Is there any way to know the balance for spring rates for coilovers? I'll try to explain...
The stock FC spring rates i believe are about 17% difference between rear and front (front being stiffer).
So, generalizing that assuming all other parts of the car remain equal, to maintain proper balance for the car, would you be looking at around the same difference for coilovers, even though the rate might be 4 times the stock?
What would be the expected difference between 7kg-6kg (~15% difference f:r) and 8kg-6kg (~23% difference f:r), assuming the dampers have enough range to handle either spring rate combo?

Sorry if this question is kind of vague, it's just that people seem to just be picking 2kg seperation for FC coilovers, and there isn't really any technical basis for why...

 

Yes. This doesn't mean other combinations won't work well, but you are correct in assuming the relative balance stays the same if the percentage difference stays constant as rate increases.

 

From the factory, a lot of cars come so the springs put a lot of understeer into the handeling. It seems most american cars a natorious for doing this. This may be a safty thing and to prevent lawsuits. Those aftermarket systems may come with a different balance since they might have found it to provide more neutral handeling.
Theres also issues like chassis flex that may change the handeling characteristics when the srpings rates start to get really high.
It seems that a lot of FC coilover kits intended for racing in the 400-600 lbs/in range have the rear spring rates 100 lbs/in lighter then the fronts.

 

Well that 2kg seperation is kinda the standard and it depends on what you want.
If you like the feel it should work. Same principle can be applied to a car after being corner weighed, as long as you lower all corners equally after a corner weight, the corner weights should remain the same.

Most cars come tuned from the factory with understeer in mind, since it is easier to correct understeer than oversteer.

 

thanks for replys, good info.

what about how much 1kg rate difference will have towards balance? will it be a big difference between 7/6 and 8/6?

 

There should be a noticable difference in the handling balance of the car with a 1kg/mm change in spring rate on one end of the car. Personal preference, swaybars used, driving style, alignment, power, weight, wheels and tires used are amongst factors that will determine the right spring rates for a given application. I've heard of two different ITS racers using the same spring rates (450/325), and the same sways (Eibach), but one left the rear bar off, the other put it on. That's a big difference in the handling balance, but each liked his setup well enough.

Rates I've heard of working well on race cars in lb/in are 400/275, 450/275, 450/325, 500/375. These equate to approximately 7/5, 8/5, 8/6 and 9/7 in kg/mm.

When fooling around with spring rates and suspension tuning having adjustable sways is a huge benefit, as it allows you to fine tune the handling balance to accomodate spring rates that may be off from "ideal". Even without adjustable bars you can still substitute the stock bars back in on one end, or both (assuming you've got aftermarket sways), or you can leave one bar off altogether (done fairly commonly on the rear, I've never heard of it done on the front).

When I get coilovers next year I think I'll be getting 7/5 or 8/6.

 

thanks for that info. yeah, of course you want to play around with the set up, but i would rather not have to buy another spring set down the road, and take the suspension apart again to put them in. so i'm just trying to make sure that, if i go with coilovers, that i make a proper decision for the spring rates. you talked about sways, and i do have the RB adjustable end links for the front sway.
i'm not looking for the fastest setup, but rather the most balanced, and predictable based on how the car was designed stock. this is because i have just started to track the car, and it will be used primarily on the street.

i see you didn't mention 7/6...is that too much rate in the rear? it's only 2% more stiff, in terms of balance, than stock, so it should be closer to stock than 7/5, which is 11% off balance towards the front (sorry, i'm doing this math crudely, i am no suspension expert)...

 

Quick question, has the car been tracked yet?

You might go with the stiffer "stock" springrate but then when you head out to the track you might want a tad more oversteer or more understeer etc..

Well, I guess you can tune that with sway bars as well, and even some adjusting of the shock dampening.

 

I hear you, I'm in the same position, playing is nice, but I want a setup that's perfect out of the box (when I get coilovers next year). When I talked about asdjustable sways, I meant ones with multiple holes to adjust the stiffness, not adjustable endlinks.

Well for balance on the track, the most common starter spring rates in ITS are 400/275, which is closest to 7/5 (391/279). Most who use the 400/275 rates run without a rear bar, and either a stock or aftermarket bar in the front. I would think that 7/6 might be good for autocross, at it'll probably be fairly easy to get the rear end to come around, but on the track it'll probably be far too tail happy, especially if a rear bar is used. RETed uses the 400/275 rates and he has said that it's about perfect for the street. It's got an acceptable ride (especially when good shocks are used) and has good handling.

