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Race car suspension Class

by Ranger Mike
Tags: class, race, suspension
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prankster16a
#37
Sep9-09, 09:20 AM
P: 21
thanks guys......

Kingpin inclination angle is 10 degrees. Hmmmm.........wut if I was to build a RF spindle with only .........lets say 6 degrees ?
I say I would like to run around 2" of stagger, because the super late models here run that kind of stagger. I figured that if that was good enough for them then I should be able to run the same. Theres guys out here looking for 5 and 6" of stagger for the sprint cars.......They must be nutz.

Dont get me wrong.....my cars not a pail, and I run very well, But Im allways interested in learning and going faster. I appreciate all your inputs.

Hopefully next year Ill have a set of scales, so I can try like you said Mike...............Put the car on the scales and see what it does as you turn left.

I have 1 race left this year.......Ill try a panhard change. I will start with the rear bar level and will lower the front bar..........Ill make a axle bracket with +1 and 2" drop and try them both.

Thanks again........Kenny
prankster16a
#38
Sep9-09, 09:25 AM
P: 21
I am going to measure our track this weekend...............when u say diameter of track Mike..........do you mean at the goove?.............out side of track ? Add inside and out side then divide by 2 to get an average ?
Im interested in seeing what this formula says I should have for stagger

Kenny
Ranger Mike
#39
Sep9-09, 09:57 AM
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Quote Quote by prankster16a View Post
I am going to measure our track this weekend...............when u say diameter of track Mike..........do you mean at the goove?.............out side of track ? Add inside and out side then divide by 2 to get an average ?
Im interested in seeing what this formula says I should have for stagger

Kenny
Kenny i would measure the dfiameter of YOUR groove you run..or the hot dogs hot groove as this is where you want the stagger to work...i have driven to various round tracks on off days and actually tape measured the turns and took a protractror level fionder to measure the banking...
also we ran nitrogen to make sure the stagger grew minimum amount...
you are right in that 5 inch stagger is HUGE...go with the super late model boys as starting point..

keep the rear roll centers about 1 to 3 inch taller than the front or it will push..and i know you know this but make one small change at a time and document everything.
before messing wit hthe roll centers try adding more up hill angle to the top links like 2 degrees at a time. then when you are really hooked up and start pushing..look at RC changes...
prankster16a
#40
Sep9-09, 12:37 PM
P: 21
Yes.......I use nitrogen in the tires as well as tire reliefs.

Now...........heres an argument Ive had with more then a few people about setting tire reliefs.

If you ask Hoosier they tell u to set them 5PSI higher then your starting pressure..this doesnt make sense to me.........if my RR tire says it wants 15PSI.....should I not set my releif to 15PSI to start with, even when the tires cold ? I know you build pressure as the tire gets hot, so isnt that why we run a relief ??
Typicalaly what I set my bleeders to is

LF 14PSI RF 15PSI

LR 7-10PSI RR 15PSI

I have found that buy varying LR tire pressure that the car is much more responsive the using the adjuster nut on the spring ( Im told that 1PSI change in tire pressure = 1/2 a percent change in cross )

As far as hooked up and pushing..........thats where Im at now.........front end feels real light coming off
Ranger Mike
#41
Sep9-09, 02:29 PM
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tire relief valves ( pop offs) are tire valves you can pre set to pop offor open at a specific PSI. ( kenny i know you know this,,,i detail this for the uninitiated)
these come with springs set for a PSI range. I have Longacre pop offs and they have a set of springs for 3-15 PSI and springs for 15 and up PSI. they tell us to set the pop off PSI 2 pounds above desired range. Just like a tire valve stem that has a spring to close the valve..these have a spring to keep it closed. The springs are linear and pretty accurate. so you just have to live with the preload..Rebco, i think.. has a higher default rate and wider range (which means the pop off value is not as sensative ) so i would check with the manufacturer. it is all relavent anyway as you will pyro the tire at three places to see the temps and adjust anyway..
prankster16a
#42
Sep11-09, 01:10 PM
P: 21
Mike..............where does rear panhard bar adjustment most effect chassis handling ??
Through the middle and coming off ??
Front panhard bar adjustment gettin in ??

Thanks...........kenny
Ranger Mike
#43
Sep12-09, 05:51 AM
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The distance between Center of Gravity (CG) ad the Roll Center (RC) is important. The panhard bar is easily adjusted ( hence the RC). the shorter the distance, the softer the springs because the lever length is shorter. with this in mind let review the three phases of handling problems..note if a car is loose going in to the turn, there are ten adjustments you can do, with brake bias , RC height , stagger, cross weight and spring rate being easiest to change.

