How are stiff spring rates determined, if you would like to keep the stock handling. I know there is a lot of R & D involved in fine tuning it but I would like to know the general principle behind stiffening up the spring rates. For eg: the stock spring rates are:

180lb/in (3.2K) front and 225lb/in (4K) rear

So, when increasing the rate while all else stay constant do you:

1. Increase the rates proportionally? eg: to stiffen by 2 (make the springs twice as hard), do you multiply both front and rear by 2 to maintain stock handling, giving:

360lb/in (6.4K) front and 450lb/in (8k) rear

or

2. Increase the rates by the same amount front and rear keeping the difference between them the same? eg: Increase both front and rear by 200lb/in to maintain stock handling characteristics, giving

380lb/in front and 425lb/in rear

From some of the research I have done it seems Vishnu and Chronohunter supposedly use:

450lb/in front and 550lb/in rear

Which is approximately 2.5 times the stock front and rear spring rate. So what is the correct way to figure out spring rates while maintaining stock handling characteristic w.r.t the rest of the suspension components staying the same? Something tells me increasing rates proportionally is the way to go.

Suraj

 

mmm a lot of changing springs is to alleviate stock handling characterisctics right?

a lot of increasing spring rate is also due to lowering, the lower you are the harder you have to be so you don't bumpstop out.

the last part of increasing spring rate is likely the most important and that's your method or choice of chassis response, fast or slow and that all depends on which end you're talking about (front or rear) and how fast or slow you want each end to go.

the thing is you can work around spring rates with anti roll bars and stuff, it's the wheel rate that ends up mattering in the end. of course you get less mucking if you start with something that is well "centered" so your adjustments for particular situations are based around a centered rate rather than being at the ends of your adjustments already.

after you have a well tested spring rate then the more important discussion of damper tuning comes into place.

with that said it's not really about multiplying or adding a certain amount to stock settings, but if you wanted to keep handling EXACTLy like stock then you could mimick the ratio, it would do essentially the same stuff at that point except faster, it would load the tires the same but faster it would transision the same just faster, understeer the same but faster etc.

however if you want the car to behave a certain way, a way more conducive to doing a certain type of racing... then you'd have to start fresh. abandon the stock like settings.

on a final note it's not surprising that gerrard's rates are multiples of the factory rates as he uses the factory bars. that said he most likely increases his front grip with aero and alignment settings to achieve more favorable driving characteristics.

 

IIRC, the rule of thumb is that your front rate should be around 80% of your rear rate. The stock EVO is just like that (180/225x100=80%). On my SE-R racecar I run 550 front and 650 rear which is around 80%. Vishnu seems to use this same formula, if your numbers are correct. Ofcousre, this is not a hard and fast rule. There are other things that go into selecting spring rates.

 

i think you mean stock 'balance' not stock handling. by definition, heavier spring rates change the handling.

 

Devils advocate here....if you like the stock handling......why change it


But if you feel you have to and you want to fit coilovers, I have found running moderate spring rates and having good valving adjustment gives you the best all round suspension. Run sensible spring rates (a personal preference based on your own tolerance to harsh ride) and then adjust the valving based on what you are doing with the car. Button the valving off for day to day, then wind it up at the track or for an aggressive hills drive.

 

Ok can someone tell me the difference between handling and balance. The way I understand things is, balance is the the distribution of weight and handling is the ajility/nimbleness of the car. So if a car understeers or oversteers at the limit does that describe it handling or balance? Doesn't the balance determine the handling characteristics?

Trinydex:What do you mean by wheel rate? are you talking about the frequency of the wheel bouncing around in the suspension or the roll characteristics of the chasis due to the suspension?

I think, you are partially correct about increasing the spring rates having to compensate for the lowering the car. But I don't think it has to do with not wanting to hit the bump stops alot of cars actually hit the bump stop under extreme cornering, at that point the spring rate turn to infinity (aka having no springs). Isn't the real reason is so that you don't bottom out the pistons on your damper thereby destroying them? Because by lowering the car you essentially reduce the amount of available travel you have on you damper. But that is only a minor part, on some dampers you have a higher limitation by their design.

