Decreasing CASTER???

[Dixie]

Can anyone confirm that aftermarket shock hats will allow me to reduce the front caster, as well as increase negative camber?

I'm experiencing some substantial physical discomfort after tracking my 911 for a weekend. It's due to shoulder problems that resulted in surgery a year ago. I've been told my shoulders are as good as they're going to get. (Hey, it was way worse before the surgery.) So it's either dial down the caster, or buy a 993 with power steering.


Thanks in advance, as I'd hate to let this puppy go.

[Quicksilver]

Not sure how much difference reducing the caster is going to make. Most of the steering feedback actually comes from the tires self-aligning torque. There have actually been cars with negative castor such as the late 70's Chevy Monte Carlo which had -5° of castor.

When a tire distorts from cornering forces it generates a "slip angle" which is literally to contact patch being twisted. This twist is the feedback that you feel. The more cornering force you generate the greater the feedback.

That is why you feel less feedback when the tire starts to break away when the car is pushing. The tire has broken loose and isn't twisted as far.

[pjv911]

Maybe reducing the front tire width and bumping the tire psi may help.
Negative caster will in fact reduce steering effort but it certainly wont help handling in anyway.
I see your car has been lowered. Are you fighting bumpsteer. That will wear down a healthy shoulder. Also did you install rack spacers(washers) under the rack bolts ? If so make sure your not binding the steering universal joint. You would need to loosen the u-joint clamping bolt and turn the wheel lock to lock a few times. This will help it settle in a comfortable area.
Oh I forgot to ad that adding negative caster will also reduce the action of the steering wheel turn back to straight once your through the turn. Meaning you will then have to help it return back to straight. This would be completely unacceptable for street or track use.
My suggestion would be forget about changing the caster.
Make sure your rack is set at the correct height
Make sure your u-joint is in a relaxed(as straight as possible)position.
Lastly try going with a 390mm steering wheel. This alone will lighten your steering input by about 20% over a 350mm wheel.


Now if all else fails go ahead and consider trading me your car for a beautiful power steering equiped 85` 944 that im trying to sell. I will give your car a happy home among many 911 peers. Yes im kidding (i think).

Kurt Williams

[stlrj]

As far as I know, there is no shock hat that will reduce caster.

I was able to reduce my caster to 2.6 degrees by grinding out my shock towers enough to reposition my stock hats forward.

Feels like power steering now. But here's the kicker...it handles better, virtually enliminated front end push.

Go for it!


Cheers,

Joe
Redwood PCA since 1976
74 w/ 86 3.2

[911pcars]

"...virtually enliminated front end push."

... at the expense of directional stability as well. Was that +2.6 or -2.6ΒΊ caster?

I too would recommend using a larger steering wheel to reduce steering effort.

Sherwood

[rusnak]

I hate myself for saying this, but a larger steering wheel may help. I don't know if something like a decambered ball joint turned sideways might work, try Elephant Racing for tech advice.

[pjv911]

Originally posted by stlrj
I was able to reduce my caster to 2.6 degrees by grinding out my shock towers enough to reposition my stock hats forward.

Feels like power steering now. But here's the kicker...it handles better, virtually enliminated front end push.

Go for it!

If you moved your hats foward you then positioned the wheel more foward in the well. Thus increasing your wheelbase which effectively put more weight on the rear wheels and increased your front wheel caster. I dont know off hand what correct factory spec is for caster but 2.6 degrees worth of increase is substantial and should have adverse affects on handling. Maybe you ended up correcting an existing problem with this change ?
My front end alignment knowedge is based on everyday cars. I have only aligned a few 911 cars so please take my advise as general knowledge, not specific to Porsches. However in theory its all the same concept.
Hopefully someone who is most knowledgeable will add advise to this thread.

Kurt Williams

[pjv911]

I should also add that increasing your caster will give you better straightline stability. It with also cause your toe measurement to go towards toe out and will need to be reset.
Did you just shoot in the dark with this caster change or was this professional advise. Im curious to know for my own knowledge.

Kurt Williams

[78targa]

How about getting a bigger steering wheel (larger diameter) to reduce the steering effort? Yep, I agree with the guys that have already said it.

You could also position your seat closer to the wheel or alternatively get an adapter to bring the wheel closer. With more of an angle in your elbow you will have better leverage.

You could also put a little + toe on the car to make it ever so twitchy. Might make it easier to make the initial turn in. Besides, it's a nice setup.

[Wil Ferch]

It is noteworthy that early 911 caster specs are 5.5 degrees ...and later models at 6-6.5 degrees.

I think 1 degree delta makes a big difference in effort...I'm simply amazed how light steering the early cars are.....way out of proportion to their lighter weight.

380+ mm diameter steering wheels and reducing caster 1 degree should get you there and still get acceptable straight-ahead stability.....you can try it and change back if you don't like it....

- Wil

[stlrj]

... at the expense of directional stability as well. Was that +2.6 or -2.6ΒΊ caster?

That was +2.6 degrees as compared to +6 degrees nominal.

Who said anything about reducing directional stbility? It tracks straight as an arrow.

I have a Grand Caravan that specs at 2 degrees caster and never had any stabilty problems either. In fact, there are many cars today that are spec'd far less than 6 degrees caster that have never had stability issues.

Did my homework...

Cheers,

Joe

[Wil Ferch]

So did Mercedes Benz...their "incredible" straight-line tracking just *might* be due to their 12 degrees ( ! ) caster....at least it was that way for earlier models.

At a standstill...if the wheel was cranked full left to full right...this enormous caster caused the front-end of the car bob up and down visibly.... !

The obvious answer is that the designers are blending and matching a number of suspension characteristics into their cars...and we can't single-out one variable and transpose them from one car brand to another...there are too much "other" things going on.

- Wil

[stlrj]

I recall from my old VW days how delightfully feather light the steering effort was and how stable and fun to drive they were. Back then the standard Beetle used 3 degrees and the Super Beetle was someting like 1 1/2 degrees of caster.

My aim was to get as close as I could to those early settings and make my 911 more enjoyable which is what it's all about IMHO.

Cheers,

Joe

[Wil Ferch]

As I said...try early 911 setting of ~ 5- 5.5 degrees vs later 911 settings of 6-6.5 degrees.

One degree difference is reported to lighten things up considerably....

- Wil

EDIT: here's more to chew on---> Why does the steering feel so much heavier?