Which suspension to get?

[lukits01]

Looking at this price list LINK It looks like the N1 dampers are about 60,000¥ each, and you will need lower brackets at the front and top mounts at the front and rear. A set of Swift springs is about 4-500 dollars at the outside, Mugen lower brackets can be use with Tein N1s and are around $800 I think. You will probably want to change spring rates down the track in any case if you are racing seriously so you should expect to outlay some money on different rates .

This LINK shows the Super Racing are around 400,000¥, that seems comparable to the N1s, they are at least in the same league cost wise.

Rates of 5 or 6kg/mm at the front or rear of a DC5 are barely enough to keep the car off the bump stops at stock height . The stock rear rate is somewhere in the region of 7kg/mm I believe although obviously progressive. I don't think any circuit in the world is bad enough that rates like that would be faster than something a bit stiffer.

I don't like stiff springs that much, but I am a big fan of rates that allow the ride heights that I like with big tyres . For a real race DC5 chassis my (limited ) experience suggests that nothing below 10kg/mm should be considered.

Not going to argue if that setup works for you, mate. You obviously
have found a lot of speed with that setup.
But I find it rather peculiar that
companies like ohlins/nitron/ast/kw would market megadollar race
suspension with roughly F6/R9 spring rates.
If a car that weights in the 1100kg range would hit bump stops with
6kg spring rates (in my also limited experience) that suggest a suspension setup that is severely short on suspension travel!

anyway with regards to the topic at hand (if we ignore the setup for one sec) I wouldn't know what the build quality of the Zeals are like, but from what I've seen of the Tein SRC, their build quality is top notch, nothing like the PoS Tein HA of old. The adjustment knobs seem to work better too, more linear and predictable.

[SpoonS]

Ok guys, after much reading, suggestions from you guys, deliberation, and talking to suppliers, a very good deal that couldn't be refused turned up and i'm pretty much settled in getting the Tein SRC.

Now i just have to wait the 8 weeks for them to arrive...

Thanks for all your comments on this matter

[Samm928]

fightexxxxxxxxxxxxx or cusco zero 2's. go all out.

[ChargeR]

Ok guys, after much reading, suggestions from you guys, deliberation, and talking to suppliers, a very good deal that couldn't be refused turned up and i'm pretty much settled in getting the Tein SRC.

Now i just have to wait the 8 weeks for them to arrive...

Thanks for all your comments on this matter

Good work! Did you go with their standard spring rates?

Not going to argue if that setup works for you, mate. You obviously
have found a lot of speed with that setup.
But I find it rather peculiar that
companies like ohlins/nitron/ast/kw would market megadollar race
suspension with roughly F6/R9 spring rates.
If a car that weights in the 1100kg range would hit bump stops with
6kg spring rates (in my also limited experience) that suggest a suspension setup that is severely short on suspension travel!

My car isn't fast at all, the main thing holding it back is the driver. I know this, it is only momentary bouts of inflated ego that propel me into modifying my suspension to get more performance.

We aren't arguing we are having a enlightened discussion . If we spoke in person I would be the first to say not to listen to some guy on the internet, but since the issue of what dampers SpoonS should get has been decided I think we should discuss setup now .

I agree that it is peculiar that those well respected expensive damper companies would try to sell me a race suspension with rates like that. If I am paying European damper money I want whatever spring rates take my fancy . Out of interest for pure circuit use in a DC5 would you recommend similar rates to what KW etc. sell in their kits? And why? I have already stated the sort of rates that I think are a good starting point for a race DC5 so I am curious as to what you think and why my recommendation is bad. On a fairly simplistic level the way I would set spring rates is to go as high as possible with consideration for bump compliance and driver comfort also also with consideration for the tyres being used. Then set the car as low as possible before the geometry goes all pear shaped.

When I referred to a DC5 with 6kg/mm rates being all over the bumpstops, what I really meant is that the car would totally run out of suspension travel, as in the tyre would be about to contact the chassis. I didn't mean to imply that the damper would have run out of bump travel, that was an error on my part, and bump stops coming into play long before tyre interference is another issue entirely.