Loose going in ( corner entry) oversteer
too much rear brake bias, RC too high, rt. ft. spring too soft, right rear spring too stiff, ft. sway bar too soft, too much stagger, more cross weight ( add wedge) rt. rear tire over inflated, shocks need tuned, wheel tracking- rt. rear wheel moved outward too far relative to rt., front

Middle of the turn car is loose
more cross weight
reduce stagger
lower rear RC
rt. ft spring too soft
rt. rear spring too stiff
rt. rear tire pressure to high
ft sway bar too soft

loose coming out of the turn
stagger is main thing to look at, if loose coming out, reduce stagger
increase cross weight
soften rt. rear spring or stiffen left rear spring
rt. rear tire over inflated

if you have under steer..( pushing..) do the opposite of above

so instead of changing the springs you can tune by the panhard bar..but..ultimately you want to run lower RC than the other guy and this will mean changing to different springs
prankster16a
#44
Aug25-10, 12:21 AM
P: 21
Back again............Mike, Im curious about the front roll center location left to right in a pavement sprint car. Ive noticed that Beast and a few others have the stand off on the right front for the panhard mount quite close to the frame, where as my car has the stand off quite close to the coil over. Lets say for arqument sakes that my front panhard bar is 6" longer then on a Beast chassis. Assuming that the roll center falls in the middle of the front panhard , then my front roll center would be 3" farther to the right then the Beast chassis ( also assuming that they both mount to the axle in the same location relative to the LF ) ??? Now Bob East is no dummy and Im assuming hes done this for a reason. My friends tour car has a front roll center 3" under the left front tire ( Kelly Tanner's old chassis ) I have to assume this was done on purpose as well.

As allways I look forward to your response......Kenny
Ranger Mike
#45
Aug25-10, 05:34 AM
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I had to read your prior posts ..you have 10 high Roll Center..and run pavement, not dirt track
i know the Emod guys run RC offset 4 inch bias to right for jacking effect..but these Emod guys use the General Motors Metric frame..A-arms coil springs off big GM cars as cost saving measure..( cost savings and Racing is like saying you get lots of sex after being married for 5 years...yeah right...)
straight axle rockets like you have use leaf springs / panhard bar set up on the front which are least expensive, lightest , simplest form of positive locating method.
the axle does not move purely vertical, it arcs around the chassis pivot with radius equal to the length of the P rod, so either the axle or the chassis has to shift sideways a bit whenever the axle moves vertically up or down over bumps...you got perfectly smooth track , right??
one draw back is the spring tries to fight the panhard bar during movement so to keep the lateral movement to a minimum the longest Panhard bar as possible is used.
finally the roll center is located where the center line of the P bar intersects with the center line of the car so it moves some what when either axle travels vertically or the car rolls.
i would stick with offset to the right..dirt guys run offset to the left..which is their hot setup..exactly where is your front RC offset from vehicle center line?
prankster16a
#46
Aug28-10, 06:41 PM
P: 21
Mike......my front panhard bar length is 31" OAL. From the center of the axle to the panhard mount on the left side of the axle is 11.5"
prankster16a
#47
Aug30-10, 04:21 PM
P: 21
Mike.....one more thing. Should I make a " bolt-on " front panhard bar bracket for the axle so I can tip it up and down to keep the bar level as I move it up or down on the frame ??

Thanks........kenny
Ranger Mike
#48
Aug31-10, 05:02 AM
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Kenny
i am in dallas for sales meeting but will post when i get back..
thanks..
rm
Wetmelon
#49
Aug31-10, 09:34 AM
P: 154
*Bookmarks and links to FSAE Forums, if you don't mind me doing so?*
prankster16a
#50
Aug31-10, 05:10 PM
P: 21
Quote Quote by Ranger Mike View Post
Kenny
i am in dallas for sales meeting but will post when i get back..
thanks..
rm
Thanks Mike................preciate it
Ranger Mike
#51
Sep1-10, 05:08 AM
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Quote Quote by prankster16a View Post
Mike......my front panhard bar length is 31" OAL. From the center of the axle to the panhard mount on the left side of the axle is 11.5"
Kenny, please confirm the distance the pbar crosses the vehicle center line as this is the roll center.
prankster16a
#52
Sep2-10, 11:53 AM
P: 21
Quote Quote by Ranger Mike View Post
Kenny, please confirm the distance the pbar crosses the vehicle center line as this is the roll center.
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
#53
Sep2-10, 12:53 PM
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kenny
sounds like we can not change the RC via panhard bar...let me talk to some old hands at the track tommorow..
prankster16a
#54
Sep2-10, 10:26 PM
P: 21
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


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