Spring Rates for Track Use

[Flyhalf]

Medium seems to work fine. According also to cortex.
Body roll is huge issue in my 3789lbs car.
However
What i found out is a medium sway bar seems to work better with bigger tires (305)
While it is easier to overdrive and then understeer a 285mm tire. (I use the 285 for time trials due to class limit)
Next year i will move to a real coilovers system (probably JRi)
But I'm running like many shelbys now with FP and Bmr shicks/sway bar.
So i think is really a great combo.
Actually I used to run stock struts and Bmr springs and they were good too.
My point is :
a coilovers isn't always faster and 95% of us probably don't need them in the first 2 years of hard tracking.
Feel free to contact me in pm if you need !

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[Ewheels]

If you're running significant aero, or slicks, the higher rates become more necessary or advantageous to account for the downforce and also to maintain ride height. For a track only car, I definitely see the desire to go there. For a mixed street car, they can be a bit much. For autocross, they can be an advantage because the time between corners is less and you need the sharp response for the best run. Once again, you'll need to spend $2500+ to get dampers that can properly control those springs. They will be better on track, but not necessarily better for your goals overall.

The FP/BMR combo fills the dual purpose requirement very, very well. It's not by accident that it was developed. See the spring rate sticky, page 9-10 .

Ok, did some reading and some number crunching. Excellent post @BmacIL in the spring rate sticky. Using your info and I found another article about ride frequencies (http://www.optimumg.com/docs/Springs&Dampers_Tech_Tip_1.pdf) I have a better understanding of suspension balance and how it all pieces together.

Using the numbers from your post (3188 lbs sprung mass and 53% F weight distribution) I get a sprung mass per front corner of 844 lbs. Then using the chart in the above link, I get a spring rate of 195.2 lbs/in for 1.5Hz ride frequency and 347.1 lbs/in for 2.0Hz. Then interpolating for the BMR 250 lbs/in spring rate, I get a ride frequency for the BMR Handling springs of 1.68Hz which seems about perfect for a track focused street car. Additionally, using the chart in your post Bmac, I see that the SP083 springs have a F/R ride frequency split of 4%, which again is right in line where it should be.

I just wanted to mathematically prove this to myself, lol.

EDIT: Now I see Bmac already calculated the frequencies for all these springs haha! I guess I didn't read close enough. Oh well, doing the math never hurts.

 

[SteveW]

I'm going to chime in about another factor I don't see being considered in this rates discussion and that's packaging. I think one important reason you don't see spring rates much above 250-300 lb-in for springs that use OEM style struts and upper mounts is the spring won't stay safely in place at full droop. The stiffer a spring is the shorter it needs to be to maintain the desired ride height.

A 950 lb corner weight acting on a 165 lb-in spring is going to compress it 5.75"

A 950 lb corner weight acting on a 250 lb-in spring is going to compress it 3.8". Figure also this spring lowers the car an inch over stock like most lowering springs do therefore, the free height of the spring is probably going to be ~3" shorter than the factory spring.

A 950 lb corner weight acting on a 400 lb-in spring is going to compress it only 2.75" so, this spring needs to be another inch shorter for the same ride height if you were using the same OEM style struts and perches.

Trying to keep a 250-300 lb-in, 3" shorter spring safely mounted in the OEM style struts and mounts is probably the most you can get away with before the spring becomes unloaded and loose at full droop. Or you go progressive and have a bunch of soft coils bound together under load that extend under droop.

Coilovers can go stiffer because they have adjustable spring perches but eventually you run into the same problem of a loose spring at full droop. 400 lb-in is about the limit to keep some preload in the spring at full droop and the perch above the tire. Yes, a longer spring and lowering the perch also works but now you may not have room to fit those 11" wide wheels and 305mm+ wide sticky tires. Something else you're trying to do when you get to this point in a setup.

Just my $.02 as I fumble around with my own setup trials and tribulations.

 

[BmacIL]

I'm going to chime in about another factor I don't see being considered in this rates discussion and that's packaging. I think one important reason you don't see spring rates much above 250-300 lb-in for springs that use OEM style struts and upper mounts is the spring won't stay safely in place at full droop. The stiffer a spring is the shorter it needs to be to maintain the desired ride height.

A 950 lb corner weight acting on a 165 lb-in spring is going to compress it 5.75"

A 950 lb corner weight acting on a 250 lb-in spring is going to compress it 3.8". Figure also this spring lowers the car an inch over stock like most lowering springs do therefore, the free height of the spring is probably going to be ~3" shorter than the factory spring.

A 950 lb corner weight acting on a 400 lb-in spring is going to compress it only 2.75" so, this spring needs to be another inch shorter for the same ride height if you were using the same OEM style struts and perches.

Trying to keep a 250-300 lb-in, 3" shorter spring safely mounted in the OEM style struts and mounts is probably the most you can get away with before the spring becomes unloaded and loose at full droop. Or you go progressive and have a bunch of soft coils bound together under load that extend under droop.

