mahcah

iTrader: (3)

I have an IS250 and I want to install my BC Racing coilovers. The spring rate on them are 12k front and 10k rear. I plan to drop it with one finger gap between the tire and fender on stock 18's.

My question: should I put a one centimeter preload on it or should I do "0" preload? I am looking for a comfortable every day ride. Thanks in advance!

dubsesd

4mm preload from what i read in past threads

mahcah

iTrader: (3)

Was that for the 10k/8k? Or 12k/10k?

Thanks!

mdgrwl

iTrader: (7)

close, BC Racing says 5mm. I spoke w/ Tim there not too long ago.

I have 10/8 and I would say go 12/10. 10/8 is a bit too soft for my liking.

lobuxracer

iTrader: (2)

Preload has nothing to do with ride quality. Only spring and damping rates affect ride quality.

mahcah

iTrader: (3)

I'll do a 5 mm preload on my 12k/10k.

lobuxracer: That makes sense. thanks for the information.

Is it true that the reason why people put more preload is because they want a lower/aggressive drop?

dubsesd

its to avoid hearing clunks and squeaks in the suspension, the the more you compress the spring, the ride will be harsher for sure....with less travel

dubsesd

if you preload the spring by 2" you will defienlty feel a difference in ride quality

lobuxracer

iTrader: (2)

How? The spring's rate isn't changing and the damping rate isn't changing. You're just raising the car a little.

And yeah, I've had adjustable suspension on a number of rides over the last 30 years or so - I've never felt a ride quality difference from preload except when it kept me from scraping some part on the road under compression.

mdgrwl

iTrader: (7)

you just reduced the shock travel by 2 inches, thats how.

lobuxracer

iTrader: (2)

No, I haven't. The only way I can reduce shock travel is to shorten the piston rod. I've changed static height and nothing more.

Would you like to see the supporting math?

juice14

On mine BC racing, I have 10/8....I had too much preload, After I went back and fixed it the car jumps less on bumps. The ride is the same as far ar on the hwy and when going through rough roads. However, when going through a road with alot of bumps the car jumps less, basically rebounds less. If that makes any sense.

mahcah

iTrader: (3)

Juice14,

Based on the 10/8 you have, are you at 5mm preload?

When you said "too much preload," how much preload was that?

You mentioned: "The ride is the same as far ar on the hwy and when going through rough roads. However, when going through a road with alot of bumps the car jumps less, basically rebounds less." <------ Is this with the "too much preload" or with your current setup/preload?

dubsesd

if you compress the spring completely using more than recommended preload, you are definelty going to change the static height, but you are also reducing the amount of travel the spring is going to have. how can you say it wont affect ride quality?

With linear springs like in the BC coilovers, when you put the weight of a corner of a car (probably around 700lbs) over your spring it compresses to absorb that weight. With 400lb spring, it will compress about 1 3/4". So, if you start with the lower collar so that it is just tight enough to hold the top of the spring against the upper perch this would be 0 preload. Raise the collar 1 3/4", and you now have 700lb's of preload. (arbitrary #'s for the sake of illustration.) Since you have preloaded the spring, the same weight as the car's corner, when you put the car on that spring, it will not compress at all, and will simply sit on top of the spring. If you were to hit a bump, the force would still compress the spring the same amount it normally would if you had set the spring to 0 preload. Now if you set the spring to say 900lbs of preload, when you hit the bump (say its a bump that generates around 250lbs of upward force), the spring will compress much less b/c the spring is already beyond the load specified to absorb the bump. Since there is only 50lbs beyond the preload, the spring will only compress about 1/8th inch, and the car will likely be launched over the bump. Preloading can provide you with more suspension travel in certain situations. In the ideal world, having the spring at 0 preload would place the piston inside the shock exactly halfway through it's stroke (middle of shock) once the car's weight is resting on the spring. This is almost never the case. by preloading the spring, you can adjust the amount of rebound, or compression travel you have in the shock. If you preload like 200lbs, this will give you more compression travel, and will help keep your car from bottoming out when cornering.

juice14

Man, when i mean too much preload I mean about a friking inch of preload, It was my fault that it got so high...long story.... However now I have it at around 3-5mm preload, and the car definitely jumps less than before, I mean its a huge difference without a doubt. Im thinking of going almost 0 preload on the rear to see how much comfy it can get. roads around here are not very forgiving.