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Kirkham Motorsports

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  #1 (permalink)  
Old 04-06-2021, 06:30 PM
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Default castor on CSX car?

What are you guys running in terms of castor on your CSX car? I am at about 3.5 degrees castor and the billboard tires are at 25psi. The around town is fine but on the freeway it is bad... no bueno... I am being told by a good source that I need to be running 5-7 degrees castor... and 30 psi...

This person is probably the best cobra builder in the world... I am courious at what other CSX guys are doing...
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Old 04-06-2021, 06:42 PM
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Try a set of Avons.
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Old 04-06-2021, 07:18 PM
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Quote:
Originally Posted by Tom Kirkham View Post
Try a set of Avons.
my question was castor...I am well aware that Avons are great, But some gys are getting great results with Billboards if the suspension is correct. Tom, What are you running for castor?
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Old 04-06-2021, 07:30 PM
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I can’t speak to billboards......but you need to run as much castor as you can.....5*-7* degrees is adequate....but, it makes your steering difficult..... and you need to check your bump steer.....that will have a wandering effect as you go down the road....add that to bias ply tires and you have a equation for not very stable driving on any road.
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Old 04-06-2021, 07:47 PM
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Originally Posted by Morris View Post
I canít speak to billboards......but you need to run as much castor as you can.....5*-7* degrees is adequate....but, it makes your steering difficult..... and you need to check your bump steer.....that will have a wandering effect as you go down the road....add that to bias ply tires and you have a equation for not very stable driving on any road.
steering difficult in terms of in a parking lot? at slow speeds? I think I am willing to sacrifice a little effort at slow speed and gain stability at freeway speeds.

My ERA car was perfect at about 4 degrees castor. But I am being told that that is not enough for a CSX... advice?
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Old 04-07-2021, 10:01 AM
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Are you running Toe-in or Toe-out.....what is the camber settings.....

Many items can cause a car to wander down the interstate.....especially Bump steer.....that’s the second time I’ve said that @nd you have not commented.....
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Old 04-07-2021, 10:13 AM
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Bob P. at ERA was always harping about his correction of bump steer in the ERA suspension. But when I asked him "what if I run off the road but hit a big bump and that steers me back on to the road?" He said, "well in that case bump steer is a good thing."
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Old 04-07-2021, 10:26 AM
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Quote:
Originally Posted by Morris View Post
Are you running Toe-in or Toe-out.....what is the camber settings.....

Many items can cause a car to wander down the interstate.....especially Bump steer.....that’s the second time I’ve said that @nd you have not commented.....
I am running 0 toe in the front and about 3.5- 4 degrees castor 25 psi front and 28 psi rear on billboards. I have checked several times the suspension components, the car seems very tight on the road. It seems like the tires are causing a shutter in the front end around 75MPH.

The problem is that every time I want to make a change to the castor I need to take it to the alignment shop. I can easily give the heim joint a turn on each side to see it this helps but I dont know what affect this will have on the rest of the geometry of the front end? What do you do at the track? this is a CSX car so its very easy to make adjustments.
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Old 04-07-2021, 12:08 PM
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Quote:
Originally Posted by Morris View Post
Are you running Toe-in or Toe-out.....what is the camber settings.....

Many items can cause a car to wander down the interstate.....especially Bump steer.....thatís the second time Iíve said that @nd you have not commented.....
sorry I missed your question on camber. I am at 1/2 degree negative all 4 corners.
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Old 04-07-2021, 12:20 PM
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I can't add much with regards to alignment settings, however I suggest you run less pressure. I'm running 18R/22F in my Avons, and I was running about the same on the track with Goodyear Slicks.
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Old 04-07-2021, 07:26 PM
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Your settings are fine for a street car.....except you need to have 1/8”inch Toe-in....that’s why the car is wandering on the highway.....

If you change any Heim in the suspension....it will change every setting on all of the other Parts of the suspension....

There are set up procedures for the street and also for the track and they are not interchangeable.....therefore...you must make up your mind on which set up you want....example....street - 1/8” Toe-in.....-1/2* degree negative camber & 3*-5*degrees positive Castor....

Race setup....5*-7*degrees positive Castor...-2* to -3*degrees Negative Camber....1/8” Toe-in .....

Each setup requires complete alignment of the wheels to the chassis ....which means you don’t go changing settings independent of each other.....

Further more you have to know what to change when you get the tires hot enough....and I doubt you will ever be able to get the tires up to temperature....we have a procedure when we come off the track.....tire temperatures across the tire and pressure on each tire starting with the front tire that is loaded the most then proceed around to the rest of the tires. Those readings will tell us exactly what to do to the suspension......

So to answer your question......it is a very involved process that takes years of experience to know what to do to any vehicle.....and how you drive the vehicle.
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Old 04-07-2021, 07:44 PM
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Your castor is fine. Get the toe setting correct and you will be good. Also drop that tire pressure. I am running 19.5 psi. all the way around in my Billboards.
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Old 04-07-2021, 07:46 PM
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BTW.....Back in 2004 when I bought KMP259.....I was the first one that brought the bump steer problem to David & Tom K......and showed everyone how to check it and what needed to be done to fix the problem......when I checked the bump steer on KMP259 the first time...it had as much as .350” movement from toe-in to toe-out....you should only have at most, .015” of a inch per inch of travel in the suspension.....up or down. ......Tom K and I worked on changing the uprights to reduce the amount of bump steer....then I built a whole different steering rack to go with their upright to accomplish our minimum amount of bump steer so we could go around a corner at high speeds....these cars are inherently distorted with lots of bump steer.....that is why I ask the question before I discuss suspension issues.
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Old 04-08-2021, 11:24 AM
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thanks guys,
I am more confused now than before. One guy says 5-7 degrees castor and 30PSI another guys says 5-7 is fine. One guy says 19.5 PSI... I guess I will just stay with the 4 degrees castor for a street car and play with the tire pressures my self. I will change the toe to 1/8" in.
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Old 04-08-2021, 11:50 AM
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Take Morris's word on this, he knows these cars, he was a champion race driver, and taught Paul Newman to drive, yes, Paul Newman the actor.
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Old 04-08-2021, 11:56 AM
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Quote:
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Take Morris's word on this, he knows these cars, he was a champion race driver, and taught Paul Newman to drive, yes, Paul Newman the actor.
Just ship the car to Morris with instructions to get the car in the best possible condition he can. Tell him to keep it all under ten grand and just pin his bill to the steering wheel when he ships it back. I absotively assure you that will work better than anything else you can possibly do.
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Old 04-10-2021, 08:24 AM
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Billboards need toe in, 1/8" or maybe a little more. It is the easiest thing to try and should fix your issue.
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Old 04-10-2021, 06:41 PM
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Quote:
Originally Posted by 6TNCRZY View Post
Billboards need toe in, 1/8" or maybe a little more. It is the easiest thing to try and should fix your issue.
Totally agree. Your zero toe-in is the first thing to correct.
If toe-in is zero, the slightest amount of wear (or tolerance slackness) gives you toe-out, and "wander"; hence the suggestion of 1/8" toe-in.

Cheers,
Glen

Last edited by xb-60; 04-10-2021 at 10:06 PM.. Reason: edit
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Old 04-11-2021, 03:21 AM
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Unless your front end is fully rose-jointed, you need some amount of toe-in.

4 degrees of positive is fine, increasing it to 7 will show little benefit while your main cause is no toe. Leave the castor alone, adjust the toe to 1/8 inch, and note the immediate difference.

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Old 04-11-2021, 10:03 AM
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ty i will have it toe in 1/8"
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