Caster How much?

[hotschue]

If you get the scrub radius right it addresses the "diagonal weight" issue......I have 13.5 neg caster with no wheel flop on 130" wb....I started with 3.5" of neg. scrub, thru machining the spindles and custom front wheels got it down to "0" scrub.....

[Peter Jack]

Taking things down to 0" scrub radius definitely cuts down the "diagonal weight transfer" or "wedge" as it's commonly known. As long as you have caster in the front end you will get some wedge, loading the inside front wheel and the outside rear wheel. This should lead to a loose condition turning conventionally while tightening the chassis up if the car gets "crossed up". This may not be all bad. I think we're dealing here with a combination of competent engineering and driver preference.

Pete

[Peter Jack]

Hotschue, are you running negative caster or more likely positive caster? Positive caster is when the kingpin is leaned back and is stable while with negative caster the kingpin is leaned forward and would normally be very unstable.

Pete

[Freud]

Sorta like steering while going backwards.............even on the freeway.

FREUD

[mrfab]

I'm building a straight tube axle for a lakester and plan on running more than 20 deg caster so I will need stops. I'm using early ford spindles. Any suggestions where to locate the steering stops?

[SPARKY]

You will need stops and I would re-read the above before I welded anything. 

[hotschue]

PJ.........Your right....king pin inclination toward the rear (positive caster).....fingers engaged....brain not!

I can turn the wheels lock to lock without much effort, I have no chassis lift due to caster, axle width is 52" pin to pin...In days of old when we push started the dragster, after I made the turn around, a pit crew would have to grab the front wheels to straighten them, one of the front wheels would be totally off the ground at that point, steering was impossible until it was centered. Wish I new something about "scrub radius" back then.......

[Blue]

OK, please forgive an old motorcycle racer here. On bikes we separate rake (castor) from trail ().  Trail is the physical dimension between the intersection of the steering axis with the ground and the contact patch, while rake is simply the steering axis angle vs. vertical.  It is trail that is primarily responsible for centering forces irrespective of rake angle (castor).  Trail is a combination of rake, wheel diameter, and axle offset vs. the steering axis all projected to the ground plane.  I'm missing how all of this discussion of "castor" translates to the physical dimension of trail.  Clearly, a given castor angle will translate to different amounts of trail based on different wheel diameters and steering axis offsets.

On bikes, rake is primarily responsible for steering response while trail is responsible for stability.  Too much trail and the bike will want to go straight in the corners.  However as Willie points out: LSR is about going straight and lots of trail is a good thing.  Rake and trail are varied <somewhat> independently on motorcycles, castor and "trail" are easily varied independently on cars.  What is the car term for "trail"?  And the question of "how much castor?" is better expressed in these terms.

[interested bystander]

Methinks if you put a little CASTOR oil on yer kingpin bushings you can get away with less CASTER.

Sorry, Blue, don't hate me.

Rex can't spell worth a . . .. either  but his advice is solid.

[Rex Schimmer]

Come on guys!! I can spell it is just that spell check doesn't agree with me!!

Rex

[John Burk]

 "Methinks if you put a little CASTOR oil on yer kingpin bushings you can get away with less CASTER".

 Don't laugh , steering friction can kill handling .

John

[Blue]

Methinks if you put a little CASTOR oil on yer kingpin bushings you can get away with less CASTER.

Sorry, Blue, don't hate me.

Rex can't spell worth a . . .. either  but his advice is solid

Why should I hate you, if I can't laugh at a good pun what fun would all of this be?

[Jonny Hotnuts]

I am currently working on a front end that utilizes a threaded shaft that will allow me to adjust camber from 5 to 30 degrees.

~JH

[Peter Jack]

I hope that's caster Jonny.

Pete

[Anvil*]

OK, please forgive an old motorcycle racer here. On bikes we separate rake (caster) from trail ().  Trail is the physical dimension between the intersection of the steering axis with the ground and the contact patch, while rake is simply the steering axis angle vs. vertical.  It is trail that is primarily responsible for centering forces irrespective of rake angle (caster).  Trail is a combination of rake, wheel diameter, and axle offset vs. the steering axis all projected to the ground plane.  I'm missing how all of this discussion of "caster" translates to the physical dimension of trail.  Clearly, a given caster angle will translate to different amounts of trail based on different wheel diameters and steering axis offsets.

Since cars generally have no steering axis offset and caster being a measurement taken during wheel alignment with a fixed wheel diameter the concept of trail generally gets washed over and forgotten. Always good to have a reminder from time to time.