Track shock/spring advice

[docs302]

After a few track days with the Cortex coilover set-up that I purchased from a member here I came to the conclusion that I need to make some changes. The set came with Koni SA up front and JRi DA out back with spring rates of 450F and 225R. I have an 18mm rear bar and 32mm Strano hollow bar up front. I have played with combinations of camber from -3.0 to -5.0, front bar full stiff and middle and front struts full stiff to full soft. My two biggest complaints are front dive under braking that gets the rear very loose and excessive understeer in slower turns.

With the camber at -5.0+ the turn in was amazing as expected but the rear wanted to come around so I had to dial it back. My first thought is I need a much higher rate front spring and/or shock to resist dive. Rear grip was pretty good with the 18mm bar and I am even thinking of going with the 13mm for more bite but that will worsen the front push.

Any suggestions on spring rates? Better shocks? I know there are some very high-end (expensive) remote reservoir shocks that are available but even if I can afford them I doubt I can tune them correctly. Front sway bar size?

Any help would be appreciated. I have all winter to work it out.

Thanks

 

[bpracer]

Stiffer front spring, smaller front bar would be more resistant to brake dive but still have similar roll rate.

Are you running a square tire setup? What kind of differential?

Sent from my SAMSUNG-SM-G900A using Tapatalk

 

[RodS197]

Brake dive is also a component of damping. You don't mention that you have adjusted your damping or what your damping settings are. My spring rates (450/250), bar configuration (35MM/18MM) is very close to yours. I am running SA Koni Sports. I am running 87.5% stiff in the front and 12.5% stiff in the rear.

I would recommend increasing (stiffer) rear rebound damping as a way of controlling dive. Under heaving braking, weight is transferred from the rear to the front and if the rear damping is soft on rebound, the rear will rise. Increasing (stiffer) rear rebound should help with that without necessarily a change in spring rate.

You mention the car is understeering in the slow corners. Which phase of the corner are you understeering? (entry, mid, exit). That might change the adjustment you would make. I agree that a smaller rear bar might not be the best direction for what you describe, but possibly softening the front bar would. I assume you have a Torsen in your BOSS? If it is a trac-loc, this can have a huge effect on understeer from apex to track out under acceleration.

 

[docs302]

Are you running a square tire setup? What kind of differential?

Yes, square 18" on 305 slicks. A smaller front bar was what I was considering so that makes sense. I have the stock Torsen right now but likely going to drop down to a 3:55 ratio and swap in a Wavetrac differential.

 

[docs302]

You mention the car is understeering in the slow corners. Which phase of the corner are you understeering?

Mid-corner to exit the car just won't keep the line and ends up drifting wide but it may be the used slicks that are the problem as well. I have brand new 315 BFG R1S tires that I hope make a big difference in traction.

I assume you have a Torsen in your BOSS?

Stock Torsen.......soon to be a Wavetrac unless there is a better option.

 

[RodS197]

Seems like your damping could be too soft all around. You seem good on all the other settings, it should be able to be tuned with the damping. I would set the front dampers (SA) at about 80% stiff (I think those are rebound only on Koni), and the rear compression damping to about 40% stiff and the rear rebound to 40% stiff and try it there.

Granted you are working with 100 more horsepower than I am, which makes the handling more of a challenge, but perhaps some of the BOSS guys can chime in.

I have the Torsen T2R and love it. Certainly your new 315 tires will change things a bit as well. Before diving in the spring rates and sway bars I would mount those tires and set the damping and see what you have.

Also, if you feel no difference going from full stiff to full soft on dampers, you may want to see if the dampers need attention.

 

[docs302]

RodS197, thanks for the suggestions. I think the rear rebound needs to be checked. I don't believe I even checked the setting before I mounted them.

 

[Mad Hatter]

For track, Filip at Cortex. recommended 600F/350Rear for the springs... With the rear 18mm bar I like the front shocks at 90% stiff and the rears at almost full soft.... With the rear bar out, I set the rear shocks at near 50%...... Just bought a set of 500F/300R springs to try our. Car is very sensitive to changes to its rear.... (aren't we all)... With no rear bar I need to set the front bar to middle stiff or less for the slower corners

PS... I only have the koni SA shocks front and rear....

and don't forget your LCA angles and Squat/antisquat!! Not too mention....Tire pressure and all those other important variables!!
Steep LCA angles really affect braking among other things

 

[docs302]

and don't forget your LCA angles and Squat/antisquat!! Not too mention....Tire pressure and all those other important variables!!
Steep LCA angles really affect braking among other things

Yes.....so many variables and some that confuse the hell out of me!

