| Here is some information on
aligning a 911. It started with a specific question, then I added to it. Hope it answers
more questions than it generates! Someone asked about adjusting rear camber on his
911 to a more negative setting without changing toe, to decrease oversteer in
autocrossing. This is what most people want to to to their camber, so the answer is
If you adjust the rear camber
more negative, you will need to pull the wheel forward with the toe adjusting bolt to toe
it back in again. I have found that there is a simple and pretty accurate way to do this
with only a tape measure. There are plenty of home alignment methods- here is my personal
method which has been proven effective on the autocross course and race track.
It is much easier to adjust camber if
you can get under the car in an inspection pit or on a lift, then you can loosen the 19mm
bolts slightly and adjust the camber and toe from below without removing the wheels, and
get an idea of the changes by measuring the camber directly with the method explained
below. But most of us dont have access to a pit or lift, but we can use this method
of adjusting :
Before adjusting anything, support the
car on jack stands, remove the rear wheels and make sure that both rear suspension arms
are at full droop. Then measure from a convenient point on the torsion bar cover (I make a
dot in the center of the round end), to the hub of the rear brake (to the closest point on
the hub). Both sides of the car (left and right) should measure about the same if your
wheels are aligned correctly and your car is symmetrical. Now you can loosen the two 19mm
bolts at the rear of the spring plate, and the two 19mm eccentric (cam) bolts. Turn the
rear-most eccentric bolt with a hex wrench from behind to adjust camber more negative. You
will want the eccentric part of the bolt to be at its lowermost position for maximum
negative camber. I find it useful to remove the eccentric bolt and mark the bolt at
its most eccentric part so I know when that part is down I have maximum negative
camber and will not turn it further which reduces the camber.
It is hard to measure camber while you
are adjusting it, but you can use a modified version of the camber measurement method
below to get an idea of how much you are changing it.
To set the toe back in, pull the wheel
forward a bit with the forward eccentric bolt to get the same toe measurement as before.
After doing this, drive the car over some bumps and check the camber to see if it is set
where you want it. If not, you can repeat the procedure above and move it a bit more or
less. When the camber is OK, you must check the toe-in to see if the toe is still OK. The
following method was suggested by Pete Albrecht and seems to work fine, and is easier than
most methods. It works great on front or rear wheels.
An easy method of measuring toe can be
done by sticking a thumb tack into your tire in a full tread area near the center of the
tread, at the frontmost point of the tire (not too deep!). Hang a string from the tack
with a weight such as a plumbers bob which almost reaches the ground. Make a mark on
the ground (an X with a pencil is good) where the weight rests. Repeat this a few times to
make sure it is correct and repeatable. Use another tack and do the same on the wheel on
the opposite side. Now push the car backwards until the tacks are at the most rearward
positions of the tires. Make the marks at the current positions on both wheels. Now you
have two sets of marks, one is the width of the front of the tires, the other is the width
of the rears. Measure between the two front marks, then between the two rear marks. If the
two distances are the same, you have 0 toe. If the front distance is less than the rear
distance, you have toe-in. If more, you have toe-out. Usually about 1/16" to
1/8" of toe in is desirable. For autocrossing, you may want to toe-out the front
wheels by this amount, especially if your car is understeering or turning in sluggishly.
You can measure the camber accurately
and easily with a good bubble level. You must first make sure the car is on perfectly
level ground. You can check this with the bubble level on your garage floor and a long
straight rod. If it is not level, you can use some cardboard or something under the low
wheels to make it level.
First drive the car to settle the
suspension. Now check the distance the top of the level is away from the top of the wheel,
when the bottom of the level is touching the bottom of the wheel. Dont measure from
the tire, as it is very distorted. Choose a nice flat spot on the wheel rim to measure
from. You will probably have to fabricate something that you can hold the bubble level
against, that will fit against the wheel without hitting the tire. I sawed-off a bubble
level to fit the wheels diameter, and inserted a thumb-screw into the top which
presses against the top of the rim. I adjust the thumb screw until the bubble is level,
then measure the length of the screw sticking out, and calculate the camber.
Use some math : camber = inverse sin
(measured distance / vertical length). Vertical Length is usually about 1" more than
wheel diameter, so 9/32" at the top of a 15" wheel is about one degree negative.
I run about 9/16 (2 degrees negative) at the front and .7" (2.5 degrees) at the rear
for autocrossing. For the street this will wear out the insides of the tires quickly, so
you should try for about 1 to 1.5 degrees negative in the rear, and ½ degree less
negative in the front (more if youre serious about handling). If you dont have
a scientific calculator handy, you can approximate the measurements for a 15" or
16" wheel by using 4.5 / 32" for each one-half degree. (For our metric friends,
about 3.5 mm per half-degree camber).
