road race/autoX : Koni> typical coilover?

[nlzmo400r]

I have d2 coilovers right now, and love them. I do a lot of autoX but am getting more into full course road racing on our local 1.8miles circuit. Has anyone had any experience with Koni dampers on their S chassis? I know they're not cheap, but the honda guys rave about them and usually pair them with GroundControl spirngs. Another reason im looking into them is because I can get them custom valved. Anyone used these before? opinions welcome

- Rob

[turtl631]

I considered this too, but the Konis aren't very practical for the S chassis, especially with all of the full coilover options available. The fronts are inserts so you have to cut your stock struts to recycle the lower mounts, and the rears aren't externally adjustable so you have to take them off the car to adjust the damping. Getting them made externally adjustable, along with springs, etc will end up costing more than a set of nicer coilovers and you still won't have camber plates in front or rear pillowball mounts. I went with Stance coilovers instead and I'm happy with them so far, but no track events yet. I imagine the Koni Yellows have a little better damping, because most JDM coilovers aren't too digressive and tend to make a lot of damping force, but that's fine until you hit big bumps. Another option would be Buddy Club coilovers- they cost a bit more than Stance or KTS, especially once you add pillowball mounts, but honda guys love them for track stuff, and I've heard of a few guys using them for track stuff on 240s and really liking them.

[HaLo]

I have d2 coilovers right now, and love them. I do a lot of autoX but am getting more into full course road racing on our local 1.8miles circuit. Has anyone had any experience with Koni dampers on their S chassis? I know they're not cheap, but the honda guys rave about them and usually pair them with GroundControl spirngs. Another reason im looking into them is because I can get them custom valved. Anyone used these before? opinions welcome

- Rob


Hey, I think I am best to answer that question, as I have both, on 2 different S13s. :)

My "race" S13 has D2 coilovers with 9/7 springs. On a absolutely perfect surface, they work pretty well. PERFECT surface: dry, no cracks, no bumps, etc. When you get to something a little more bumpy (parking lot, local roadcourses, street), it doesn't do as well. The car tends to jump over bumps instead of following and sticking to the road. I personally hate them for that.

My Convertible S13 has Koni dampers + Tanabe GF210 springs. I love it, it works on ALL surfaces. It might me a bit softer on damping (who cares, that's the comfort zone) but the adjustment on rebound is amazing. And I only have some off the shelf dampers. Konis work the road much better than the D2s. I will revalve my Konis and toss the D2s for sale when I get rid of my fastback.

I'd recommend Konis anytime over coilovers, unless, you're into drifting and a really stiff suspension is what you want.

[yudalicious]

I really wanted a set of KONIs too, but it was just too much hassle to take off the rears everytime you adjust OR too much money to convert them to external adjustable, revalve/shorten, buy GCs, then camber plates. With everything together it's a pretty peice of $, and I decided for me I wasn't a good enough driver to take advantage of the minute advantage that KONI shocks give so I just settled for a decent full coilover set up.

[jmauld]

The advantage of KONI Shocks is that you can actually adjust the suspension with them. Unlike the majority of coilover kits where you are just making ride quality adjustments.

If you turn a knob and both compression and rebound adjust at the same time, then that shock is not meant for racing.

[MovinUp-1]

Truechoice charges $150 to make the koni rears externally adjustable. You will find that the konis are going to give you much better damping and real adjustability compared to the lower priced coilover setups out there. They are cheaper for a reason.

[jmauld]

Truechoice charges $150 to make the koni rears externally adjustable. You will find that the konis are going to give you much better damping and real adjustability compared to the lower priced coilover setups out there. They are cheaper for a reason.


I haven't seen any of the JDM coilovers under about $2400 that don't do both rebound and compression with a single knob.

To build a good system.

Get the konis ~$550
Tein Camber plates: $153
Tein rear mounts: $144
GroundControls: $400

So for about $1300, you can have an extremely capable setup. Once you wear out the KONIs, spend another $600 to have them all rebuilt and the rears modified to be ext. adjustable.

[nlzmo400r]

Truechoice charges $150 to make the koni rears externally adjustable. You will find that the konis are going to give you much better damping and real adjustability compared to the lower priced coilover setups out there. They are cheaper for a reason.

whats up allen, its rob. Nice to see you're still on the boards. I never got a chance to ride in your s13, really wish I would have. Did you have any dislikes/likes abuot your konis?

[nlzmo400r]

Hey, I think I am best to answer that question, as I have both, on 2 different S13s. :)

My "race" S13 has D2 coilovers with 9/7 springs. On a absolutely perfect surface, they work pretty well. PERFECT surface: dry, no cracks, no bumps, etc. When you get to something a little more bumpy (parking lot, local roadcourses, street), it doesn't do as well. The car tends to jump over bumps instead of following and sticking to the road. I personally hate them for that.

My Convertible S13 has Koni dampers + Tanabe GF210 springs. I love it, it works on ALL surfaces. It might me a bit softer on damping (who cares, that's the comfort zone) but the adjustment on rebound is amazing. And I only have some off the shelf dampers. Konis work the road much better than the D2s. I will revalve my Konis and toss the D2s for sale when I get rid of my fastback.

