Spring rates and damper bump/rebound.

[Kozy]

No doubt many of you will have heard me bitch about the ride quality in my EK4, well I have a theory on how it could be sorted...

At the moment, my setup is Tanabe GF210 progressive springs, 4.1kF/2.8kR (229lb/inF, 156lb/inR) and Koni Yellows all round. The primary ride quality on this setup is ****, however the secondary ride is actually quite supple, and is quite soft for track/autotest work as the car rolls quite a bit.

The primary/secondary ride conditions lead me to believe that the springs are actually a little too soft for the stock bump valving on the Konis, which is non adjustable. This means that the progressive section of the spring is easily overwhelmed by small low speed bumps, so the job of primary ride is being taken up largely by the dampers, which have a lot less give in them than the springs. As the speed increases and secondary ride takes over, elimating the job of the soft, progressive part of the spring, the ride becomes dictated by the spring and the damper simply reduces bounce as it was designed, leading to the better ride. In this equation the adjustable rebound on the Konis is of little concern, rebound is more about cornering balance than ride and bump is visa versa.

While this setup gives me an excuse to hoon it everwhere because the 'ride is better going balls out' (the missus doesn't buy in to that theory unsuprisingly), it is undesireable because I am getting the worst of both worlds, **** ride and roll on the limit.

My thinking is that by purchasing some higher rate, (say 275lb/in front and rear) linear springs, I will infact improve both aspects of the suspension, as the primary ride may be improved slightly and on the limit handling response will be much improved.

I also understand that upping the rear rate is a big factor in ride quality, but it will offer better balance and is a comprimise I am willing to make.

Anyone got any thoughts on the matter? I am not looking for recommendations on suspension makes/setups as such, just some ideas on this theory. If the theory is sound then I can specify springs based on the Koni's bump valving (if I can find this out)

 

[_JT]

Sounds plausible. Your springrate is even softer on the rear than EK9 stock so I can imagine the Koni's are simply too stiff. What rates are you thinking of? 5kF 3,5kR?

 

[Kozy]

I'm considering 275lbin front and rear, about 4.9kg.

I am trying to find out from Honda-Tech the stock bump valving on the Konis, I can then get a perfect match which will be optimum for both ride and roll. I will be going for Ground Control hieght adjustables too, I reckon with a correctly matched set they will outperform most coilovers at much less cost.

 

[blinx9900]

275 in the rear is pretty stiff.

 

[Kozy]

EK9 is 250 though is it not? With the added weight of an EK4 (plus a rather portly driver) I would have thought 275 all round would be ok.

 

[vinnY]

look into the eibach sportlines
they should be about 310/275

i'm currently running a h&r cup kit which i'm lead to believe is just koni yellows rebadged for h&r plus the h&r sport springs which are 330/280(though the drop makes it look more like the h&r race springs)
whether h&r get koni to revalve the shocks for the springs, i'm not too sure

 

[Kozy]

Are the sportlines linear or progressive?

I would consider getting the Koni's revalved, I think they need softer high speed bump and stiffer low speed bump than they have as stock, no idea how much revalving costs though?

 

[iceman]

tricky one

i ran almost identical setup, koni yellow sport adjustable (brand new kit) with gf210 springs and was horrid just as you describe, then tried new set of eibach pro kit and exact same (only difrerence was uneven ride height with eibach)

then switched to oem ek9/shocks springs, amazing, bar maybe 1 or 2 setups (mugen and spoon) there is nothing out there that will match that set up for overall compromise imo and even then the mugen/spoon spring/shock combo will improve handling/feel but at same time greatly reduce comfort and are mor harsh/crashy on bad roads

 

[Kozy]

OEM EK9 suspension would probably be the best solution for me, it's undoubtedly going to be better than the current setup on both ride and performance.

Do you find this rides much higher than the Koni/Tanabes? The ride hieght is about the only thing I actually like about the combination!

 

[iceman]

oem ek9 will ride higher, at a guess id say about 15mm

 

[Kozy]

Right, back on the subject again, I have done some research and calculations (while I was supposed to be working, obviously) and I have a quantifiable answer which sort of proves my theory at the beginning.

My basic theory on **** primary ride and good secondary ride was that my progressive springs were being overdamped at high damper speeds (tracking the road surface, and only at low speeds (controlling chassis movement) were the higher rate sections of the spring working properly with the damper to provide a smooth ride, spilling into excessive roll in track conditions.

My suggestion to fix an overly stiff ride on the road and overly soft track handling was to fit higher rate linear springs. This sounded a little bit retarded, even to myself. Logic would suggest that you can only improve one at the expense of the other.

At the time, I didn't know much about spring/mass systems, and now I do, the whole business makes a lot more sense, and kind of proves what I had been thinking.

Here is the result of my procrastination today, a Koni Sport Dyno plot on to which I have overlayed the ideal plots calculated for my spring rates, motion ratios and sprung weights.

