Caster ?'s again

[Cajun Kid]

Well, After I got the new wheels and tires on the car I thought it was time to check the front end.

Man was it way off.  The Caster was Right  2 3/4 and Left 1 7/8  Toe in was 1 5/8
(not sure if changing wheels and tires caused it to be that far off, Last time I ran, it had a "wandered a bit" at over 100mph.)

The front in guy set the caster at 8 1/4  degrees and the toe in at 1/16th.

I was told that for slower steering and greater straight line stability that I needed 6 to 12 degrees caster ??

Well we split the differance at 8 1/4 caster.

Any Ideas how this will change the handling ?

I just took it down the old bypass and it did ok at 125mph, considering the croswind.

Charles

[manta22]

Charles;

If your front end has no appreciable play, you might set the toe- in at 0 and reduce the rolling resistance a little. Otherwise, a bit of toe- in is desirable to compensate if the wheels can be deflected outward. You sure don't want ANY toe- out.

Regards, Neil  Tucson, AZ

[Sumner]

........................... You sure don't want ANY toe- out.

Regards, Neil  Tucson, AZ

Funny thing happened with us with Hooley's Stude this year.  When he brought the car to my place we checked the toe and it was toe-out.  We adjusted it to about 1/16 toe-in.  On the first run on the salt Hooley aborted the run on a miss-shift, but was running about 160 or so and said the car was not handling right.  We decided to check the toe again and it was where we had set it.  Next he looked in his notes to see what his friend had set the toe a couple years back.  Low and behold it was set to .080 toe-out.  We set it back there and the car again handled great up to 253.

I want to get a hold of his friend and see why he set it to .080 out in the first place.  This guy is the service manager at a Chrysler dealership and also has a fast drag car so he must of had a reason.

c ya,

Sum

[t russell]

We set my truck at 1/8 in at rest at speed it gos to 0.
terry

[Cajun Kid]

Terry, that seems good from what I understand.  My front end is all new and tight so we opted for 1/16th at rest.

My bigger concern is the Caster. I have never driven a straight axle car with more than 5 degrees, and today we put 8 1/4 in Caster. 

As I understand it, the more caster the slower the front end steers and this is supposed to be more stable at higher speeds.  Are we thinking correctly about Caster ?

Charles

[RichFox]

That's supposed to be the deal. I don't run more that stock caster on my Vega or my '32 Ford when I had it. 32 went 158mph Vega has run 208mph. The Vega runs straighter of the two. My roadster was built with a bunch of caster. I think it's just a pain in the pits.

[Richard Thomason]

We have found that to get an accurate toe-in measurment, to make sure you run the car forward at least two wheel revolutions before taking your measurments. Otherwise you end up with a different number after the first run.
rht

[GH]

IN 06, I had problems with my front axle on the trip out to the salt (broken) and ended up with 1/4" toe out (my own fault) the car occilated left and right the whole time (see video on my site). I have mine set up on a front end machine, 1/32" toe in, goes straight.

[Cajun Kid]

GH, yeah with that much or any toe-out would seem to  make the term "driving the car"  have real meaning....

Charles

[t russell]

I  :?ment1/8 toe out I put a jack under the front and raised it till it was level it took 3 trys to set it  but it took all of the hunt and bump steer out.
terry

[Cajun Kid]

   
/  \  Toe In          \ /   Toe Out

l l   0 Toe

[Cajun Kid]

Terry , if I understand you. you set the toe to 1/8 out and as you go faster it goes from 1/8 out to 0 r nuetral ?

As speed and down force increase does it effect Toe and Caster

Assume Toe was at 0   as the speed increases and down force compresses the suspension does this cause toe in or toe out ?

Same with Caster ?  How does speed and down force change it ?

Charles

[manta22]

"...as the speed increases and down force compresses the suspension does this cause toe in or toe out ?"

If the toe- in changes much under those conditions, it is caused by "bump steer"-- not a good condition.

Regards, Neil  Tucson, AZ

[willieworld]

charles---describe your front suspension---------willie buchta

[JimL]

Hey Sumner....any chance that car has negative scrub radius (deep backspace on the front wheels, to get them into the fenders)?  We had a BUNCH of that on the Prius project, in 2004, due to the fender shape and putting the front end on the ground (we actually clocked the transaxle 28 degrees to get the axles at a reasonable angle).

If the scrub is inboard, the car will need toe out to settle the lash in steering pivots/linkage.  I remember seeing that setup on a production RWD car with Vor Lauf (spelling?) geometry, in the late 80's (our joke was that "Vor Lauf" was German for "hold left" because that model pulled right on road crown!   ....old mechanics jokes....makes sense to us!)

Regards, JimL