Caster??? How much is too much?

I am setting up my chassis / front suspension for my T coupe. Long story short I was curious what is too much caster. I know original specs are around 6 3/4 degrees. I am around 10. Too much? Bitch to steer? I know a lot of older drag cars and FEDs ran a lot more caster, but they just needed to go straight.



DuckusCrapus

 

What are you referencing the caster against?

It should be measured on a level floor.
Most home garages have a 1 degree slant to the slab so liquids will flow out the door so depending on which way the car is facing there could be an additional degree added to the mix.

Regardless, ten degrees strikes me as too much for street use.
You'll find that the car takes more steering effort than perhaps you think it should.
I've seen one coupe backed off from 8 degrees to about 5 1/2.
It still handled well, but steering effort was easier.

 

The purpose of a little caster is to make the steering have a tendency to return to center. The more the caster, the more effort to turn, and the more the tendency is to return to center when you let go of the steering wheel, that's why exagerated caster is useful on dragsters. Also, because the tire tilts and tends to dig in when turning there will be more tire wear. On clean concrete pavement, while turning, you might even make black marks.

 

I understand the purpose of caster....just wasn't sure how much a few degrees made.

I wasn't totally sure on how to measue so I stuck my angle finder on the floor. It was zero. The I placed it on the top of the king pin / spindle and it read almost 10 degrees. I knew that was a little more than what it was supposed to be, but just didn't want to do something dangerous.

So what would be "acceptable" for the street? Seems like you could alter the stock degree listing a little and still be okay. Right?


Thanks for the input.


DuckusCrapus

 

Seven degrees is as much as you really want to put in it and that is a tad to much,as you said it will go down the road nice and straight but you will find it will push when trying to turn whilst going slow and if you are on loose ground,gravel dirt etc you will just lose the front end and go straight on as it pushes.
Not good when making a tight turn amongst other cars.(don't ask how I know)
john

 

Trust me you will like 10 deg. especially if you drive it a lot.The difference in steering effort between 6-10 deg. is nothing compared with how twitchy a transverse leaf car is at 6. At 6 it will wear your ass out tryin to keep up with it on other than perfect roads.
I like 12 personally.
T.OUT

 

One more thing to consider... If there is ANY slop in your kingpins at all, using more than about 6 or 7 degrees of caster can cause severe frontend shake. I experienced this problem a few years ago (on a friend's model-A coupe); cruising along 40 mph, hit a bump with one of the front wheels and the frontend began shaking uncontrollably. The only way to get it under control was to come to almost a complete stop. We temporarily overcame the problem by increasing the toe-in... to one inch! We later readjusted the radius rods to get the caster down to 5.5 degrees and everything was fine then. If you have installed new kingpins and bushings already then 10 degrees will work fine.

 

Like building a house, ya gotta start with a good foundation. Just sticking the angle finder on the floor in one spot doesn't necessarily mean that the car is sitting level - concrete ain't exactly a surface plate!!

Front & rear wheels (all four) have to be on the same plane & level to get an accurate reading. I like to place a 1/4" plate about 12" square, on the concrete where each wheel will rest. I then use a string level strung between front & rear and cross-ways to ensure the level. Shim the appropriate plate to get 'em level, if necessary. Push the car onto the plates and then check the caster.

If you're checking caster by placing the angle finder on the axle housing near the king pin, bear in mind that the top of the forged axle probably isn't exactly square to the king pin. Place a piece of round stock (with the ends square to the center line), a little smaller than the king pin, on top of the king pin and then set your angle finder on top of the round stock. Admittedly, a lot of screwing around, but if you want it right, the extra effort is worth it.

My 2¢

 

That skooting isn't caused by caster, maybe you have a posi', or the spider gears binding a little bit.

push when trying to turn whilst going slow and if you are on loose ground,gravel dirt etc you will just lose the front end and go straight on as it pushes.
Not good when making a tight turn amongst other cars.(don't ask how I know)
john[/QUOTE]

 

.........and now, you're all set. Putting an artificial number on it don't matter to a hill of beans. Hang a plum bob from the ceiling and measure the angle at the kingpin. Personally, the more the tendency to return to center, the better, if'n the load to turn it isn't a bother. Of course, there's a limit, but anywhere from 1 to 14 degrees won't be unsafe. Obviously, worn steering linkage is bad. As another post pointed out, worn kingpins ain't good, but that goes without saying. Got shimmy? Let me out and I'll walk home, don't ask me to ride with you until your machine is safe.......

 

I have also run into the 40mph "Shake" problem with a Chevy based tube axle all new parts set at 10 degrees... AS was stated. You had to stop to get the shake under controll. Violent. Only on certain roads. Tried everything from 1" tow out to 1" tow in. Lots of tire wear and sometimes almost impossible to BACK UP straight.

Back at 6 degrees and A ok!!

 

Whatever it takes........all cars aren't the same.

 

As a matter of curiosity I just looked it up and the caster spec. for Fords according to the 1933 Motor Manual is 7deg. loaded.
However,it has been my experience,if you have the shakes or stiff steering at 10,then something else is wrong.
Either a component is loose,the axle is twisted (one side has more caster than the other) or some other matter needs attention.
T.OUT

 

I wouldn't consider building an early Ford with a solid axle without using a steering damper. Cheap, easy to install and in most cases will greatly tame a front-end shimmy which can bedevil even a new build where everything is tight and properly set up. Good insurance.

A light car may get by with as much as ten degrees of caster but a heavier rig like a full fendered sedan is going to be rather harder to steer than most might be comfortable with. A friends 31 sedan sails down the highway without drama or wheel sawing and it has only a little more than 5 degrees tilt. The SoCal steering damper works like a charm as well.