I'd recommend Konis anytime over coilovers, unless, you're into drifting and a really stiff suspension is what you want.

I have the 9/7k spirng set up on my d2's as well. I thought they were too stiff for our local road course. I had to try to keep the car in line on large bumps beceause the front of the car would not hold the road, it kept pitching everywhere, causing the rear to break loose and make me oversteer. I just installed a pair of 7k springs in the front today, and of course haven't been able to track them yet, but I think itll do wonders for soaking up bumps on the track. Im sure I'll have to return the dampening to get it back to where I like it. And, no im not really into drifting at all, just autoX and as much road course as possible.

You're getting rid of the hatch? Does this mean you're going to race the convertible?

[drift freaq]

Truechoice looks pretty sick and considering they have a facility at Infineion I am pretty stoked. I was already working on putting together a Koni coilover setup with Swift springs . Now I am going to go nuts hahahhahha :D

[HaLo]

You're getting rid of the hatch? Does this mean you're going to race the convertible?

You got that right! Not really competitively, more for fun... I am contemplating a VQ35 swap in her and putting a rollbar. We'll see the interest my hatch generates after FnF3...

[nlzmo400r]

so you think the cost of 240's will go up again after the movie makes millions?

[yudalicious]

I haven't seen any of the JDM coilovers under about $2400 that don't do both rebound and compression with a single knob.


I think there are some JDM shocks that change very little in compression as a residual affect of changing rebound due to the design I guess (this is from looking at dyno shocks on honda-tech), in fact, I think even the KONI yellows change a bit in compression when adjusted.

with that said, could you explain why it is better to adjust rebound and leave compression alone?

[TurDz]

I think there are some JDM shocks that change very little in compression as a residual affect of changing rebound due to the design I guess (this is from looking at dyno shocks on honda-tech), in fact, I think even the KONI yellows change a bit in compression when adjusted.

with that said, could you explain why it is better to adjust rebound and leave compression alone?

Konis Sports change minimally for compression, according to the data plots they have on their website.

[jmauld]

Increasing the compression decreases the springs ability to work over bumps. Halo alluded to this in his post. It makes the car unpredictable and difficult to drive. On a perfectly smooth surface, increase compression can work out, because it's very similar to adding spring rate.

With a stiffer spring you can get away with running less compression. but you need to add rebound force. Which is backwards of the way that cheap shocks work.

KONIs have a very small amount of bleed over from adjusting rebound It may be noticeable on a dyno, but no one would notice it in practice. Do you mind linking to some of the JDM coilovers that adjust just rebound?

[Wiisass]

When considering the compression damping, you have to think about the low and high speed effects. At low speed you want higher damping, a lot closer to critical than most would think. At high speeds, you want lower damping. The low speed damping range is for handling inputs. The high speed is for road inputs. This would mean, that the best bet would be a shock with a digressive compression curve, meaning that the slope of the compression curve decreases as the speed increases. Essentially this allows the suspension to take a harsh road input and have the forces from the shock fall off. This allows most of the force to be taken by the spring and not transmitted to the chassis. But at lower speeds, you would want higher compression damping because it will control the time it takes to transfer the weight during transient manuevers. For a digressive curve, you can have something closer to the best of both worlds, but if you're working with a linear damper then you're going to have to compromise. That compromise usually means that the low speed region of the compression curve will suffer. Which is the right choice because rebound is more dominant in this range when just considering the shocks and having all the force transmitted to the chassis from a high speed bump will greatly upset the chassis.

I don't agree with saying that with a stiffer spring you can run less compression damping. It goes back to the difference between high and low speed damping. I still think for the low speed, the damping ratio should be higher than most people have said in the past. Too little compression damping compared to rebound can lead to jacking down. Where the rebound damping won't allow the wheel to extend back to the static position. An increase in spring rate should see an increase in both rebound and compression damping coefficients.

About single adjustable dampers that adjust both compression and rebound. It's a horrible idea, you'll never get both right at the same time. From what I've seen regarding the koni's, there is a slight difference in the compression curves based on the rebound adjustment, but I think that's just residual pressure effects inside the damper that can not be removed.

Another important thing to note, is that most of the published dyno graphs are peak velocity plots. This means that the test are run at a couple different speeds and the peak velocity at each of those speeds is recorded and then the data in between those points is interpolated. These plots are not meant to show much. They are mainly used for manufacturing tolerances and you will never see something like that in a real race shop. The plots you want to see are continuous velocity plots. These plots record a whole cycle of data. This shows hysteresis and cavitation effects if present in the shock. These plots use more that 2000 data points for a 10ips sweep compared to the 8-12 used for a 10ips Peak velocity plot. So you just have to take the data on the peak velocity plots with a grain of salt.

Tim

[yudalicious]

From looking at the honda-tech dyno thread (honda-tech.com > suspension forum > sticky at top) it seems buddy clubs and tokico illuminas change very little in compression, while alot of other JDM ones do change in compression.

