Dirt setup help

[canabl]

Hi fellow dirt guys.
Had great success with the base setup last season in a four bar sedan chassis that had the base guide from on here.
FL180 FR200 RL165 RR140.
I had a cross of around 50 as I like to keep it straight, rear of 52 and 52 left weight.
Bought a new car and put all the old springs in and scaled close with only left weight being 52.8 with driver and rear weight 50
Ride heights about the same give or take a turn to get weights.
Took it out last weekend at home track and was a handful to say least.
Pushed into and mid corner with a loose exit and twitchy steering under power.
Worst of all is the way it is lurching into corners and lifting the front up.
Is it just the stiffness of the new chassis and shocks over the old gear? It's only around a second off the pace in its maiden race in the equivalent conditions from last season.
Just after suggestions from other experienced in these cars.

[VMS Motorsports]

You might try running a 150 in the RR. New chassis could be causing the difference

[justfreaky]

Adam,

As Jim pointed out, the new chassis is likely in much better shape than the old car. Also; New parts do not have the wear and tear as the old car. Set up will change. As I don't run dirt, not a lot I can help you with.

Steve

[canabl]

The strange thing is by just standing on the corners to settle the car and measure, it does feel very stiff on all corners compared to the last car. 
we pulled all the old car apart when we bought it as the suspension had no travel (binding heims) and from that point on the car had great response to any changes we made and predictable in any way on the track with steering and throttle response. I used to be able to drive it with the throttle and very little steering input.
On the scales though, i have noticed that it takes a lot of adjustment to transfer weights and in turn makes the ride heights way off we are used to or like. old car would need a turn on the front right to change from tacky to dusty track. new car is more like three turns to scale up same figures.
I will try the heavier spring and see where we sit on the track next time.
our way of thinking was maintaining a 2 1/2" - 3" shock travel on all corners without bottoming out, this may be incorrect?

[justfreaky]

The strange thing is by just standing on the corners to settle the car and measure, it does feel very stiff on all corners compared to the last car. 
we pulled all the old car apart when we bought it as the suspension had no travel (binding heims) and from that point on the car had great response to any changes we made and predictable in any way on the track with steering and throttle response. I used to be able to drive it with the throttle and very little steering input.
On the scales though, i have noticed that it takes a lot of adjustment to transfer weights and in turn makes the ride heights way off we are used to or like. old car would need a turn on the front right to change from tacky to dusty track. new car is more like three turns to scale up same figures.
I will try the heavier spring and see where we sit on the track next time.
our way of thinking was maintaining a 2 1/2" - 3" shock travel on all corners without bottoming out, this may be incorrect?

Standing, or Jumping, on the car may give you some sense of feel. Trying to keep some kind of standard shock travel on a dirt track may be next to impossible. Dirt tracks change drastically compared to paved tracks. Ruts, holes, surface moisture (or lack of)... Check for binds, wear, loose bolts. See if that helps. Couldn't hurt! What you "Were Used To" may likely have been a very worn chassis or parts. That will change a lot of what you were used to.

Steve

[canabl]

thats why i thought the reaction of the car would be opposite running new stiff shocks and stiff chassis, the older car would have been more boatish than the new car running the same setup.
The tracks we have been given are usually very smooth and the travel is more as a guide than exact measurments.
will a car running the RR 140 spring scaled with a cross of 50% work the same as a car with a RR175 scaled at 50%........
we dont have practice sessions until september so just didnt want to show up at the track next time with a car thats too hard to adjust to my liking.

[FFmedic]

Does your car have the braces on the front clip to the roll cage?  If so cut them off.  My buddy got a new chassis and he couldn't get it to work, cut the braces off and it was a whole diff car.  I think on dirt the braces stiffen the chassis to much. 

[canabl]

The new car does have those braces. Was thinking of softer springs up front since the shoclks are so tight and newer than my old car. it just seems to squat too much in the rear.
very loose but i cant get the cross right with keeping ride heights at decent level.
may spend weekend on the scales and see what i can work out.

[Earnst85]

From the photo, your track looks like it stays pretty heavy... with such a soft spring on the right rear and stiff spring on the right front, my guess would be that the weight transfer into the corner causes the pushing up front and laying over on the right rear. This would be good on dry slick, but on heavy clay, you might want to go to either a softer RF spring or stiffer RR spring. It sounds like your getting too much side bite on the RR, which raising you rear ride heights or lowering you cross may help. How much does you & your car weigh?

