fdls6

iTrader: (9)

Hi Guys,
Well, I'm about to pull the trigger on some of the Function T coilovers for my FD. I've got 285/30/18's in rear and 255/35/18's in front. I'll be primarily driving on the street with some occasional drag racing and maybe road racing. The default spring rates they suggest are 9/8. I've read Howard C's thread and see that he likes the 8/6. I can spec the 8/6 with my order but want to take in any suggestions folks may have. Since the rear wheel/tire is a little heavier, would it be advisable to increase the rear spring rate relative to the front. Seems like that might cause a little more oversteer which should even our the tire size stagger. Or.. maybe get the 8/6 and preload the 6 a little if I find it is a little soft. What do you think? Thanks in advance.

fdls6

iTrader: (9)

Well, I went ahead and ordered the 8k, 6K. I hope it works out well!

I'm still curious to know abour increasing the preload on the rear if needed to bump up the rate. Anyone know the ratio of preload increase to spring rate increase?

Josh18_2k

iTrader: (3)

preload doesnt affect spring rate at all.
preloading a spring gives you more bump travel (in the event that you bottom out your suspension somehow). its also a way to raise the car, if height adjustment isnt seperate. any decent coilover has seperate heigh adj tho.

fdls6

iTrader: (9)

Hmm. I think it would. My feelings won't be hurt if I'm wrong, but here's my thought. Here's a quote from Howard Coleman's thread:

"The stock FD spring rate is 263 pounds per inch in front and 195 pounds in the rear. These are my numbers from my Longacre Digital Spring Checker. Just FYI, with linear rated springs the rate increases with contraction. The second inch of the FD front spring is 526 and the third is 789…"

So, if my spring is stock, and 263 lb/inch.. If I preload it(raise the perch an inch) I will have compressed the spring an inch and my first actual inch of shock compression will start out seeing 526 lb/in and up from there... (not taking into consideration ride height in the stock scenario)

If I apply the same theory to the rear shock, I should be able to do the same. Raise the perch 1/4" and this time, drop the height adjustment 1/4". Same ride height, slightly stiffer spring rate. Makes sense to me. I don't think you would want to get carried away here, but it seems like a little strategic preload could help to slightly stiffen the spring/shock combo.

I'm I completely off with this theory?

Josh18_2k

iTrader: (3)

Stock springs are usually progressive. A spring's rate is a property of the spring, and does not change, no matter what you do to it (besides extreme heating or something obvioulsy).
As you compress a spring, the force to compress it further increases, but thats exactly what the rate implies.
100lb.in spring for example takes 100lbs to compress 1 inch. the second inch takes 200lbs. the 3rd takes 300, and so on.
so if you preload that spring 3", it would take 400 lbs to compress it 1" further.
as soon as you set the car down on the ground, the spring compresses further than your preloaded setting, and so has no effect.
The only way preloading would affect the basic handling of the car, is if you preloaded it beyond the static corner weight of the car. It would then be basically rock hard in light cornering or bumps.
There are advantages of preloading, but thats serious track business (no advantage on the street)

fdls6

iTrader: (9)

Thanks for the feedback, but I'm pretty sure I still disagree. If I have a 100 lb/in spring, and have preloaded it 1 inch, the first inch of travel will require 200lb, the second 300. Seems like the suspension will see this as a 200lb spring since it will not move the inch unless it receives 200lb of force. If it was setup with no preload, it would need 100lb to move an inch. big difference.

Preload with regard to corner weight......... I have independent height adjustment so the rear springs could have their preload cranked, the height adjsutment dropped, yeilding idential corner weight with increased spring rate due to preloading or pre compressing the spring.

ARD T2

iTrader: (22)

Just for reference I have seen a spring dyno of the X coil that you're referring to.

You will definitely see a difference in spring rate when preloading a spring, but ideally on a linear rate spring it should only be progressive for maybe the first 20-30% of compression, after which it should maintain it's "linear rate" up to 70-80% compression. Beyond that you approach coil bind and the rate increases infinitely.

Now on shitty linear springs I've seen dynos showing they only maintain ideal linear rate from about 40-60% compression, that's a horrible 20% of linear rate.

A good race proven linear spring should have at least 50-60% of it's stroke to be a linear rate.

Keep in mind, once you load your suspension you will compress your springs about 20%. So you'd want the spring to obtain it's linear rate at about that much compression to maintain a good degree of predictability.

From this I can infer that if you preload the spring 20% it should maintain that linear rate almost to coil bind. ONLY DOWNSIDE IS YOU'RE LOSING COMPRESSION STROKE OUT OF YOUR SPRING. Make sure not to preload the spring so much that you can't utilize full damper motion.

I hope this makes sense, it's pretty late now. i'm tired.

Rishie

Josh18_2k

iTrader: (3)

http://www.sportrider.com/tech/146_9510_tech/index.html
its about impossible to find any real info about preloading outside of bike tech. but the property of a spring is the same whether its attached to a bike or car.