Coilovers can go stiffer because they have adjustable spring perches but eventually you run into the same problem of a loose spring at full droop. 400 lb-in is about the limit to keep some preload in the spring at full droop and the perch above the tire. Yes, a longer spring and lowering the perch also works but now you may not have room to fit those 11" wide wheels and 305mm+ wide sticky tires. Something else you're trying to do when you get to this point in a setup.

Just my $.02 as I fumble around with my own setup trials and tribulations.

Definitely true. The BMR handling front and GT350R front basically are uncompressed at full droop. There isn't free play but it's exactly that length just before there is. They're as stiff as you can go with a linear rate spring and not be basically back at stock height.

 

[Biggsy]

I end up (maybe as the op has) in the black hole that is suspension threads, wondering if/when I should upgrade springs and dampers. And I emerge thinking I should upgrade springs and dampers without any real info to back it up. But my car is a street car as most others, so the Steeda ultralites and FP dampers combo works great. As stated previously, I decided I should get a set of 11” wheels and sticky tires, and get into some more events until I “outdrive” my suspension, then I’ll upgrade

If you ever want to "try before you buy" I got you kind sir ...

 

[BMR Tech]

Love seeing educated posts. Thats exactly right...you really want to be at 10"~ minimum free height for the front spring. Going less than that is risky - I spent a lot of time on the 250lb front SP084 spring to get it "just right". It is the absolute stiffest linear rate drop spring possible for the S550 chassis.

-Kelly

 

[ModularKid21]

If you ever want to "try before you buy" I got you kind sir ...

I plan on pulling the trigger on some wheels/tires when Black Friday/cyber Monday comes around, along with a few other little goodies. I think that’ll show me once and for all that the my suspension is just what the Dr. ordered

 

[shogun32]

Coilovers can go stiffer because they have adjustable spring perches but eventually you run into the same problem of a loose spring at full droop.

If you didn't dial in a minimum of 1/4" of preload into your coilover springs, you did something VERY wrong.

From the sounds of it we need a MD/VA get-together to test ride/drive each other's cars and the various suspension upgrade combos that have been done to them. Now if only the weather would cooperate.

 

[ModularKid21]

If you didn't dial in a minimum of 1/4" of preload into your coilover springs, you did something VERY wrong.

From the sounds of it we need a MD/VA get-together to test ride/drive each other's cars and the various suspension upgrade combos that have been done to them. Now if only the weather would cooperate.

I concur

 

[Grintch]

This is exactly what I hear from everyone about the Ford shock/BMR spring combo and exactly why this was my plan forward. But it had me thinking if these 250 rate springs are flat and balanced, then why would racers need spring rates 3 times that? I would love to personally feel these BMR springs for myself before purchase if possible.

Racers always need more. But a good dual purpose setup and a good full race setup are miles apart. Just test drive a ZL1 1LE, and you will see how going too stiff can ruin a car for the street. And that is with supper trick $20k shocks, and everyone says expensive shocks handle stiff springs better. Plus the whole springs and shocks are ideally a package, and no one makes standard shocks meant to deal with 600lb/in spring rates (or 600 lb springs that work with standard shocks).

 

[shogun32]

Plus the whole springs and shocks are ideally a package, and no one makes standard shocks meant to deal with 600lb/in spring rates (or 600 lb springs that work with standard shocks).

Say what?
If you want good suspension you have to pay for it. $4-8000 for JRI or Penske setup or the various offshoots like RideTech. If you're serious about suspension you re-shim your pistons to match your use case, your personal sense of 'feel', and not the least the spring rate equipped. And then you dyno your assembly and drive it in a repeatable manner. The two are absolutely a package. Unfortunately few car suspension providers make the effort and furthermore dyno every shock they build.

That said I just installed Steeda's 800/1200 springs on a set of their Pro-Action adjustables. Very nice but have some outstanding issues that need to be sorted till I'm happy.

 

[Grintch]

Say what?
If you want good suspension you have to pay for it. $4-8000 for JRI or Penske setup or the various offshoots like RideTech. If you're serious about suspension you re-shim your pistons to match your use case, your personal sense of 'feel', and not the least the spring rate equipped. And then you dyno your assembly and drive it in a repeatable manner. The two are absolutely a package. Unfortunately few car suspension providers make the effort and furthermore dyno every shock they build.

That said I just installed Steeda's 800/1200 springs on a set of their Pro-Action adjustables. Very nice but have some outstanding issues that need to be sorted till I'm happy.

I assume those are the Pro-Action coil overs? Not the OE style Pro Action struts?

My point was you couldn't compare spring rates from standard lowering springs intended for mounting on stock shocks or at best heavy duty stock type shocks (E. G. Koni Yellows) with spring rates from off the shelf or custom valved coilovers. And if you tried to use those rates on stock style shocks, even if it was possible, it would be terrible with off the shelf valving not intended to deal with such high spring rates.

 

[Bahndvr]

Completely agree on the front bar. It was a huge improvement to front end grip and overall balance vs the stock bar.

It made that much improvement?

 

[BmacIL]

It made that much improvement?

Yes. Particularly coupled with the roll center correction front arms.

 

[Bahndvr]

Yes. Particularly coupled with the roll center correction front arms.

I was wondering about those arms ever since Steeda put them out. Now I have more money to spend.
Thanks

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