Hey what is the best spring rate for coil overs for a fc.

 

Depends on what you are doing with the car, but 8K front 6K rear is a pretty good place to start.

 

totally depends on tire and usage...

i run 9/7 with a fat front bar and no rear for staggered wide/sticky tires (255/275 direzzas for street/track, and 285/315 v710's for autox)

 

im looking for something that willl offer good grip. i want to run 255 all around. when do you need/want to remove the rear bar? i have always heard it makes everything work better but they never say when its needed

 

the FC is a totally different animal than the FD in terms of suspension and it is this difference that also makes it different in terms of spring rates.

the FC has a strut front and as such no camber gain on bump. if the car rolls 3 degrees the tire goes positive 3 degrees. evil.

therefore if you are tracking the FC you need more spring rate to keep the suspension travel as minimized as possible.

OTOH, if you are just aggressive street i agree w post 2

do tailor your FC spring rate to your driving application.

the other problem w the FC chassis is that it is way too flexible. put alot of spring in the car and the chassis just flexes giving up your suspension settings.

hc

 

Another thing that's different about the FC and FD is that the FC has a motion ratio of about 1:1 on both ends, so it requires a lot less spring to get the same wheel rate as the FD. Ground Control's standard FC rates and the rates that many, many road racers use is 400 lb/in front and 275 lb/in in the rear, this is about 7 and 5 in kg/mm. That is what I use with an RB front and stock rear bar for the track and I think it works pretty well (some instructors have commented that it works well too).

When the rear bar can be ditched depends on the driver and the setup. Don't think of it as a stage in development, it's a tuning tool. If the car handles well with it, then keep it, if it handles better without, then get rid of it. Race cars tend to be stripped, so they have less weight in the back with contributes to them not needing the rear bar, but if you choose your spring rates to be a bit more rear biased, or use a smaller front bar, then you could get rid of the rear.

 

The range is usually 7 / 5 at the low end, 9 / 7 at the high end.

 

NOT TRUE, I wish you'd stop repeating this, as a lot look to you for guidance and you for the most part give great advice. I've corrected this particular quote on more then one post of yours with no response about it.

McPherson strut cars DO gain camber in suspension stroke, it's just not very much when compared to un equal length dual A-arm suspension designs. This is why it is important to keep your outer lower ball joints BELOW your inner arm pick up points and also why your lower arm center line (center of ball joint to center of pivot) should never make a right angle to your strut center line in it stroke (other wise it will have POSITIVE camber gain).

~Mike..........

 

Do you have a picture detailing an optimal arrangement of a McPherson Strut?

 

I currently run 8k front 6K rear with RB sway bars F&R with 235/40/17s all around. The car is close to neutral.

 

No I don't have a picture of "optimal" strut geometry, does such a thing exist? What is optimal for one isn't for another. OEM car manufactures would want the most leg room possible and a cheap way to manufacture suspension components, so they choose a McPherson strut arrangement rather than a double control arm, that particular arrangement might make zero or even positive camber gain, it would still be optimal for their goals though (more leg room, cheaper cost to manufacture). There are too many parameters such scrub radius, wheel clearances, etc etc to have an optimal drawing that is generic and not specific for anything I suppose. But if you’re asking for maximum negative camber gain, I suppose you'd want the lower arm to be parallel with the ground at full compression and have as little of an angle between the arm and the strut as possible. Just grab a couple of straws and tape and fiddle around with it and you'll understand how the geometry affects the mechanics of it.

Another bonus of moving your lower/outer ball joint pivot point lower aside from putting your lower arm at more of an angle for more negative camber gain is your also putting your roll center closer to the center of gravity on a lowered FC so it's a win win.


~Mike.........

 

What would be optimal for street driving?

Would 7 / 5 be a smoother ride than the stock T2?

 

Keep in mind that even the "soft" spring rates of 7/5 are still many times higher than stock spring rates, which are about 2kg/mm. So no, it won't ride like your stock car, it will feel much stiffer over bumps. Another thing to keep in mind is that dampers have a big influence on the ride quality of stiff springs. A really good damper will make the ride better than if you use some of those cheap, low end coilovers.

 

Yes, 7/5 will be firm but liveable on the street provided you have them damped to match.

 

springs dont make the car harsh, shocks do. people never seem to grasp this concept...

i have 9/7 on konis and its smooth as butter. freeway expansions, railroad tracks, etc. not harsh at all.

 

My local roads (including highways, etc) are filllllled with pot holes. It sucks. I'm trying to get a slightly smoother ride around town then up the stiffness when I need it. Would riding on the softest setting for a long time blow out the struts/shocks?