Topic: Adjusting shocks to accommodate spring rates

[RufusMacblorf]

After reading several threads about optimal front/rear spring rates, I contacted the supplier of my BC coilovers to see what I have.  It turns out I probably have 7k springs front and back.  As I understand it, Kappas benefit from something like 7k rear and 5k front.  I'm not too enthusiastic about getting new front springs, so I had a couple of questions for the gurus:

1) As I understand it, harder front springs increase understeer on our cars.  I've also read that setting the adjustable dampers harder in the back than the front reduces understeer, and that the Z0K rear anti-roll bar, when paired with an FE3 front bar, also reduces understeer.  To what degree, if any, can I use damper adjustment and an anti-roll bar swap to compensate for the spring rates, or are these unrelated dynamic factors?

2) I do some autocrossing (I'm mediocre at best) but I really enjoy canyon-carving.  I don't mind spinning on the solo course, but I don't want surprises when there's a 1,000 foot dropoff a few feet away.  I've been told it's best to set the front and rear dampers to the same settings for canyon carving.  Is it safe to make the back a little stiffer than the front (e.g., 6 from soft in front and 11 from soft in back) when you have the same spring rates?

[Carbon Sky]

After reading several threads about optimal front/rear spring rates, I contacted the supplier of my BC coilovers to see what I have.  It turns out I probably have 7k springs front and back.  As I understand it, Kappas benefit from something like 7k rear and 5k front.  I'm not too enthusiastic about getting new front springs, so I had a couple of questions for the gurus:

1) As I understand it, harder front springs increase understeer on our cars.  I've also read that setting the adjustable dampers harder in the back than the front reduces understeer, and that the Z0K rear anti-roll bar, when paired with an FE3 front bar, also reduces understeer.  To what degree, if any, can I use damper adjustment and an anti-roll bar swap to compensate for the spring rates, or are these unrelated dynamic factors?

2) I do some autocrossing (I'm mediocre at best) but I really enjoy canyon-carving.  I don't mind spinning on the solo course, but I don't want surprises when there's a 1,000 foot dropoff a few feet away.  I've been told it's best to set the front and rear dampers to the same settings for canyon carving.  Is it safe to make the back a little stiffer than the front (e.g., 6 from soft in front and 11 from soft in back) when you have the same spring rates?

I'm no guru, but from my understanding what you say about 1) is pretty much dead on.  The problem with dampening is that will mostly affect the initial moment and transition towards loading up the suspension, but not nearly as much once the car has transferred weight and settled into a turn.  At that point, it's in the springs and roll bar.  So the dampener adjustment will only be able to help at the initial turn in, and not nearly as much in the middle of the turn with the weight transferred.

Doesn't BC use a typical sized coilover spring?  Springs are relatively cheap.  You should be able to get a pair for $150 ish.  Most of the money is in the dampener.

I disagree with what you have to say in 2) about what you've been told.  Arbitrarily setting the front and rear dampers to the same setting can be ideal, but could similarly be not as well.  I bet even at the stiffest dampening at the rear and the softest dampening at the front, the car won't be "dangerous".  It'll just be more prone to oversteer, it won't produce "snap" or sudden oversteer.  You're more likely to get that with something like an unusual alignment from a street alignment.  Yes it'll oversteer at a lower throttle input, and at a lower cornering g-load, but it won't be all grip and neutral and then suddenly oversteer on you.  Set it to what ever generates the best handling characteristics, or rather the handling characteristics you prefer.  What I may consider ideal will definitely not be for others.

In my opinion, I say keep a log book, make a few runs at various settings like mid/mid, or more damp/less damp, or less damp/more damp, front to rear.  And be sure to include info like weather conditions and tire pressures.  I seem to like a lower pressure than lots of people with kappas, and a hair more in the rear than the front on my stock goodyear F1 GS-3s.  I can reliably detect a 3 psi difference these days from the driver's seat.

Personally, I say, if you can afford it, get the lower rate front springs.  If not, adjust as best as you can with the dampeners.

And if you don't already have the ZOK rear sway bar, get that first.  I bet it'll put a smile on your face if you like to be at the limit of traction often enough.  And don't forget all the requisite convertible chassis stiffening, i.e. backbone, probeam, and even a front chassis brace as well.

[wspohn]

I use the same shocks and springs with the GXP ZOK bars and find it works well.  I set the fronts half as hard as the rears (10 clicks vs. 20) which works well for me.

[RufusMacblorf]

I'm no guru, but from my understanding what you say about 1) is pretty much dead on.  The problem with dampening is that will mostly affect the initial moment and transition towards loading up the suspension, but not nearly as much once the car has transferred weight and settled into a turn.  At that point, it's in the springs and roll bar.  So the dampener adjustment will only be able to help at the initial turn in, and not nearly as much in the middle of the turn with the weight transferred.

Doesn't BC use a typical sized coilover spring?  Springs are relatively cheap.  You should be able to get a pair for $150 ish.  Most of the money is in the dampener.

I disagree with what you have to say in 2) about what you've been told.  Arbitrarily setting the front and rear dampers to the same setting can be ideal, but could similarly be not as well.  I bet even at the stiffest dampening at the rear and the softest dampening at the front, the car won't be "dangerous".  It'll just be more prone to oversteer, it won't produce "snap" or sudden oversteer.  You're more likely to get that with something like an unusual alignment from a street alignment.  Yes it'll oversteer at a lower throttle input, and at a lower cornering g-load, but it won't be all grip and neutral and then suddenly oversteer on you.  Set it to what ever generates the best handling characteristics, or rather the handling characteristics you prefer.  What I may consider ideal will definitely not be for others.

