Springs, Bars, and Rake

Been looking thru old threads and the "Panoz Tribal Wisdom" document for spring rates and other advice that would improve suspension performance. This is after a friend of mine took my GTRA (Sebring) out at Road America and showed me that the car has tons of understeer. Knowing this is a can of worms, here goes:

Car currently has the 350#F/200#R springs, front bar set at furthest setting, and no rear bar. It also just had an alignment and was set back to the original settings for rake / corner balance with a 200# driver. Shocks are standard Koni's.

I've seen recommendations of 550#F/350#R and 750#F/550#R. How have these held up over the past couple of years? Any recommendations on spring companies / part numbers would also be appreciated.

Recommendations on front bar setting? BTW, the front bar linkage seems to hit after 1" of travel. Thinking this isn't a good thing...

Recommendations on rear bar (buy one or not / setting)?

References on Rake or other parameters that need to be set when changing out the springs?

Since I'm changing springs / going to need to corner balance again anyway, what's the thoughts on changing shocks?

Anyone that has a spare set-up for sale, feel free to PM me with details.

Thanks in advance for your input!

Other than 550 frt and 350 rear springs mine is same as yours. It had very mild understeer. I run the stock rims and Hoosier R6's (used). When i ended up putting newer R6's on the front, the car when to corner off oversteer. The backs still have rubber, but need replacing to restore the balance I had. You might look at tires, pressures and shock adjustment. I'm interpreting your front bar adjustment as full hard.

Mike

Hi Mike! Thanks for the post! Kenny Brown was at Road America and checked tire temps. Fronts were fine. Added 1 lb to rears. Correct, full hard on the front sway.

Running used Continental Challenge tires from last year. I need to have 2 replaced (cracked), but just found out my source dried up (and I'm headed to Gingerman this weekend)... They are saying they have plenty of 275, 285, and 305 widths in the 18" sizes. Any help with rim width and offset for the 18" would also be appreciated. Figure I can pay for rims with the delta in tire prices (~$200 per corner).

On rim width, you want to keep them about an inch narrower than the advertised section width or less. For example a 305 converts to 12 inches. My son is running this size on 10.5 inch rims and that appears to work fine. The original GTRA tire width was 275 (about 11 inches) and they were mounted on 9 inch rims. I thought that caused some crowning of the tread. When I used those rims with Hoosier R6's, I went to 245 and the tire temps were pretty consistent across the surface and wore pretty much uniformly at about 22 pounds cold.

Lowering rear pressure should move it toward oversteer, raising to understeer. Raising the front pressures should move it toward understeer and lowering them toward oversteer. A rear sway bar should move it toward oversteer. Softer front bar should move it toward oversteer. You should be able to move it toward better balance by softening the front bar and playing with air pressures, lower in the front and higher in the rear. If you are running race slicks, you can lower your cold pressures into the upper teens as needed. The wild card is the possibility of the front sway bar being limited in travel. When it reaches it's limit, it becomes infinitely stiff so major understeer. You might need to try to lengthen or shorten the end links to eliminate that issue. If you do all that and it still understeers, adding the rear sway bar should be pursued. PAD can supply that as it is common to the GTS.

I'd try soften the front bar first and see where you are. Then try to balance with tire pressures. I'm not sure how much difference in tire pressures is a good limit. That might depend on compound and construction. As you make the changes, keep track of tires temps and don't let them become extreme high or low. Try to make your adjustments under consistent conditions, number of laps and with good, equally used tires.

Hope you get it dialed without any major changes.

Mike

Thanks for the ideas! I did make one mis-statement, the swaybar IS at the softest setting (furthest hole from the pivot point). Your point is well taken / it may not be set correctly, I have never touched it and don't believe that it was changed when the alignment / balance was done. I pulled the instructions below from the GTS Manual. Any mods or finer points (like spacer length on the lower shock mount)?

