Are Castor and Kingpin angle fixed with design ?

[firasf1dream]

hello guys,
i would like please to know about castor and kingpin, i have read about them in the Race Car Vehicle Dynamics book, what i conclude is that the kingpin and caster are built into the upright so it can't be changed in the race right ? only thing to be change are the Camber and Toe angle so i want to know if i am right or wrong about this ?
about the camber it is changed by changing the length of the wishbones and before i got an answer which is shims by searching i found some pictures that shows the shims are between the connection and the upright but when we put shims that way i conclude it will affect the kingpin angle ! so how exactly it is done !? is it by inserting shims in the wishbones ?

[tuj]

Some designs allow the adjustment of caster. In particular, the Miata alignment is done in such a way that usually camber is set to max negative (in front) and then caster is set to maximum possible without losing camber.

In practice in racing, alignment is done via precisely machined shims.

[godlameroso]

Honda's S2000 has caster eccentrics, some Ferraris as well. Caster, camber, and toe all affect each other. My experience is static numbers mean much less than dynamic ones. Particularly the toe curve. Anyway caster is simply the relationship between the upper and lower ball joint on the wishbones. So you have a couple of choices as to how to achieve. If you're using shims, you can increase caster by putting shims only at the rear leg of the upper wishbone. This is preferable to using an eccentric on the lower compliance bushing because it can give you more range. If you take away shims from the front leg you will affect camber as well.

[firasf1dream]

Some designs allow the adjustment of caster. In particular, the Miata alignment is done in such a way that usually camber is set to max negative (in front) and then caster is set to maximum possible without losing camber.

In practice in racing, alignment is done via precisely machined shims.

so you suggest to "go wild" in my design to be able to adjust later? like for example consider a range of -5degree camber +1 degree camber ? because positive is not needed

[firasf1dream]

Honda's S2000 has caster eccentrics, some Ferraris as well. Caster, camber, and toe all affect each other. My experience is static numbers mean much less than dynamic ones. Particularly the toe curve. Anyway caster is simply the relationship between the upper and lower ball joint on the wishbones. So you have a couple of choices as to how to achieve. If you're using shims, you can increase caster by putting shims only at the rear leg of the upper wishbone. This is preferable to using an eccentric on the lower compliance bushing because it can give you more range. If you take away shims from the front leg you will affect camber as well.

but wouldn't adding shims which means making the leg longer and that would only affect the camber :/ in my 3D design it shows me that it would only affect the camber and when you change the length of the steering rod it will affect the toe

[godlameroso]

Hey, you don't have to listen to me, you can put an actual car on an actual laser alignment rack and find out for yourself. Camber is affected if the length of both legs of the wishbone is altered, and caster as well, but if you only want to adjust caster then shimming ONLY the rear leg of the upper wishbone will change your caster. This is because it's the front leg of the upper and lower wishbone that set your camber. Look at any double wishbone car with front camber adjustment, the eccentric is ALWAYS on the front bushing, the caster eccentric is ALWAYS the compliance bushing, or the one on the rear lower leg.



If you look, you'll see the front of the arm on this car deals with camber, and the rear deals with caster. Although one will influence the other.

[firasf1dream]

Hey, you don't have to listen to me, you can put an actual car on an actual laser alignment rack and find out for yourself. Camber is affected if the length of both legs of the wishbone is altered, and caster as well, but if you only want to adjust caster then shimming ONLY the rear leg of the upper wishbone will change your caster. This is because it's the front leg of the upper and lower wishbone that set your camber. Look at any double wishbone car with front camber adjustment, the eccentric is ALWAYS on the front bushing, the caster eccentric is ALWAYS the compliance bushing, or the one on the rear lower leg.

https://robrobinette.com/images/S2000/A ... anual2.jpg

If you look, you'll see the front of the arm on this car deals with camber, and the rear deals with caster. Although one will influence the other.

oh ok you mean on road cars ! but i don't know about road cars, i am just referring to race cars, what i can see on the wishbone of a F1 car like this for example http://www.kaiser-wzb.eu/images/stories ... shbone.png
it doesn't show any place where you can add shims, but let's assume you can, so you mean it will push the connection hole point backward and that way would affect the caster ?