There has been some very informative and interesting posts, in regards to compmression vs. rebound and most dyno graphs showing only peak velocity data. ::thumbsup::

[jaae86]

It's weird how Im running the TEIN HE's on my S13 but still getting good results. I just adjust the dampers to really low settings and running some Kuhmo V710s. So far it's working out just fine.

[MovinUp-1]

whats up allen, its rob. Nice to see you're still on the boards. I never got a chance to ride in your s13, really wish I would have. Did you have any dislikes/likes abuot your konis?

No, I can't think of anything I dislike about the shocks at all. The only downside is with the ground control setup you have to run a very short spring on the front for tire clearance. It's not a big deal if you are set up properly but a helper spring would not be a bad idea in case you hit a big bump. Having a short front spring is a minor compromise to get a far superior shock compared to most of the inexpensive coilovers for sale.

In regards to the other comments, I hope the price of 240s go up again after the next movie comes out. I'm probably going to put mine up for sale.

[jmauld]

I don't agree with saying that with a stiffer spring you can run less compression damping. It goes back to the difference between high and low speed damping. I still think for the low speed, the damping ratio should be higher than most people have said in the past. Too little compression damping compared to rebound can lead to jacking down. Where the rebound damping won't allow the wheel to extend back to the static position. An increase in spring rate should see an increase in both rebound and compression damping coefficients.


That reads to me like you are asking the shock to do the job of the spring. It's the springs job to keep the car from jacking down. Also, you mentioned using compression to control weight transfer. You are the first person I've ever heard make that suggestion. I've always been told to use rebound for that. Why do you prefer to use bump instead of rebound?


For the original poster, here's a good read on how to properly adjust shocks
http://www.koniracing.com/roadsetup.html . This should help to further explain why adjusting both at the same time is a bad idea.

[DuffMan]

The main problem with Koni is that they have the same stroke as stock, which means they can't be lowered very much. With helper springs, you get them lower but it's not really ideal.

I'm going to try S13 shocks on the rear of an S14 (s13 is shorter) and some universal koni inserts that are shorter than stock, and see how that works out. The idea is to get koni quality but without shelling out a ton of money for custom short-stroke modified ones.

[yudalicious]

It's weird how Im running the TEIN HE's on my S13 but still getting good results. I just adjust the dampers to really low settings and running some Kuhmo V710s. So far it's working out just fine.

I have the KTS and so far it's working "well" for me, though I don't have anything relevant to comapre to, nor am I experienced enough to discern minor differences yet. With linear damping you either give up damping in the lower velocities or have tons in the higher ones, the KTS does the latter, to quote LeeCRX from KONI (after he looked at a dyno of the KTS) "you can't blame them for not making enough damping force" lol.

[drift freaq]

The main problem with Koni is that they have the same stroke as stock, which means they can't be lowered very much. With helper springs, you get them lower but it's not really ideal.

I'm going to try S13 shocks on the rear of an S14 (s13 is shorter) and some universal koni inserts that are shorter than stock, and see how that works out. The idea is to get koni quality but without shelling out a ton of money for custom short-stroke modified ones.
DuffMan keep us updated on the universal Koni inserts that have a shorter stroke than stock. I am after the same kind of setup. That or a completely threaded strut housing so I can adjust my lower pickup point.

[Wiisass]

That reads to me like you are asking the shock to do the job of the spring. It's the springs job to keep the car from jacking down. Also, you mentioned using compression to control weight transfer. You are the first person I've ever heard make that suggestion. I've always been told to use rebound for that. Why do you prefer to use bump instead of rebound?


For the original poster, here's a good read on how to properly adjust shocks
http://www.koniracing.com/roadsetup.html . This should help to further explain why adjusting both at the same time is a bad idea.

What parts makes it sound like the shock is doing the work of the spring? The part about running more compression damping with more spring rate? You need to think about it this way. With an increase in spring rate, you will be increasing the natural frequencies of both the sprung and unsprung mass. This also increases the critical damping coefficient. So assuming you wanted to run the same damping ratio for compression with the stiffer spring, you would need to increase compression damping to achieve that same value.

In reference to jacking down. I'm speaking of jacking down as what happens when the rebound damping won't allow the shock to extend back to the static position and over a series of bumps will cause the car to lower itself. This usually happens when the compression damping is low and the rebound is too high when compared with the spring rate.

About compression damping in general. Koni will tell you and I agree that compression damping is mainly used to control the motion of the unsprung mass. Now this is perfectly fine when analyzing the performance at each wheel seperately. Koni will tell you to dial in compression damping by driving around and feeling the bumps, this is basically tuning the high speed damping and how it affects the movement of the wheel. Koni's instructions have been around for a while and haven't changed, so they might be a little out of date and could only be considering a linear damper, so if you're using a digressive damper, these instructions will differ slightly.