Wangracing: Altought I like the stock handling/balance characteristics I would like there to be a little less body roll, squat and dive, thus the necessitating the use of stiffer springs. The more important part (for me) has to do with reducing body roll, dive and squat. There by reducing amount of weight transfer and maintaining higher amounts of overall grip and at the same time increasing handling response, acceleration grip and braking grip.

I have read about how factories come to determine the spring rates given a certain chasis and it is a lot of work. Alot of chasis bending and figuring out the frequency factor (I think thats what its called) on what rate springs to use and then fine tuning those rates with damper and sway bars. It is something I'm not willing to do as it is a PITA. I am also aware of how one can change the basic handling/balance to over or understeer but I find the factory setup very well designed and would like to keep the same handling/balance (???) dynamics. Because to me the balance is constantly changing based on driver inputs. And yes I have little faith in aftermarket companies designing suspension components .

IMHO, the problem with doing basic adjustments is, it effects the handling/balance characteristics through the entire speed range for the car. What turns really well at low speeds could be disasterous on high speed sweepers. What seems balanced and stable in high speed sweeper would be unacceptable understeer in low speed corners. Yes there are inputs the driver can use to mayke the car behave a certain way but IMHO a car should also be easier to drive in order to make the driver faster.

If given the choice to tune the car with springs or swaybars, I choose springs as sway bars do not aleviate the problem with diving and squatting (aka front to rear weight transfer). Yes there is a nasty side effect of increasing spring rates as it makes your chasis absorb more shock and makes for a harsher ride but that is also true for swaybars. What is even worse is thicker sway bars make you suspension less independant = less overall grip. In my opinion if you can design/tune a suspension without the use of swaybars that is the best. If you have to use swaybars to tune until you get the handling characteristic you want go with the thinnest swaybar possible. As far as I know the stock swaybar is the thinnest.

How you want each end to go out is determined to a large extent by how you drive and what the limits of your car is. I am a firm believer in mod the driver not the car. IMHO, a big difference in how quickly the front or the rear loses grip is determined by the difference overall stiffness between the front and the rear and then to some extent side to side.

Someone please correct me if I am wrong.

But my original question still stands, how do I keep the handling/balance dynamics for the car the same as stock through the entire speed range just using springs?

 

the wheel rate is the final spring rate that the wheel experiences after sway bars and other such springing devices are accounted for. you can have a 3k spring and run a 27mm bar on full stiff and have an effective 8k wheel rate (numbers totally made up).

you're absolutely right about the suspension travel, my caveat was more directed towards your uninformed buyer and manufacturer who doesn't necessarily CREATE a suspension for a specific application but may ADAPT from some previous UNRELATED application. that said even if a certain suspension contains the right measurements and geometries where it can have very good performance potential if you're not using the correct BASE springing and the appropriate damping and subsequent damping adjustability in either direction then you'll end up with a suspension that is running on one of it's extremeties and that will limit your ULTIMATE adjustability, which is a shame.

btw caps don't mean i'm yelling i just can't do the underscoring sometimes when i'm typing fast.

to address your former question, handling and balance is all terminology. in the end a suspension setup serves you and you as a driver dictate your own driving style, philosophy nad the method by which you will employ such talent through your suspension setup.

we've seen a few competent suspension tuners come here nad debate about how THEY like to drive their cars. and THEIR setups and suspension philosophy then reflect those attributes.

in the end balance is what YOU want it to be. but it's more of an overall encompassing term. if you want your car to be balanced in such a way where you can full throttle it and get just a tinge of oversteer at corner exit then you can most assuredly achieve that with a certain type of suspension setup.

handling is a similarly vague term. in the end... we have one judge and that's the stopwatch and we have one way of getting the best time and that's to minimize the time. it can be achieved through increasing grip, increasing horsepower etc. but in the end the HANDLING is up to you and whether or not something improves your handling also much depends on YOUR personal driving style.

