Aerodynamic vs. vehicle stabilty

[nebulous]

akk
Could you build a couple of models one with inline and one with side by side tires,then blow air at each?
jack

[Jerry O]

I have to agree with Jack on the 0 caster. Most drivers use a lot of caster to help make the car go straight. This will make the car track straighter with less driver input but can cause a big problem when the car starts to spin. Just imagine making a run at Bonneville and the car starts to spin to the right. Naturally you are going to counter steer to the right to get the car straight again. What happens is when you counter steer to the right or the left depending the direction of the spin, a car with a lot of caster will cause the cross weight to jack weight to the opposite side at the rear. Now you lose traction on the right side and cause the car to want to spin even more. The more input you put into the spin the more the car will want to spin. This is not as big a problem for longer and more narrow cars like liners but I can see it being a big problem for short wheel base cars with a wider track, like roadsters. Just my opinion, but I think running as little caster as possible and slow the steering. The driver steering input is what keeps the car going in the direction needed, not more caster.

[Peter Jack]

Good to see you back on the board Jerry. Hope you start another project.

Pete

[Rex Schimmer]

Jack,
Is the reason that you go with 0 caster related to the solid aluminum wheels? My thinking is that caster gives camber gain when turned and your front wheels probably don't like camber.

Rex

[saltfever]

Hmmmm . . . . good point Rex. And when they turn do they "knife edge" into the track with caster?

[willieworld]

it is the design of the steering ----0 caster (rake )  0 trail  0 camber--going straight or turning it remains the same  0                willie buchta

[jl222]

  The 222 camaro has front wishbones and spindles with 22 deg caster made by Stock Car Products for high speed tracks
like Taladega and Daytona, when Pro Chassis was building the car they had a 16 deg unit on and I had them change it
to the 22 deg as some of the bville cars had far more at the time. I know a lot of caster can cause the rear chassis to move up when the steering is turned because I have seen it happen on a bare roadster chassis and I was surprised that stock cars used that much, this was in 1989. Still weight jacking from caster must not be a problem for them or they would not use that much.
  Anyhow their the pros racing for big bucks with a lot of learning miles. This is what I was told, I have no knowledge of actual caster settings used today
  We get a confident ride at over 300 mph with no need of wheel correction, accelerating and decelerating with or with the chutes. [ look at videos in build diaries under getting ready for Bonneville]
  I also have no eyeball vibrations because we are suspended, unlike some streamliners that see the cones as being 3 ft. high.
 We also have toe in on front tires as we have front brakes and don't want them going into toe out when applied, which is an unstable condition.

[willieworld]

let me make something clear here---i know about jacks steering because im building a vehicle with similar steering---the bike i run now has 54 degrees of rake (caster) i did that for a couple of reasons mainly to slow down the steering--i do not recommend 0 or 54 degrees when i first started building drag cars i found a good front alignment shop and went with what they recommended 10 degrees and never had a problem with any car i ever built---there is a lot of things that come into play on each vehicle--do the research ---if you cant figure it out ask someone  with a vehicle like yours --------willie buchta

[akk]

For a while I thought this thread was dead...we were in the dyno room...speed week cometh but there is still time to learn something...

The jacking effect of caster is caused by scrub radius and wide tires...if the king pin points to the center of the tire contact patch going straight  ..minimum jacking...I think!??!

Akk

[Peter Jack]

If the king pin points to the centre of the tire contact patch going straight the car has no caster.

Pete

[willieworld]

if the kingpin hits the ground in the center of the tire you have 0 scrub--that has nothing to do with caster--caster is the rake of the front axle looking from the side of the car---Akk is very close--the raising of the car (jacking effect)  is caused by caster --the more caster the greater the effect--the problem with to much caster (rake) is the jacking effect only effects the wheel on the inside of the turn--if the inside front wheel raises the chassis in a turn then the opposite rear wheel will see the extra weight applied ----some caster is usually required  its what makes the front wheels want to go straight---on a car its called caster on a bike its called rake ---i have built race cars and street rods all of my life and have built almost every kind of front and rear suspension and steering there is ---the one im working on now has 0 rake (caster) 0 camber 0 trail---i must admit i did get some help from jack---mine is not the same as his --hopefully i will have it done for speedweek 2011---thats what i like about lsr there is room to do your own thing so far if it changes i will do something else--when i get a chance i will do some suspension stuff on willies builds                                                                                                           willie buchta

[Peter Jack]

Willie:
If there is caster in the axle the extension line from the kingpin will hit the ground ahead of the center of the tire patch.

Pete

[Rex Schimmer]

Isn't most of this discussion regarding caster etc pretty much a moot point related to a land racing car. Johns (JL22) likes caster because it makes it stable going straight, Jack's cars run 0,0,0 because of the type of front tire/wheel and the zero suspension that he runs and it goes straight which is really all they are looking for. Sprint cars and go karts run lots of caster and scrub radius because both of these types of vehicles are ran in a very "loose" condition and the extra caster and or scrub radius will transfer weight to the opposite corner which will both help forward drive and also lessen the chance of spinning out. Sprint cars and land racing cars run in very different enviroments and both require different approaches to suspension parameters based upon the way they are designed and their designers thinking of what will work best for their car.

Rex

[willieworld]

pete  the more caster the farther that point moves forward ---and the more the steering will raise the car-- and the more it will try to steer straight                   willie buchta  



pete  sorry i missed your point in an earlier post --you are right king pin angle center of contact patch (viewed from side) = no caster   

[nebulous]

Rex
Read Jerry O's Reply Over and over and over!
Those are my feelings exactly!
Although, this is only one of the things that improve straight line controllability!
jack