LegendsRacer - Legends & Bandolero Racing Forum
LEGENDS => Setup and Handling => Topic started by: canabl on July 28, 2013, 02:11:23 am
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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.
(http://i24.photobucket.com/albums/c8/CANABL/null.jpg) (http://s24.photobucket.com/user/CANABL/media/null.jpg.html)
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You might try running a 150 in the RR. New chassis could be causing the difference
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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
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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?
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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
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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.
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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.
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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.
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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?
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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.
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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.
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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.
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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.
(http://i24.photobucket.com/albums/c8/CANABL/null-9.jpg) (http://s24.photobucket.com/user/CANABL/media/null-9.jpg.html)
rear shot of the new car laying over.
(http://i24.photobucket.com/albums/c8/CANABL/null-8.jpg) (http://s24.photobucket.com/user/CANABL/media/null-8.jpg.html)
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.
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http://www.persh.org/images/Corvairs/WhatMakesCarsHandle02.pdf
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.
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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.
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While there are those who like big caster "splits" as they make the car easier to turn. You are at the high range with 5.5 difference. At the high end caster can make the car a bit unstable and twitchy---here's why.... positive caster on the right front lifts the spindle when turning left. This takes weight off the right front and reduces "cross" making the car looser. When the steering is turned right to "correct", the opposite happens--the spindle is pushed down, increasing "cross" and making the car less loose. This process is beneficial, but if carried to an extreme it makes the car feel unstable as it changes from one tendency to another.
Good that you are checking your springs. Did I understand you to write that you could make the left front move 4 inches by standing on the bumper? That's a lot more deflection than should be possible with a 180 lb spring IMHO.
One piece of data I maintain is the "static" compression of each spring. Since you know the length of the spring, measure the spring with a tape measure or rule with the car on the ground and the difference is the deflection. (10-8.62=1.38) 1.38 " on a 180# spring is 250# of "sprung" weight on the spring. (My data indicates that is in the range for the "sprung weight" on each front wheel.) This information can be correlated to your actual scale readings (affected by "motion ratio" and "unsprung" weight) and you can get a better feel for changes to "cross" made at the track when putting in or taking out wedge. (Motion ratio is simply the ratio of shock movement to wheel movement.)
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in relation to the front travel, I have set the ride height at 4" and adjusted up from there. the front left has around 2 3/4" travel at that ride height and with the 185 spring i can get it to bottom out with a good stomp on the front bar.
The springs have all come back and they are only 5-8pnd softer than the ratings printed on them.
is there two types of Bilstein shocks as the part numbers on my old chrome ones were different to the new painted units in this car? Think its only one number at the end different.
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Sorry, can't help you on the shock ID--need to get info from someone with more specific information as to part numbers.
I would be less concerned with the compression of the left front (although it does not seem very "stiff" judging by the crude "stomp on it" method)--I would be more concerned if the right front or right rear "bottomed out". My experience is that very weird things happen when suspensions suddenly become "solid"--many times leading to loss of control. The loads on the right side are more likely to cause that problem yet I have not heard of anybody experiencing suspension "bottoming out" with the spring/ride height combinations you indicate.
If the shocks have insufficient compression damping or "bump" resistance, you should be able to tell that by testing them off the car. I can say that my new shocks from INEX this year are quite stiff in compression.
In the past, I've worked with Penske in configuring custom shocks. I've not seen shock dyno data, but I think the Legends car shocks from INEX have sufficient compression damping for dirt cars---I wish they had a bit more damping under rebound. IMHO as an engineer, their rebound setting allows a relatively rapid rate of weight transfer in roll and contributes to the car having a bit of twitchy feeling.
The handling complaints you have could possibly be caused by weak shocks--but I think they would have to be so weak that you would notice by a crude manual off the car push by hand test.
Here's a crude method that has worked for me: I lean over and (I weigh 200 pounds) push the shock down as hard as I can against a bathroom scale. (Use a block of wood to distribute the weight so it is not a "point load" and so it does not damage the scale.) For my Legend shocks, the shock will compress at a consistent speed and the scale will read between 100 and 110 pounds. It will take just about a second to fully compress. ) If the shock is worn out, the scale reading would be much lower and the speed higher. If the shock is bent or the cylinder is damaged, the reading would be higher and the speed lower or jerky--you would sense it binding up.
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After more reflection and your comments about: "new stiff shocks" and "not responsive to wedge changes" and since you found nothing binding in the suspension (not including the shock), logic to me says something is wrong with the right front shock-bent or damaged in some way making it not move freely.
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I got that the springs were weak out of Adams comments. Just got back from vacation, so haven't had much time to catch up on things. I'll do some re-reading and see what I am missing.
Steve
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i took the shocks out of the car and did the crude push down and release to time the return rates, all were spot on the same. approx 2.5 seconds from compressed to extended.
They certainly are not worn out in any way as they have only turned 15 laps prior to me pulling them out.
I am fairly strong and with the shocks alone in the car (spring removed) i can bairly lift the wheel against just the shock compression, take out the shock and the car rolls through its entire travel no resistance. after every event i have a habbit of spraying a lanolin based spray in the heims and work them through their movements to make sure all the water or clay is out.
I do think that the front end alone is too stiff with the rate of compression in springs to the rear end. every video i have seen of the new car has the front atleast an inch higher in ride height. I am going to stiffen the rear right up a fraction and lower the front rates down down and see how we go.
Our rules have just been adjusted back to be more in line with INEX, and the grooving of tyres has been struck out for this season, we must run a stock 57 AR on right rear and the grooved tyres we have from last season can be run on the other three corners till they either need replacing or are damaged throughout the season.
we have a practice session in a few weeks so i will try it out and give it a good run even try with it setup loose to try adapt to a tail out style as there will be less chance of getting hit if i spin.
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Is it rolling over on the RR through the corners, or is it rolling over just on exit, ie, when on the gas?
What's your pinion angle?
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seems to be rolling over on entry through to mid corner when im partially on the gas and on exit the rear squats equally.
I have been rolling off the throttle on turn in and then feathering power in through the corner then as soon as i can get it ligned up for a straight exit the pedal is floored.
pinion angle is about 5 degrees as any more seems to have the uni smacking on the cross bar on rutty entry to corner.
the diff is also set to the right of the chassis, but there is only around 1/2" travel left to right overall.
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Re-balance the chassis for that style driving. Lower the front ride heights and raise the rears
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If i am to fit a stiffer RR spring to help hold it up, then dial in a tighter cross? will this in effect act the same as a light RR with a lower cross?
I have squared the rear end up and set the front camber caster correctly with a gauge i bought from VMS (thanks again) and it now looks like it has good amounts of both now.
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I submit humbly that relative changes in difference between right and left rear springs will affect the "dynamic" handling in "transition" from off throttle to on throttle, but will NOT ultimately affect the "static" cross weight. Increasing the right rear spring rate while keeping the left spring rate the same causes the car to be more loose or less tight immediately upon application of the throttle as the car begins transfer of weight from the front to the rear--the transfer will happen faster on the stiffer spring. (mid corner) But once the weight is transferred, the cross weight in not determined by the spring rate but by the actual weight on the wheels equal to spring rate times deflection. When you change the right rear spring, you will need to set "static" ride height and cross weight to compensate for the stiffer right spring. I would set the cross the same as you had on your previous car (50%) that seemed to suit your driving style--then go out and drive it on different track conditions (tacky and slick) before making too many more changes. On the other hand, theoretically, changing the right rear spring to a stiffer rate would generally call for more cross.