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Old 11-22-2016, 10:56 AM   #1
greg1333
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Too much Caster?

is 15 degrees of caster too much?

Between the ground control plates and the SRS offset "eyeball" bushing I currently have around 15 degrees of caster. I can dial some out with plates, but I was just curious if there is such a thing as too much caster.

Highly modded e30 with e30/e36 five lug conversion.

thanks
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Old 11-22-2016, 11:41 AM   #2
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Unless it's too much to fight the wheel, I'd say leave it.
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Old 11-22-2016, 11:52 AM   #3
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Positive or negative?
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Old 11-22-2016, 02:07 PM   #4
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Positive. If it was negative, he'd be dead before he could post!

I managed to get that much caster on the 2002-
it was awesome with radials in faster corners (it effectively adds camber to the outside wheel when you turn, which is very helpful- to a point.)
With bias slicks, it hurt grip- they didn't like being cambered up that much, and
lost grip in moderate to tight corners. In hairpins, it was a little spooky- I'd wash
out when I got just so much lock in, and the only way to regain front grip was to unwind-
not what you want to do at Mission when you're pointed right at the wall.

I guess you'd have to do what we do for all suspension things- do a suspension sweep
to see what gives you the fastest lap times on the tires you like best.....

t
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Old 11-22-2016, 03:08 PM   #5
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Yep... my friend has a ton of caster in his 5 lug e30 and it has a pretty weird mid corner push in tighter stuff
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Old 11-22-2016, 06:16 PM   #6
greg1333
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Thanks for the input.
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Old 11-23-2016, 08:06 AM   #7
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Just for reference I run 9.8 degrees and I still get some mid corner push, but the car feels very stable in a straight line. I'll be taking a little out for the beginning of next season to see if turn in improves a little. I did manage to dial out most of that push with suspension adjustments, but that lack of turn-in really bothers me still.
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Old 11-23-2016, 10:55 PM   #8
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If you're running radials, I'd be a bit surprised if the caster's causing your understeer.
(but only a bit. suspension tuning has an element of black art to it...)

I found that radials really liked the caster, since it only adds camber in corners.

For turn- in, add toe- out, in 1/16th increments. And camber, too. Also, slow hands.

hth

t
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Old 11-24-2016, 07:05 AM   #9
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If you have double adjustable shocks that work you can tune around anything pretty much, but its pretty tough to do that on a forum with no real time feedback. Adjusting toe and camber to fix stuff is so time consuming, and it can be tough to go back and forth accurately depending on the car. I like to have a go to toe and camber set depending on the track and fix the cars behavior with shocks, only problem is that this doesn't really work with lower to mid range shocks- gotta have the good stuff. Another easy thing to try for turn in is rear ride height. Raise the rear if you are trying to fix a push on entry

My theory on the too much caster mid corner push is with that much you are overloading what is now a smaller contact patch. My friends car rotated nicely on entry, would start to take a set and then just push. We didn't tune on it much unfortunately, so can't say
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Old 11-27-2016, 06:12 PM   #10
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Definitely such thing as too much caster, primarily on a McPherson strut. Keeping it close to 10 or less is ideal. With a really high angle the strut cannot do its job well especially while turned (hence the mid corner understeer). There are other things affected with this also, but this one is an important one for an e30.
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Old 11-27-2016, 06:30 PM   #11
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How does this differ with AWD cars?
I have about 9.5 degrees of caster in my E30 race car. But, I just installed treehouse M3 FCAB's and Ground Control camber/caster plates in my IX. I know that the IX has significantly less caster than the rwd models do.
Why do you think they did that?


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Old 11-28-2016, 10:46 AM   #12
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Quote:
Originally Posted by TobyB View Post
If you're running radials, I'd be a bit surprised if the caster's causing your understeer.
(but only a bit. suspension tuning has an element of black art to it...)

I found that radials really liked the caster, since it only adds camber in corners.