[lukits01]

Good work! Did you go with their standard spring rates?

My car isn't fast at all, the main thing holding it back is the driver. I know this, it is only momentary bouts of inflated ego that propel me into modifying my suspension to get more performance.

We aren't arguing we are having a enlightened discussion . If we spoke in person I would be the first to say not to listen to some guy on the internet, but since the issue of what dampers SpoonS should get has been decided I think we should discuss setup now .

I agree that it is peculiar that those well respected expensive damper companies would try to sell me a race suspension with rates like that. If I am paying European damper money I want whatever spring rates take my fancy . Out of interest for pure circuit use in a DC5 would you recommend similar rates to what KW etc. sell in their kits? And why? I have already stated the sort of rates that I think are a good starting point for a race DC5 so I am curious as to what you think and why my recommendation is bad. On a fairly simplistic level the way I would set spring rates is to go as high as possible with consideration for bump compliance and driver comfort also also with consideration for the tyres being used. Then set the car as low as possible before the geometry goes all pear shaped.

When I referred to a DC5 with 6kg/mm rates being all over the bumpstops, what I really meant is that the car would totally run out of suspension travel, as in the tyre would be about to contact the chassis. I didn't mean to imply that the damper would have run out of bump travel, that was an error on my part, and bump stops coming into play long before tyre interference is another issue entirely.

I hope the OP doesn't mind that we are having this "enlightened discussion" haha

Right... where to start.. I understand that you are speaking from your experience from racing your DC5, I have to admit first up that I do not own a DC5 so having to come up with a spring rate number without any sort of data to back it up wont mean much to anyone.

What I cannot agree on is setting spring rates to go as high as possible.
IMO spring rates should be set to keep the suspension within a nice camber curve when weight transfer occurs during cornering. So I would start with setting rear spring rate + roll bar to get the rear inside wheel to "just" lift up under cornering. So now we've maximized weight loading on the other 3 wheels which are actually generating the cornering force. Front spring rate are then set to keep check total roll angle to ensure the outside front tire is still more or less flat with the road (together with static camber).

So if the springs rates are too high there wont be any sufficient weight transfer. Too little and you risk the suspension falling outside the nice camber curve (pear shaped geometry). Key aim is to find that sweet spot but the suspension needs to be able to move to work, otherwise you will be relying solely on the tire to generate grip and with little "mechanical" grip. Its all about maximizing the camber curve, if lowering or stiffening the suspension compromises this, then I believe the car wont be maximizing its cornering capability.

With regards to suspension travel, my understanding is that bumpstops is there to stop tire interference with the fenders or other. If the tires are already hitting the fenders before hitting the bumpstops, isn't that setup suffering from an even worse lack of travel?

[SpoonS]

Good work! Did you go with their standard spring rates?

Ya i'm going with the standard spring rates for now. If i end up not liking it, i can always just change the springs

[ChargeR]

I hope the OP doesn't mind that we are having this "enlightened discussion" haha

Right... where to start.. I understand that you are speaking from your experience from racing your DC5, I have to admit first up that I do not own a DC5 so having to come up with a spring rate number without any sort of data to back it up wont mean much to anyone.

What I cannot agree on is setting spring rates to go as high as possible.
IMO spring rates should be set to keep the suspension within a nice camber curve when weight transfer occurs during cornering. So I would start with setting rear spring rate + roll bar to get the rear inside wheel to "just" lift up under cornering. So now we've maximized weight loading on the other 3 wheels which are actually generating the cornering force. Front spring rate are then set to keep check total roll angle to ensure the outside front tire is still more or less flat with the road (together with static camber).

So if the springs rates are too high there wont be any sufficient weight transfer. Too little and you risk the suspension falling outside the nice camber curve (pear shaped geometry). Key aim is to find that sweet spot but the suspension needs to be able to move to work, otherwise you will be relying solely on the tire to generate grip and with little "mechanical" grip. Its all about maximizing the camber curve, if lowering or stiffening the suspension compromises this, then I believe the car wont be maximizing its cornering capability.