When using a double adjustable damper, or even a more than 2-way adjustable damper, things start to get a little more complicated. After the preliminary damping adjustments have been made, which is usually along the lines of what Koni suggests, you're going to need to tune to the track and the driver. This involves adjusting compression and rebound damping to allow the car to corner better. For example, if you're having trouble with braking turn entry, you're going to adjust rear rebound and front compression. These are all low speed adjustments which is the range where I believe that rebound and compression damping should be a lot closer in value than most people usually suggest.

You also have to remember that dampers only control the time it takes to transfer the weight and not the amount of weight transfer. You have to tune compression and rebound to adjust the behavior of the car. This all depends on what the car is doing during what situations. Some situations call for just a rebound adjustment, some just a compression adjustment and some do both.

Duffman, I think the rear S13 shocks might be too short when compared to the S14 rear dampers. For the front, which koni's are you looking at? The 8610s? or the 2817s?

[ep510]

I am kind of late getting in on the conversation--but just ordered the GC kit and camber plates for my s13 (already has the Koni sports-w/ Whiteline springs)

Jay at GC suggested 525 or 575 lb springs for the front
(just over 9K and 10K) and 350 for the rears (just over 6K) with the Yellows. Car weighed in at 2730 at the Devens Tour
( Hey Halo--DJ with the Red CA 240)

As far as the current set up --soft springs--but I really like the konis. Excellent at Watkins Glen last Mon-Tues --although--again soft springs meant a little rear wheel lift in Turn 10 on a few occasions.

At the Devens Tour --faster than Halo in the wet (softer?) and he spanked me in the dry.

I think I have read the Konis will handle up to about 700lb springs before they max out--although most of the IT racers I spoke to do not run them that high. I assume I will get them revalved and made externally adjustable this winter---as it is a pain in butt to have to remove to adjust the rears.

[AceInHole]

What's up DJ, it's PJ (Grey G35) from Devens.

Anyways, having run both Koni's and D2's, I honestly thought them to be fairly comparable in terms of dampening capability. The big downside to the Koni's is the inability to really lower the car, which has been a necessity to get the 240 to actually handle (honestly I've felt best in the car with it pretty much fully dumped). That said, if you're really looking at maximizing performance, Koni 28 series all the way. Untill then, if you already have D2's and just want the car to perform well, you don't really *need* to upgrade at all.

ep510 - blah just read the results a bit closer... you got me on Saturday too... but 2 seconds behind an FStock car on Sunday?? (just teasing :P) Hope to see you at Divisionals, or next year when I have my SM 240 back.

[ep510]

ep510 - blah just read the results a bit closer... you got me on Saturday too... but 2 seconds behind an FStock car on Sunday?? (just teasing :P) Hope to see you at Divisionals, or next year when I have my SM 240 back.

Yes -yea yea---I need more time behind the wheel in this car--wider tires and hopefully the springs and camber plates will help a lot.

Just signed up for Div's--and need to make it back to Ayer really soon. I like the more open courses---our sites suck

OH and about Saturday---I used to Ice race--great for learning to drive in the rain....(until I flipped the car and was trying to steer it upside down--no more Ice racing)

[HaLo]

i'll be back next year at Devens, hopefully with a VQ powered s13 convertible, on revalved Konis... :p

[ep510]

ep510 - blah just read the results a bit closer... you got me on Saturday too... but 2 seconds behind an FStock car on Sunday?? (just teasing :P) Hope to see you at Divisionals, or next year when I have my SM 240 back.

Hey PJ and Oktay-- A Picture is worth a 1000 Words--or some crap like that

Soft springs
http://public.fotki.com/jdwinchester/scca_national_tour/155.html

stiffer springs and camber plates
http://public.fotki.com/jdwinchester/scca_national_tour/page4.html

I hope to give you guys more of a challenge next time.

[HaLo]

OMG!!! I had no idea I was lifting the inner wheel that much... :(
Forget S15 diff, it'll never work well in these conditions...

[ep510]

OMG!!! I had no idea I was lifting the inner wheel that much... :(
Forget S15 diff, it'll never work well in these conditions...

Are you running a rear Sway bar? Is it adjustable? How stiff a setting did you have it on?

( Boy I guess we really hijacked this thread)

[HaLo]

Yeah I am running a rear sway bar, non adjustable, it's the Tanabe sustec chromoly 22mm rear sway bar.

[MovinUp-1]

IJay at GC suggested 525 or 575 lb springs for the front
(just over 9K and 10K) and 350 for the rears (just over 6K) with the Yellows. Car weighed in at 2730 at the Devens Tour
As far as the current set up --soft springs--but I really like the konis. Excellent at Watkins Glen last Mon-Tues --although--again soft springs meant a little rear wheel lift in Turn 10 on a few occasions.

At the Devens Tour --faster than Halo in the wet (softer?) and he spanked me in the dry.

I think I have read the Konis will handle up to about 700lb springs before they max out--although most of the IT racers I spoke to do not run them that high. I assume I will get them revalved and made externally adjustable this winter---as it is a pain in butt to have to remove to adjust the rears.

