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Old 01-15-2007, 12:06 AM   #1
jruben4
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Default What is the "Best" Spring rate for coilovers?

This is a pretty open-ended question subject to a lot of personal preference, etc....

BUT - what do you think the "best" spring rate for a STI coilover would be. My application is for a car that is mostly for track road courses and some limited local driving. Doesn't need to be comfortable on the street, but it is not trailered so I do have to drive it to the track events w/o rupturing my spleen.

I think the stock spring rates on the STI are:

STI stock front = 4kg/mm = 224 lbs/in
STI stock rear = 3.5kg/mm = 194 lbs/in


Looking at the Megan Racing coilvers, for their "street" version their rates are:

fronts 10kg/mn = 560 lbs/in
rear 6kg/mm = 336 lbs/in

For the MR "track" versions, they use a 12k front and 10k rear spring rate...

It seems like a lot of coilovers use even lower rates, like 8k/6k or 7k/5k... are these low rates more of a compromise for comfort? Will 12k/10k be able to be driven to the track w/o a trailer?

Thanks!
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Old 01-15-2007, 12:23 AM   #2
sportek1
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There is no BEST spring rate. It all depends on what the application is, how you want to use your car.

Also, you cannot only compare spring rates without knowing what the valving is on the shocks, shocks and springs need to match!
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Old 01-15-2007, 12:29 AM   #3
jruben4
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That's why I described my application and how I use my car in my original post, to help people give educated opinions.

And as far as valving, let's assume the manufacturer matched the valving correctly to whatever spring rate came with the coilover.
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Old 01-15-2007, 12:40 AM   #4
boost junkie
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What tires are you running? What size swaybars? How much camber are you willing to run? These things make a big difference in choosing spring rates.
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Old 01-15-2007, 03:22 AM   #5
Mykl
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What a question... like has been said already, there really is no straight answer to this.

What exactly do you plan to do with your car and what tires do you plan to run?
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Old 01-15-2007, 08:23 AM   #6
jruben4
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Quote:
Originally Posted by jruben4 View Post
My application is for a car that is mostly for track road courses and some limited local driving. Doesn't need to be comfortable on the street, but it is not trailered so I do have to drive it to the track events w/o rupturing my spleen.
I run on 255/40/17 RA-1s.
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Old 01-15-2007, 01:15 PM   #7
boost junkie
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Give Myles at RaceComp a call. He can talk spring rates with you but it sounds like for your application, the RCE Tarmac IIs with the 500/400 rates would work very nicely.
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Old 01-15-2007, 04:25 PM   #8
Scooby921
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Quote:
Originally Posted by sportek1 View Post
There is no BEST spring rate. It all depends on what the application is, how you want to use your car.

Also, you cannot only compare spring rates without knowing what the valving is on the shocks, shocks and springs need to match!
Quote:
Originally Posted by boost junkie View Post
Give Myles at RaceComp a call. He can talk spring rates with you but it sounds like for your application, the RCE Tarmac IIs with the 500/400 rates would work very nicely.
Yes. Even for a car that is mostly track, european style valving (or in this case independent compression and rebound adjustability) has its advantages. No road or race track is perfectly flat. While the nicely stiff japanese spec stuff is decent on the track, they are more prone to skipping over rough surfaces instead of absorbing and maintaining grip. This is one reason why the european coilovers tend to cost more. There is more development put into proper valving and matching spring rates.

AST Sportline I or II, Ohlins Sportline, and Bilstein PSS9 are single adjustable european coilovers. Spring rates are a bit on the softer side (7k/5k for the AST and Ohlins I believe, and maybe 8/6 for the Bilstein). This doesn't automatically mean they have less grip and handling though. The better valving means you can do more with a softer spring.

To step it up a notch you have the KW V3, KW V3 Competition, AST Raceline, Racecomp Tarmac II (race), and Ohlins Flag. European type valving with the addition of separate compression and rebound adjustment. If you know how to adjust them, these options will let you dial in one setup that you like for the drive to and from the track and then tailor the setup to whatever surface you happen to be racing on that day.

As stated before, its not completely about what the best spring rate is. Its about the most balanced setup and what you want from it. The 7k/5k Ohlins Sportlines will likely give you faster lap times than the 12k/10k Megan race version simply because you won't bounce as much. You can take corners at higher speeds and not have to worry about that one bump that is going to kick the back end out and spin you.

In the end...call Myles and discuss your needs. He sells all of what I listed and has used most, if not all of them. The big factor is going to be your budget. In most cases you get what you pay for with coilovers.
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