With regards to suspension travel, my understanding is that bumpstops is there to stop tire interference with the fenders or other. If the tires are already hitting the fenders before hitting the bumpstops, isn't that setup suffering from an even worse lack of travel?

I was only being an arse when I asked you what rates would be better, it obviously isn't ideal to be expected to recommend rates for a car you don't own . I am very wary of recommending rates as well, I just thought I might be able to trick you into recommending some numbers that I could try dispute .

I generally agree with some of the points you make for deciding on spring rates, and I think my comment of run as stiff as the track/driver/tyre will tolerate and slam the car was a little simplistic. I agree that the point where the car will jussst be unloading the inside rear totally at maximum cornering Gs is a good point to be at, however I have bolded a couple of parts of your post that I don't quite agree with.

It will be the front and rear roll couple, or the differences in relative roll stiffness, that determines when and how high the inside rear lifts off the ground, so you need to have already decided on front springs and sways, a ride height etc. and then be testing before deciding if you have enough rear roll stiffness to just lift the inside rear, so the process would have to be iterative. As in start with X front springs and Y rear springs and then go from there. You can't get it right first pop unless you have put a lot of effort into modelling the suspension. So you can't very well set the front rate to keep the tyre in a good part of the camber curve at maximum cornering load if you need to have already set the front rate to determine the front and rear relative roll stiffnesses to just lift your inside rear.

You state that too stiff springs will prevent weight transfer. I define weight transfer as the change in vertical loads on the outside tyres relative to the inside tyres and I believe you are incorrect. 2 cars with the same CG height, track width and undergoing the same cornering force but sprung completely differently (one stiff, one soft) will have nearly exactly the same weight transfer. They will be slightly different due to the centre of gravity migrating a bit more on the soft car and other effects inherent in a non-ideal world. So one shouldn't pick springs to minimise weight transfer, if you want to minimise weight transfer then widen the track or lower the centre of gravity. Selling your production car and buying an open wheeler is the best approach to achieve both these things .

I have redded out a bit of your post that I think is very important. Camber gain with compression at the front of a DC5 is nearly negligible, and this is one of the reasons that I think that relatively high rates are needed to prevent the car cornering on the outer shoulder of the tyre, to the detriment of grip and speed. This might be our main point of contention, because unless you are running nankangs I think the rates needed to keep the outside front tyre on a DC5 happy in a corner are pretty high, unless you like running a great deal of static camber. "Any suspension will work if you don't let it"

I don't understand what "mechanical" grip is? I have heard the term before and often wondered what it meant. I prefer to use tyres to grip the road surface on my cars. Do you have a recommended book I might read to understand it better, because I am just not getting it.

I think a car that has tyre to chassis interference is pretty screwed you're right, but I guess it has the same or more suspension travel as an otherwise identical car that has bump stops installed to prevent said tyre interference. The bump stop by definition must come into play before the tyre bottoms out. I have zero experience with using bump rubbers as a tuning tool but I feel like they would be a last step thing that you install to give yourself a bit of highly progressive spring right at the travel. And if they are being encountered more than a couple of times a lap then the car is too low.

I am liking this discussion, I think we would probably arrive at pretty similar rates we are just approaching the problem from a different direction. I still think the rates you mentioned earlier in the thread are far too soft though .

[SpoonS]

Anyway, since i decided on what i'm getting, ChargeR and lukits01, you have my permission to "hijack" this tread for your discussion

[yellows2k]

i would have suggested cusco zero 2, had them on my evo9. felt really good and had the electronic in car dampening adjustment

[lukits01]

Anyway, since i decided on what i'm getting, ChargeR and lukits01, you have my permission to "hijack" this tread for your discussion

cheers, bud. hope this thread jack has been somewhat useful to you (or at least entertaining) haha

I was only being an arse when I asked you what rates would be better, it obviously isn't ideal to be expected to recommend rates for a car you don't own . I am very wary of recommending rates as well, I just thought I might be able to trick you into recommending some numbers that I could try dispute .