Since I was told Filip recommended the current spring rates as a track/street combo I would think that increasing the rates might work better for a track-only car. I will look at my LCA angle but I believe it's horizontal as it sits or pretty close with the brackets set at middle. Roll center is also a subject that seems to play into this whole discussion so it's just more to work out. I just don't want to waste money throwing stuff at the problem and hoping something works.

 

[Eric62]

Lemme toss out a few helps for brake dive...
A bit more aggressive rear brake pad. That will make the rear squat down a bit more making overall dive less but not affect the front dip. The ABS will prevent rear lock and it will take some heat off the front brakes.

More rebound damping in the rear, as others have said. That helps the initial brake spike induced pitch. It also will help turn-in, a lot. Too much rebound will make the car feel like it has a bunch of oversteer at turn-in that you can't balance mid-turn. You can go too far here, but the car will let you know when it is too much.

Third, drop the mounting points on the axle attachment point on the rear lower control arms with a control arm relocation bracket. That adds brake-anti-lift to the geometry which helps hold the rear down under braking. I mention this last because it will affect other things like turn-in. It will make the car turn in more aggressively because the axle initially steers away from the turn as the car rolls but then steers the axle back in as the car gets to the max roll at mid turn. Yeah, hard to visualize. Big effect on my '07 S197, not as much on my '13 S197. But the brake anti-lift effect is significant for both cars.

 

[docs302]

A bit more aggressive rear brake pad.

Went from Pagids to stock this year so that didn't help. May be getting an upgraded system for next year so the pad will change.

Third, drop the mounting points on the axle attachment point on the rear lower control arms with a control arm relocation bracket.

I do have Kenny Brown's spherical LCA's and FRPP brackets with the arms lowered so I think I'm good there. Will recheck how they are angled with the current ride height just to be sure.

 

[Grant 302]

I think the rear rebound needs to be checked. I don't believe I even checked the setting before I mounted them.

This is probably the area where the most important fine tuning adjustments are available to you. Learning how to adjust the DA is difficult, at best and most need to dig in to how the low speed and high speed rebound adjustments work. My suggestion is to look at the CorteX thread on DA adjustments and to write down your settings and make notes as you make adjustments.

My first question when I saw your first post was what your rear shock settings are. Next would be what the rest of the complete suspension setup is.

Looks like most of the info has been explained since, except your front geometry like ride height/A-arm angle/roll center. My guess is that your front might be a little low for the hardware you have.

I don't think you need more hardware to solve your issues. Except maybe stiffer springs (JMO) which are a little soft for 3xx slicks. I think you have enough adjustability in your setup to 'fix' everything.

from the CorteX DA thread:

Re: Help me understand my new coilover adjustments (JRI - cortex)

Here is some guidance on setting up the JRi shocks.

The JRi low speed adjuster affects both compression and rebound but in a strategic way. The rebound adjuster (high speed adjuster) only affects rebound.

CorteX recommends the following setting listed below for the double adjustable shocks and struts. The setting can vary depending on spring rates, tires used, and driver preferences.

Front Struts

Baseline (Should be as-shipped)
+5 High speed (lower adjuster - "sweeps")
-15 Low speed (Top adjuster - "clicks")

Strut Softer Setting
+2 High speed (lower adjuster "sweeps")
-6 Low speed (Top adjuster "clicks")


Rear Shocks

Baseline (Should be as-shipped)
+12 High speed (lower adjuster - High Speed "sweeps")
-6 Low speed (Adjuster at the end of the shaft - Low Speed "clicks")

Shock Softer Setting
+4 High speed (Second adjuster "sweeps")
-3 Low speed (Adjuster at the end of the shaft - "clicks")

It will make the car turn in more aggressively because the axle initially steers away from the turn as the car rolls but then steers the axle back in as the car gets to the max roll at mid turn. Yeah, hard to visualize. Big effect on my '07 S197, not as much on my '13 S197.

