[dave968]

I ran my 1st race with PCA at Roebling Road in December, had a lot of fun!!! My fastest lap was 120.915, finished 3rd in E class in the feature race.

The event was 3 days, with 3 practice sessions 1st day and practice starts/fun race, day 2 warm up, qualifying then 2 races, and day 3 warm up and then a feature race, so all told 10 sessions, mostly 30 minutes, with the feature race 40 minutes.

I started with new Hoosier R6s, 18 in 245x35 front and 285x30 rear. There was some rain the 1st day and I ran Toyo R888s on my stock 17 in wheels for 2 sessions. By the end of the wkend, my L front Hoosier was corded on the outside edge only, otherwise I could probably get 2 DE wkends out of the tires. Usually I get 2-3 DE wkends on a set of Hoosier R6s.

My car wt after the race was 3244 lbs, LF 860 LR 783 RF 781 RR 820 lbs, so my LF+RR diagonal wt is 1680 lbs, my RF+LR diagonal wt is 1564 lbs with me in the car.

My suspension is a Racers Edge setup with spherical bearings, RE front A arms and Billet hubs, Leda shocks, front springs 800 lbs, rear springs 700 lbs, rear torsion bars turned down to 10mm.

My prior alignment specs were: front camber -3.2, caster 7, toe -0.10; rear camber -2.7, toe 0.

I had my alignment rechecked after the race, and it was LFront camber -3.6, RFront camber -3.0, front toe 1/4 in toe-out; LRear camber -3.2, RRear camber -2.6. I know that is too much toe out in the front, and plan to get the car re-aligned.

I have had different opinions on the wear of the L front outside edge of the tire, both suggesting too much front understeer, with 2 different recommendations:

1- change rear springs to 1000 lbs

2- change front springs to 550 lbs

At a DE in January, Bob Woodman from Woodman Tires looked at my Hoosiers and suggested my LF+RR diagonal corner wt at 1680 lbs was too much compared to my RF+LR at 1564 lbs, so I raised the LRear of the car to get this corner wt: LF+RR= 1546, RF+LR=1628, total wt 3224 lbs. Bob suggested for a track with mostly R hand turns like Roebling Road or Road Atlanta the diagonal corner wt for the RF+LR should be on the order of 1-2% of total car wt greater than the diagonal corner wt for the LF+RR.

Regarding changing my springs, I am concerned that 550 lbs for my car wt will be too soft in the front, or that 100 lbs is too hard in the rear.

I remember reading some posts in the past that for 968s, having equal spring wts front and rear to having heavier springs in the rear will reduce understeer and move the car towards neutral or even to oversteer if the rear springs are heavier than the front.

So, any advice on spring rates for my 968???

Thanks

Dave

Partial Post: Please Login or Register to read the full post.

[flash]

i presume the weights are with you in the car and a full tank



what sway bars are in the car?



with those spring sizes, even the M030 bars are too soft, and i would change those out



have you done any chassis reinforcement yet? i presume you have a full cage, but what has been done to the underside of the car?



if nothing, i would start there



when you say "turned down to 10mm" what do you mean? did you have them removed, turned to a 10mm diameter, and reinstalled?



if yes, then yes, your front to rear spring balance is out of whack, and the rear needs to come up, or the front down - if the lower chassis is unreinforced, then you are already too stiff for it up front

Partial Post: Please Login or Register to read the full post.

[dave968]

yes, wts with me and 1/2 tank gas

M030 sway bars

full welded in cage, nothing done to underside of car

tbars removed, turned down to 10mm, reinstalled



Dave



[quote name='flash' post='66083' date='Jan 24 2009, 05:15 PM']i presume the weights are with you in the car and a full tank- yes



what sway bars are in the car? M030 bars



with those spring sizes, even the M030 bars are too soft, and i would change those out



have you done any chassis reinforcement yet? i presume you have a full cage, but what has been done to the underside of the car? full welded in cage, nothing done to underside of car



if nothing, i would start there



when you say "turned down to 10mm" what do you mean? did you have them removed, turned to a 10mm diameter, and reinstalled? yes, removed, turned down to 10mm, then reinstalled



if yes, then yes, your front to rear spring balance is out of whack, and the rear needs to come up, or the front down - if the lower chassis is unreinforced, then you are already too stiff for it up front[/quote]

Partial Post: Please Login or Register to read the full post.

