ReverendDexter
ReverendDexter HalfDork
7/19/09 12:09 a.m.

Wondering how one goes about avoiding the alignment shops and does an alignment at home.

Toe makes sense to me, as does camber, but how the heck do you get a good caster measurement? I see some stuff about "turn the wheels 20 degress one way, measure it, turn the wheels 20 degrees the other way, measure it again"... but how do you accurately measure 20 degrees of steering angle?

Also, what tools do you guys suggest? I'm all for homebrew solutions, just so long as they don't involve welding (I know, I know, it's a skill I need to pick up).

If it needs more specificicity, this is on a '90 Mustang GT with Maximum Motorsports CC plates.

fiat22turbo
fiat22turbo SuperDork
7/19/09 2:33 a.m.

Caster is typically the angle of the strut fore/aft of the car. A decent camber/caster gauge will work.

friedgreencorrado
friedgreencorrado HalfDork
7/19/09 2:45 a.m.

And caster's usually something that relies on the original suspension mounting points, and can't be adjusted for more than a couple of degrees. Rocking your aftermarket strut top mounts back & forth, shimming the control arm a few mm one way or the other in its mounting holes..

fiat22's right. A gauge will tell you how much you have, but caster's pretty much set unless you have a crazy modified suspension.

Travis_K
Travis_K HalfDork
7/19/09 3:13 a.m.

I have a harbor freight toe gauge that works alright if you have something to set it on. Most stock vehiles dont have adjustable caster, actually alfa romeos are the only ones i know of that its actally designed to be adjustable.

kingbeann
kingbeann New Reader
7/19/09 7:38 a.m.

Most of the replies seem to be overlloking the fact that the original poster says he has adjustable camber/caster plates. Depending on the method of install of those plates, caster has likely moved from stock specs (if only marginally).

In response to the question, I did some ggogling on the subject when I went to cc plates on my wrx. My initial attempt to hold a digital level to the coil springs was far too inconsistent. Unless your particular setup has a consistent measuring point that is either parralled or perpendicular to you strut centerline, the best option I have seen is a gauge that uses the "turn the wheel 20 degrees, measure, 20 degrees the other way, measure method".

Most of these gauges use an indicator that will tell you when you are at x degrees based on a line parrallel to the car. You can also get out your compass and protractor to either scribe on the garage floor or make a template on scrap wood or something.

I too would be curious if anyone has devised an alternative way to measure.

Jensenman
Jensenman SuperDork
7/19/09 8:15 a.m.

Caster is actually pretty easy to measure on a strut setup. It's the angle of the strut in relation to the ground as viewed from the side. Easiest way: jack up and level the car, remove the front wheels, put jackstands as near to the outside of the front control arm as possible. Recheck the car to make sure it's level. Now stick your angle finder on the front of the strut and record the reading, there's your caster. Like this:

You can do the same thing on short/long arm suspension systems but you have to have a good place to stick the angle finder and on most SLA knuckles that's not going to work real well. Caster is measured on a straight line between the ball joints and most knuckles do not have a flat place parallel to that line. That's where the 'turn it 20 degrees both ways' method is really handy.

BTW, I'd be careful of going with real big caster on that car. The spindle will, as the steering is turned, point downward on the inside and up on the outside. This means the tire's contact patch moves around quite a bit to begin with and really goes all over the place with a lot of caster. Also, on our Fox body T Bird LeMons car, big caster resulted in the front of the car going UP as the steering wheel was turned.

SkinnyG
SkinnyG Reader
7/19/09 10:25 a.m.

But high caster can help counter the excessive camber loss due to the strut's high Steering Axis Inclination. Struts really need more caster. How much does a BMW have? 7°?

All cars will have the inside go UP as the wheel is turned. More caster will have a greater effect.

G

iceracer
iceracer HalfDork
7/19/09 10:41 a.m.

If you adjust camber at the strut - knuckle it has an effect of reducing the steering axis inclination. Caster is nice because it adds negative camber to the out side wheel and positive to the inside. It also tends to load the inside wheel, which in turn can transfer some weight to the outside rear. In theory.

44Dwarf
44Dwarf Reader
7/19/09 3:35 p.m.

camber and caster you need one of theses.

http://cgi.ebay.com/Digital-Angle-Gauge-Gage-Set-Table-Saw-Blade-to-0-1_W0QQitemZ330345822273QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item4cea253841&_trksid=p3286.c0.m14&_trkparms=65%3A12%7C66%3A2%7C39%3A1%7C72%3A1240%7C293%3A1%7C294%3A50

Place car on as flat of a surface as you can. Put angle cube on the ground ans hit Zero button. next put it on the brake rotor theres your camber. To do caster yes you need 20 deg from center use plumb bob off center tread. mark spot for center. Next use some math to figure out the lenght of a short side on a RT triangle with a 20 deg angle the lenght of the short side is how far you need to turn the wheel and move the plumb bob.