I have always been told that the konis for S13s won't handle anything over a500lb spring for very long. And I can back that up with my own personal experience. Plan on getting these re-valved this winter as they will more than likely be blown. Of coures I have only autocrossed the car and autocrossing can put harsher loads onto shocks than track days.

[AceInHole]

I've heard good things about the OBX helical, which I'm thinking of swapping into the Panda. Can't wait to show you guys how SM 240's are supposed to run :P Engine is already at the shop getting torn down ^_^

[ep510]

I have always been told that the konis for S13s won't handle anything over a500lb spring for very long. And I can back that up with my own personal experience. Plan on getting these re-valved this winter as they will more than likely be blown. Of coures I have only autocrossed the car and autocrossing can put harsher loads onto shocks than track days.

For sure I will get them revalved --I need to get the coilovers set up--corner weight it--and see where it goes. And I agree fully about AutoX being harsher --For the track --I could easliy get by with a much lower spring rate--Trying to compromise.

Hey what do you guys run for Camber /Caster/Toe?

[HaLo]

-2.8 / stock / 0
-1.5 / stock / stock

[jmauld]

Halo, here are some things you can do to help with lifting the rear tire.

1) more front bar or spring
2) less rear bar
3) rear tender springs
4) use street tires ;)

[jmauld]

What parts makes it sound like the shock is doing the work of the spring? The part about running more compression damping with more spring rate? You need to think about it this way. With an increase in spring rate, you will be increasing the natural frequencies of both the sprung and unsprung mass. This also increases the critical damping coefficient. So assuming you wanted to run the same damping ratio for compression with the stiffer spring, you would need to increase compression damping to achieve that same value.


I'm sorry man, but I think you are overlooking something. Maybe it's the fact that the shock is seeing less travel with a stiffer spring, regardless of the frequency? Like I said, you are the first person I've come across to make these recommendations.

This is taken from a Penske Tuning manual
If the spring/shock combination was balanced, the rule of thumb is a stiffer spring requires lower compression and higher rebound. A softer spring requires higher compression and lower rebound.

So, that's both Penske and KONI that make that recommendation.


In reference to jacking down. I'm speaking of jacking down as what happens when the rebound damping won't allow the shock to extend back to the static position and over a series of bumps will cause the car to lower itself. This usually happens when the compression damping is low and the rebound is too high when compared with the spring rate.


I'm aware what jacking down is. A lot of stock-class autocrossers use this to their advantage. :) Again, if you have enough spring and the appropriate rebound for that spring, then compression really shouldn't play a part of this.

[AceInHole]

[QUOTE=ep510
Hey what do you guys run for Camber /Caster/Toe?[/QUOTE]

-4.5 / 7/ 0
-2.5 / stock / 0

[jmauld]

Am I the only one that runs toe-out in the front?

Ace, how are you getting -4.5 degrees of Camber? Mine is at -3.1 and I can't push the plates in any more.

[tchenku]

hey jason! this is Seng from CN.com. i went to the auto-x at Lowes this past weekend and well, i didn't do too well to say the least. but i did have fun, though! wish you could've been there. but i too run d2's and like halo said, these coilovers tend to be jumpy on bumpy surface. this is the problem i had at Lowes. is there any other way to reduce this effect on d2's? this question goes out to anyone.

[jmauld]

IMO, I would run them at the softest setting that you can get away with.

[tchenku]

front and rear? i'll have to try that. well, then, that is what i'll be doing tomorrow on my day off.:)

[Wiisass]

I'm sorry man, but I think you are overlooking something. Maybe it's the fact that the shock is seeing less travel with a stiffer spring, regardless of the frequency? Like I said, you are the first person I've come across to make these recommendations.

This is taken from a Penske Tuning manual


So, that's both Penske and KONI that make that recommendation.



I'm aware what jacking down is. A lot of stock-class autocrossers use this to their advantage. :) Again, if you have enough spring and the appropriate rebound for that spring, then compression really shouldn't play a part of this.

Alright, I don't know the best way to explain what I've been saying or explain how everything that Penske and KONI says isn't always true. In what I wrote previously, I talked about damping ratios. If your familiar with vibrations, you know that the damping ratio is the actual damping coefficient divided by the critical damping coefficient. The critical damping coefficient is calulated using the sprung mass and ride rate for the sprung, and the unsprung mass, wheel rate and tire rate for the unsprung. If you increase the spring rate, both the ride rate and the wheel rate will increase. This will also increase your critical damping coefficient. If you don't change the damper at this point, you will have the same damping coefficient divided by the increased critical damping coefficient which will result in a lower damping ratio. You can base your damping coefficients for rebound on the sprung mass calcs and your damping coefficients for compression on the unsprung calcs and both will result in a lower damping ratio with an increase in spring rate and no damper change.