I generally agree with some of the points you make for deciding on spring rates, and I think my comment of run as stiff as the track/driver/tyre will tolerate and slam the car was a little simplistic. I agree that the point where the car will jussst be unloading the inside rear totally at maximum cornering Gs is a good point to be at, however I have bolded a couple of parts of your post that I don't quite agree with.

It will be the front and rear roll couple, or the differences in relative roll stiffness, that determines when and how high the inside rear lifts off the ground, so you need to have already decided on front springs and sways, a ride height etc. and then be testing before deciding if you have enough rear roll stiffness to just lift the inside rear, so the process would have to be iterative. As in start with X front springs and Y rear springs and then go from there. You can't get it right first pop unless you have put a lot of effort into modelling the suspension. So you can't very well set the front rate to keep the tyre in a good part of the camber curve at maximum cornering load if you need to have already set the front rate to determine the front and rear relative roll stiffnesses to just lift your inside rear.

You state that too stiff springs will prevent weight transfer. I define weight transfer as the change in vertical loads on the outside tyres relative to the inside tyres and I believe you are incorrect. 2 cars with the same CG height, track width and undergoing the same cornering force but sprung completely differently (one stiff, one soft) will have nearly exactly the same weight transfer. They will be slightly different due to the centre of gravity migrating a bit more on the soft car and other effects inherent in a non-ideal world. So one shouldn't pick springs to minimise weight transfer, if you want to minimise weight transfer then widen the track or lower the centre of gravity. Selling your production car and buying an open wheeler is the best approach to achieve both these things .

I have redded out a bit of your post that I think is very important. Camber gain with compression at the front of a DC5 is nearly negligible, and this is one of the reasons that I think that relatively high rates are needed to prevent the car cornering on the outer shoulder of the tyre, to the detriment of grip and speed. This might be our main point of contention, because unless you are running nankangs I think the rates needed to keep the outside front tyre on a DC5 happy in a corner are pretty high, unless you like running a great deal of static camber. "Any suspension will work if you don't let it"

I don't understand what "mechanical" grip is? I have heard the term before and often wondered what it meant. I prefer to use tyres to grip the road surface on my cars. Do you have a recommended book I might read to understand it better, because I am just not getting it.

I think a car that has tyre to chassis interference is pretty screwed you're right, but I guess it has the same or more suspension travel as an otherwise identical car that has bump stops installed to prevent said tyre interference. The bump stop by definition must come into play before the tyre bottoms out. I have zero experience with using bump rubbers as a tuning tool but I feel like they would be a last step thing that you install to give yourself a bit of highly progressive spring right at the travel. And if they are being encountered more than a couple of times a lap then the car is too low.

I am liking this discussion, I think we would probably arrive at pretty similar rates we are just approaching the problem from a different direction. I still think the rates you mentioned earlier in the thread are far too soft though .

wow, you are really making me work for my words haha
I can agree with you on those points, even on the ones you disagree with me lol. What I should have said is "if the springs rates are too high there wont be sufficient suspension movement (mostly compression) from weight transfer." If any sort of suspension compression puts the DC5 suspension in a crappy geometry then Honda have done a terrible job and I don't believe that is the case.

Like you said the main point of contention is choice of spring rates, I just can't see such high spring rates is maximizing the good parts of the camber curve. Unfortunately I don't really have data to back this up, but fortunately picking a starting spring rate from a simple suspension model is not too hard.

Don't suppose you have a rough corner weight data from a DC5? If we can get sprung weight measurements I believe we can use the table at the bottom of this pdf Spring & Damper Tech Tip1 The rest of the pdf covers the model used to derive that spring rate table. I believe a front natural frequency of around 2Hz would be a good start. If the outcome of this is a setup requires you to run lots of static camber, then I think that's still the way to go.

