Technical Pos. Caster vs neg caster

Spadaro mentioned that patch, and used the term "caster trail". After I read that, I thought about it a lot, and figured that there is a lot to be understood about front end design and settings...

As we increase positive caster, the caster trail gets longer, which lifts the front end more(on one side) on turns as well as adds steering effort.

Just a thought to consider how it is not just caster alone, that can change the trail length; Lets say you buy the popular aftermarket dropped spindles for a Chevy IFS pickup that lower the front two inches, then add two inch lowering blocks on the rear.... Then the caster has not changed at all, but because the "wheel bearing spindle centerline" has moved upwards towards the upper ball joint, it also now is further towards the rear of the vehicle?...so that must increase the caster trail length, which should raise the front end more on turns as well as should increase steering effort?

One more idea, is that the caster trail length will be changed when comparing a tall tire vs. a short tire.

Does anyone have any thoughts on the caster trail, and why caster settings are not just some random number tossed around, such as the old wives tale about "7 degrees for any solid axle hotrod" ?

Also, the caster trail apparently is a straight line, and then the tire height(with some amount of camber), as well as wheel offsets, will pull the centerline of the tire contact either inboard or outboard of that trail...and then caster as well as camber settings would technically need to be adjusted if we changed wheel offsets and tire heights?

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Up until now we have been concentrating on live axle front ends but you are correct that under heavy cornering with an independent front end there can be camber variations depending on the geometry of the arms. Depending on the anti dive/squat geometry there can also be caster changes with IFS in the dynamic condition.

Roo

 

That is the understatement of the week/month/year.

Roo

 

Wouldn't the same hold true for live axles? The king pins are tilted inward at the top, and the spindles longer to compensate, so if you turn the spindle from straight ahead to say 90 degrees wouldn't the camber be different?

 

Yes. And all these somewhat subtle changes in geometry, that by and large, go unknown to many "enthusiasts" is what makes my head explode every time I read one of numerous posts about changing wheel offsets to counter too wide or too narrow suspension grafts and myriad other modifications made for expediency's sake with no understanding of the consequences.

That is bad enough, but when those issues are raised in following posts, the OP and other like minded, but uninformed posters, chime in with "I did it and it works great!". I suspect they don't know the difference between a good handling vehicle from an ill handling fright pig.

If the foregoing sounds elitist....then you may be one of those people.

Ray

 

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What I meant to imply, is that if a person has no mental picture of what a caster trail is, and "what goes on there, in that small area", then how can we begin to understand how the wheel behaves at whatever steering radius, or whatever caster and camber we choose..

How many people in the hobby really knew about "caster trail", in other words..

I hope the thread keeps going...there is a lot of interesting info out there for us to learn..or to share

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You sound like my type of guy, Ray. And anyone who uses the term "fright pig" can't be all bad.
Incidentally I use the William C. Mitchell software to plot wheel paths etc when I am doing anything apart from live axle front ends.

Roo

 

you mean backwards ( negative )

they used to handle real bad if you did that , they would get the dreaded grocery cart shake above 35 and had to fight the wheel back when you turned anything sharper than a lane change while rolling

and dropping in Rb series motors in my case didn't help . I was a walmart grocery cart getting the cars to my buddys shop to get it on the alignment rack it shook that bad till he modified the lower strut and upper control arm mounts so I could use radials , the guy was Genius with Mopar front suspensions . As for the above mods , I didn't do that to mine , change the axle out to a monaco sqad car 9 1/4 rear which was shorter and stronger ( than the 7.5) and big brakes had to get rid of the cop cruiser gears ( low 2's ) and went to a 3:90's and kicked in the springs and later mini tubbed/shortened the axles it as I was eating up 235's with the 340 then when I went to the 413 I had to run a 295 BFG and still would smoke them down the block .