Alignment spec question:
 

Another question for the Pelican brain trust.

Just rebuilt the front suspension on my 76. Swapped out the 23mm front torsion bars for a new set of 21mm, new a-arm bushings, new ball joints, turbo tie rod ends, upper shock mount bushings and Koni sport adjustable inserts. Already has a 22mm through the body sway bar.

Rear is 27mm T-bars with 19mm factory sway bar, Bilstein sports. (which I may change to Konis)

Next step is alignment, and I'm wondering if most of you guys provide specs to the alignment shop or do you just let them align it to factory. Car is 100% street, spirited driving with some canyon carving.

If you do provide specs what are some numbers that seem to work well on these cars based on the common mods I've done?

(tires 255/45/17 and 315/35/17) car is a wide body backdate with turbo 3.2

This may help with some ideas for set up.

https://www.youtube.com/watch?v=MPVV04V7Zcc

Feel free to pm me with your number and I'll give you a call

Ian

Cool video! Thank you Ian, I will probably take you up on this.

Grappler, Ian will provide you good specs. The front suspension is not hard to align, however, you must find a shop that really knows how to align the rear suspension.

I'm a proponent of doing it yourself. That way you learn how the alignment works, and you develop the skills and sight picture to quickly check the alignment if you hit a big pothole or curb. It's not hard to do, it just takes patience and attention to detail the first time or two you do it.

Alignment is not hard at all, just tedious- more so if you don’t have a lift.


Sent from my iPhone using Tapatalk

Hi - first, thanks for posting the video, great info!

Q: Is there a good way to understand ride height vs roll center in a pre-89 911 WRT what we should be shooting for? From this older thread it sounds like "euro" ride height about right? It would make sense if the engineers knew what they were doing but did real world stuff get in the way? Just curious, I have a lot to learn! TIA. (I am at euro height now)

https://forums.pelicanparts.com/porsche-911-technical-forum/1132370-ride-height-roll-center.html

JMO but it's well explained in the referenced thread

when a car is lowered 2 things happen in the front
1) the roll center drops, this lengthens the lever arm through which roll forces push, the operating end of this lever arm is the CoM at that end of the car, the longer the arm the more amplification of the roll force, the more roll

to counter this raise the spindle heights

stock RoW front ride height is 108+/5mm, say you are nearer the low end of that to start, i.e. 110mm
if the car is lowered by 20mm the roll center drops, to restore the original roll center CoM relation raise the spindles 20mm. now you have exactly the same R/C to CoM relation as you started w, spindle changes are limited by the wheel diameter, 15' have a limit of ~+19mm, 17: have a limit of ~+40mm, just me but I'd be very wary of taking it to the limit.

2) the other thing that happens is the relationship of the steering knuckle to the steering rack changes and increases bump steer(aka roll steer), if the front is lowered 19mm install a 19mm rack spacer. The original bump geometry has now been restored. the thickness of the rack spacers is the limit here, from my spotty memory 19mm is the lilt for a rack spacer.

alternately or in conjunction you can raise the steering knuckles, the best wat t do that is w/a double sheer bracket allowing the knuckles to be placed in a ~2" range of heights, 19mm rack spacer +21mm rise of the steering knuckle compensates for a 40mm drop in suspension height

both 1 and 2 need to be done in tandem