From what I've seen from many stiff suspensions, to get the car properly balanced one must increase the front spring rates more than the rear. Don't ask me why, it's just something that I've noticed.

As for a starter rate 7/5 should be nice, decent ride and good balance, adjustable between oversteer and understeer with swaybar choice. I've done a ton of reading on spring rates for the FC so that I can hopefully get a good setup first try.

 

pat mcgroin: the car has only been to autocross a few times. i should be going to a road course within the next few months, but i am doing more autocross.

Black91n/a: that's some good info on what people are running. and yeah, now i know what sway bars you are talking about. where can you pick up one of those for the FC?
the car is mainly street driven, followed by autocross, and some lapping days at a road course in the near future. so i need something that can compromise between all that.
from what i can gather so far, the car seems to understeer, unless there is some upset in balance mid-corner (my fault usually). it seems that 7/5 might be a SAFER set up almost, and i think that might be good. i'm not competitive really at this point in any track events, so i just want to have fun and not go off the track.

i know this is a generalization of spring rates, because the actual damper valving will affect spring choice also. related to this, and i hope this isn't too big of an issue, is that all the coilovers i am looking at come with 9/7 standard, so going 7/5 will mean i am restricted in the lower part of the damper adjustability (or run the risk of being slightly overdamped)...but, i'd rather that than too harsh a ride.

 

I do beleive the best source for adjustable sways in North America is Eibach. I've read conflicting reports on them. Some places seem to indicate that both the front and rear are adjustable, other places indicate that only the rear is adjustable. The Suspension Techniques front bar is apparently adjustable too.

For the 7/5 rates, running a rear swaybar could help get the desired oversteer at autocrosses, and taking it off could provide a nice stable track setup. With a set of stock and aftermarket sway bars you should be able to find a good mix for both autocross and track driving. That's what I'm betting on.

As for damping, on most coilover kits that I've seen where guidance has been given on an acceptable change in spring rates it's been +/- 2kg/mm, so having 9/7 and switching to 7/5 should be ok, and as an added bonus, when the shocks get old and tired you'll have more room to crank them up to get a little more life out of them (theoretically). Another option would be to use 8/6, and you should get a little more oversteer and you won't be changing the spring rates nearly as much, so the damping can stay closer to what it was designed to run at.

I know what you mean about being uncompetetive, I'm in SM2 in autocross and I get killed every time I go out. It's hopeless to win, but I still have fun, and at the track I don't have enough power or tires to keep up with most of the crowd.

 

there is no such thing as a 'perfect' setup. every driver has a different 'ideal' setup, how he or she prefers the car to handle. I don't think there's anyway you can find the best setup for you without just some good ol' trial and error. on another note though, I think that most coilovers setups available (with the rates they come with normally) are all probably neutral enough setups that you would be able to achieve your desired setup with just shock adjustability.... esp. if you had the adjustable sway bars(although I think someone may have already said that). also, alignment will make a huge difference, as well as tires.


now... I'm running 9k/7k on my FC. stock sway bars, 215 front/235 rear azenis tires. haven't done any grip driving on it yet, but I'm going to this weekend. I'll let you know how the car handles. I'm sure I'll be playing with shock adjustability quite a bit. drifting on it is... well, fairly predictable. can't comment on oversteer/understeer as the way I'm driving it effects that more than anything. also, street driving on these rates(the little that its done), really isn't that bad. its stiff, obviously, but as long as you slow down for bumps and avoid potholes and stuff, its not too bad.

but anyway, I don't think there's anyway you can do enough research and get the 'perfect' setup for you without any guessing. maybe you can get lucky, but I think thats about your best chance for getting your perfect setup out of the box, as everything else is way to variable to determine 'proper' spring rates by looking at other people's cars.

 

I know about there being no "perfect" setup, I've preached the same thing. I guess I should have said a little more about that. Through thorough research one can at least get a better idea of what a good setup will be with less $$ spent on trial and error tuning.

Even if what I get's only close, I can adjust the balance by switching between my RB and stock sways on either end, or by leaving the rear off altogether.

It's actually quite hard to find good info on spring rates for the FC, as most people use shocks and springs (not coilovers), or they've got a race car, so street ride isn't a concern. There's very few people out there with a street/autocross/track car with coilovers, so it's harder to research because there's not much out there.

