm (231lbs/in)
Rear Passenger's Side Spring Rate: 3.6kg/mm (200lbs/in)

On the car's, we made sure that there was nothing in the car that would upset its balance from the factory (eg. the trunk was empty, etc). Swaybars were NOT disconnected. For unsprung weight calculations, shock/spring and LCA weights were halved. D1 and D2's distances used in the motion ratio calculations were measured flat, unlike the illustration above. Distances measured using the method in the illustration above would still yield the same ratios IMO since the angles were not THAT terrible, although I'll post up some pictures as soon as I can for you guys to judge.
Considering the spring rates we have available, however, I feel that more precise measurements would still result in the use of the same spring rates. Eg. we came up with 4.12kg/mm suggested spring rate for the WRX's rear passenger side, and while more precise measurements might yield 4.78kg/mm or 3.9kg/mm, we would be using 4.5kg/mm springs either way, since those are the closest rates we have at our disposal.
I was absolutely giddy while doing these calculations. It looks like some of the spring rates that we are used to seeing are correct (500lbs/in springs up front for the Civic), and some are pretty far off (300lbs/in out back). However I understand that we might be missing something here, so I'm not saying that these numbers are fact. Nonetheless, they are interesting. Needless to say I will be picking up the Millikens' and Gillespie's books as soon as possible. Let me know if any of this seems way off though, and if you think that more accurate measurements would yield dramatically different results. Again, I haven't taken tires into account here, but the more I think about it, the more it seems like they are a variable that simply cannot be accounted for due to customers using all different types of them. Sort of like the weights for the LCA's and shock/spring combos; for those, we used factory weights.

 

Looks good so far. 500/300# seems to be what some of the other aftermarket kits are selling.

So you now have spring rates based upon a desired front/rear frequency. One problem is that bounce and pitch are not decoupled, but what you have is fine. These would be possible spring rates if you only cared about ride ("ride" doesn't mean "comfort"; it is vehicle motion without considering "roll"). You can do calcs to find the roll moment front and rear and then find the roll moment distribution. You will want it to be closer to rear biased than what you already have, but don't go too extreme or you may risk problems with people spinning themselves into walls. Things get more comprehensive from here, so if this is a universal kit, then you might do more harm than good by getting more complex. However, you can determine the "yaw gain", which is the theoretical increase in yaw angle per degree of steer. It basically tells you the tendency of the car to spin when you steer it. Both books have the equations...let me know if you need me to look them up for tomorrow.

 

The more I get to thinking about these results, the more worried I am For one thing, the 10kF/8kR springs on the WRX I've tested felt perfectly fine, not uncomfortable at all, and even during longer drives its not uncomfortable. But those spring rates should be well upwards of 150 CPM, which according to the suspension frequency theory should be highly uncomfortable. Same goes for the EG and my DC2, they don't follow these results but are still comfortable.
So I am wonderin this about suspension frequency: other than comfort levels, is this a good way to calculate spring rate? Comfort is a relative term, so maybe some can tolerate CPM's of 200+, and some can't?
Also, I learned this recently. The factory that I have producing my prototype coilovers has tested 6kF/4.5kgR springs before on an EK hatch in the past, and when the car is lowered onto the ground the shocks will be compressed until there is only roughly 15-20mm of shock travel left. According to these formulas, these spring rates are adequate, using 120 CPM for suspension frequency. But when you actually go to apply these numbers in the real world, it doesn't work. The shocks we are using are short-travel shocks to begin with, if that matters.
So now, I am also wondering if there is something I am leaving out of my calculations that would account for this problem. Should I be accounting for shock travel somehow? Is suspension frequency only useful in determining ride quality, and not for performance purposes? I'm also entertaining the idea that my weight measurements are just way way off. In any case, I'm told that 4.5kg springs are simply too soft for our independent rear suspension cars, and 6kg springs are too soft for the front. ANd yet my calculations say otherwise. Where could the discrepancy be? I've been seriously racking my brain all day about this, I can't figure it out and it bothers me.
Again regarding suspension frequency, I'm now told that for daily driving purposes and putzing around town, a lower suspension frequency in the front and higher in the rear is preferred. And for racing purposes, the opposite is true. First off, is this true? Secondly, does this account for why so many japanese touring cars choose to use much higher front spring rates than rear?
Lastly, how is suspension frequency related to a car's drive layout? As far as I can tell, suspension frequency (and so ride comfort) is independent of this. BUT, if we are using suspension frequency to determine spring rates in the end, it *should* matter, no? I mean the car's drive layout plays a huge part in its handling characteristics, so it should somehow be accounted for. But I don't know how to do that. If I simply go by my numbers, then a WRX should be running 5kgF/4kgR springs. I'm told that these are way too soft (by the factory, who has tried this combo), and at least 8kgF/6kR is necessary (which does not follow the suspension frequency idea but as you can see I'm still not too sure about its validity anyhow).
Sorry, this post is all over the place and I'm sure it sounds crazy, but I am definitely going a little crazy here. Nothing seems to be working out and I'm still unclear on the whole suspension frequency idea.

