gt2 or x73 specs are in ( most? ) every alignment database in the conus. here are the gt2 specs which are a bit more aggressive than the x73: a street car should begin or just go with the x73 #'s.

gt2: Front Toe + 5 ' ( toe in ) ALL

Front Camber 0 ( US Turbo) , - 30' ( TurboRoW), -1 (GT2)
Front Caster 8 deg ALL

Rear Toe + 10' ( toe in ) ALL
Rear Camber -1 deg 25' ( US and RoW Turbo), -1 deg 50 'GT2


x73


Front:
Camber USA 0' +/-15'
Camber RoW -30 +/- 15'
max difference left to right 20'

Rear
Camber USA and ROW -1d 25' +/-15'
max difference left to right 15'
996 Turbo repair manual group 44-1 page 2...

X73 alignment specifications.

FRONT

Front Toe Unpressed (total) = +5' +/- 5'
Toe difference angle @ 20D lock = -1D50' +/- 30'
Camber = -45' +/- 15' with a max difference left to right of 20'
Caster = 8D +/- 30' with a max difference left to right of 40'

REAR

Rear toe per wheel = +10' +/- 5' with a max difference left to right of 10'
Camber = -1D40' +/- 15' with a max difference left to right of 15'

 

many thanks 02!

 

cheers!

 

I am curious; do you understand how those #'s work and what they do to a cars set up Vs handling and tire wear.
How are they different from my specs I recomended and what do you base that suggestion on.

 

absolutely not.

 

Bummer! I was hoping someone could explain all those numers to me so that one day maybe I could understand what they all actually mean instead of just making stuff up.

 

I actually found all factory specs in the downloaded workshop manual. The manual starts with ride height measurement, then the various specs based on ride height/model. I would probably not be too far off in assuming Porsche tried to strike a balance between street use and track use for the more aggressive GT models.

 

that's probably the same reason i rely upon porsche's factory suspension recommendations for lowered cars as a baseline. since i surely know no better. although it is racing fanatics and shop owners here with cup cars that have advised me and setup my car, they too see the wisdom of allowing the engineers at porsche who probably know best to provide a GUIDELINE, and then tweak from there

..and although i detected a faint degree of sarcasm in your earlier question to me? i knew you couldn't have wanted me to explain why porsche devised the x73 numbers in the first place i figured you'd figured that out by yourself and were just being cheeky

but back on point!? dave4s asked for the numbers, and i found them for him and posted them. wasn't nobody asking you about "yours";.. or making any comparisons or calling into question your own vast experience lol so i'm not sure what you were on about actually so have a great day anyway kyle!
... and thanks for playin!

 

perhaps more specifically, porsche provided different alignment numbers to address the availability of their oem sport suspension ( x73 ) ( approx a 20mm drop from stock ) and also the gt2 which is a bit lower still? so different specs for different heights, and according to porsche. works for me.

 

Quote:

Originally Posted by '02996ttx50

..and although i detected a faint degree of sarcasm in your earlier question to me? i knew you couldn't have wanted me to explain why porsche devised the x73 numbers in the first place i figured you'd figured that out by yourself and were just being cheeky

but back on point!? dave4s asked for the numbers, and i found them for him and posted them.

Well that is playing politely so I tried to rep you but I guess I need to spread some around first.

An example à Here are the specs for my own car street car that is lowered Via Ohlins TTX shocks, ride height adjusted and corner balanced.
Frt toe .25mm per side
Front camber -2.5 deg
The Caster adjusted to 8deg.
Rear Camber -1.9 deg
Rear toe 1.75mm per side

Here are your GT2 specs but I edited out the other extra info
gt2: Front Toe + 5 ' ( toe in ) ALL
Front Camber -1 (GT2)
Front Caster 8 deg ALL

Rear Toe + 10' ( toe in ) ALL
Rear Camber -1 deg 50 'GT2
X73 alignment specifications.
FRONT
Front Toe Unpressed (total) = +5' +/- 5'
Camber = -45' +/- 15' with a max difference left to right of 20'
Caster = 8D +/- 30' with a max difference left to right of 40'

REAR
Rear toe per wheel = +10' +/- 5' with a max difference left to right of 10'
Camber = -1D40' +/- 15' with a max difference left to right of 15'
So an understanding of the degrees and minutes above.
1 deg 30’ (1 deg 30 minutes) is actually 1.5degrees. Every 15’ (15 minutes) is .25 degrees. So you can interpolate other numbers between those on your own.

Actually here is a handy dandy online conversion chart that someone made up for you all to see.
http://www.trackace.co.uk/Manual/Conversion%20Chart.pdfI would suggest copying and saving this for your future reference in case it gets pulled down sometime.