[godlameroso]

A wishbone is a wishbone, geometry and masses involved is slightly different but the effect is the same. You still have bushings on a race car, they're just metal spherical bushings instead of rubber ones on most road cars. Shims would probably go where the metal tab joins with the carbon fiber, at least like on the arm you showed me, but on that specific one, it probably uses another mechanism for adjustment.

You can have a fixed built in caster, but just know that camber and toe curves will affect it to some extent(depending on how much slop there is in the suspension for instance), particularly in the dynamic range, but this is all depending on your geometry not just of each individual wishbone but the relation of the upper to the lower.

If you're looking for a magic formula that's going to give you perfect dynamic range based on the suspension motion you're out of luck, the benefit of using shims is that you can make quick changes to the geometry to get the desired curve in the range of suspension motion you're trying to achieve. As opposed to constantly adjusting eccentrics for a static value all the while not accounting for the curve through the suspension articulation.

[firasf1dream]

A wishbone is a wishbone, geometry and masses involved is slightly different but the effect is the same. You still have bushings on a race car, they're just metal spherical bushings instead of rubber ones on most road cars. Shims would probably go where the metal tab joins with the carbon fiber, at least like on the arm you showed me, but on that specific one, it probably uses another mechanism for adjustment.

You can have a fixed built in caster, but just know that camber and toe curves will affect it to some extent(depending on how much slop there is in the suspension for instance), particularly in the dynamic range, but this is all depending on your geometry not just of each individual wishbone but the relation of the upper to the lower.

If you're looking for a magic formula that's going to give you perfect dynamic range based on the suspension motion you're out of luck, the benefit of using shims is that you can make quick changes to the geometry to get the desired curve in the range of suspension motion you're trying to achieve. As opposed to constantly adjusting eccentrics for a static value all the while not accounting for the curve through the suspension articulation.

ok what i chose to do is this :
because i have limitation on the size and ways of production i decided to go by what the Race Car vehicle dynamics tell me and chose to make a 7 degree KPI, and a castor of 5 degree both fixed, the camber will be adjustable by adding shims between the wishbone and the ball joint wish will affect both length of front wishbone leg and rear wishbone leg, and the toe will be adjustable by same way adding shims between the ball joint and the wishbone

[godlameroso]

I wish you luck, and I commend you for taking this learning experience =D>

*Edit not that I taught you something, but that you're willing to try things and learn on your own.

[firasf1dream]

I wish you luck, and I commend you for taking this learning experience =D>

*Edit not that I taught you something, but that you're willing to try things and learn on your own.

thank you godlameroso for your help i needed the information for now and for future

[godlameroso]

Where are you planning to mount the steering tie rods relative to the upright?

[firasf1dream]

Where are you planning to mount the steering tie rods relative to the upright?

well the theory says if you are mounting a front steer according to the arms joints it should be down, and if you are mounting a rear steer it should be up, but doing some research i see that it is mounted in front and up in F1, couldn't know the exact reason except for the aerodynamical reasons so they make like one body sometimes between the steering rod and the front leg of the upper wishbone or just steering in front of the leg, but for my case i decided to put it just in the middle and that because of the geometry limitations which i have for later to add the steering servo and mount, as a disadvantage i might be sacrificing a part from the direct surface going to the cooling intake openings

[godlameroso]

Well depending where you put the tie rod you can either have compliance understeer(front steer) or compliance oversteer(rear steer), that is, the outside wheel will either tend to toe-out(CU) or toe-in(CO)

As a general rule of thumb mounting the tie rod in front and below the wheel centerline and above and behind the centerline will give CU, and CO in the inverse positions. Also, if you have the KPI so that an imaginary line drawn through it from front view intersects the wheel/tire axis at the center of the tire tread you'll have center point steering and avoid any "kickback" from the scrub radius.

[Tim.Wright]

These quadrants for the steering rack are suggested for road cars which typically have compliant bushings on the control arms but ball joints on the steering link. Putting the rack in these locations keeps your lateral compliance steer from the suspension in an understeering direction.

For race cars it's not really as critical since the main toe compliance is likely the steering assist and this will be way greater than the control arm deflections.