[canabl]

the total weight of me and the car all up is 1327 with 10L of fuel and our tyre pressures set to our feature roll out, cross of 47% left WO driver 51.7% rear 52%.
I do prefer to drive the car opposed to sliding it in to the corner, the picture is how the track was at the start of the first heat, this was also a day meeting opposed to our night races when our season starts in september. Usually it is a dry billiard table when the yanks come out for the sprintcars and the 1200 comes to life over the monster 1250 tyre spinner.
Typical for our class here is cars crossed up and spinning mid corner. My original car took a lot of scale time and patience since we had engine troubles early into the season.
With consistent top 5 finishes for the end of the season and holding the track record after 5 races for the entire season, the upgrade to the new car was bound to be a new learning curve.
we did find with the springs as they are, the car would not scale up easily to our liking.
we may try to drop the front end down somewhat and see how it goes.

[Earnst85]

The reason I asked the weight question was that I struggle with the same symptoms that you are describing. I am 240 lbs and my car weighs 1427 with me in it. (I have yet to attempt any weight savings on either of my cars)
Because of having such a "fat pig" and me preferring not to throw the car into corners, I am almost always tight in.  On my short track car, I run a softer spring set closer to what you do (if you swap ur rear springs) and it looks identical to your photo. I believe the softer rear spring are allowing it to lay on the RR to much.
 Another thing to look at is if your stering rod (what you adjust toe with) on the RF might be hitting the frame when RF is fully compressed. It could be binding and not allowing car to roll over onto the RF like it should. I believe this has been my issue with being so tight into the corners. I won my first legends race friday night, then on saturday between heat & feature, we noticed I had that bar mounted incorrectly and that it was making contact witht frame rail. I left it alone for the feature (since I had just won with it that way) and still finished 4th. I will be changing that for the next race and fully anticipate to be looser into the corner.  My cross is about 46% without me and 47% with me.

[stroutmail]

If the photo you provided is an indication of the car's attitude during acceleration I think Earnst85 is correct. Looks like the car is really rolling over on the right rear and lifting up the left front excessively.  I'm a rookie in Legends...I've looked at a lot of photos and your car is the first where the change in camber on the left front from chassis roll seems to have overcome the static positive camber so that the effect is the tire is leaning in at the top.  Most photos I've studied shows the left front pretty square to the track under hard acceleration mid-turn to exit.

[canabl]

same springs in the old car on the same track last season, it always layed over but not quite as bad as the new car, once the track dusted off the old car would sit flat and was a gem to drive, the new one just has so much twitch and overly loose i feel at the same scale levels.

rear shot of the new car laying over.

Not sure if anyone else with the new series car has had smae issues with the rates of springs or possibly shocks that may have some suggestions.

[stroutmail]

http://www.persh.org/images/Corvairs/WhatMakesCarsHandle02.pdf

http://www.persh.org/images/Corvairs/WhatMakesCarsHandle02.pdf

The issue you are dealing with probably has to do with what if called "roll couple distribution".   The link above gives a good explanation (although they are talking about a rear engine vehicle, so just adjust concept for a front engine car.).  Essentially, there is a certain amount of weight transfer that occurs from left to right in a turn--caused by the center of gravity being higher than the ground.  This total L-R weight transfer is distributed to the front and rear proportionately based mostly on the spring rates.  So if the spring rate is high on the front and low on the rear, the car will push at entry and mid turn--then will probably suffer from the tight/loose problem on exit--a heavy mid turn push usually results in a loose corner exit.  The effect will be higher on a tacky track than on a slick one as there is more weight transfer on a tacky track.

You did not mention whether your rear shock/springs are mounted inboard or outboard of frame.  If mounted inboard, the spring is less "effective" and therefore weaker.

Since right rear traction increases with weight, many believe that increasing RR weight is good, but keep in mind that the weight transferred to the RR has to come from other wheels, so what is gained on the RR is lost on other tire positions.  So there can be too much of a good thing.

The best advice I ever got was that the first thing you should always do is to make the car as "neutral" as possible (not loose or tight) in mid-corner and then make adjustments from there to reduce lap times.  Clearly, you need a heavier spring on the right rear.  I would also check to be sure nothing is binding up on the right front.  Your "new and stiffer" chassis should be just as responsive to adjustments (weight change from turning spring perch nuts)--if not, something is probably binding up or out of adjustment. And do recheck your caster settings.

[canabl]

The shocks are mounted on the inside of the chassis at the top as per our last car, plus the body work is not cut on the outside to permit them to be mounted (easy fix).
We just took our entire spring commection to a new sponsor for testing so we can see what we are working with. while these are out we checked for full travel and there is no binding through travel of the front or rear apart from when the wheels are at a big lock to lock, the steer arm does touch on the shock thread. caster we are running .5 LF, 6 FR (leaning back)
I did find last season that after we bent a LR shock in an accident and we put a new painted bilstein on (had chrome bilstein originally) the car responded differently and definately was tighter with that being our only change.
We have set the car at 4" ride height and adjusted from there up to get our percentages right and the front left actually bottoms out at 4" when i am standing on the front bar.
I will sit down tonight and have a read through the links u posted.