proper caster settings?

[redstack]

My 84 has incredibly heavy steering. Is there a suggested "sporting" alignment? In my miata days there were special setups for autox vs touring. I saw one mention of caster to 6*, that seems like a lot of caster. I was used to getting the caster to 1 or 2 in the miata, which gave it a very nimble handing.

running 205/50/17 in front

[javadog]

Porsche usually specified a little over 6 degrees. Maybe 6 degrees, 5 minutes, plus or minus 15 minutes. A higher ride height and zero camber would probably help.

JR

[Bill Verburg]

Originally Posted by redstack

My 84 has incredibly heavy steering. Is there a suggested "sporting" alignment? In my miata days there were special setups for autox vs touring. I saw one mention of caster to 6*, that seems like a lot of caster. I was used to getting the caster to 1 or 2 in the miata, which gave it a very nimble handing.

running 205/50/17 in front

caster spec for all 911 from '72 thru '89 is 6°5'+/-15'

wheel/tire size doesn't really matter here.

Running less caster affects on center return more than effort

toe should be 0° pressed

camber 0°+/-10'

[javadog]

You might also ponder what effective offset you now have, with those wheels and any spacers you may have installed.

JR

[Walt Fricke]

Right - increasing the scrub radius is going to make the steering harder.

[redstack]

Ok, so if I have the alignment checked and set to the specs in the book, it should be as good as it will get. No "sporting" alignments.

Scrub radius, I understand in concept. So without taking the wheel off, reading what I can find on the ET for those front cup II wheels, they should be about ET55. There is a fairly narrow spacer on there, maybe 20mm to bring it into the the range of 23ET needed. I will pull the wheel and check all this soon.

Yesterday I was talking with a fellow Gulf Coast region PCA member with a 87 who had 205/16 width tires on his fuch wheels and also a spacer. He said his steering was very light.

Would a wheel with a normal 23ET and a 20mm spacer have a different scrub radius than a ET55 / 20mm wheel?

[GaryR]

You might consider a steering rack rehab also before having it aligned again. They are all getting to be 30+years old... including the u-joint.

[redstack]

yea that's true, plus a turbo tie rod install and bumpsteer kit.

[GaryR]

Originally Posted by redstack

yea that's true, plus a turbo tie rod install and bumpsteer kit.

If you don't have the turbo tie rods get them vs. those rubber parts. Bumpsteer is good if your car has been lowered also, but I never had one in my quite low SC and never had an issue with steering..

[Bill Verburg]

Originally Posted by redstack

....
Would a wheel with a normal 23ET and a 20mm spacer have a different scrub radius than a ET55 / 20mm wheel?

yes
things that change scrub radius
wheel ET
spacers, which change wheel ET
camber
spindle angle or height adjustments
ride height changes
caster changes

Scrub radius change is usually felt as a stronger feedback through the wheel, our cars have a lively wheel, even in normal driving you can feel it moving in your hands, In a corner the more the scrub radius differs from stock the more effort is felt an and the less feedback is felt, the steering gets heavier and flatter

[redstack]

I get plenty of feedback, a good kick going over bumps etc.

Can you measure scrub radius by picking up the center of the tire? or average of front and back of the tire to get the average for the center of the wheel? Imagining some sort of toe in.