This is risking derailing our initial discussion but my understanding of the term "Mechanical Grip" is a suspension setup that maximizes the tire contact patch and maintains it as much as possible over a varied course/condition with little or no help from down force. Rally cars are usually a great example of this as the variation in road condition they encounter is massive and therefore their suspension travel is equally massive. I can only offer you this online article: Weight Transfer Theory

Mechanical Tyre Grip Theory

Tyre grip depends on the ability of the tyre rubber to interlock with the grain of the road surface. The surface of the road causes continuous small movements of the suspension, and variation in load on the tyre. For maximum grip, we need to minimise this variation. Grip increases with suspension pressure. We want to push the tyre into the road surface harder & longer. The suspension pressure results from the sum of the tyre, spring, and anti-roll bar rates and shock loading, and could also be influenced by the torsional stiffness of the car.

So we have two competing requirements here. If we run spring rates as soft as possible, the lower suspension frequency (the suspension moves up and down so many times per second) will allow the tyre to be pressed into the road longer. But harder spring rates will press the tyre into the road harder. The best solution can be hard to find. Optimum grip requirements will change with each race car, tyre and road surface. But the trend is to run softer springs, and reset the shock to maintain the pressure on the tyre.

The shock must also control the rebound of the suspension very accurately so as to reduce the amplitude in these small displacements of the suspension. It appears that only an expensive racing shock is precise enough to do this over a race distance.

[ChargeR]

wow, you are really making me work for my words haha
I can agree with you on those points, even on the ones you disagree with me lol. What I should have said is "if the springs rates are too high there wont be sufficient suspension movement (mostly compression) from weight transfer." If any sort of suspension compression puts the DC5 suspension in a crappy geometry then Honda have done a terrible job and I don't believe that is the case.

Like you said the main point of contention is choice of spring rates, I just can't see such high spring rates is maximizing the good parts of the camber curve. Unfortunately I don't really have data to back this up, but fortunately picking a starting spring rate from a simple suspension model is not too hard.

Don't suppose you have a rough corner weight data from a DC5? If we can get sprung weight measurements I believe we can use the table at the bottom of this pdf Spring & Damper Tech Tip1 The rest of the pdf covers the model used to derive that spring rate table. I believe a front natural frequency of around 2Hz would be a good start. If the outcome of this is a setup requires you to run lots of static camber, then I think that's still the way to go.

This is risking derailing our initial discussion but my understanding of the term "Mechanical Grip" is a suspension setup that maximizes the tire contact patch and maintains it as much as possible over a varied course/condition with little or no help from down force. Rally cars are usually a great example of this as the variation in road condition they encounter is massive and therefore their suspension travel is equally massive. I can only offer you this online article: Weight Transfer Theory

Thanks for the explanation on mechanical grip and the link, I understand the term a bit more clearly now.

I guess you are right, it is a great big assumption on my part that the camber gain at the front is so small that we need big rates to keep it from rolling over even with decent static camber. My only evidence for this is anecdotal; with anywhere from -4.5 to -5.5 camber on the front of my car with rates varying between 10-24 to 14-28 my track tyre wear has been extremely even, and the limited tyre temperature data is also positive with the inner being a handful of degrees hotter than the outside. I don't think that tyre wear is a great indicator of how well a tyre is being used though.

I don't have accurate unsprung weight data for the DC5 sadly, although if you are interested the motion ratios are generally accepted to be around 0.91 at the front and about 0.55 to 0.6 at the rear but I haven't measured these myself. I have attempted to attach a zip file of a ride frequency calculator written by a fellow over at ClubRSX (who's name escapes me at this moment) and I believe the default values in that program are the measured values from someone with a DC5. Even accepting those values as pretty roughly accurate and calculating my frequencies puts me a long way above the suspension frequencies you are advocating, but I don't think I trust the numbers in that program enough to work out what sort of spring rate is necessary to achieve the 2 Hz you mention. I guess it would be in the region of 8-10kg/mm though.