 

First off, you said that the frequencies you desire were obtained from a table listing human tolerances to vibration (or something like that). A well performing system will most likely not be comfortable. My car is rough as ****, but feels great on a track.

Secondly, the desired frequency is not going to equal front and rear (see above post)...equal frequencies means that bounce and pitch are decoupled which they aren't. You have to choose a good frequency to try and obtain.

Third, what the hell is CFM? I only work with Hertz or at least rad/s.

The compromise for choosing a suspension frequency is to choose a freq that provides stiff enough control (in pitch, roll, bounce, etc.) to keep the tire on the ground, while not going so stiff that there is too much (and too fast tire force generation).

Read my post above. Here's the equation for yaw rate gain. [Note I am pretty nervous about throwing equations out since you don't have any text books to help you sort through it.]

Gain = (V / L) / (1 + K * V^2 / 57.3 * L * g) deg/s

where K = [(Wf/Cf - Wr/Cr) + Wf/Cf * 2 * b * Fzf^2/Cf - Wr/Cr * 2 * b * Fzr^2/Cr]

V = vehicle speed
L = wheelbase
g = grav. const.
Wf = weight on front wheels
Wr = weight on rear wheels
Cf = cornering stiffness of front tires (choose 100)
Cr = choose 100 also
Fzf = lateral load transfer across front wheels for .9g lateral accel
Fzr = lateral load transfer across rear wheels for .9g lateral accel


Modified by GSpeedR at 9:32 AM 6/10/2005

 

Basically you plot r (deg/s) versus V (m/s). You want the plot to stay pretty linear.

SIMPLER APPROACH:

- Roll stiffness front = 1/2*Kf*s^2

Kf is front spring rate.
s is lateral distance between front springs. (measure it)
This uses small angle approximations.

- Do the same for the rear.

- Determine roll center height (steady-state) for front and rear. Google search how to do this for independent suspension cars. Don't forget to use the ride heights that the springs will drop to, not stock ride height (unless they are adjustable sleeves, then choose 2")

- Calculate the height difference between CG and roll axis.

To do this you make a line of the roll centers (height), by connecting them with a straight line...this is the roll axis. The longitudinal position of each roll center is at the wheel centerlines. You then need the longituduinal position of the CG (either google.com search or ask me). At the CG position, subtract the CG hight from the roll axis height. Call this Hdiff.

- Roll rate equation

RR = W * Hdiff / (Front Roll Stiff + Rear Roll Stiff - Hdiff * W)
or
RR = W * Hdiff / (Total Roll Stiff - Hdiff * W)

where W = vehicle wieght

Set RR = 3 deg/g and solve for your Total Roll Stiffness.

- Back out the total spring rate from Total Roll Stiffness using the above equation: .5*K*s^2 , assume that s is equal front and rear. This "total spring rate" is front and rear combined. You need to split it based upon the handling charactersitics you want. 60/40 f/r for an understeering car. 40/60 for an oversteering car. This is where the yaw gain equation would help you, but I don't think you have enough info to solve it without a book.

 

Ah that CFM was a typo. Initially I was writing CFM all over the place for some reason, even though in my head I knew that it was cycles per minute; musta forgot to fix that one lol.
You say Yaw Rate Gain is the car's tendency to spin during steering. So if the gain is high, the car will oversteer very easily, correct? If thats the case then I suppose you would want to keep this number as low as possible, unless you wanted the car to spin... I appreciate the formula, but you are probably right, at this point it can't help me much because I have no way of figuring out some of the individual variables.
I have been trying to figure out how to choose a suitable suspension frequency for front and rear, and just today started considering different frequencies for the front and rear. I am currently having a bunch of shock/spring combos produced for an EG sedan we have here and that we will be using as a test car for this suspension frequency business. Since it looks like suspension frequency can be generalized across all drive layouts (fwd, rwd, awd), I think that it is a suitable factor to test. However, my concern is that I am relying too heavily on suspension frequency to design these coilovers, and that there is something else I am not considering. You're right, I don't want to get too complex, because I would like to design a coilovers that are suitable for the majority of enthusiasts. Then again, I would like to cover more than just the basics.
I think I am at a good starting point. We will see how the testing goes with the EG. I am having 6k and 8k rear coilovers made, along with 8k, 10k, and 12k coilovers for the front to be equipped and tested in all sorts of combinations. These run the range from ~110 CPM to ~180 CPM I believe. I would've liked to have been able to test the 4.5k rear and 6k front coilovers, but I don't think we know enough to deal with the difficulties associated with those yet. Other than this little obstacle, the initial numbers look promising and I think the project is going along smoothly. Its too bad our actual road testing will be so limited, but it can't be helped as we all have conflicting schedules and time is short. I'm not sure if the results of actual road testing can be generalized to cover all other applications (eg. The Civic works well with 180 CFM up front and 115 CPM out back, so the WRX and Evo should use these as well). Anyhow, I'm keeping my fingers crossed.
I'm having my dad order the Millikens' book and send it over here to Taiwan, or at least have him browse through it to see what exactly we are missing. I will pass the yaw rate gain idea along to him as well and have him think about it as well
Thanks again for the info