44

ReverendDexter
ReverendDexter HalfDork
7/19/09 3:54 p.m.
44Dwarf wrote: camber and caster you need one of theses. http://cgi.ebay.com/Digital-Angle-Gauge-Gage-Set-Table-Saw-Blade-to-0-1_W0QQitemZ330345822273QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item4cea253841&_trksid=p3286.c0.m14&_trkparms=65%3A12%7C66%3A2%7C39%3A1%7C72%3A1240%7C293%3A1%7C294%3A50 Place car on as flat of a surface as you can. Put angle cube on the ground ans hit Zero button. next put it on the brake rotor theres your camber. To do caster yes you need 20 deg from center use plumb bob off center tread. mark spot for center. Next use some math to figure out the lenght of a short side on a RT triangle with a 20 deg angle the lenght of the short side is how far you need to turn the wheel and move the plumb bob. 44

I'm not really understanding the trigonometry behind turning the tire 20 degrees each way, nor where you're really measuring when you do so... can someone go into more detail regarding this process?

Jensenman
Jensenman SuperDork
7/19/09 4:40 p.m.

The angle finder goes on the rotor face. The difference in angle from right 20 degrees to left 20 degrees (actually is a 40 degree arc) is your caster.

kingbeann
kingbeann New Reader
7/23/09 10:25 p.m.

Here is an alternative and intuitive (i didn't think of it) way of measuring caster ... description is about half way through this post and it includes pictures:

NASIOC

ReverendDexter
ReverendDexter HalfDork
7/23/09 11:18 p.m.
kingbeann wrote: Here is an alternative and intuitive (i didn't think of it) way of measuring caster ... description is about half way through this post and it includes pictures: NASIOC

I likey.

Something's definitely wonky with my setup. I ended up taking it into a shop to get aligned, and with the CC plates maxed out, I've only got -0.5 degrees camber on one side, and -0.9 on the other. Maxed on a CC plate should be more like negative 5 or 6 degrees, right? (maxed to the rear was only 4.5 degress of caster, too).

I'm hoping to (but not above) notching my struts, but I need to check some stuff out and see what's going on there. Part of my issue could be that these plates are for '79-'89 cars and I have a '90 (yes, there was a minor front suspension geometry change for '90-'93), but I fail to see how that would cost me so much camber.

Jensenman
Jensenman SuperDork
7/24/09 10:51 a.m.

That NASOIC post is a cool way of checking the caster.

On the camber plates, are you running stock diameter springs? Reason I ask, in many cases if the springs are the large stock OD then you won't be able to move the strut in far enough to get a lot of camber.

Also, is the plate mounted backwards (180 degrees out)? The plates on my RX7 could be mounted backwards.

ReverendDexter
ReverendDexter HalfDork
7/24/09 3:48 p.m.
Jensenman wrote: That NASOIC post is a cool way of checking the caster. On the camber plates, are you running stock diameter springs? Reason I ask, in many cases if the springs are the large stock OD then you won't be able to move the strut in far enough to get a lot of camber. Also, is the plate mounted backwards (180 degrees out)? The plates on my RX7 could be mounted backwards.

Spring diameter's irrelevant - fox chassis cars have an inboard spring setup, and the plate cant' be mounted 180 out - there's two mount holes on one side and one on the other, and where the two holes are is forward on the driver's side, and aft on the passenger (yeah, Mustang suspension == WONKY).

Pictures would probably clarify... I'll try and snap some later today.

Jensenman
Jensenman SuperDork
7/24/09 4:24 p.m.

D'oh! (smacks forehead) I forgot we were talking Fox body. Yeah, something is weird, on the Thunder Turd we were able to get ~2.5 degrees negative with the stock mountings. No idea what the caster was, though.

ReverendDexter
ReverendDexter HalfDork
7/26/09 4:22 p.m.

So, I read the destructions that came with the CC plates again... according to the manufacturer, with a stock k-member maxing out a ~4 degrees caster is totally normal (so, my extra .5 degrees there is bonus), as is maxing at about -1.0 degree of camber... and they only suggest running about 3/4s of a degree of camber anyway.

So, I think all has determined to be well. I just need my buddy to get with the freakin' program on finding me some spec Miata take-off tires for my 15s, and get my panhard bar and SFCs installed.

Our Preferred Partners
yphii8pBy8LbN61OnnSfxi4EgSGz8lCDRO9iYJyL9w9x2rnaqgkWXCIShKYhaE20