For turn- in, add toe- out, in 1/16th increments. And camber, too. Also, slow hands.

hth

t
Turn in at corner entry is pretty good already, and when I added some toe out the entry became a bit more crisp but it made the car very twitchy otherwise. I'm already running 3.5-3.8 degrees of camber (depending on the track), and have a good contact patch based on temp readings. The car doesn't push until I'm mid corner and the slip angle starts to get high. I can add a bit of power when this happens and make the car four wheel slide, which works out just fine, but it is and issue I'm driving around instead of fixing, and I don't like that approach. Running 275/35-15 Hoosier A7 on a 10" wheel fwiw.
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Old 11-28-2016, 11:18 AM   #13
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Quote:
Originally Posted by berlow94 View Post
How does this differ with AWD cars?
I have about 9.5 degrees of caster in my E30 race car. But, I just installed treehouse M3 FCAB's and Ground Control camber/caster plates in my IX. I know that the IX has significantly less caster than the rwd models do.
Why do you think they did that?


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Caster does more than just camber change, it also raises and lowers the sides and it effects load transfer. I think with the IX one of the uses for the car are slippery conditions which require a lot less camber and camber gain as you turn in, plus the extra weight over the front axle will make the steering heavy. The axles will also likely struggle with the articulation. One of the design uses being slippery conditions is likely the main reason for it. Oh and bumps/terrain is transferred less into the steering with less caster.

As far as the push goes, a nice test would be to ride a chopper with a high rake and ride a sports bike. You can't turn a chopper very well. It's not the greatest analogy, but it may be easier to visualize.
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Old 11-28-2016, 08:11 PM   #14
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Quote:
Originally Posted by Pavlo View Post
Caster does more than just camber change, it also raises and lowers the sides and it effects load transfer. I think with the IX one of the uses for the car are slippery conditions which require a lot less camber and camber gain as you turn in, plus the extra weight over the front axle will make the steering heavy. The axles will also likely struggle with the articulation. One of the design uses being slippery conditions is likely the main reason for it. Oh and bumps/terrain is transferred less into the steering with less caster.

As far as the push goes, a nice test would be to ride a chopper with a high rake and ride a sports bike. You can't turn a chopper very well. It's not the greatest analogy, but it may be easier to visualize.
Yes i understand the effects that caster has on handling with 2 wheels. (Also known as head angle or trail on bicycles & motorcycles)

Aside from the different surface the car was meant to be driven on, my question was specifically about how the awd system might effect the amount of caster that a manufacture might want compared to a rwd car.
E30's don't seem to be the only awd cars that have much less caster than their rwd counterparts...
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Old 11-28-2016, 09:58 PM   #15
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Quote:
Originally Posted by Pavlo View Post
...effects load transfer...slippery conditions which require a lot less camber gain as you turn in, ... heavy front axle will make the steering heavy... axles will also likely struggle with the articulation... bumps/terrain is transferred less into the steering with less caster.

Summarized.

Subaru STI runs around 6 degrees, similar to a performance RWD car and it's purpose is not exactly getting to the grandmas house in the snow. Caster is also used to counter the affects of the included angle, so that goes into consideration; design of the rear suspension; manufacturer's tire choice (suspension is designed with this as one of the most important factors), projected vehicle use, limitations of space from other components of the car...

There is no one answer for your question unfortunately. Every design is essentially a set of compromises based on other design criteria that a group of engineers are given. VW, for example, used an axle beam alignment specifications that was designed for 50% on road and 50% off road use for nearly 30 years. It may not apply to a driver in an urban area, but some person that does statistics found that many of their cars globally are used in such conditions. A suspension engineer is pretty limited by all of these criteria. After a car is designed, more groups of engineers go and test to find what works better and that's when part revisions become a thing (such as offset control arm bushings and offset strut mounts).

I know I just explained how the clock-making industry works when you asked for time, but take it as an explanation to why your question cannot be answered in a simple way.
Hope this helps.
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