How does the tyre type and the extent of modification allowed to the car affect what sort of suspension frequency you think is a good compromise? Our suspension frequency gives an indication of bump compliance but what if we need additional stiffness to compensate for aero loads and also to aim to run the car extremely low to maximise the performance of aero aids, and it is an acceptable compromise to loose a bit of comfort over bumps? I think that in a fairly street oriented car your suggestion of starting at around 2Hz at the front sounds good, but perhaps if other areas of the car become more prepared then higher rates might become a better compromise. What do you think?

Really I am just arguing because I like the rates my car is on, and I like my cars low . I guess driver preference is something that needs to be considered as well, some probably prefer a more stiffly sprung car and others the opposite. It is unfortunate that the fellow making suspension changes to my car is the same guy driving it .

[TeMp]

Gee aren't you guys having fun.

Regardless there's some quality info there.

[lukits01]

Thanks for the explanation on mechanical grip and the link, I understand the term a bit more clearly now.

I guess you are right, it is a great big assumption on my part that the camber gain at the front is so small that we need big rates to keep it from rolling over even with decent static camber. My only evidence for this is anecdotal; with anywhere from -4.5 to -5.5 camber on the front of my car with rates varying between 10-24 to 14-28 my track tyre wear has been extremely even, and the limited tyre temperature data is also positive with the inner being a handful of degrees hotter than the outside. I don't think that tyre wear is a great indicator of how well a tyre is being used though.

I don't have accurate unsprung weight data for the DC5 sadly, although if you are interested the motion ratios are generally accepted to be around 0.91 at the front and about 0.55 to 0.6 at the rear but I haven't measured these myself. I have attempted to attach a zip file of a ride frequency calculator written by a fellow over at ClubRSX (who's name escapes me at this moment) and I believe the default values in that program are the measured values from someone with a DC5. Even accepting those values as pretty roughly accurate and calculating my frequencies puts me a long way above the suspension frequencies you are advocating, but I don't think I trust the numbers in that program enough to work out what sort of spring rate is necessary to achieve the 2 Hz you mention. I guess it would be in the region of 8-10kg/mm though.

How does the tyre type and the extent of modification allowed to the car affect what sort of suspension frequency you think is a good compromise? Our suspension frequency gives an indication of bump compliance but what if we need additional stiffness to compensate for aero loads and also to aim to run the car extremely low to maximise the performance of aero aids, and it is an acceptable compromise to loose a bit of comfort over bumps? I think that in a fairly street oriented car your suggestion of starting at around 2Hz at the front sounds good, but perhaps if other areas of the car become more prepared then higher rates might become a better compromise. What do you think?

Really I am just arguing because I like the rates my car is on, and I like my cars low . I guess driver preference is something that needs to be considered as well, some probably prefer a more stiffly sprung car and others the opposite. It is unfortunate that the fellow making suspension changes to my car is the same guy driving it .

I think you and I are bound by the same constraints, we both want to drive faster and make our cars faster but are limited in resource (time or money, etc.) I've tried to compensate for this by pawning off experience from other people that have time and money to test, so I don't have to test them myself! I try to read a lot of articles that have some facts to back up their claims, so let me make it clear that from this point its mainly my opinion based on probably 2nd hand information.

It seems its widely accepted for a production based FWD race car a NF of 2Hz front and 2.5Hz rear is a good place to start. Like you said it'll be an iterative process to determine your optimum setup, but I can't imagine it to be off by more than 0.5Hz so if my spring rates puts me at 3Hz or more, I'd seriously start to reconsider my setup. If anything I'd try a little bit lower than those starting numbers and see what happens before going higher.

Things that I would consider to go softer
1. bump compliance, some race tracks require you to ride kerbs or cut ripple strips. Rally guys likes to let their inside wheels drop into ditches when cutting corners, etc.
2. lots of weight loss, makes sense, less unsprung weight, technically you should be recalculating your spring rates anyway.

