Straight Axel Caster and Weight Distribution

[Cajun Kid]

How much caster should I have ?  Also what is the best front to back weight balance?  Is it 50/50 ?

I assume I should check the weight and balance with me in the car ( I weigh 365 so I know that makes a big differance)  I am however setting kinda far back and towards the center of the car.

I have never driven a straight axel car, so at 120mph plus it felt like it was just wondering a bit, hard to keep it right on the line ? 

I think there was a 10 to 15 mph cross wind,  With my area brick and  side area profile, maybe the cross wind had more to do with it than the caster.


Charles

[Dr Goggles]

search the forum under "Caster" there's lots on this one.....

[GH]

Cajun Kid, do you have a panhard bar on the front axle? If you don't, it will wander a little, at least my Willy's coupe did when I first built it. I run about 10 degrees caster on my Studebaker and about 51 % of the weight is on the front end.

[Cajun Kid]

I have a panhard bar on front.  My caster with a dial type degree checker thingee is about 4 degrees...

I will weigh the car later this week on all fours... My guess is it is well over 50% up front and with me in it more on the left side too.

I have no idea what the  front to back weigh balance should be ?  I assume the left to right I should get exact with me in it. ??  Am I correct ?

Thanks

Charles

[GH]

I weigh my car with me and all my safety gear in the drivers seat, the correct amount of gas in the tank and the engine full of water and the intercooler full also. I adjust ballast so left and right weights are near the same.

[Cajun Kid]

What is the right front to back weight distribution?  is 50/50 it?

Does my ride height or body style have a bearing on front to back weight distribution ?

I also assume if I need to add weight to the right rear  I need to keep it as low and far back as possile?

Would rear weight be better behind the axle? maybe as far back as the rear spreader bar  or push bar area ?

[Sumner]

What is the right front to back weight distribution?  is 50/50 it?

Does my ride height or body style have a bearing on front to back weight distribution ?

I also assume if I need to add weight to the right rear  I need to keep it as low and far back as possible?

Would rear weight be better behind the axle? maybe as far back as the rear spreader bar  or push bar area ?

You don't want the weight way behind the rear axle if you are going to run on the salt.  Back there it will act like a pendulum if the car starts to go around.  Read this about CP and CG.....

http://purplesagetradingpost.com/sumner/bvillecar/bville%20-%20LSR%20Thoughts-4.html

......... or someone else's thoughts on it.

Also to figure the weight you need on the rear axle you can use the " Drag Force-HP-Thrust-Weight " spreadsheet here...........

http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html

........ hope that helps,

Sum

[836dstr]

Cajun Kid,

With a straight axle you should probably be running something in the 10-15 degrees of caster. The closer you get to 20 degrees the more you need steering stops.

Tom

[interested bystander]

IMHOP 836 is in the caster ballpark- but check your TOE-IN also!

Toe out or zero toe CAN make a vehicle seek or "wander" as you described.

[jl222]

   Cajun
  On the 222 camaro we run 64% on rear tires 36% on fronts,car is glued in at 288mph +. What do you think lakesters,streamliners,and rear engine modified roadsters are running? Formula 1 cars run around 65-35 %.
                                      JL222
   

[interested bystander]

222 - gonna throw some S##t in the game before I go nite-nite. I wanna emphasize - no criticism intended, cause there be a whole lot of DIFFERENT solutions out there!

 From what weight balance you've described I feel you must run a lot of body rake and run LOW to the ground with a good air dam.

I woulda thought that thing would weathervane MAJOR. I.E. swap ends.

(The old CP/ CG thing.)

REX, BLUE, DAHLGREN? Opinions?  - Even Willie!

[maguromic]

I have set up my roadster weights 65 - 35  and with 8 degrees of caster.  I don't want to start a debate but I think anything more is a crutch for the set up.  I know lots of guys run 12-14  degrees, but what happens when you have to correct the wheel.  One of the rear corners picks up and when you go to correct that.  The car comes around.  Just build a simple model out of wood and try the different caster angles and see what happens to the chassis.  But then again I dance to a different drummer.

[willieworld]

ok you asked for it --i think in order to figure out a problem you have to understand how everything involved works --im not sure im the one to try to explain it all but here goes --many things effect the steering on the front of a car some are easy to fix some arnt the easy ones are --tire pressure and tire wear easy to check- next is camber and caster these can be checked with a degree wheel--then toe in and toe out check with a tape measure--then scrub radis probibly the most important next to caster have someone turn the steering wheel lock to lock and visually check if you can see that its off its too for off--and last the ackerman principle unless you have the spindles on wrong you will be ok in lsr ---all of that should be easy to understand --lets start with tire pressure you all know what happens when you drive on a low or flat tire--tire wear if your tires are worn on the outside or the inside it will cause the car to wonder if they wore that way on your car you have a alignment problem---camber  on a street car the camber is usually set different on  the left as on the right because of the crown in the road on flat ground the camber should be the same --caster and rake are the same thing it is the angle of the king pins the angle will be slanted back at the top in degrees  if you have a arms and ball joints you wont have a kingpin but the angle is still there its a line through the top and bottom ball joint --there is another line that goes through the kingpin or ball joints this one angles out and when it reaches the ground should be in the center of the tire if it is you are in good shape that is the scrub radis you all know what happens to your car when you put a set of offset wheels on the front handling goes out the window--toe in and toe out if the front wheels are closer in the front than they are in the back you have toe in ---some other notes --when cars are built new they are made for comfort not speed --i am going to make some reccomendations just what has worked for me through the years ---caster 10 to 16 degrees if you are going to error do it on the high side--camber 0 degrees  if not make sure both sides are the same---toe in none  if you dont have new  parts 1/8 toe in  --scrub radis as close to 0 as possible (center of tire)  no thats not the end  the rearend in the car can effect steering it can be in out of square with the front suspension  --the rear end housing can be bent and cause toe in toe out most that ive worked on i had to straighten first especially if they have been welded on --rear tire dia. if they are different especially with a spool rearend can make your car handle bad --there are things i forgot im sure but remimber im a motorcycle guy and i run 55 degrees of caster (rake) on my bike so what the hell do i know    just some thouhgts  willie buchta

[Cajun Kid]

Willie, thanks good and  "understandable" info...

I got all of that except I am a bit confussed on Scrub Radius.. I have never heard that term. (my past experiance was drag cars and bikes and I don't recall that term or measurement, but is has been 20 years since I raced or worked on a car....)

My caster is at 4 degrees, toe in approx  1/16.

My tire preasure seemed to be low for some reason, cold preasure dropped to 30 psi.

I also think my front tires are to wide ?  195/60/15 

Thanks

Charles

[Cajun Kid]

Sum,

I am having trouble with the Car 3 speed RPM gear chart excel format.. It will not let me change the gear ration in rear end.  Something about sheet protection,

I know the Works version allows me to do that as I did it at home and MAN  it is dead on..  I am my office and do not have MS Works..

Is there a way you can email me the excel file for 3 speed car tranny's

Charles