Front
A: Front sway bar has two adjustments.
B: It is best to have the driver in the car for this
adjustment.
C: Remove bolts from both sides of the sway bar.
D: With driver in the car, lengthen/shorten heim
until bolts slide into sway bar holes easily.
E: Front hole (front of car) is soft;
rear hole (closest to firewall) is stiff.

Worst case, I'll have to run the weekend on street tires... Best case, I find a set of rims that work in time... The GTS Manual also stated:
WHEELS: 18”x10”
TIRES: 285/640x18 (no offsets provided?!?)
Tire Rack has optional rears for a 1999 Mustang Cobra (They also show a 2007 Esperante, but only go up to 9.5)? Below is from the Cobra:
18x10, Offset: 24mm, Backspacing: 6.50", Bolt Pattern: 5-114
Weight: 27.6lbs."
If there is a better vehicle or website to use, please advise...
Not sure if I'll be able to find 10.5" or 11" rims that would fit the 305's that are available... What style / and offsets is your son running?
Thanks again for the help!

Not sure about the rims he used but I believe they were the 18x10.5 TSW Nurburgring. They were reasonably priced and I think intended for Mustangs as well. It's been a while since he converted. He and his car are in Georgia and I am in Texas. No idea about off set. Since they are 1.5 inches wider, looking at mine, I'd be tempted to put at least an inch of that toward the inside compared to the 17x9's. He hasn't had issues. The rear should be easy, the fronts should be OK with that and could be moved outward with a thin spacer if needed.

I think that sway bar adjustment process is correct. I believe it may be possible to reindex the arms so that they will clear the lower control arms. Might be able to do that by lengthening both end links.

Mike

Cobra77,

Let me preface by saying my response may come across as arrogant or as smart-ass. That's not my intention.

I am new to a Panoz platform, but not road racing and especially not to racing in general. I have heard folks say how "neutral" a Panoz feels, and it makes me wonder. Is the car neutral, or is the driver not pushing the car? Your friend; is he an experienced road racer? I assume since you let him drive that you feel his skill set is better than yours? (PS- I've done the same thing..asked a good "shoe' to wheel my car around for a few laps to get an opinion) Here's why I am asking: Without a rear bar, the car is probably very tight (in my experience) An experienced or accomplished road-racer will notice that in the first lap or so. However, would YOU notice it? Under-steer will inspire a bit of driver confidence because it is relatively easy to recover from. Over-steer can destroy a drivers confidence because it can scare the s**t out of them or worse.

So here's my suggestion. YOU take the car out. Drive it until YOU start to notice the under-steer that probably exists, then gradually start making changes to get the under-steer out of the car. The car will get faster and you will be more confident. That's what I did over my first three weekends in my SCCA A/S Mustang. I went from mid 2:50's at Sebring (long course) to a best of 2:31 by slowly adding rear bar each session. On the third weekend I was comfortable in slightly hanging the rear-end out through turn #1 at 110-ish MPH. The car was flying and I had a huge smile on my face. This was all on the advice of Sebring Guru, Chuck Dawson from Dawson Motorsports.

Just my opinion. Trying to be helpful.

Mike - Thanks for the posts / advice! Now that I'm back from Gingerman, I can focus on the situation. Not sure if anyone here is familiar with the track or not. I was running 1:54 to 1:56 on Pirelli Street Tires (Penske Tracktime Tires). I have run in the 1:50's on slicks. I think these times are reasonably fast for DE, but I'm definitely not the fastest guy out there.

Mark - Yes, my friend is a seasoned road racer (runs an Alpha GTV6 in SCCA EP) and I did talk with him a little more on this to get clarification. His opinion is that it starts pushing somewhere around 55 to 65 MPH. Made him nervous driving through the kink at Road America. I didn't get the same feeling and am sure I am running similar speeds there (around 90MPH in 4th gear). My best time at Road America was 2:49 on slicks.

