The most effective way to set caster on a single seater

[Belatti]

FWD cars likes arround 12 to 15 degrees of caster. You will need assisted steering for that.

RWD cars have the problem of lifting the inside rear when there is too much caster, so the kind and setup of the differential is important here under acceleration.

[riff_raff]

alonso,

static caster is defined by the kingpin axis that passes through the static centers of the upper and lower lower upright pivots on a double A-arm suspension. The static caster angle is different from the active caster angle. The caster angle has a self-steering effect on the suspension, with a large caster angle (and large steering trail) tending to produce a heavy, self-centering steering effect. And a small caster angle (and lesser steering trail) tending to produce a lighter, more sensitive steering effect.

A lightweight, mid-engine, RWD single seater with no aero downforce and no under steering is probably OK with a large caster angle, since the steering force will still be light. But a heavier car, that requires limited steering inputs and has lots of downforce like an AUDI R15, probably wants a somewhat smaller caster angle and trail.

Good luck.
Terry

[Belatti]

A lightweight, mid-engine, RWD single seater with no aero downforce and no under steering is probably OK with a large caster angle, since the steering force will still be light. But a heavier car, that requires limited steering inputs and has lots of downforce like an AUDI R15, probably wants a somewhat smaller caster angle and trail.

Good luck.
Terry

Yep, but check out for inner rear slippage. A good way of doing that is measuring temperature in the inner rear right after a hairpin, with the tyres into the working range. Large caster angle were a problem for me in light weight - no DF single seaters without differential auto-lockup (dont know if this term is the appropriate).

The basic confusion here is between caster angle and mechanical trail, like J Tom mentioned earlier in this post.



As you can see in the picture, you can configure a suspension geometry with a nice caster angle and no mechanical trail, simply by "moving" the king pin axis a little bit to the rear. Is that good? Well, you tell me! That way you would have a large caster angle with a "not so heavy" steering. Many times thats not practical because of the whole geometry configuration...

In most instances we are able to set ours with a digital bubble on the upright before turning from lock to lock to see what readings we are getting. Obviously different vehicles have different optimum values.

Russ, could you be more specific, please?

[Belatti]

Here I found a bit more "serious" way to measure caster.

http://www.hunter.com/pub/undercar/2573 ... inggeo.pdf

Check out at equation #8 and its limitations.

[Krispy]

Here I found a bit more "serious" way to measure caster.

http://www.hunter.com/pub/undercar/2573 ... inggeo.pdf

Check out at equation #8 and its limitations.

Belatti, you sir are my hero. I have been having some probelems with caster measurment and (KPI) here at work and this is EXACTLY the missing piece of the puzzle. Thanks

[BreezyRacer]

Just a little note about how I set my caster. I have a single seater race car with double A arms and it's pretty difficult to get it on an alignment rack, etc so I string align it. But when it comes to setting up for caster, I put it on a set of scales, corner weight the car, and then check the corner weights with the wheels turned at max in each direction. If it balances out then I'm happy. While I cannot tell you exactly what my caster angle is I can tell you that I maxed out one side and balanced with the other side so the weight jacked, it gave the same result with wheels turned.

That's worked well for me, but then my car responds well to lots of caster.

[speedsense]

Another "cheap" way to check castor. By turning the wheels to full lock left, measure the camber... turn the wheels full lock right, and remeasure the camber (same wheel), the difference in the change of camber, is your castor amount.

Other reasons that castor works well... increases camber gain to the outside tire whilst turning the wheels (good for radials,not good for bias ply). This also has another effect, as it lightens the load on the inside front wheel (witness a stationary go kart with lots of castor, turning the front wheels fully to the left will raise the left wheel into the air)
The diagonal weight transfer to the inside rear wheel is increased, and further increased under acceleration while still turning.

[Krispy]

Another "cheap" way to check castor. By turning the wheels to full lock left, measure the camber... turn the wheels full lock right, and remeasure the camber (same wheel), the difference in the change of camber, is your castor amount.

Not quite, a caster amount is usually measured in degrees, The difference between camber gain does give you an idea if you caster is equal.

Other reasons that castor works well... increases camber gain to the outside tire whilst turning the wheels (good for radials,not good for bias ply)

This is a very general statement, while I believe it is good for Radials, I wouldn't say it is bad for bias ply. Too much caster (IMHO) is when steering effort goes through the roof.

I have heard of cars running 29 degrees of caster with a bias ply tire in testing (with good results I might add)