Race car suspension Class

prankster16a

These #'s are correct Mike. I cant move the mount on the axle any farther to the left, because the coil over is right there. There is about 1/2" clearance between the frame and the coil over and its only 7" to the king pin CL from there ( just enough room for the steering arm to clear the coil over and 4 link brackets.) This car has exceptional LS for a sprint car at 58.2% LS without driver. From the center of the rear end its 31" to the outside of the LR and 43" to the outside of the RR ( the max offset allowed by our rules ) the front end is 1/2" narrower on each side.

Ranger Mike

kenny
sounds like we can not change the RC via panhard bar...let me talk to some old hands at the track tommorow..

prankster16a

Mike.......would it matter if the panhard bar was mounted off the back side of the axle ??? I could get it closer to the LF then......between the 4 link brackets ??


Thanks......Kenny

Ranger Mike

http://www.afcoracing.com/tech_pages/panhard.shtml
this is a very good link to study..about panhard bar

dr dodge

as again...

ranger rules...lol

it helps that the first 2 books you list I have

dr

prankster16a

thats great......thanks Mike

Ranger Mike

Kenny let me check with my software guy to see if he has program to calculate roll center on your car..we are at the point where we got to look at other things to drop the RC..all you do is tape measure mounting points and plug them into the program to see how it effects RC location..

prankster16a

Thanks Mike.................I eagerly await your response

kalyani

How do we inplement skyhook control for this semiactive suspension systems?

prankster16a

So ........Mike. Here's one for ya. Ive got 4 pavement sprint cars that I tune. Two of which I built. 2 of the 4 are a long 4 bar ( to the motor plate which is 42" to rear axle CL ) both of these cars use almost the exact same setups and are both very quick. The third has a z link rear like a BEAST chassis. set up is also the same as the long 4 bar cars with the exception of rear spring rate due to the coil over being mounted to the lower arm and not directly to the birdcage. The rear arms are 14.5" CL-CL and the coil over is mounted 4.5" back. I come up with a motion ratio of 1.9 ( I round it up to 2 - 1 for ease of conversion ) This car is VERY quick and at times has been almost a second quicker then the rest of the field. Now........the last car. I built this one with a short 4 link ( 27.5" CL - CL ) this car has allways wanted to push coming off.............actually more like lifts the front wheels under excelleration. Ive gone up in rear split ( 50# more on the RR.......I usually only run 25# split ) moved the top wing forward and put a bunch of rebound in the front shocks. This has made the car waaaaaaaaaaaay better, but allways near the end of the main, the car goes tight again.
Any thoughts ????

Thanks.............Kenny

Ranger Mike

Kenny
i been in chicago at trade show..btw..best show in years...
i have not heard back from my software guy yet on software..
ref car pushing at end of the race...

push or under steer means the car has too much rear weight and the front tires can not turn the car so it snow plows toward the wall, not good..
we know in order for the right front to work properly it needs enough weight transfered to it to stick...( take a front tire off the car and place it on the garage floor and stand it up like its on the car. now place eahc hand at the max diameter and slide it across the floor..pretty easy..right..now get the fat kid next door to come over and sit on the tire and try this again...putting fat boys extra 100 pounds on it makes the sliding more difficult..right--DOWN FORCE)

think about this...the fuel has been used and you have a lot less weight on the rear of the car...normally

this coupled with the fronts heating up, change in stagger, the wedge changes..all contribute to late race push..one thing you can do is switch to nitrogen in the tires..will cut out thermal growth and this will control wedge change to some degree..

prankster16a

Mike..................I do use Nitrogen in the tires. All tires grow exactly 2lbs

prankster16a

One more thing Mike. All 4 cars run the front panhard bar uphill to the chassis 1/2". This is good for about 2 - 3 tenths on all 4 cars I tune.When I run the front bar level, the cars are all loose on initial turn in. Is this telling me that Im a little light on my front springs ??? I run a 400 on the LF and a 425 on the RF. Should I level the front bar and put more spring in the front ??? Keep the front springs the same, level the front panhard bar and lower the rear bar ???

Thanks..........kenny

Ranger Mike

Kenny.. just got home and dug up my old dirt track notes..

If my memory serves me correctly, and your talking about your roll center along your panard/j-bar axis, raising the roll center will minimize the roll. But, this will only work solely for roll center if your raise both ends of the panard/j-bar. If you only raising the chassis end, you're now introducing a percentage of bite in wheel loading depending on your rearend geometry. As for the left or right, that is dictated by the length of your bar in relation to the center of your chassis and weight distribution. The more you bring it closer to the center, the more you'll allow the chassis to roll.

Lowering the roll center will help the car roll over more which helps generate more side bite. The roll center is the axis of rotation for the car when the body rotates left to right. The lower you place the roll center, the longer the "torque arm" you are generating. Longer torque arm's give the chassis/body more leverage which produces more roll which makes the right side tires grip the track harder. The principal is the same as a torque wrench. The roll center on a torque wrench would be where the socket attaches. The torque arm would be the location you place your hand on the wrench. The point you position your hand around the wrench is where the force gets applied. The further you move your hand away from the socket(roll center) the longer the torque arm you produce. This helps multiply the force you are generating with your hand generating more leverage.
So back to the racecar....The weight of the chassis/body is the force that causes the car to roll. The chassis/body is the same thing as your hand turning a socket wrench.

Increasing the distance between the roll center (socket attachment point) and the center of mass of the chassis/body (where you stick your hand on the wrench handle) you create more roll (leverage) due to a large torque arm or lever arm.

