Hello All

ANy ideas for obtaining more caster from the stock suspension ?

I initially got excited about mixing the old and new front suspension , but it only misses out on clearance by a small amount ,measured by fitment and trial and error . I am also using the 928 international eiback lowered springs .

THanks

 

John,

How much caster are you looking for? You should be able to get 5 degrees 30 minutes on a stock system- maybe a tad more- do you need more than this? I run 2 degrees camber, minimal toe and find that you need more caster to offset the twitchiness factor caused by the toe setting- doesn't half turn in though!

Regards

Fred

 

You can gain caster (at the expense of negative camber range) by adding shims between the front of the upper inner control shaft and the body. This moves the upper balljoint out and to the rear about 3 out for every one back. The shims come in U shapes with handy tabs on them, and in various thicknesses. They are somewhat old-school solutions on mid twentieth century 'murikan cars when they had double-wishbone front suspension. Should be able to get them from any real local parts place.

 

Using the shorter S-4 upper arms (longer early lowers) you NEED such shims just to get the negative camber back down to 3 1/2 or so.... easy to stack for more caster if you desired.

 

You are asking for more caster,

stock you should be able to get about 5.

If you want more, you can modify the LCA to achieve a higher caster.

Camber is pretty easy to get more though.

 

Thank you all for that great information, but excuse my ignorance in this area, but I may be confusing caster and camber , reading the manual they state the adjustment for caster are the 2 outer nuts on the lower suspension mount , is this right?
as this will tilt the lower wheel contact patch out , which is what I want to do , but is this actually camber adjustment ?
and if so how much tilt is too much ?
My race car is nearing a rolling chassis so am looking for some basic settings to start the experiment with ,(colins cams will be going in this engine also).

 

caster tends to be pretty good....I have mine set at 4.5' and it handles well...I also have the longer lower A arm with the short S4 upper.....JIm Bailey is right....my camber is at the minium at its around 3.3'...I would guess I could get as much as 5' if I wanted

 

Caster and camber are both adjusted by the TWO eccentrics on the lower arm. one pushes the ball joint out farther making the wheel lean in at the top...negative camber. The other moves the ball joint forward or back setting the caster.
depending on what tires you are running, how low you set ride height, what you use for an anti/roll sway bay and very important spring rates...you have different ideal camber settings....Note Iceman's avitar and the amount of roll but his outside tire looks pretty flat and the inside tire is just barely touching the asphalt. And static he is minus 3 1/2.
I max out the caster as I LIKE the car to self center....I will sometimes let the wheel slide between my fingers when the rearend starts to try to pass the front end...The steering wants to go straight ahead.

 

The V-8 Supercars up up around 4 1/2 to 5 in front and around 2 negative rear..but very stiff so little travel and gain or loss as the a arms run their short arcs...

 

To start as a base try these settings.

Front
1/32"-1/16" toe in
Max caster able to be matched side to side. 5+ deg best
2.5 deg camber

Rear,
0 toe,
2 deg camber.

If you are setting your ride height lower than stock (very likely) make yourself a bumpsteer kit and keep your tie rods level for the most neutral handling.

These settings will be a good base for a good solid handling 928.

Before adjusting past these settings I would be monitoring tire temps/wear inner and outer, as well as dialing in your dampening/compression/rebound of the shock.

 

Thats a fantastic lot of information thank you all so much , will be use all this and progress nicely.
Great forum !
AS a side note is there a general rule as to what positive or negative castor feel like from the drivers seat?

 

Castor is always positive, else the steering won't self-center. The lower balljoint is always ahead of the upper balljoint.

Decades ago I watched a 'racer' with his just-built never driven race car roll out of the pit lane and turn almost immediately towards the barrier. Fortunately he never made it to grid. Suspension pick points were chosen for convenience, not the same on either side, and both neg caster. Toe and camber looked great, car was undrivable. I couldn't figure out how he got it on and off the trailer.

 

I know negative camber is mostly a tire wear issue...as the suspension travels (compress) it helps keep the tires more or less square to the ground.....adding static negative camber also helps with the inherent heat to the outside of the tire....so on the same car with say 1.5' camber will blow the shoulders off the outside of the tire due to overheating in that area..... A lemons race 928 I drive (not my old estate) does this....it is set to less than 1.5' of camber.....I find it also much slower to turn in as well.....Casper has lots of camber...maybe too much....but it turns in FAST...by far the fastest race 928 I have ever driven....its also the most neutral...bordering on loose....but thats how I like it!!!!!

I also agree with Jim....I like the self centering castor....a few times when I got REALLY twisted up sideways the castor helps straighten things out....

 

Actually nearly every model of car there is camber change built into actual arc as the spindle goes from full droop to full compression. So when we lower one to race heigth we also change negative camber gain/possibly loss now that it is working about a different part of that arc. Any difference in the length of the upper and lower a arms changes how much camber you have at any point of the arc. Only way to KNOW for sure is to mount up with no spring and run the supension up and down checking camber at several points.
I got black flagged at the Streets running the bowl because under hard compression exiting the highly banked corner one of the workers was so alarmed by how far over the right front wheel (outer) appeared be leaning so negative that they thought the wheel was going to fall off, so threw a mechanical black flag. But it was just fine

 

Lots of modern tires like a little extra negative camber for the reasons Brian states. Face it, tire technology has improved ever so slightly since the suspension was designed forty (!!) years ago now. On top of that, a vast majority of 928 owners seem to like sagged/lowered front suspensions. As JB points out, this results in additional negative camber static, and can cause wierd handling characteristics under hard compression it it isn't considered in the initial settings. Bottom line is that your static camber settings need to consider how much the car is lowered/sagged. A car at 150mm needs more static camber than the same car at 180mm as-delivered height.