Not always. Depends on the specific setup regarding the roll steer properties. Otherwise, great post!

 

[Mad Hatter]

Funny after-thought that suprized me...... When switching from the stock Boss shocks and P springs to the Cortex 600/350 spring Koni Track setup.... I was prepared to give up ride quality.....

Suprize!! The car felt nicer with the Cortex setup then the P springs!! I guess that goes too show what a better quality shock can do!

Going to try the 500/300 setup that @ajaquilante suggested because,... well because he suggested it!!

Maybe my SA Konis are not up to the job,....

 

[Coz]

Went from Pagids to stock this year so that didn't help. May be getting an upgraded system for next year so the pad will change.

Did you upgrade to the bigger rear 13-14 GT500 13.8" rotors? When I did, I felt a little less dive probably because the backs were a bit more effective.

 

[docs302]

Did you upgrade to the bigger rear 13-14 GT500 13.8" rotors?

Yes, I got the Blowfish bracket and did the upgrade. But as I previously mentioned, went back to stock pads instead of keeping the Pagids so that was probably not the best idea.

 

[Fair]

Buying someone's second hand suspension is always a gamble. The 450#/in front spring rates are great, for a dual purpose car that does a lot of street use. But brake dive is largely a function of spring rate. Sure, damping can "slow" that down, but it cannot make up for a soft spring. That's something the magnaride guys need to get through their heads, too - a shock is not a substitute for a spring.



If you are on "slicks" then you should be on significantly stiffer spring rates. That's where the twin tubes (Koni SA) lose their effectiveness (well, way below even 450#/in). We used 450/175 rates with proper Motorsport monotubes in our S197 early on, and still recommend them for mostly street car S197s (and light track duty). But, like you, we noticed a lot of dive/squat/roll/heave with rates that soft. On the measured test day above we were on 450/175 rates with a 315mm A6. It would almost drag the LS front splitter under hard braking and in corners. Movement on track was significant, as you can imagine. And that was with real dampers.



As we developed our S197 for better road course handling with wider race tires we went up in spring rate several levels. Adding aero upped that even more, otherwise the ride height would compress at high speed. Sounds like you need to talk to someone who understands all of these variables, and who can get familiar with your particular setup and end use. This ain't for the general public to answer via forums or facebook, in my honest opinion. Give us a call if you want to chat... but be prepared to hear things you might not like, such as the need for better dampers to work with the spring rates you need.

Cheers,

 

[docs302]

Learning how to adjust the DA is difficult, at best and most need to dig in to how the low speed and high speed rebound adjustments work.

You are correct.....I'm really at a loss when it comes to adjusting. I do plan on sitting down this winter and really figuring out how to work with the DA shock.

I do have one question.....what the heck is the air valve doing on top of the shock? Didn't see any explanation.

 

[docs302]

This ain't for the general public to answer via forums or facebook, in my honest opinion.

Absolutely correct.

Give us a call if you want to chat... but be prepared to hear things you might not like, such as the need for better dampers to work with the spring rates you need.

Thank you.....may take you up on that. Spending money on this hobby is a given.

 

[Mad Hatter]

darn, their goes another hobby..... does that mean we should quit TMO and spend more time on Netflicks?

I guess it would save us all a ton of money

Just kidding, I find this forum exceptional with the loads of free advice given by people who have raced their cars. Obviously If you can pay a top shop like Vorshlag or Phoenix to set up your car then thats the way to go. But kind of like tinkering.......... and seeing how many different ways one can get to a desired end!

 

[docs302]

I find this forum exceptional with the loads of free advice given by people who have raced their cars.

Obviously If you can pay a top shop like Vorshlag or Phoenix to set up your car then thats the way to go.

I agree.....didn't want to give the impression I don't appreciate and use the advice I get here. It's the reason I kept my Boss instead of selling it for something recent. I did bring my car to Phoenix for the basic set up as it sits today and likely will continue to use their advice and services if I have to. But it costs some serious change for the pros to do the work and I would really like to learn how to work out the kinks from this forum. But as Terry said, some subjects are complicated there are a lot of different opinions and it makes sense to get an pro's angle to come up with the best combination. Everyone here has helped me get to where I am today and that won't change!