The roll center is located between the two heims on your panhard bar. If you are using a J-bar it is in the center of the two heims as if the bar was straight. The more weight you put on the right side of the roll center the more it will allow the chassis to roll. This is why you use a j-bar or a shorty bar on a dirt car and a long bar on an asphault car. You want roll on dirt and not on asphault.

Raising the chassis mount on a long bar tightens up the car. It's from the increased angle on the bar.

i think you have stagger growing on right front..late race push comes from right front diameter growing due to heat..this is like running a stiffer right front spring, this means the front end is not accepting the same amount of weight transfer from left rear to right front going into the turn and at end of race you are keeping more weight on the rear springs ( rear springs are acting like softer springs) and the car starts to push. your " wedge" is changing.

as far as swapping out the front springs...and changing the attack angle of the bars...i would first start with trying to get a set up running same size springs and tune to that set up.
all cars are different but the trends are there and you found them..you obviously got the hot set up on the present angles and there is some weight jacking going on.

The handling balance for a Sprint Car needs to be a dynamic balance just as in a stock car. All four tires need to be in contact with the racing surface and have the most load ending up on them as possible. If we have a truly balanced setup, the LF tire will carry a decent load and the car will turn better.

For a winged Sprint Car, it would make sense that our spring rates, side to side, would be the same. Spring split on a solid axle suspension has a dramatic affect on roll tendencies. Since the cars roll first to the right on entry and then left at mid-turn due to the aero forces on the wing, we need to have the same roll stiffness in both directions. If a stiffer RR spring (over the LR spring) promotes roll stiffness in a roll to the right, then the reverse would be true for a roll to the left.
Our handling can be much different from corner entry to mid-turn if we run different rate springs on each side for winged Sprint Cars. The Panhard bar height, or Watt's link moment center height, must also be tuned to the spring stiffness as well as the spring base. The idea is to develop a setup for your Sprint Car that has the same roll characteristics for the front and rear of the chassis so that the handling balance is equal all of the way through the turns. Again, this has been tried and proven to work.

The setups for the winged Sprint Cars vs. wingless Sprint Cars is necessarily much different due to the high amount of downforce produced by the wings. The spring stiffness must be more for the winged cars, especially on asphalt. The speeds are much greater when Sprint Cars are racing on asphalt with wings attached.

More loading means more traction and the lateral g forces go up considerably with the increased speed through the turns. This necessitates a higher overall spring stiffness and in some cases, a spring split with the right side springs being more rate than the left sides.
Here too, we see a definite need for chassis setup balance. We really want all four tires to carry maximum load. At the LF, we need for that tire to carry load to help the car to turn. Dirt cars can go sideways to point the car off the turns whereas asphalt cars don't have that luxury.

Kenny all these set ups are band aids to deal with weight transfer that THIS SET UP has...any time you change a par setting you change degree of weight transfered and rate of transfer. hopefully my software guy will tell me Monday about the capability of using it on sprint car set ups..what we really have to do is find the front and rear roll centers and figure how to lower them in a practical manner and get as nuetral a set up as possible..then by tweaking the P-bars we can adjust to the changing track conditions..

these are from my track notes and may be rabbling but i am not a dirt tracker..and only helped a winged sprint car team one season..hope it helps

prankster16a

Mike..............I value all your input. I run 25 split across the front ( 25 more RF ) because I have found the car to " squirt " loose on initial corner entry with anything less. I have also found that almost every car has had better corner entry with the front panhard bar running uphill to the chassis 1/2 ". I have been running 25 - 50 rear spring split ( more spring on the RR ) for two reasons. I have tried it straight up as well as more LR spring. Both of which made the car push horribly coming off the later of the two being the worst. Also with less then 25 pound rear split the car wants to hike the LF coming off.........my goal has been to keep the LF on the track, as I feel this has to help the car turn.
I guess what I would like to know is this..........If I lower the panhard bar.....either front or rear......do I have to go up in spring rate to control chassis roll ???
Ive also been thinking......I run a very low crank height in my cars........7". Im wondering if I might be able to help bite by running the motor a bit higher........lets say a 9" crank height. much like a dirt car.
Thanks...........Kenny

Ranger Mike

Kenny t he following messgae came from my software guy..


Mike,

Our Circle Track Analyzer DOES allow for straight axles on the front. However, it does not do all the detailed 3D analysis of the Susp Anzr. Click on Link below:

http://performancetrends.com/Circle_Track_Analyzer.htm


It won't do all the jazzy stuff the door slam software does but is well worth the dollars to see RC change when you change mounting points..
i swear by it for my late model and formula car!



Thanks.

Kevin Gertgen
Performance Trends
feedback@performancetrends.com
248-473-9230 fax 248-442-7750

the dr.

I was directed here but a friend, who reads here but never post, and I have spent the last 3 nights reading the info here and find all of it to be very informative, I have been in racing for over 30 years, as a driver mechanic and crew chief, this year I have been talked out of retirement, to work on a car racing in the heart of the south, on dirt tracks, this willl be my first venture in the 3link's, I have worked with the 4 links and torsion bars and leaf spring cars in the past, any one got any pointers or links where I can cram on the 3 link? it is a full body 2800 lb car, tube chassis firewall back, stock clip on front, I feel I have a pretty good understanding of chassis' just have never worked with a 3 link before, been reading all I can find on the variations of the 3rd link, solid bar VS buscuit bar, and spring bar... looking for any input what so ever....thanks

the dr.