Things that I would consider to go harder
1. Super special sticky racing slicks means you can corner harder & faster == more weight transfer (I really do mean weight transfer this time ) Quite possible the suspension geometry has gone all pear shaped at peak roll.
2. Meaningful downforce, let me iterate that I am extremely skeptical of any aftermarket "aero" aids as a source of "downforce" the way I see it, for downforce to work the car has to be REALLY REALLY low. How low? I take it you guys are familiar with Cyber EVO at recent time attack event:

At this point the car is useless on public roads, so if I were looking at Aero parts, it would be for either increasing cooling efficiency, reducing drag, or maybe even decreasing lift by channeling air away from certain parts of the car. Possibly the only exception to this rule are rear wings, but even then for FWD I'd be using that only for high speed stability, not enough to drastically change my spring rates. But if you do find yourself with meaningful downforce then I can see why you'd need high spring rates, you'd be tuning the suspension for max aero grip and sacrificing mechanical grip. I'd imagine it would center around maintaining that minuscule ride height without bottoming out the car (at this point all aero & mechanical grip disappears)

If I'm lowering my car, I'd do it for mechanical grip rather than some mythical downforce. I personally haven't lowered my car more than 10mm, tbh I haven't done the measurements to justify that lowering will be good for the camber curve so I've left it close to what Honda has chosen for me. I've seen a friend with his DC5 burned badly when he decided to lower his car with TODA-DA (FYI: F8/R12), it rode horribly and would snap oversteer often (think the record was 4 gravel traps in one event) Once he put in Roll-Centre Adjusters, it transformed the way the suspension behave completely! The ride quality was good and from what Ive been told it handled the track much better. After seeing that I'm very conservative when it comes to lowering.

Then there's the subject of driver preference, the thing with weekend racers like us is we try to be race driver & race engineer at the same time, which has its drawbacks. You need to question your own decisions cause nobody else is going to do it for you (except maybe today ) When I started with my car I just adjusted the suspension till it "felt" great. Car would corner flat and no excessive oscillations on bumps. At some point I was pointed to this gem of a website: Autocross to Win-Shock Forces he mentioned that suspension movement is not necessarily a bad thing if you get used to driving with it, so I started to soften up my settings and the car moved around a lot but my laptimes started to drop (at one point my street tire time practically matched my RE55S time) a friend would jump in the car for drive around the track and say "gee your car has a lot of body roll". Point I'm trying to make is don't rely too much on driver feeling at most times its bias and inaccurate, DATA on the other hand never lies, I'm starting to use PerformanceBox GPS datalogger myself and finding lots of my initial assumptions to be wrong.

[ChargeR]

I think you and I are bound by the same constraints, we both want to drive faster and make our cars faster but are limited in resource (time or money, etc.) I've tried to compensate for this by pawning off experience from other people that have time and money to test, so I don't have to test them myself! I try to read a lot of articles that have some facts to back up their claims, so let me make it clear that from this point its mainly my opinion based on probably 2nd hand information.

It seems its widely accepted for a production based FWD race car a NF of 2Hz front and 2.5Hz rear is a good place to start. Like you said it'll be an iterative process to determine your optimum setup, but I can't imagine it to be off by more than 0.5Hz so if my spring rates puts me at 3Hz or more, I'd seriously start to reconsider my setup. If anything I'd try a little bit lower than those starting numbers and see what happens before going higher.

Things that I would consider to go softer
1. bump compliance, some race tracks require you to ride kerbs or cut ripple strips. Rally guys likes to let their inside wheels drop into ditches when cutting corners, etc.
2. lots of weight loss, makes sense, less unsprung weight, technically you should be recalculating your spring rates anyway.

Things that I would consider to go harder
1. Super special sticky racing slicks means you can corner harder & faster == more weight transfer (I really do mean weight transfer this time ) Quite possible the suspension geometry has gone all pear shaped at peak roll.
2. Meaningful downforce, let me iterate that I am extremely skeptical of any aftermarket "aero" aids as a source of "downforce" the way I see it, for downforce to work the car has to be REALLY REALLY low. How low? I take it you guys are familiar with Cyber EVO at recent time attack event:

]http://www.dentsport.com/wp-content/uploads/2008/12/cyber-evo-1.jpg

At this point the car is useless on public roads, so if I were looking at Aero parts, it would be for either increasing cooling efficiency, reducing drag, or maybe even decreasing lift by channeling air away from certain parts of the car. Possibly the only exception to this rule are rear wings, but even then for FWD I'd be using that only for high speed stability, not enough to drastically change my spring rates. But if you do find yourself with meaningful downforce then I can see why you'd need high spring rates, you'd be tuning the suspension for max aero grip and sacrificing mechanical grip. I'd imagine it would center around maintaining that minuscule ride height without bottoming out the car (at this point all aero & mechanical grip disappears)

If I'm lowering my car, I'd do it for mechanical grip rather than some mythical downforce. I personally haven't lowered my car more than 10mm, tbh I haven't done the measurements to justify that lowering will be good for the camber curve so I've left it close to what Honda has chosen for me. I've seen a friend with his DC5 burned badly when he decided to lower his car with TODA-DA (FYI: F8/R12), it rode horribly and would snap oversteer often (think the record was 4 gravel traps in one event) Once he put in Roll-Centre Adjusters, it transformed the way the suspension behave completely! The ride quality was good and from what Ive been told it handled the track much better. After seeing that I'm very conservative when it comes to lowering.

Then there's the subject of driver preference, the thing with weekend racers like us is we try to be race driver & race engineer at the same time, which has its drawbacks. You need to question your own decisions cause nobody else is going to do it for you (except maybe today ) When I started with my car I just adjusted the suspension till it "felt" great. Car would corner flat and no excessive oscillations on bumps. At some point I was pointed to this gem of a website: Autocross to Win-Shock Forces he mentioned that suspension movement is not necessarily a bad thing if you get used to driving with it, so I started to soften up my settings and the car moved around a lot but my laptimes started to drop (at one point my street tire time practically matched my RE55S time) a friend would jump in the car for drive around the track and say "gee your car has a lot of body roll". Point I'm trying to make is don't rely too much on driver feeling at most times its bias and inaccurate, DATA on the other hand never lies, I'm starting to use PerformanceBox GPS datalogger myself and finding lots of my initial assumptions to be wrong.

Good comments! I agree that meaningful downforce probably isn't something worth considering for the level of preparation my car is at (and possibly yours) but I thought it was something worth mentioning to illustrate that there is more to spring rate choice than is initially obvious and that compromise is inherent in the choice.

I can't honestly disagree with any of the points you make, and your assertion regarding both of us being limited by time/money etc. is very true at least in my case. We don't really have the opportunity to test various configurations to the extent we might like, but then I doubt any race team in the world does. So we start at a best guess and then vary only slightly from that point, we just seem to have started from a different point .

You are wise not to lower your car to far, maintaining the suspension in a near stock range of motion is a good idea when we don't have any reliable data to support the change. As it is my choice to lower the car a lot has left me flying blind with only limited testing, feel and the stopwatch to tell me the difference. Not ideal as you mention.

Maybe if you did lower your car a bit more though you might find your car bottoming out and your spring rates to be insufficient . On the subject of DC5 roll centre adjusters, did your friend make any other changes at the same time? Raising the roll centre back closer to the CG at the front would have the obvious effect of more geometric roll stiffness so if we follow the general rule of thumb that that stiffening the front would promote more understeer the result is not unexpected. Interesting that the car suffered from snap oversteer though, I have never had so much oversteer that I would complain about it . Roll centre adjusters on a street car scare me a little though, replacing such a highly stressed part with something aftermarket of questionable manufacture is not something I am keen to do.

How do you find the PerformanceBox datalogger? I have considered acquiring such a device for some time but some ricey modification or some other always gets in the way . I rely too much on driver feeling. For example, at my most recent track outing I had my dampers on nearly their softest setting, after previously running them at nearer the stiffest. The result was a lot more movement on initial turn in, and the sensation of the car taking much more time to settle into a corner. It was spooky, but in hindsight I think if I had got used to it both me and the tyres would have preferred the lesser damping. The car didn't feel horribly underdamped and bump compliance was better.

[tinkerbell]

lovin' mah DC2 simplicity!