The front of a 911 (or most Porsches) is
fairly easy to adjust. Loosen the hex bolts at the top of the strut and mark the position
of the plates so you know where you started. You may have to remove some of the goop
around the plates. Then pry the strut towards the center of the car to get more negative
camber. For competition, I think you should push the top of the struts as far back towards
the rear of the car as you can to increase caster. This is not very scientific, but it
works well, just make sure your car does not pull left or right which would indicate
castor is not equal from left to right. It may be difficult to move the tops of the
struts, you may need to pry against the metal or use a piece of wood against the mounting
of the strut and hit the wood with a large hammer. It should help to jack up the car to
remove pressure from the strut.
Front toe is not too difficult to
adjust. But on older cars, the tie rod adjusting threads are often seized-up from rust.
You may need to heat up the tube between the tie rod and tie rod end with a torch. First
soak both ends with a good penetrating oil, this may be enough to get them loose. Then
loosen the clamps on each end of the adjusting tube. When loose, turn the tube to change
toe, you can use a "vice grip" in the center. You will be able to see which way
to turn the tube for toe-in or toe-out by watching the wheel as you move the tube back and
forth. You should adjust both left and right sides by the same amount, but if you are
making a very small change (for example 1/8") you really need to adjust only one side
(and it is much easier!).
---- snip -----
I know I should just pay $ and have it
done right, but assuming its out of adjustment anyway, Id rather fiddle with
it myself and learn something along the way before paying someone to set it right.
---- snip -----
Dont think that when you pay $$ to
get it done that it will be better than doing it yourself. Ive heard plenty of
horror stories about alignment shops with equipment that was uselessly out of calibration.
If you can DIY, you can check it occasionally and will always know it is right. Peter
Gabriel says "If you want some control, youve got to keep it small- DIY".
CORNER BALANCING :
Juha Vane <Vane@compuserve.com>
- It is a stock -85 Carrera Coupe. What alignment spec is recommended, I am somewhat
concerned about tire wear and would not like to go extreme here but again handling is
Id go with 1 degree front and 1.5 rear as a compromise of handling/tire wear.
>> I tried also to get corner weight adjusted, did not do too good.
Had my weight on driver seat, tank full.
I used following principle from Bruces book, Porsche 911 Performance Handbook 1st
edition, page 174, I quote Bruce;
"Assuming the 911 has a weight distribution of 40/60 front to rear, forty percent
of the left side weight should be on the left front wheel, and sixty on the left
rear" end quote. Thanks Bruce, hope You dont mind me quoting You.
Mike Piera wrote some time ago, I quote Mike;
" When you find which diagonally opposite corners have too much weight (they will
each be heavy by the same amount if you calculated right!) you should lower the 2 heavy
corners, and raise the two light corners slightly, all by the same amount, then drive the
car and measure again." end quote. Thanks Mike, hope You dont mind me quoting
I was not able to get weight transferred to
right front and keeping car level. After I leveled the car, and 8 hours of adjusting, the
car is level, but the weights are way off. LF 718, RF 561, LR 903, RR 933 (lbs) I did not
drive the car after adjustment, adjusted with wheels on ground, rears hard, but it can be
done with 2 people. After adjustment, bounced the suspension and the height adjustment was
logical. I adjusted a little, car height changed in proportion.
Mike, I dont completely understand Your wording; "they will each be high by
the same amount", please clarify.
<< Your weights are accurate, I can tell because the diagonal corners are all off
by + or - 52 pounds. Here is your car (front of car is top)
718 1279 561 (LF, Front, RF)
1621 3115 1494 (Left, total, right)
903 1836 933 (LR, rear, RR)
Here is your cars weight distribution :
To calculate the desired corner weights,
multiply the front or rear percentage times that sides weight, i.e. for left front
41% (front) x 1621 (left) = 665 pounds. You have 718 on LF so you need to reduce weight on
the left front by 53 pounds.
When you calculate the other corners you
will see that EACH corner is off by 53 (or so) pounds - and the diagonals are the same,
i.e. right rear (diagonally opposite of left front) is also 53 pounds heavy : 59% (rear) x
1494 (right) = 881. 933 - 881 = 52.
In order to KEEP YOUR CAR LEVEL and at
the current ride height, and change all four corners to the correct weight, you need to
LOWER the left front and right rear a bit (reduce weight on a wheel by lowering/loosening
the torsion bar), and RAISE the right front and left rear by the same relative amounts. By
doing so the car will stay level and at the current ride height.
You can also change the corner weights
by just adjusting two diagonals, i.e. just lower the LF and RR and then drive the car to
settle it in and weigh it again to see if you did enough. This will lower the entire car
however. But if you did want it a bit lower then this is just the trick to do! Likewise if
you want to raise the whole car a bit then just raise the RF and LR. If you need to keep
the ride height the same then do all four corners.
Then if you do everything right you
should have a perfectly balanced, level car that weighs:
Of course this is easier said than done
and may take a few trials but if you are within 10 pounds or so youve got it!
Good luck and let me know how it turns out!
72 911S Targa, 73 911 RS lightweight clone
2 time SCCA SCCA Solo-II A-Stock national champion.
2 time Porsche Parade fastest of any stock "P" class.