Basically, for any given corner weight and spring rate, there is an undamped natural frequency, and for this frequency there is an ideal damping ratio in order to bring the oscillations back to normal as quickly as possible. Working backwards through the calculations, I figured out how the ideal damping for my setup compared to that of the OTS Koni Yellows.

Now there were admittedly a few assumptions made and the chart is by no means comprehensive, but the ballpark figures are OK, and the calculations fairly involved. Ride frequency once an assumed motion ratio of 0.7 is taken into account is 2.0F / 2.36R, which is about ideal for an occasional tracker, if a little too rear biased. Baseline figures were calculated from 70% critical damping.

One thing I am uncertain on, is whether I should be basing my front/rear plots on seperate dyno runs for F/R dampers, but I have never found anything suggesting differences on Honda applications, just dyno runs for the generic Koni Sport. I am open to suggestion on this, while I have found numerous plots, they all have the same figures, so I am assuming they use the same valving.

What the graph basically shows is that, true to my uneducated guesses, the high speed bump valving is far too stiff on the rear axle, which is the primary factor in ride quality. What did suprise me was to see that the low speed bump is also quite seriously overdamped. This is less of an issue than the high speed bump, but will negatively affect handling response, especially in autocross type conditions.

If I decide to keep the car purely on autocross/trackday grounds (which after seeing my mates win last week at a local event in his stripped EF, I am sorely tempted to) then it looks like some higher rate linear springs will be the order of the day, although my previous 275lb front and rear suggestion would skew the handling somewhat spectacularly, I figure 275F/180R should sort it out nicely.

 

[Kozy]

Later on I recalculated, using an altered vehicle weight of 1260kg to include the driver and assuming a less harsh 65% critical damping ratio, converted the results from lb/in/sec to N/cm/sec, and overlayed the resulting graph onto the official Koni dyno plot to compare:

Although the results from this data were closer, it still shows the same trend, seriously overdamped at high piston velocities. The result, soft springs that give a shitty ride!

 

[iceman]

ill admit i dont undertand the fine technical aspects of suspension design but graph if im reading right justifies why i hated koni's on mine

 

[Kozy]

Yes I can understand your point now. Trying to get advice from the tech heads on Honda-tech but they seem to be skeptical of newbies.

 

[iceman]

id almost give up on shock/spring/coilovers selection after buying highish end set but currently playing with different springs on them (blindy so not good basis tbh) but also other little touches as well

spoke to friend few times and at point where my car will be going to him anyway to sort handling/chassis and discussing having him design custom coilover set just for my car now, very very technical though so lot is beyond me but only way im gonna get what ive been pursueing for so long from car

 

[Kozy]

Thing is I'm still against coilovers, even participating in AutoX/trackdays in a daily driven car I simply cannot see the need for the adjustment everyone raves about.

A given spring rate and corner weight has an ideal damping force, it should be a set and forget affair.

 

[iceman]

Thing is I'm still against coilovers, even participating in AutoX/trackdays in a daily driven car I simply cannot see the need for the adjustment everyone raves about.

A given spring rate and corner weight has an ideal damping force, it should be a set and forget affair.

i agree with you 100% on coilover comment, i only recently gave in after several years as want to take car to higher level and sadly coilovers were only way (still **** for road imho )

 

[Kozy]

Back on this again, I have now junked the Koni/Tanabe setup in favour of Spoon fixed dampers and progressive springs. Rates have increased from 229F/156R to 352F/308R.

Although I have changed the dampers, the vastly improved ride kind of proves my theory, despite increasing the rate by around 50% in front and nearly 100% in the rear, the car tracks over bumps so much better, the whole thing is more composed at speed and driving on the abysmal Isle of Wight roads is made a little more bearable now I don't have to wince every time I see an imperfection in the road.

So, in conclusion, if you are planning on buying springs and dampers seperately, don't just take the advice of the retailer, do a litte research to find out if they are well matched. I am more than happy to help people out with this if they wish, however it does seem that buying coilovers mostly eleminates this problem...

 

[Salami]

Kozy I have been reading your threads; doing some math and mostly beating my head against the wall trying to get my car to ride better. I feel the same way about the ride on my hatch. It doesn't ride like **** but I believe it should be able to ride better as it did before.

Current set up is Neuspeed Sport springs on a set of brand new KYB AGX. Previous shocks were some worn out Tokico Illuminas. Car handles much better now but I seem to notice every imperfection in the road.

I spoke to some one at Ground Control and he told me the AGX have a lot of compression damping. I have been thinking that increasing the spring rate will help as it appears the AGX are overdamped for the spring rates I am using.

Can you tell me if simply increasing the spring rate with the current shocks seems to be going in the correction direction?

I am going to pull the trigger in the next 24 hours as I am getting tired to going back and forth. I am hoping I am going in the correct direction.

 

[Salami]

Another thing I have been wondering about is how ride height has factored into the equation. I don't know anything about the Spoon springs but does your car ride higher know than with the GF210's?