My own alignment and view point explained

Frt toe of .25mm per side is 1.5’ minutes per side. The GT2 spec is 5’ toe in per side or .7mm toe in per side. That toe in (IMHO) is huge. It contributes to a nice stable car at speed but it under steers more than it should due to the way the Ackerman angle difference works when you’re toed in so much.
Ackerman angle is a designed parameter that controls where either front wheel is pointed when turned either right or left. Acccckkkkk how do I explain this easily..... When you turn a car at a consistent rate the car will drive a perfect circle but the inside wheel will have to turn tighter then the outside wheel... Well the Ackerman angle dictates how much each wheel varies its turn by as you get closer to a full lock turn... What is normally a neutrally balanced car is to have both tires exactly follow the exact radius of their own respective circles. Thus the inside tire needs to turn slightly more than outside. Toe a Porsche in too much and you get a car that pushes or under steers due to this designed Ackerman principle.
A neutral toe set up with a 4WD 911TT actually leaves the inside wheel turning slightly more than it should which (IMHO) is very desirable as the lightly weighted inside tire will actually help pull the car around. Add power and it contribute to slight over steer, back off on the throttle and the car will steer slightly less. That makes for crisper, safer more predictable steering when you get the other variables right. Yes the rear wheel set up can drastically affect the steering balance of these cars too.

Front camber. The GT2 spec is -1 degree, my own cars spec is -2.5 degrees. 1 degree for a 911 is still real real mild.
I run a high # and I do not get significant inside front tire wear. Actually because of the way I use my car, for cornering pleasure not straight line, my front tire wears almost dead even. I use a sticky extreme performance summer tire and my front tires will last through 3 sets of rear tires. The front end of these cars is that easy on tires even with greatly increased camber.

The rear end
My rear spec recommendation for Camber is 1.9 deg to go with my toe spec. Even Porsche does not recommend going less than 1.5 degrees; and for good reason! The GT2 spec is 1deg 50’ which is so close to my 1.9deg. I would not go more for a road car. I would definately not go less than 1.5deg.

Rear toe
Well my car is 1.75mm toe in per side, that translates to almost 13’ of toe.
I say to run up to 2mm of toe in which is 15’ (15 minutes) or .25 degrees toe in (1/4 degrees). Hmmm Seems familiar right as the X73 spec is 10 minutes + or – 5’.... Well go to the high end and those are very close to my recommendations. I would not go to the low end because of the way the suspension works. Go to the low end of the X73 spec and you throw off the balance I try and achieve with a 911 by matching a front spec to a rear spec.
Reduce that Toe in number too much and you will get a car that likes to swap ends when cornering hard or when hitting bumps; even more so if you have a over steer biased front alignment set up............. as the rear of a 911 compresses (either from cornering, accelerating or bumps) the rear wheels toe out. If you start with less toe in the wheels can actually start to point out making the car very unstable.

Now remember this is all just my opinion (the opinion of a know it all windbag ) Also I vary all my recommendations by what my customers will use their cars for! (straight line racing, road racing, road use age either spirited or granny like)

OH boy should we get into cars with adjustable ride heights and the ability to corner balance. I think not!!!!


I hope this info helps someone wanting to know more or someone fighting with the handling of there car. It really is and can be a fine balanceing act when setting up a car. The numbers front and back can either work together or fight each other, you can not just change one set of numbers without considering what it will do to the overall picture!


PS: TTX50 --> This is in no way meant as an attack of what you added to this thread. This is just my opinion with a bunch of info added in for good measure!

 

and to you sir as well. you've been repped lol

add: i couldn't have posted all that you just added, as i make no claim to having any more than a base understanding?.. and knowledge of what works on my car. rather than "why" lol
cheers kyle.

 

This was very interesting and quite helpful, which in a way spurred me on to another solution. I like the idea of using factory specs as a starting point. So with the table of ride heights from Turbo US (highest) through GT2 (lowest), I came up with a table for my custom height. Seems the H&R springs lowered my car 3mm lower than GT2 in front (115mm) and 9mm rear (124mm). So where to start?? I made a table of all the factory ride height numbers (converted to decimal degrees). Then I extrapolated to my ride height. Once graphed, it was very clear where some things should move in an extrapolated way, and where other settings should match GT2. I'll hand it all over to my indy tomorrow - and see where it leads. Here are my numbers (sorry for the spacing - was a cut/paste out of excel):
Front Axle height 115
rear axle height 124
Toe Unpressed (total) 0.1163
Toe Difference Angle at 20 deg lock -1.9728
Camber (w/ wheels straight ahead position) -1.0750
Camber max. difference, left to right 0.2232
Caster 8.0000
Caster max. difference left to right 0.6670
Toe per wheel 0.1991
Toe max. difference left to right 0.1127
Camber -1.8488
Camber max. difference, left to right 0.1960

 

i think that's a wise decision. though for my part i think i've clearly established i can't "read" or even interpret fully those numbers by way of explanation lol i also am on h&r springs with mo30's so car is approx gt2 height and if i was at an alignment shop and didn't have my cars numbers at the time. the x73 alignment would work just fine. with the kinds of understanding y'all seem to have, by rights, i shouldn't even be posting here

here's an interesting old doc i found just now...

 

I just installed front 997Cup toe arms with bump steer (tie rods) and did my first alignment and corner balance today. It's a very tedious and time consuming process but quite rewarding in the end. Having the Cup arms makes setting toe a breeze compared to the traditional arms with jam nuts.