Here's what the 10mm rack spacer does, the lower red line is the new x axis, the upper red line is where the toe will be w/ ~43mm of compression, to avoid bump steer you want to keep the the curved dash line operational zone at no more than 45°
http://forums.pelicanparts.com/uploa...1482763786.jpg

OK, first off today I'm going to go and measure ride height, cement to top of wheel arch.

Then I'll flop down and take a picture of the A arm angle to see what it looks like.

There is an article in Grass Roots Motorsports about roll centers and roll levers. Getting an idea of what someone meant earlier when implied that the lowering of the car had caused the excess roll in the photos when autox. If the roll center was below ground level then it leads to excessive rolling right?

OK ride height measured in my pretty level driveway, with a tape in inches converted to cm.

I think they are kind of wonky
Pass Frt 64.293cm
Pass Rear 64.135 cm
drv frt 63.658cm
drv rear 64.293

I doubt the weird front is from corner weighting. I think it's just out of whack. My large posterior isn't helping anything I'm sure.

So in addition to bumpsteer and all the other chores I'm just establishing my base line.

Lowering reduces the effective spring rate due to geometry, although the torsion bar spring rate is unaffected. Upgrading to larger bars to compensate is common practice.

Cheers,

Joe

measuring the fender arches is next to useless, to get meaningful data measure the factory way
front
a - b + front height(108+/-5mm is the spec) bigger # is lower, max(lowest) used on a streetable 911 by the factory is ~158mm
http://forums.pelicanparts.com/uploa...1483388904.gif
rear
B - A = rear height(16+/-5mm is the spec for a'84-89 Carrera) smaller # is lower, nin(lowest) used by the factory on a streetable car is 12mm
http://forums.pelicanparts.com/uploa...1483388904.gif

here's another setup sheet
http://forums.pelicanparts.com/uploa...1483389037.gif

Oh ouch, that means that I will need to get it up on a lift to measure the fronts.

I did see a good photo of a guy who built a wooden ramp that you drive up on and then pull the middle section out so you can work all around the car.

To measure ride height, the car needs to be sitting on it's tires

Right, by up on a lift I was thinking of a 4 post lift, but I don't have access to one right now anyway. Or that cool wood ramp I mentioned. Maybe I can measure while lying on the driveway.

BTW, is there a way to determine what size the installed torsion bars are other than pulling them out? I see that stock is 18.8 forward and 23 aft, I would bet that I still have stock size but don't know for sure.

Well I guess technically you could do force / displacement to figure out your spring rates, but I think at that point it would be easier just to pull the t-bars and have a look.

Good stuff. I would not have thought the factory bump steer curves were published. Awesome.

FWIW Red you can measure the front heights on the ground semi accurately. Maybe slightly more accurately on a lift. Probably close enough for what you are doing on the ground. I dont see why you could not measure the rears using the factory procedure on the ground but I dont recall doing it.

@Elombard Yea the rears should be easy enough. With the car lowered and the rubber spoiler I'm thinking that getting a shot at measuring the TC height will be a bit tricky. Maybe I can come in the back side of the tire.

Bill is an amazing source of information. It sometime goes over my head, but I think I understand the last diagram he's posted.

Yes that's how I do it, from the backside