A group of us were talking about the situation and I mentioned heavier springs (550/350). They didn't think that was the main issue / suggested looking into the front sway bar set-up and verifying how much upward travel there is in the suspension. If something is hitting, that would make things overly stiff / make the understeer worse.

I will be at Blackhawk at the end of August. Planning to check out the front sway bar and suspension travel situation before then… Also want to get back to slicks and will definitely consider the heavier springs and rear bar. Thanks for the advise on adding a little rear bar to sneak up on the improvements.

The other thing I will try is having him ride in the car with me. We didn’t have time to do that at Road America…

Larry

"The Kink" is notorious. I dropped my left front off the pavement on three consecutive laps before I realized that I'd have to lift at the apex. Of course that was in a Sedan based car with McPherson struts. Anyway...

IMO, the fool proof method of determining faults and adjusting suspension is skid-pad testing. It removes the driver variables of turn-in, apex, and track-out and focuses on the balance of the car itself. It is time well spent if you can find one. Sebring has a 100ft pad as part of Skip Barber, but you gotta know somebody to use it. I've heard of guys using airports or other flat concrete surfaces. On the pad, you just continue faster and faster around the skid pad until one end gives up. When it does, take tire temps ASAP. With the skid pad test and the temps, you'll have a much better idea of which way to go/adjust.

IMO, if you can eliminate the car as a handling variable, then you can start experimenting with different turn-in points and lines.

Thanks for the advice on the skidpad / I'll have to check and see what's available locally.

BTW - I was bench racing at the FCA 50th Anniversary at RA over the weekend (never saw so many Ferrari's in one place before / first time seeing an Enzo in person) and someone thought that imbalance due to speed alone could be related to the rear spoiler / imbalance in downforce. This is a stock school car and does not have a splitter in the front. Any thoughts on that? Thanks!

Larry

someone thought that imbalance due to speed alone could be related to the rear spoiler / imbalance in downforce. This is a stock school car and does not have a splitter in the front. Any thoughts on that? Thanks!

Larry


Disclaimer: I am NOT an expert, but I've been doing this for a long time.

Sure anything you do to cut air from under the car is going to help at higher speeds, but I do not think it is a remedy for a tight car. Rather, it's a Band-Aid and won't fully solve your problem. The only way it would is if your car does NOT have understeer at lower speeds. In my experience with other cars, aero doesn't really become noticable until you're over 90-100 MPH, and doesn't come into full effect until you are approaching 150.

My thoughts? Work on the mechanical grip. To me; your spring rates seem in the ball park, so I would concentrate more on the rear than the front. Generally, increasing rear roll stiffness and wheel rate will loosen the car up. Once you get the car to rotate the way you want it, then work on aero for the higher speeds and those aero changes will then be more noticeable and beneficial.

My only other though is that it could be in your differential. You could be experiencing what is known as a "posi-push", where the differential is trying to drive the car straight forward while your are trying to turn. Normally a car with posi-push will push to a snap-oversteer condition, where it pushes and suddenly its way loose. I had that in my Mustang with a limited slip posi until I switched to a TORSEN style differential. Biggest, most noticeable change I ever made to that car. The only way to really diagnose a posi push is a skid pad. The car will immediately push "on-throttle" but return to neutral if you get off the throttle slightly, if that makes sense. Some guys I raced with actually used spools, then wondered why they couldn't accelerate off the apex until the car was nearly straight. Anyway....

Car doesn't seem to have understeer at lower speeds (~below 50). I am running 70 to 80 MPH in the carousel at RA. It's possible that my friend was running faster. That is where he showed me that he could give significant steering input without much vehicle output. He did make a comment about steering the car with the throttle. I have noticed that myself and have learned to use it a little. This makes me think that your differential suggestion could make a difference. Are there multiple models of the Torsen / any particular one better? Of course, changing that out opens up to ratio changes... The 3.50 is OK, but could easily run a higher ratio...