In my opinion, I say keep a log book, make a few runs at various settings like mid/mid, or more damp/less damp, or less damp/more damp, front to rear.  And be sure to include info like weather conditions and tire pressures.  I seem to like a lower pressure than lots of people with kappas, and a hair more in the rear than the front on my stock goodyear F1 GS-3s.  I can reliably detect a 3 psi difference these days from the driver's seat.

Personally, I say, if you can afford it, get the lower rate front springs.  If not, adjust as best as you can with the dampeners.

And if you don't already have the ZOK rear sway bar, get that first.  I bet it'll put a smile on your face if you like to be at the limit of traction often enough.  And don't forget all the requisite convertible chassis stiffening, i.e. backbone, probeam, and even a front chassis brace as well.

Good feedback.  Thank you!

[RufusMacblorf]

I use the same shocks and springs with the GXP ZOK bars and find it works well.  I set the fronts half as hard as the rears (10 clicks vs. 20) which works well for me.

Do you run those settings on the road, or just in autocross?

[wspohn]

Do you run those settings on the road, or just in autocross?

That is what I run on the road (as I do not autocross this car). Those running solo events may find that they have too much push and seem to prefer a little less front roll stiffness, which they accomplish by running the stock GXP front bar. I prefer to use both GXP ZOK bars on the street.

[elff]

I Run FE3 front, ZOK Rear on the street.  I also run 275s on the rear.  I was having traction issues with 245 and decided to go wider vs stickier.  It's worked out well.  My Sky carves up the corners.

If you are going to swap out a pair of springs, you might want to look into some really excellent springs for all 4 corners.  It will only cost $400 with shipping.
I have a bunch of friends who have used these to replace the stock springs on various coil overs
http://www.swiftsprings.com/
All you need is the inner diameter and length of your current springs. 
BC offers these springs as an upgrade option on their website, so they understand and accept that they are better than their own stock springs.

[Carbon Sky]

 

The FE3 front and ZOK rear sway bars is as close to sublime as I think you can get in terms of roll bar balance.

Don't forget that elff make significantly more power than a lot of guys with just stock turbos, even with a tune.  So he could definitely use more grip in the rear under acceleration in a turn.

While I regularly have traction issues in 1st and 2nd, I don't often have nearly the traction issues in 3rd that elff does.

And at $400 for the rest set of springs you'll need, I think that's very fair to get what you want in your setup.

[RufusMacblorf]

I ordered the Z0K rear bar.  I'll take it one step at a time and see how it goes.

I did a little reading on the Swift Springs.  Interesting, but I wonder if it's worth the cost if you're not driving a hardcore race car.

Thanks for the input, everyone.

[rlhammon]

After reading several threads about optimal front/rear spring rates, I contacted the supplier of my BC coilovers to see what I have.  It turns out I probably have 7k springs front and back.  As I understand it, Kappas benefit from something like 7k rear and 5k front.  I'm not too enthusiastic about getting new front springs, so I had a couple of questions for the gurus:

1) As I understand it, harder front springs increase understeer on our cars.  I've also read that setting the adjustable dampers harder in the back than the front reduces understeer, and that the Z0K rear anti-roll bar, when paired with an FE3 front bar, also reduces understeer. 

A better way to say this would be:

If your car is over or understeering more than you wish then the general guidelines are as follows:
1. To induce oversteer because your car won't turn in quickly enough:
- Stiffen the rear of the car with bigger springs, shocks, anti-sway bar, or some combination of these or. . . .
- Soften the front of the car with smaller springs, shocks, anti-sway bar, or some combination of these

2. To induce understeer because your car is "tail happy", reverse the above:
- Stiffen the front of the car with bigger springs, shocks, anti-sway bar, or some combination of these or. . . .
- Soften the rear of the car with smaller springs, shocks, anti-sway bar, or some combination of these

To what degree, if any, can I use damper adjustment and an anti-roll bar swap to compensate for the spring rates, or are these unrelated dynamic factors?

For a balanced GXP/Redline I would go with FE3 front sway, and Z0K rear sway.  From there, tune the springs for Natural Frequency you desire (with the rears slightly higher than the fronts), then tweak with damper adjustment.  You'll get closer changing the springs than you will with damper adjustments, IMO unless you have some serious adjustment range.  Counting the number of clicks doesn't tell you how "much" you change things though, they are not a measurement of magnitude in force changes on a force vs. displacement chart
(see this: http://farnorthracing.com/autocross_secrets20.html)

In fact, read that whole dang website... great info!

2) I do some autocrossing (I'm mediocre at best) but I really enjoy canyon-carving.  I don't mind spinning on the solo course, but I don't want surprises when there's a 1,000 foot dropoff a few feet away.  I've been told it's best to set the front and rear dampers to the same settings for canyon carving.  Is it safe to make the back a little stiffer than the front (e.g., 6 from soft in front and 11 from soft in back) when you have the same spring rates?

In general, yes this would be safe.  Remember that 1 "click" is different on each brand of shocks, so the magnitude of change is different on KW's vs. Koni vs. Brand X.  Depending on quality control, one set of Brand X could differ greatly from another set of Brand X "click" for "click".  See link above for damper dyno plots and explanations.

As to springs to purchase... the 7k (I assume N/m units) is in the ball park, slightly lower than where my front is.  My rear is closer to 8k N/m... though I'm using Hypercoil springs (I really like these, similar to Swift, a bit cheaper) and measured in lbf/in.

[RufusMacblorf]

Thanks!