C5_Z06

Is more caster always better? I've seen that 8 degress is often recommended. Are there any cons with more camber (slower steering perhaps)?

RX-Ben

by camber you mean caster.

davidfarmer

You are usually limited to (roughly) 7deg of caster if you are running much camber at all. You would generally not want to give up static camber to gain caster

Increased caster gives you more camber in the corners (for a given static camber), but will also increase steering effort.

In most alignments I do, I'm camber-limited on at least one side of the car, so I have to use the caster on that side as the baseline for the other side (unless it is an all out race car)

C5_Z06

Since I got no feedback, apart from above, on the real reasons behind the caster settings I'll try to summarize what I've found out and let you comment instead. There must be someone out there with knowledge about this topic.

More caster results in:

1.) Increased dynamic camber during cornering.
2.) Increased straight line stability.
3.) Increased steering effort.
4.) Decreased steering responce, "slower steering". Think chopper-style rake compared to sports bike rake.

My assumptions are:

1.) Is the major factor to why you want more caster on a track oriented setup. Especially if you run a more street friendly camber like below -2.

3.) Creates more feedback due to increased steering force/effort.

4.) You don't want to have to much caster due to this issue. E.g stock C5Z06 setting is 6,9 and stock C5 is 7,4. To much caster kills the steering responce.

Any input would be greatly appreciated.

Also, can anybody comment on how the steering responce and feedback changes by going from lets say 6,5 to 8 degree caster?

MSR

Speaking only in racetrack terms, more caster isn't necessarily faster. You have to test to determine most optimum caster for your particular combination.

Adding caster changes how load transfers across the car when cornering. This is because increased caster also changes how much the outside front wheel centerline changes in height. To visualize this, consider a simplistic suspension (ignore spindle geometry and kingpin angle), zero caster means the tires stay completely level through the range of steering motion. Now switch to the extreme of 90 degrees caster. Again, ignore things like scrub radius, now the tire swings through a motion that has significant impact on the front ride height of the car.

Now add back spindle/suspension geometries that are realistic. Something like 10 degrees of caster has the outside front tire pulling up into the fender, and the inside front tire pushing down into the ground. This changes load transfer, unloading the inside rear tire at the very least.

I don't know anything specifically about how a C5 or C6 responds, but my C4 is faster when backing off the max caster that can be dialed in. If your specs for the C5 vs C5Z are correct, it appears GM believes that chassis is a touch faster with less caster (probably at the expense of some directional stability on the highway, although that difference is really splitting hairs). Generally, too, camber makes a much more significant difference in lap times. Personally, I'd run the least amount of caster I can. How I'd tune it is to see how well the car maintains cornering balance in very slow corners (high steering angle) vs fast corners. If it is well-balanced most of the time but understeers too much in the really tight stuff, you could try more caster.

-michael

C5_Z06

Thanks for the input, I guess that GM sometimes are doing things right. In this case reducing caster for the "performance oriented" Z06.

Solofast

It depends a lot on how fast you are going.

As speed increases the car oversteers more because you are applying power (which adds oversteer). More caster reduces weight transfer in the front, but increases weight transfer in the rear, which adds more oversteer.

For low speed work you want as much as you can get, and more if you can get it too. Caster was a big help for the later C4's. If you look at the front suspension bushings that Guy Ankeny made for is all conquering C4 BSP car, he moved the upper control arm aft about an inch to get a huge amount of caster. He didn't do that for any other reason. Remember that for autocross work you run so much negative camber that braking can suffer with stiff tires. In that case more caster lets you run less static negative camber and as a result improves braking while still giving you the effective negative camber that you need for cornering.

Remember too that that kingpin angle plays an important role here. If the kingpin angle is increased (as it is on the later C4's) you will lose effective camber as the wheel is turned. To reduce that effect you can add more caster and it will keep the front wheels more upright in cornering. Since steering angles are high in autocross, the effect of kingpin angle can become really important, and that's a key reason you want a lot of caster in low speed events.

The faster you are going the less effect caster has, since the steering angles decrease for a given G loading as speed increases. While the effect of the caster on front ride height reduces front weight transfer, and increases oversteer, you can get the balance back with more front roll stiffness. If you are getting loose as a result of having some caster, add more front roll stiffness and balance it back that way.

So it depends a lot on the front end geometry and how fast a track you are running as to how much caster you want.

C5_Z06

Excelent info thanks. Setting is for a C5, no auto-x, medium/high speed road tracks, street tires.