Larry

These cars came with the Tru Trac diff., in my opinion the best road race diff there is for moderately powered cars. I have never had an issue with diff induced push except when using a Detroit Locker with low grip tires, in an early Mustang. Under power it seems to act like a spool. I have no experience with the Torsen, but my understanding is that it is very good, but more expensive and higher maintenance. I'm about to find out because my '12 Boss has a Torsen and I intend to start tracking it this Fall. Some folks run the 3.89 gear set, especially with cars that have a higher power band, like 4.6 motor. I think that decision needs to be made based on the tracks you generally run, rpm range and tire diameter.

Mike

OK, I "thought" the cars came with a limited-slip, clutch-type diff. I don't know where I got that. The easiest way to tell quickly is to raise the rear tires off the ground and spin one wheel. On a TORSEN, the other wheel should turn in the opposite direction, as if it were an open differential. In Limited-slip diff's- the other tire will turn in the same direction like a posi. IMHO, the best TORSEN style diffs are from Black Gold. They are the most expensive as well, go figure. http://www.colemanracing.com/Differential-Black-Gold-9-Ford-P3746.aspx DPI also makes the platinum series. I have heard nothing but good about them, but have never used them personally. http://www.dpiracingproducts.com/differentials-and-service-parts/

Larry, I am better crew-chief than I am a driver. Probably because I am always trying to diagnosis the car on-track rather than just driving the fricking thing. What worked for me may not work for others, but I spent several weekends trying to wrestle Gremlins out of my former car. I would take big swings at the car with camber, toe, spring pressure, and sway bars. Then at a friends suggestion, I used the skid pad at Skip Barber in Sebring. My problem was in the rear-end wheel rate (spring rate) and rear tire pressures. The springs were too weak and the tire pressures were too high. Before lunch, I had the car accelerating through the pad and skidding all four tires at the same time, when I lost traction. After that session, all I ever had to do to adjust the car was adjust the rear bar. More bar for a hot, sticky track. Less bar for a cold or wet/moist track. I would know after the Saturday morning warm-up/practice on race weekends, which way to adjust. Then I could concentrate on the loose nut behind the wheel. I had a bad habit of dive-bombing the turns trying to get the car to "Take a set" as if I was still circle-tracking. Truth was, there was only two or three turns in all the tracks in Florida (Daytona, Sebring, PBIR and Miami/homestead) that would allow for that style of driving. I got a GoPro and started recording my braking/turn-in/apex/track-out routine and was personally embarrassed by what I saw on play-back. I had no idea I was driving that way. I eventually fixed the loose nut problem by using my buddies suggestion of setting the car up to push, then slowly (session by session) dialing more bar into the car until I was confident the car wouldn't step-out the rear and plant my butt in the tire wall.

OK, sorry about the rant. My point is that once I removed the car as variable, I realized I was losing more lap time from poor driving than anything else. The skid pad proved what the car would do, so the rest was up to the driver. As far as the diff problem I experienced...I didn't know the car was doing that until I had it well balanced. Three corners in particular. Turn #7 at Miami, Turn #6 @ Sebring (long course) and turn #5 at Daytona. The limited-slip was inertially engauged because of the speed and HP, and was pushing/driving the car off-line. I changed to a Detroit Tru-Trac and the car was as good as it ever got. On my one trip to the June Sprints at Road America, my problem at the kink was lack of aero down force and too small of a tire (both were limited by rules) I tried tightening the car up for the kink, but it was plowing everywhere else afterwards, so lifting slightly was the only solution.

Car doesn't seem to have understeer at lower speeds (~below 50). I am running 70 to 80 MPH in the carousel at RA. Larry

I know I keep saying this, but are you driving the car fast enough to get it to understeer? My one weekend in 2010 at RA, I driving the carousel with the throttle. I was at the edge that if I applied the throttle slightly more than I was, it would induce oversteer. I remembered that because it was reminiscent of my circle track days.

Again Larry, I am truly not trying to be an arrogant smart-ass, but if you are not having 3-4 "pucker" moments each lap at nearly any track, you are not driving fast enough.