[flash]

well, the first thing i would do is tie the lower castor blocks together - then add a strut brace - this will isolate the enormous amount of chassis flex that will prevent you from utilizing the front springs to their fullest



then i would invest in larger sway bars front and rear - something along the lines of a 32mm front and 21-22 mm rear - the M03O bars are nice, but too soft in my opinion - i am currently running a 31.75 front and a 22.25 rear - the car is much more settled and transfers very nicely - i am only running 300 up front and 550 rear right now, but have had 400/600 and it was even better on the track (too much for street though), and suspect that a 550/750 would have been very nice



with larger sway bars, you should be able to reduce your negative camber up front considerably



as for springs, if you are determined to run an 800 up front, then you will need something around 1000 rear - this is way too stiff for this car though - it likes a bit of softness - it likes to drop in, settle down, and plow through



i would reduce the front springs to around 550, and then run a 700 or so rear



call pete - he can fill you in on this a lot more with recent experiences on multiple setups

Partial Post: Please Login or Register to read the full post.

[dave968]

txs

I do have a strut brace in place

Dave

Partial Post: Please Login or Register to read the full post.

[flash]

cool - now you just need to get a lower brace to prevent the castor blocks from moving - you would be amazed at how much they move, and now badly it affects the camber angles - really crappy design - makes for a very compliant street car, but lousy when you load it up, like on a race track

Partial Post: Please Login or Register to read the full post.

[Jim Child]

Your rear springs are too soft. I run 800 lbs front and anywhere between 800 to 1,100 lbs rear depending on the track and conditions. I probably run my 1,000 lb rears most often. Springs are cheap and the rears are easy to change. I'd recommend that you get a set of 900's and a set of 1,000's and play around with them to see which one works best for you. A word of caution though, the difference between 700 lbs and 1,000 lbs in the rear is dramatic. The car will be much more loose than what you're used to, so start slow and take as much time as you need to get used to the change.

Partial Post: Please Login or Register to read the full post.

[flash]

jim - what have you done to the lower chassis for reinforcement? are you precluded from that by rules?



i ask because i've been doing a lot of homework lately on the inadequate structural integrity of the chassis, and have discovered just how weak it is, and how many people make big mistakes in setup that could have been corrected by working on the bottom of the car - i can flex the chassis over 1/4" with hand tools - that results in HUGE geometrical changes that most people try to overcome the symptoms of with big springs - big springs have their place, but only after you have worked out the chassis first



but, if the rules prohibit it, then that is an entirely different story altogether

Partial Post: Please Login or Register to read the full post.

[Jim Child]

[quote name='flash' post='66120' date='Jan 26 2009, 04:58 AM']jim - what have you done to the lower chassis for reinforcement? are you precluded from that by rules?[/quote]



So far I haven't done any reinforcement underneath. To date I have kept the car legal for racing in two different classes, NASA GTS2, and PCA E-Stock. In NASA GTS anything goes, so I could do whatever I wanted underneath. PCA stock rules are far more restrictive, and its not exactly clear what you could leagally do under the car. The fact that the PCA stock rules specifically allow adding a strut tower brace, but remain silent on any bracing underneath the car leads me to believe that it may not be allowed.



What specific reinforcement modifications are you suggesting?

Partial Post: Please Login or Register to read the full post.

[flash]

well, start with a brace that connects the castor blocks - those things flex an incredible amount - like i said, i can flex them with hand tools - heavy g-loads are certainly moving things around



then, if you haven't already, spherical bearings on the castor blocks and front lower control arms - that helps a lot with limiting movement



after that, there is room for an x-brace under the car - the cab has an entire under-structure that does a great job of stiffening things up - you could even add that in there



the logic here is that the lower the bracing, the more effective the suspension, and the less the need for band-aid corrections like big springs and camber angles

Partial Post: Please Login or Register to read the full post.