The damping ratio determines the overshoot that the damper will see. There's a good graph in racecar vehicle dynamics that shows plots of displacement versus time for different damping ratios. Things are a little different in this situation because of the different damping coefficients for rebound and compression. But the closer the damping ratio is to 1, the less overshoot you will see. For example, you know how an inspection place will bounce the car to check the dampers? This is a way to measure the damping ratio of the system. Depending on how my cycles it takes for the car to settle, that determines the damping ratio. A lower damping ratio will cycle more, a damping ratio of 1 won't cycle at all.

For example, out formula car this year in it's final suspension tune, had a damping ratio @3ips of 0.97 for rebound and 0.82 for compression and a high speed compression damping ratio of 0.6. This was the setup that turned the fastest lap time and kept the driver the happiest. The only thing I wanted to change, but couldn't because the dampers wouldn't let me go any lower, was the high speed compression damping. I felt that a little softer would have allowed the spring and damper to take more of the force from the big bumps rather than transmit them back to the chassis. I could see a lot of people saying that my rebound damping ratio was way to high and wouldn't work, but the car handles beautifully.

So if you are analyzing your spring damper combo based on vibrations data, and to do this you need real numbers, you will see this decrease in damping ratio. So if your revalving the dampers to adjust for this spring rate change, you will add compression and rebound damping. But you also have to notice that both rebound and compression won't be changed the same amount. Compression damping is less affected by the spring rate change than rebound damping will be. THis is because compression damping is based off of the tire rate and wheel rate in parallel, so the additional wheel rate from the spring rate is minor compared to the change in ride rate. This is all getting a little too deep into spring/damper vibration theory, so I'm going to stop with this now, I just want to make sure that is it understood that an increase in spring rate will increase natural frequencies and critical damping coefficients therefore reducing the damping ratio if the damper remains unchanged.

Now to address this "rule of thumb." The rebound part makes complete sense and I completely agree with it. In terms of the compression part, I'm assuming this is based off the force distribution of the spring, damper and arb during cornering. I don't know if I can find the graph I'm looking for, but it's pretty simple. It shows the force generated by the spring damper and bar during a turn, for simplicity I'm just going to discuss a 90degree bend and just the front outside corner. We'll assume braking to steady state to acceleration. The only part the damper matters is during the braking and acceleration. And since we're talking about compression damping on the front outside corner, we're going to ignore the acceleration part of the turn because the damper will be in rebound at this point. So Penske and Koni are saying to keep the car behaving the same, you want the same amount of force generated during these maneuvers. So a softer damper will produce less force, but a stiffer spring will produce more, so they're assuming that during the time the car is braking the soft damper/stiff spring will produce the same amount of force as the stiff damper/soft spring. They also mention that this is for spring changes, meaning a quick change at the track. So this "rule of thumb" will work as a baseline if you don't have the time to retune the setup like you should. And also, since this is meant for a spring change, it doesn't mean that every spring/damper setup with a stiffer spring should have softer compression settings. This is more what I was talking about, the actual design and valving of the damper rather than the tuning at the track.

Just a general comment on these manuals. They're good guides for baseline stuff, but they aren't meant to be the final word, you have to figure out what works for your setup/track/driver preference/etc. I'm pretty sure I saved some good papers and such on my laptop, I'll see if I can post them later today if I get the chance. I think there's a good one in there that talks about tuning the dampers past the baseline settings that are discussed in the penske and koni manuals.

You also have to consider there are several different ways to achieve the same result. For example, to get a desired roll rate, you would run soft springs and a really stiff sway bar or you could just run stiffer springs. It all depends on the situation, the intent and preference. That's why is you get your shocks revalved somewhere, they should be asking what your planning on using them for. I mean you wouldn't valve a set of shocks the same for road courses versus rally. Well, I hope all of this makes sense.

Now for jacking down, compression will play some part in this. Jacking down happens over bumpy surfaces. Bumpy surfaces meaning high speed compression territory. If the high speed compression damping ratio is high, then the damper will transmit most of the force before the spring even has the chance to compress, meaning that rebound could be as high as you want and the shock would never get the chance to compress enough to jack down. Now assuming rebound is too high for the spring rate but compression is right where it should be, when the car goes over the bumps, the shock will compress because it takes the spring and damper longer to generate the necessary force, so with rebound too high this will lead to jacking down. But up compression damping a lot on that last case and the shock won't move. I'm not saying this is the case all the time or even at all, but you can't ignore compression from the equation. Just look back to those numbers I posted for my formula car, rebound is high and this could lead to jacking down if compression wasn't so high.

[TurDz]

What Wiisass said is similar to the guidelines seen when you modify your suspension GT3, GT4...just for kicks.

I understand most of what he says because I am also a mech. engineer...but honestly it is a little drawn out.


If anyone didn't understand...

- Stiff springs need more control in general (i.e. the damper)

- Too high of a damping force on the compression side will force the sprung mass (chassis,engine,tranny) to move w/ the unsprung mass (wheel, tire, suspension arms)...leads to bumpy or nervous handling

- lots of options to get the same results. you can change the stiffness/force on the damper to your liking, but it can also depend on the type of damping chracteristics on the damper (i.e. progressive, linear, degressive)

- IMO, degressive is best on street & uneven road surfaces

Wiisass, I would like to talk to you some time about the stuff. It's something I want to get into in my career...I know from these posts and others ones that you are headed in the same direction (FSAE, etc.)