 

If you look at most stock cars go though a corner, you will notice that the front end will hunker down and the tail will be up in the air. The best example I can think of is a sn95 mustang going through a turn.
You can see how the suspension is transfering the weight of the car to the front tires; to the point of overloading them. Thus making the car understeer when grip is finally lost, because the fronts lose grip first. By putting stiffer springs in front, you can transfer some of that load to the rear tires, balancing the car out, making it handel more neutral and have better grip since it will use all the tires more efficiently.

thats why.

 

Making the front springs stiffer will ADD understeer.

 

everything in this statement is opposite... stiffer springs in front will increase understeer. and more weight on the front will increase the grip in front, and decrease it in the rear. period. there is no 'too much weight in front to the point of overloading it' ....

 

on another note.... got done racing my car last night, and it was awesome. balance was absolutely right on for my driving, just a slight be of oversteer at the limits. I would def. reccomend spring rates 9k/7k. I never adjusted my setup once. it is as follows.
tires: azenis 615 (215/40R17 f/ 235/40R17 r) 42psi front, 40psi rear (cold)
KTS coilovers 9k/7k . shocks adjusted to full stiff all around.
poly bushings all around and DTSS bushings.
stock sway bars and end links(with poly bushings)
camber -1.6 f ... don't know rear... not much. lol maybe -1 at most.
very slight toe in rear, slight out in front.

and btw, azenis 615's are mazing. first time I've ever driven on them. I was outgripping my friend's S13 with 225 michelin R-compounds.

 

Every book i read says exactly what you state here. And then i went to the track and tested it myself. Maybe its the cars that im applying it to. One of the books i have, Competiton Car Suspension: Design, Construction, Tuning by Allan Staniforth says what you say, too. but then he also goes on to say that this is by no means true for every car.

So far, the cars I have really messed around with, a MA70L supra and a SN95 Cobra mustang. Both of which seem to have a forward weight bias and tend to have more oversteer with an increase in the front springrates. I also noticed that the cars also leveled out and didnt have the rears way up in the air under heavy cornering and braking.

For a while, the supra was plowing everywere, we kept upping the rate and stiffness of rear because thats what all the books said, and it would plow even worse. then we decied to do the opposite and that really balanced the car out.
The supra has a 18k front and 10K rear now and is awesome.

Please give an explanation of why this is.

 

Increasing the spring rates will keep the car from rolling as much, which can help keep the wheels in a better alignment relative to the pavement. This could be part of the reason why many cars need to have the front springs stiffened more than the rears.

 

hmmm.... very interesting. I've never thought of or had any experience with anything like that... what were the initil front spring rates on the supra when it was plowing so bad?

 

constant motion, like going around a long corner, and quick decel are two fairly different things that the suspension has to handel. so maybe some cars require suspension tuning that may seem different because it caters to, for example, improved performance under braking.

 

The previous springs on the car were around 12k front and 5k rear... but they were progressive rate, and thats the 'stiff' part of the spring. It would plow all over, but those were springs desinged for the street. When we went with the upped rates, it was a lot better but would still plow. The addition of a bigger front sway bar to the front finally leveled the car out. We found what end needed to be stiffer by just adjusting the stiffness of the shocks.

 

Be careful with that...
Most expert will tell you that steady-state cornering is more a function of the springs and stabilizer bars.
Transition handling is more a function of the dampers.

As with the books "rules", they are all guidelines.
They will work most of the time.
Sometimes with quirky set-up's or chassis', opposite effects are not uncommon.

Yes, suspension set-up is a very subjective thing.
Just because one person loves the set-up doesn't mean you will.
We can just offer you a general idea of recommendations, but don't be disappointed if it doesn't work for you.
Don't get too caught up in the "numbers" (i.e. spring rate front versus rear ratio), so be careful about people's recommendations especially when you're not going to be running the same kinda of dampers.
I still believe you need to pair the spring (rate) with the proper shock damping - it's more important to take care of that than to worry about the spring rate ratios front versus rear.

Tire alignment and tire size also affects handling.
Tire pressures affects handling too.
You haven't mentioned what kinda rim / tire combo you're planning to run?
An FC running 4 x 225 / 50 / 16 can run a different spring / damper combo versus an FC running 235 F / 255 R on 17" wheels...


-Ted

 

right now it is 225/50/16 all around. however i may go with a second set of 15 inch wheels for the track, 225 also probably.

 

With the taller sidewall stuff, you can actually go stiffer, since the tire sidewall itself acts a little like a damper / spring.
A 225 / 50 / 16 shod FC is going to react slightly different than a 225 / 40 / 18 shod FC...
But running those kinds of tire sizes implies you're not running that much power?

Are you looking at coilovers kits?
Or some kinda damper + GC coilovers?


-Ted