Caster angle

[fastman614]

I changed the axle in our lakester in 2010....we had been running 12degrees..... i had a discussion with"Fast" Freddy Dannenfelzer about what may be an optimum angle for a lakester.... he went into a bit of dragster history - informing me that, in years gone by, they had commonly run 45degrees of caster... he told me he was running 30degress.... I was not able to get to 30degrees as the dropped avle began "undropping".... I settled for 24degrees..... It works well, self steers and stays straight.... it is a bit of a "bearcat when steering it around in the pits or the shop as it wants to stay straight..... BTW, we have run, on more than one occasion, over 280mph with our car....

[kiwi belly tank]

All the info given here is assuming it's "Not" a front wheel drive, you didn't specify. FWD is a whole different deal.
Ackerman theory is often not addressed on cars being built & is very critical in our world. If you don't understand it, have a chat with your friend Google.
  Sid.

[John Burk]

I think front wheel doesn't change the need for caster . Scrub needs to be zero which puts the thrust directly behind the steering axis . Ken Walkey had no problem with 26 deg .

[manta22]

Sid;

"Ackerman theory is often not addressed on cars being built & is very critical in our world."

LSR ... running in a straight line???

Regards, Neil  Tucson, AZ

[interested bystander]

Just noticed the subject has reared its head again.

Caster is load (weight distribution) sensitive also.

Ask a Porsche mechanic and then ask a mechanic who has worked on say an older rear wheel drive Lincoln, Imperial, etc. Big difference.

Day and night.

The perplexing one is the front end pic of the legendary Tom Beatty Lakester on this forum one of the last times caster came around . Looked darn near ZERO yet it's a rear engine belly tank that went straight -into the record book.

Proper Scrub and Toe(in) are as important IMHOP.

All three improperly applied can cause a car to seek.

[kiwi belly tank]

Really Neil, how often does a car make a pass without some steering input?
  Sid.

[SPARKY]

"Proper Scrub and Toe(in) are as important IMHOP.

All three improperly applied can cause a car to seek".       

[manta22]

Really Neil, how often does a car make a pass without some steering input?
  Sid.

Sid;

The only time Ackerman is important (if it really is) is turning around in the pits or trying to recover from a spin. Even then, who cares if one tire isn't quite tracking the other. A little scrub on the salt under those conditions ...BFD.

Steering inputs on the course are so small that Ackerman does not matter at all.

Regards, Neil  Tucson, AZ

[Peter Jack]

Having spent most of my life doing race set ups on road racing, oval track and the odd drag race car I can honestly say that there is no one set of rules that apply to all cars for all events. Depending on the venue some factors work better for some cars than others. There are also some geometry and alignment items that are much more critical than others. A little common sense will get you close.

If anyone wants to go into things further for their particular car feel free to e-mail or PM me and we'll look at your individual situation.

Pete

[FoundSoul]

I love this forum.  The knowledge (and thirst for knowledge) here is amazing.

I found this video helpful to better understand Scrub Radius-- http://www.youtube.com/watch?v=JAnIa5wcn4E
I also found this article really helpful:  http://www.hrsprings.com/technical/scrub_radius

Gotta take a ride up to my chassis shop now and look this over--

Current plans for my Gas Coupe (RWD  - Nissan 240sx Chassis)

Neutral Camber
Very slight Toe-in, maybe 1/16"
15-20 degrees of Caster
Zero to slightly negative Scrub Radius appears to be what I want in a RWD car right?  Slight negative would cause the forces act to 'toe-in' the car at speed which should contribute to stability more-so than toe-out?


Am I grasping this concept properly?  In general does it sound like the settings above are in the ballpark or at least within the bounds of sanity? 

[Stainless1]

Found... those numbers seem pretty close to where our lakester is... the lakester is probably a little narrower than your GC but I would guess you will run fairly straight.
YMWV
 

[FoundSoul]

Thanks Stainless!

Looks like I've got about an inch of positive scrub radius currently, but we're not done setting it up yet, currently shortening the LCA's a bit and getting the caster where we want it.  I think we can get it to neutral without too much trouble.  I can have custom wheels made if needed as well.  The little 4" wide wheels I'm running only come in zero offset off the shelf. 

[SPARKY]

Check with Marsh Racing Wheels I have picked up some with a special centers they can use

[Richard 2]

So is it correct,
 That if a rear wheel drive car has positive scrub, it should be set up with toe-in
and with negitive scrub it should be set up with toe-out.