 

Finally, some encouraging numbers and results. I've gotten more accurate measurents as far as weights of the unsprung suspension components, and we've decided on roughly .88 f:r ratio for suspension frequency. What this all yielded was convincing evidence supporting our existing EG/DC2/EK spring rates (8kF/6kR, 10/8, 12/10), and some interesting numbers for the WRX (7/6, 9/8, possibly 11/10, if not equal rates front and rear), and Evo (6/7, 8/9, 10/11).
Testing will begin with the EG middle of this week, and we'll have several people testing each combination. Once this finishes, and assuming our road and track testing concurs with our data here, then we've reached the point that you described before: determing yaw rate gain and biasing the springs accordingly to achieve oversteer/understeer/neutral. At least, thats how it seems to me.
The Millikens' book is on the way to my dad in Chicago, he'll be taking a look through it and double checking our stuff to see if we're on track.

 

wow this is some interesting stuff... kind of off the subject... but ill give it a shot... ive noticed that some coilover packeges (tanabe,tein,ect.) use a small helper spring... is their a performance side to this or strickly comfort.. my tanabe sustec pros came with them and i never put them on because i was thinking they were for comfort..should i put them on or leave them off??? from a performance point of view.. i dont drive the car daily so comfort isnt a issue... thanks guys

 

Testing on the EG is done, and the popular 8/6, 10/8, and 12/10 rates are popular for a reason. Matched with our valving, they perform wonderfully, and the 12/10's are even bearable on the street.
Have a look at these results (of the tester EG). Granted they are based on estimates of some weights, and they still do not take into account some of the more complex things, but what they do take into consideration at this point is the balance between ride comfort and general performance:
Front to Rear Suspension Frequency Ratio and Corresponding Spring Rates - assuming .88 is the best compromise:
.89 - 8kF/6kF
.86 - 10.1kF/8kR
.85 - 12.1kF/10kR
Testing is *almost done*, we still have some odd rates to experiment with, but all in all these seem like the rates that we will be going with during final production. Its very cool to me to see our rates correlate so well with the .88 ratio, and even more so for our actual road/track testing to support it. Our dampers still have some ups and downs (pun intended) to take care of, but I'm confident we can hammer those out before final production begins.

A helper spring is used to keep your spring from flopping up and down during suspension travel. It keeps the spring seated at all times between the top mount and the lower spring perch, so that when your suspension is in full droop, you don't have a big gap between the top of the spring and the upper mount. If your set came with them, I'd put them on as they wouldn't hinder your performance at all, if anything they help. Their spring rates are low enough not to change the total spring rate.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Noob4life &raquo;</TD></TR><TR><TD CLASS="quote">we will be using 1:1 unless someone can suggest an alternate method for measure the D2. </TD></TR></TABLE>

hah , 1:1 and Honda ? our cars also lack the macphearson strut in your diagram.

easy way to calculate MR is to compress the suspension 1" and measure how much the shock travels.

engineering something on paper can only go so far , this is the real world way of determining the real motion ratio of the car itself.

 

You should take a hard look at the springs offered in these Taiwanese kits. The shocks might be ok, but the springs tend to be the deal breakers. Everything I have tested to date has been junk. I tested one yesterday and these were the results:

-took a 3mm set
-was off quoted rate (450lbs) by 30lbs
-had a progressive rate but advertised as linear
-leaned 10mm to one side after setting (like that tower in Italy hehe)

Not good.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Doctor CorteZ &raquo;</TD></TR><TR><TD CLASS="quote">

hah , 1:1 and Honda ? our cars also lack the macphearson strut in your diagram.

easy way to calculate MR is to compress the suspension 1" and measure how much the shock travels.

engineering something on paper can only go so far , this is the real world way of determining the real motion ratio of the car itself.</TD></TR></TABLE>
I wasn't talking about Hondas at all in that post, it was about the macpherson suspensions on the WRX and Evo.
Vtecvoodoo: I know what you mean, its a matter of cost and availability for a lot of the companies here when it comes to what steel to use for springs. Taiwanese steel is cheap to manufacture and buy, so you don't have to order in giant reels and each order is relatively cheap. The downside is coming out with the results similar to what you've seen
I've sourced my steel from a factory in Japan that takes care of a lot part of the pre-treatment in their factory, and we have those giant reels sent to a spring factory here in Taiwan where the forming process takes place. Thats one of the reasons why I am trying to limit the rates I offer, because the steel is not cheap, and the minimum order for reach reel is huge. We do get very nice certificates of inspection with each reel though We haven't had any problems to date yet with these reels.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Noob4life &raquo;</TD></TR><TR><TD CLASS="quote">
:
I've sourced my steel from a factory in Japan that takes care of a lot part of the pre-treatment in their factory, and we have those giant reels sent to a spring factory here in Taiwan where the forming process takes place. .</TD></TR></TABLE>

i have seen spring tests from japanese coilovers and they aren't good either, these are some of the more respected companies too. but they could source there stuff from a crappy place.