[Wiisass]

I think what i wrote is a little more technical that stuff you would see for video games. And yes it's drawn out, it takes me long enough to figure out how to write what's going through my head, let alone translate it so other people can actually read it. If you think that's bad, you should see some of my notes. The other night, it took me 4 sheets of paper to derive an equation for lateral load transfer distribution based on given suspension characteristics.

But Turdz summary is good. I agree with digressive dampers being better. I think they're better in almost all situations. Or at least having a digressive compression curve is important. Rebound really doesn't matter that much.

Turdz, try to catch me on AIM sometime if you want to talk about this stuff. Just let me know who you are when you IM and if I don't get back to you right away, I'm not ignoring you, I just don't put up away messages.

[jmauld]

Maybe we're just disagreeing on tuning perference, or maybe it's a difference in the type of shocks that we're using. I've been running KONIs in every vehicle that I've raced for the past 8 years, except for once when I thought I would try out those crappy AGX shocks. When I increase the spring rate and if I have the ability to do so, I decrease the compression. On my current shocks, I don't have that option except for when they are being revalved. Which they will be as soon as I get my spare set of shocks back from KONI. At that time, I'll also be taking the opportunity to increase my spring rates another 100lbs.

Good luck with your FSAE program. How long have you been in it? We have a couple of FSAE teams that run with us. Hopefully, your driver is better then the local teams. They always seem to be switching drivers and don't have one that's good enough to run consistent runs. Has to be hell getting any meaningful feedback like that.

[AceInHole]

Am I the only one that runs toe-out in the front?

Ace, how are you getting -4.5 degrees of Camber? Mine is at -3.1 and I can't push the plates in any more.

Slotted strut lower bolt holes. I was STILL getting a slight taper in tire heat, implying I needed more spring or more swaybar (whitelines on full stiff, 9kg spring). That or I was just overdriving the car :P

As for toe, I daily drove my car (with those settings) and I didn't like the way 1/32 toe out felt on the highway. Even then, I felt as though my turn-in was fine (even with the staggered tire, 275/315).

[nlzmo400r]

No, I can't think of anything I dislike about the shocks at all. The only downside is with the ground control setup you have to run a very short spring on the front for tire clearance. It's not a big deal if you are set up properly but a helper spring would not be a bad idea in case you hit a big bump. Having a short front spring is a minor compromise to get a far superior shock compared to most of the inexpensive coilovers for sale.

In regards to the other comments, I hope the price of 240s go up again after the next movie comes out. I'm probably going to put mine up for sale.

getting another project or just getting out of the scene?

As for all of the suspension tech, keep it coming. Learning a lot.

[nlzmo400r]

Slotted strut lower bolt holes. I was STILL getting a slight taper in tire heat, implying I needed more spring or more swaybar (whitelines on full stiff, 9kg spring). That or I was just overdriving the car :P

As for toe, I daily drove my car (with those settings) and I didn't like the way 1/32 toe out felt on the highway. Even then, I felt as though my turn-in was fine (even with the staggered tire, 275/315).

running this much camber was strictly for autoX correct?

[jzr]

I run -4.5 up front, with 550lb. front springs (~10k) with the stock front bar, custom Koni shocks. It works pretty well, temps are about right.
http://www.jrho.com/240_blog/frontcamber.jpg

[Wiisass]

Maybe we're just disagreeing on tuning perference, or maybe it's a difference in the type of shocks that we're using. I've been running KONIs in every vehicle that I've raced for the past 8 years, except for once when I thought I would try out those crappy AGX shocks. When I increase the spring rate and if I have the ability to do so, I decrease the compression. On my current shocks, I don't have that option except for when they are being revalved. Which they will be as soon as I get my spare set of shocks back from KONI. At that time, I'll also be taking the opportunity to increase my spring rates another 100lbs.

Good luck with your FSAE program. How long have you been in it? We have a couple of FSAE teams that run with us. Hopefully, your driver is better then the local teams. They always seem to be switching drivers and don't have one that's good enough to run consistent runs. Has to be hell getting any meaningful feedback like that.

I think this is more of a setup thing than shock tuning. When I talk about damping, I'm talking more from a design standpoint, meaning this is how the shocks would come before they were even put on the car. When tuning the car, it's going to be different.

Alright, so I ran some simulations. The simulation is a lumped mass, 4-corner model. For this example, I'm only using a braking input at 1g, ramped from zero over 0.25s, held for 1s and then ramped back down to zero over 0.25s. There is then a 0.4" bump. Here's what I came up with.

http://www.theoryinpracticeengineering.com/tech/zilvia.JPG

The yellow trace is the force generated by the spring, the blue trace is the force generated by the shock. The numbers below are the front spring rate and then the damping coefficients for both the front and rear dampers. During this whole test, the rear springs and dampers are not changed. The only change is to the damping ratio which is the second number in each of the damping coefficient equations. The larger number below each graph is the number I'm going to use to reference that chart. The first couple seconds of the simulation are the when the suspension is loaded, so car is in the air and dropped. It's only like this because this is how the program works.