Reporting back on what I found... Alignment before(Camber -1.4,-3.4, Caster 4.9,5.2, Toe -0.07, -0.13) Alignment after (Camber -2.5, -2.0, Caster 4.0, 4.3, Toe 0.06, 0.06) Also had to take a little out of the left rear spring to get weights to LF 721, RF 696, LR 760, RR 711 (cross of 1455 and1431). Ride heights were LF 4.25, RF 4.19, LR 4.63, RR 4.5.

Making these changes made a world of difference at Blackhawk (relatively flat track) and I had a best lap time of 1:21.3, which is about the same as my friend's Alpha.

I'll put the Torsen and roll bar on my to-do list. Going to Mid-Ohio in a couple of weeks with PCA, so I'll see how this works with elevation changes :)

Thanks again for all the posts / advice!

Larry

I have been to Mid-O so I have data on what an NASA ST-1 Panoz should run.

Reporting back on what I found... Alignment before(Camber -1.4,-3.4, Caster 4.9,5.2, Toe -0.07, -0.13) Alignment after (Camber -2.5, -2.0, Caster 4.0, 4.3, Toe 0.06, 0.06) Also had to take a little out of the left rear spring to get weights to LF 721, RF 696, LR 760, RR 711 (cross of 1455 and1431). Ride heights were LF 4.25, RF 4.19, LR 4.63, RR 4.5.

Making these changes made a world of difference at Blackhawk (relatively flat track) and I had a best lap time of 1:21.3, which is about the same as my friend's Alpha.

I'll put the Torsen and roll bar on my to-do list. Going to Mid-Ohio in a couple of weeks with PCA, so I'll see how this works with elevation changes :)

Thanks again for all the posts / advice!

Larry

Most of the settings you are using are similar to what we have run in our car but your ride heights seem way to high. Factory GTS setting is 3.5" for front and 4" for rear.

Any particular setup plan behind running the car so high?

Kel.

Thanks for the replies, sorry about the delay...

Brian - Any data would be appreciated. I have an AIM Solo. What format is your data in?

Kel - Thanks for the catch! Honestly, that's just where the car was running (since I bought it). Guess we got side tracked with the corner balance and didn't take any steps to lower to the GTS specs... I did find some other specs that stated 3.75 +/-.2 front and 4.0 +/- .2 for the rear. Interestingly enough, there was no spec. / tolerance for rake...

Thanks for the replies, sorry about the delay...

Brian - Any data would be appreciated. I have an AIM Solo. What format is your data in?

Kel - Thanks for the catch! Honestly, that's just where the car was running (since I bought it). Guess we got side tracked with the corner balance and didn't take any steps to lower to the GTS specs... I did find some other specs that stated 3.75 +/-.2 front and 4.0 +/- .2 for the rear. Interestingly enough, there was no spec. / tolerance for rake...

Might be worth downloading the GTS manual as figures in there. The rake takes care of itself when you set the front and rear ride heights per factory spec. You end up with .5".

Regards running .75" high on ride height, we have been doing a lot of bump steer work on my car. I am running the car at 3.5" and 4" but with the 680 profile slicks I am running we had .100" bumpsteer each way at 1.5" bump and droop. You may well find you car nicer to drive when you drop it down as you will lower the C of G and get the steering geometry back where it should be all at the same time.

Kel.

Kel - Thanks for the additional insights / impact of running higher ride heights! I might just have to check clearance on the trailer ramp and a few other places before I drop her down. :) Spoiler already drags entering the driveway (trailer won't fit in the driveway, so I have to unload on the street).

Larry

Kel - Thanks for the additional insights / impact of running higher ride heights! I might just have to check clearance on the trailer ramp and a few other places before I drop her down. :) Spoiler already drags entering the driveway (trailer won't fit in the driveway, so I have to unload on the street).

Larry

Larry,
I solved that problem by making the air dam removable using Dzus fasteners with pop rivets to secure them.

Mike