Spring Rates - Track / Autocross

[JoeBoxer]

Awesome thread guys keep up the good work!

[gmookher]

I wonder how swappable are springs, I mean if GC doesnt have a coil, is there a 3rd party or brand x product that will work fine on my coilovers, likewise, lets say your R2 vendor doesnt offer fronts in 375, but GC does, can you try those?

I'm curious what 375/400 feels like
375/430
400/430
440/430

[Miniata]

Originally Posted by gmookher

I wonder how swappable are springs, I mean if GC doesnt have a coil, is there a 3rd party or brand x product that will work fine on my coilovers, likewise, lets say your R2 vendor doesnt offer fronts in 375, but GC does, can you try those?

I'm curious what 375/400 feels like
375/430
400/430
440/430

As long as your coilover springs are standard sizes (2.5", 2.25", or 60mm) replacement springs in a large variety of dimensions are available from numerous sources.

[Dave-ROR]

Originally Posted by gmookher

I wonder how swappable are springs, I mean if GC doesnt have a coil, is there a 3rd party or brand x product that will work fine on my coilovers, likewise, lets say your R2 vendor doesnt offer fronts in 375, but GC does, can you try those?

I'm curious what 375/400 feels like
375/430
400/430
440/430

2.5" springs are pretty universal. You can get ERS/Swift/Hyperco/etc easily in many rates and lengths.

GC uses ERS (Eibach Race Springs), identical springs as the Multi Pro R2 (and any other Eibach threaded body coilover) uses.

IMO any of those three brands for springs (ERS/Swift/Hyperco) are outstanding.

edit: Already answered, should have read Miniata's reply first :P

[gmookher]

Cool....

[mla163]

I had a little downtime over the holiday and started modelling the suspension. Using a few suspension books and some help from some technical articles and Mechanical Engineer friends, I calculated the TLLTD for a few different setups. Before anyone slays me for the calcs, I am still working them out, but I did find a few relative comparisons.

Stock BR-Z
66%

(A 50% value should indicate neutral. In reality, a 58% value is as aggressive as you would want to drive on the street. This value seems a little high for me and I want to back check these calcs and measurements. Still the relative numbers work for me. I will use this value as a baseline)

Stock FR-S
65% (slightly more tail happy than the BR-Z, this is true)

I posted on the first page regarding the "ideal" spring rates for based on an ideal frequency. Basically, the idea is to match the rates so that when you hit a bump with the front wheels, the back wheels catch up. Based on this assumption, the "ideal" rate is

300F
700R

These are different than I posted before (375/650) since I adjusted a few measurements. Obviously this rate is much higher in the rear and will cause the car to be incredibly tail happy. The TLLTD for this is 56% -makes sense compared to above data.

To get closer to the same TLLTD as the stock setup with these spring rates, you'd need to lose the rear swaybar completely to bring the TLLTD down to 59% - probably too loose still.

If you stay with the same 300# front springs and stock bars, to keep the TLLTD down to say 62%, you'd need to run 450# rear springs with stock bars. So, for stock bars:

300F
450R
(Roughly what other guys are running)

Once you start messing with the bars, the variations will increase significantly.

All of this info is based purely in suspension dynamics and theory, but it's nice to get in the same ballpark as people testing on their own. Everything needs to be backed up by testing, but personally, this gives me a place to start.

Using the same spreadsheet and RCE's setup (400/400, 20/16), their TLLTD would be 65.5% - roughly the same front/rear balance as a stock FR-S.

[ayau]

Any updates to this thread? Interesting discussion.

Is there a conclusive answer yet regarding the spring rates at the front and rear (ie., stiffer in back, etc)? Is it entirely personal preference? Is one option necessary better than the other?

[Sam Strano]

I don't want the same balance as a stock car. It's too ass-happy. Not only that, but the suspensions aren't the same, all things are not equal. You can't say "I increased the front and rear the same percentage so I'll get the same balance". It just doesn't work that way. A zillion things are involved.

What's more, I'm constantly frustrated by those that are all hung up on numbers. Drivers drive the car, calculations do not. If they did, then every race car would go to the track perfect and never tweaked.

I've said this once I'll say it again. I can pretty much guarantee I've got more Front engine, rear-wheel drive, with big differential experience than anyone here. These are the kind of things I run, and prefer to run. I've never had a Subaru before, and wouldn't have one (though my parents had a Legacy GT and my sister an Outback that I recommended to them).

I run stiffer front springs than rear. I also run more front bar.. and NO more rear bar. And trust me the car isn't tight. In fact it's damned neutral both ax and track days on Hankook's. I suspect on R's it'd be a touch tighter, but I also have a pretty aggressive rear alignment camber wise which would easily change balance.

Personally, the only way I'd run more rear spring than front is with a BIG front sway bar (and not a big rear). That can work, but if you want to run soft front springs and a big front bar, I'm not sure why'd you do the opposite on the rear unless you just want to be contrary. There are two reasons I'd never do that....

[ayau]

bump.

I've been googling "ideal spring rates" for the track and there just isn't any. It really is a black art, lol.

[Dezoris]

I don't want to stir the pot since Ayau resurrected this thread but...
How many of the self proclaimed track junkies here actually do autox and have been successful?

It seems like this has become more of the trend, where the track guys never do autox or if they have either do not like it or are no good at it.

[ayau]

Originally Posted by Dezoris

I don't want to stir the pot since Ayau resurrected this thread but...
How many of the self proclaimed track junkies here actually do autox and have been successful?

It seems like this has become more of the trend, where the track guys never do autox or if they have either do not like it or are no good at it.

For those who don't have easy access to a track (probably applies to most people), I think autox is an easy/cheap way to get their fix. After attending one track event, I definitely prefer it over autox just based on the fact that you get more seat time at a track event.

[xwd]

I think there is some good info in the STX sharing thread I believe, and those guys have very well setup cars at this point.

Right now people aren't running crazy spring rates, like 300/400 but some run higher in the front and some higher in the rear.

[ayau]

I'm running on 500/650 right now. After 2 autocross the events, the back was very loose. It could also be the fact that the parking lot was VERY bumpy. IDK.... I still need to test the rates at an actual track to see how it feels.

The problem is that I sort of want to have a hybrid setup by using the same rates for both track and autox. I just don't think it will work, idk. I think I'm a little frustrated right now lol.

What's the consensus on stiffer rear? It seems like we still don't have a solid answer.

[Solid]

I would talk/listen to Sam Strano. 14X national champ doesn't happen with poorly prepped cars. Like Sam said. If number crunchers were always right, you wouldn't need crew chiefs and pit crews for chassis adjustments.