motoxxxman

So I'm finally going to be getting some coilovers for my car which is built mainly around autocross and track racing, but will also see occasional street and strip, and is often a DD when my jeep is down.

As the title states, what is typically a good front/rear spring rate ratio compared to vehicle weight distribution ratio? my car is a cool even 60/40 weight distribution.
if different ratios are better for different types of racing, please mention that as well.

flip_nl

Measure wheelloads, motion ratio and aim for the correct wheel frequency.

motoxxxman

lol, that is my aim haha

flip_nl

Automotive Spring Rate Calculator

Haven't verified if this is calculated correctly though, best to try 2 or more calculators.

Edit: this calculator is crap but you get the idea.

motoxxxman

I'm not seeking advice on actual spring rate. I'm seeking advice on the RATIO of front to rear spring rates based on vehicle weight distribution.

IE: coilovers that normally come with rates of 10k/5k would be a 66.6%/33.3% distribution. or another set that comes with 12k/8k would be a 60%/40%.
basically I'm going to be getting custom spring rates, but am looking for what front to rear ratio is best in relation to the actual vehicle's front to rear weight ratio.

motoxxxman

I measured my lca's:

front: inner pivot to bj: 14.5", inner pivot to strut pivot: 11.0"
ratio: 1.318 (or 0.759)

rear: inner pivot to bj: 17.0", inner pivot to strut pivot: 14.0"
ratio: 1.214 (or 0.824)

front and rear struts are at an 15 degree angle from vertical when car is on the ground.

someone has to know something about spring rate math... or how balanced the car should be for autocross and track racing

flip_nl

No offence but this is kind of dumb. Accusing me of not reading the question properly, while not understanding what I mean... mkay

1 more try:

Actual springrate is inherent to vehicle weight distribution: static wheelload, unspung mass, there is no solid RATIO number for this for each "setup" is different. Aim for 2hz at the front and a little higher (2.3hz?) at the rear.

Also have you even consired the shock valving, most of the time everybody blindly stares at spring rates while forgetting this essential part...

Clearly you have some reading to do.. read-up:

Autocross to Win (DGs Autocross Secrets) - ATW Home Page

Cheers.

joel n

If you just want a generic setup, just run whatever the springs are on the coilovers. Most people run higher rates in the rear to help with rotation. Race and autocross. Based on your 60/40 split you would have higher rates upfront. Your spring rate setup is completely driver dependent. A great setup one guy loves another guy hates. Some people drive a free car fast, others drive a tight car fast. Also you will need to know your vehicle weight for sorting out rates.

Maybe tell people what car you run, track you run, and general car setup, and see if anyone can give you a starting spring rate setup. Then after you track the car, you can figure out what you want to change. Id say start with 450 front, 550 rear. Thats were we started with a 2400LBS DelSol racecar.

motoxxxman

flip_nl, yes I'm aware of dampening, I have that covered, thats why I haven't inquired about it.

it's a 1990 prelude, turbo b20a/b21, 300whp 290tq, helical LSD, sunroof removed and covered with aluminum sheet, and some other misc weight reductions. current curb weight when race prepped is 2330lbs, 60/40 weight balance. 100lbs heavier when street driven, currently planning a little more weight reduction, prob down to 2200lbs when race prepped

current setup is not really comparable to much of anaything haha. cut stock springs (1.5 coils removed, while submerged in cold water) on oem struts with over 300k miles, somehow still no leaks and full of oil, but definitely softer than new. stock front bar, a few strips of angle iron welded to the rear bar. it actually handles incredibly well and is very well balanced. just waaaay too soft in both spring and dampening. I'd love an actual aftermarket rear bar, but the only one that was available was whiteline, and it was discontinued a few years ago.

front: inner pivot to bj: 14.5", inner pivot to strut pivot: 11.0"
ratio: 1.318 (or 0.759)
rear: inner pivot to bj: 17.0", inner pivot to strut pivot: 14.0"
ratio: 1.214 (or 0.824)
front and rear struts are at a 15 degree angle from vertical when car is on the ground.

I did some math and found that between my weight distribution and suspension geometry, I'd have a "level" stiffness with 10.6k front and 6.2k rear. the kit I'm considering normally comes 12k front 6.2k rear.

this is what confuses me because I see this type of setup all over the place with civics. do civics have drastically different lca geometry in the rear or something to need such a stiff rear spring?

hispanic panic

Couple things.

1) ask yourself why you're choosing springs based on ride frequency. Its probably because you read it in a book. Re read that section in the book and figure out why they said to start with ride frequency. You'll find they provide no engineering rational, just merely presented it as a rule of thumb to be taken as gospel. My suggestion, stop where you are and never consider a ride frequency again. Profesional motorsports (F1) teams began to ignore this stuff in the late 60's, it just hasn't propogated to general knowledge for obvious reasons.

2) people choose stiffer rear wheel rates because FWD platforms are front traction limited. This means they can obtain a quicker kinematic loading of the rear, allowing the front to spend more of its precious traction to help it change direction quicker or obtain higher cornering speeds. The front can only take so much load, and once that load limit is reached you can no longer corner faster. A stiffer rear allows you to load the rear more in contrast to the front. It's like adding a swaybar, except reverse because instead of removing traction with a stiffer sway, you're just allocating traction elsewhere.

3) There are a handfull of ways you can accomplish the whole "load the rear quicker" goal. You can make the rear springs stiffer, or increase the rear swaybar. By increasing the rear sway, you are forcing the outside rear to take more load, but you're also decreasing the load on the inside rear, with a net REMOVAL of traction in the rear assisting balance. This method also makes your suspension less compliant, further reducing traction over irregularities mid corner. Method #2 involves using stiffer spring rates and a softer swaybar. This method is my preferred method and in my personal opinion, you can achieve a more compliant setup and have a vehicle that has higher overall grip, yet achieve the neutral handling balance we so desire. This method can also be more complicated because it requires better dampers. Dampers much better than what a koni yellow or koni race can offer from what i've seen of their shock dynos. This method requires less high speed compression within the valving to help maintain compliance with the stiffer springs. Does this mean you can't have a more compliant car with this method on koni yellows? No, its just not the optimal way to approach this method.

motoxxxman

thank you for your input. it's still going to be a little while before I buy any suspension components, as a few unexpected expenses have popped up recently. So I have plenty of time for further research