For the first graph, the front suspension is critically damped. This would be too stiff for a normal car, but it is just to baseline the whole thing. Graph 2 is what we're going to assume as the ideally tuned setup for the car. Graph 3 shows the increase in spring rate and the dampers are left the same. You can see that it takes slightly longer for the car to settle after an input. Graph 4 is with front rebound damping increased and compression damping decreased. You can see from the increased force in the spring, that the car moves more as a results of the braking inputs and then comes back and settles, but it takes longer with less compression damping than with more. Graph 5 is with the stiffer spring and the damper set the same way as in graph 1. Graph 6 is the best guess to matching the behavior of the suspension as in graph 2. you will notice that compression damping is increased. Rebound still needs to be slightly increased to exactly match graph 2, but otherwise it is very close. Graph 7 has the damping ratios adjusted to make the damping coefficient the equivalent if they were revalved and used the same damping ratios as graph 2.

Just take a look at the graphs and look at the trend in the damping ratio compared with the spring rates. it shows that stiffer shocks in both directions are needed in both directions to better control the suspension. This does go against what koni and penske say but it seems like their suggestion is a safe way to blindly adjust the suspension at the track. But depending on the spring rate of the tire, the effect of changing the springs a decent amount is very small for its effect on compression and slightly more for its effect on rebound.

I would be very curious to see what your dyno curves would look like for your shocks now and after they are revalved. I'd also be curious to see what koni would say or plan on doing when you tell them you want to increase your spring rate by 100lb/in. I do need to call them up to ask them about something else, so if I get the chance tomorrow, maybe i'll ask them myself.

I still don't fully understand why everyone would suggest something like that. If that were the case every race car would have no compression damping. Hopefully Koni will have the answer. Otherwise this will continue to both me.

About FSAE, I'm done with that for the most part. But we had some good drivers. The kind of drivers that could give me feedback so I could actually tune the suspension rather than just make blind adjustments.

Alright, well I hope this makes sense.

[ep510]

[QUOTE=jzr]I run -4.5 up front, with 550lb. front springs (~10k) with the stock front bar, custom Koni shocks. It works pretty well, temps are about right.


Did you Slot the Strut like "ace in hole" /PJ or another way to get the -4.5?

DJ

[TheWolf]

Wiisass.. what program is that your using? thanks for the technical responses. I rather enjoy them.

[Wiisass]

That program is just Simulink, it's part of Matlab. The model I'm using is one that I put together based off a 2-degree of freedom system, which was then built up into a 7-dof system with several different inputs. And I'm glad that people enjoy some of these posts.

[jzr]

Did you Slot the Strut like "ace in hole" /PJ or another way to get the -4.5?

DJNope, I get that value with regular Tein camber plates (maxed out) and both strut bolt ear holes at the stock distance from strut centerline.

[MovinUp-1]

getting another project or just getting out of the scene?

As for all of the suspension tech, keep it coming. Learning a lot.

Getting out of turbocharged cars. I'm looking for something to run track days with and then compete in NASA CMC or AI.

I started racing V8s and I want to do it again. No replacement for displacement.

[nlzmo400r]

Getting out of turbocharged cars. I'm looking for something to run track days with and then compete in NASA CMC or AI.

I started racing V8s and I want to do it again. No replacement for displacement.

Yea I saw some pictures of you running the camaro on the track. Mustve been nice to get the beast back out there. You're going to campaign the camaro, or another car?

[MovinUp-1]

I've done a couple of autocrossers this year in Houston. I made some changes to the suspension that made a big improvement and now I'm having to re-learn the car.

I'm going to get another car for track days. The camaro is an autocross only car. I haven't decided what direction I want to go for track days and eventual wheel to wheel road racing. On one hand I'd like to race a V8 but on another hand I'd like to get into an open wheel car. I may try to do a driving school in the fall with a school that has formula cars like Jim Russel or others. I want to race and maintain a proper race car instead of having to work around a street car that is used on the track.

[MovinUp-1]

One thing you guys need to consider when looking at other people's setups is the tracks that you are running on. For instance, from what I know of tracks on the west coast and up in Indiana, Illinois, Michigan area they are quite smooth and have a lot of grip. The tracks that I run on in Louisiana and texas are rougher and less grippy. This greatly affects what spring & sway bars to use.

On a smoother more grippy surface a higher spring rate and less sway bar should generate higher cornering force. However, a rougher, less grippy surface would cause the hard sprung car to skate over the bumps, disconnecting the tire from the surface. In these cases a lighter spring with bigger sway bars to control body roll should work better. As an example, I run 425lb front springs with 350lb rear springs and whiteline sway bars. The car has won a National Tour and divisional events against nationally competitive cars.

So you see one setup is not the best. You must tailor your car to the tracks you typically run on.