 

this is a good point and this is clearly why double adjustable suspensions are superior to lesser adjustable suspensions. double adjustable allows you to adjust for the low speed dampening (high speed sweeper car lean in) and high speed dampening (low speed hard turn in and bumpy roads).

for your original question try this. increase the spring rate all around with a GREAT set of coilovers, preferably ones that have sag springs to help your tripodding and then remove your sway bars. that will be the most independant setup you can achieve. with proper damping your ride won't be unbearable... but it's not gonna be sweet of course.

this is just an on paper conjecture in the end and i'd actually recommend really just calling up one of the suspension tuners that are well known fo rtheir sucesses and tell them that you want what you just described and ask them how exactly to achieve it.

 

Since the job of springs are to limit total load transfer, changing the rates will change the way the car handles. By that defintion, if you wanted to maintain stock handling characteristics, you would use the stock setup.

There is no formula to follow, since the ultimately "correct" spring rates do not have anything to do with what the car came with from the factory (when talking about almost all passenger cars).

When you set out to change your springs, you need to determine first why you want to change your rates. What about the handling isn't right? Does it excessively over/understeer? Does it squat too much on launch, dive too much under braking? Does it crash over bumps, or is there just too much compliance and the car ends up rolling everywhere and through turns? To account for each scenario, a different method of selecting rates will be used.

Calculating the sprung/unsprung weight of each corner, the motion ratio, and strut angle (including other things) will also play a part in selecting spring rates. Wheel rate refers to the effective rate of the spring (and the spring only) that is acting on the wheel after factoring in the motion ratio. THe motion ratio is the mechanical advantage provided by the "leverage" of the control arm, or by the strut's mounting point on the hub. The wheel rate is never 100% of the spring rate, since this is physically impossible (the spring would have to be positioned perfectly vertical over the hub, and go straight through the top of the wheel/tire). The wheel rate is the spring rate multiplied by the square of the motion ratio. Typically, wheel rate figures will not incorporate other springs in the system (swaybars, tires).

 

Handling is defined by the way the car behaves given the capabilities of its suspension (tires, shocks, springs, brakes, lsd, etc), and input from the environment (bumps, dips, traction, wind, etc), and the driver.

Balance can mean a variety of things, it usually depends on the context within which you're referring to it.

This is also a reason to increase the spring rate - however, if you reach the point where you are accounting for this issue with spring rates, then you are masking a more deeply-rooted problem that should have been solved prior in the design process (insufficient stroke).

One of the most basic principles in suspension tuning - performance will come at the cost of ride quality and comfort.

You can't change the car with driver inputs, but you can affect the handling, because the driver is a factor in handling. If you have no faith in what we do, and don't have the knowledge/ability/inclination to fix it yourself, then I'm afraid you'll be a little short on options. Its true that designing the proper suspension is not easy to do, but the information is out there and there *is* a correct way of doing it - whether or not a company/manufacturer does it the correct way is up to them, and its up to the consumer to be well-educated enough to know what to look for in a well-designed setup that will be effective for their application.

This is incorrect. The car's behavior under different conditions/phases can be tuned more or less independently, and that is the job of dampers, not springs. Again, springs limit total load transfer. Dampers will control the rate at which the load is transferred, and because different situations (high speed cornering, low speed cornering, corner entry, steady state cornering, corner exit, braking, acceleration) will cause load to be transferred differently, a flexible adjustable damper will be able to account for these varying situations, not springs.

More or less correct, and a good way of thinking of swaybars: they should be used as as tuning device, not to make up for/do the job of springs.

You are using the term "overall" grip quite a bit, although I'm afraid you're not fully understanding what it means.
Firstly, swaybars do not affect ride quality (unless you are talking about an extremely stiff swaybar).
There is nothing inherently "bad" about a swaybar's tendency to reduce the independentness of an independent suspension, and a totally independent suspension is not always preferred (again, keep in mind that a swaybar does not take the place of a spring, nor does a spring take the place of a swaybar). It is only detrimental to handling at the point where the stiffness of the swaybar is too much and the tire(s) is not allowed to perform its function properly.
Hence the following is incorrect:
You are referring to roll couple. ALtering the car's roll couple distribution (how much rolling resistance each end of the car takes) will alter its behavior under cornering. While a swaybar does not directly connect the front and rear axles, they do affect the total grip on their respsective end's of the car, and therefore will affect its behavior under cornering (by changing the rates at which each end gains/loses mechanical grip).