Caster and camber.....

[09851]

Hi guys. Need your help. The car is a 99' WS6 T/A. I recently purchased new rubber and had them installed. Since I got such strange tread wear out of the old ones, I booked it in for a four wheel alignment. Just got a call from the shop who is performing the alignment. The guy asked me if the frame has ever been bent as his tech could not get the caster and camber measurements on spec in unison. Well, first of all, is the car not of "unibody" construction where there is no real frame? I did smack the curb pretty hard a few years back. The bodyman assured me that everything was on spec. Does anybody have any ideas, is it possible that the tech may just be inexperienced? I am stumped. Please advise.

Jamie Stringer

[Detroit_Bird]

The front engine cradle/ suspension mounts is referred to as the front subframe, and if it is bent in a crash, since the suspension attatches to it, the alignment will be off. This simply bolts to the rest of the body. The same thing exists in the rear, however this subframe is welded to the body instead of bolted. If this is bent it would warp the thrust angle (angle the rear end makes with car - ideally should be 90), and cause the alignment of that to be off.

Sounds like your body guy may not have put your car on a frame jig when he should have. This is a way of cheating costs especially if the frame isn't bent enough to look off.

[09851]

Thanks for that. I kinda assumed those things but was not sure enough that i would feel comfortable going to accost my bodyman. The part I left out of the story is that theengine cradle was replaced as a result of the incident. So were the rear axles and the lower control arms on the front. Oh yeah, and all four wheels and tires. Oops, there was that pesky front clip also. The insurance claim was just under 12K. Ouch, that will follow a guy around for a while. With this info I will head to the body shop at quitin time and see what he says. Thanks guys. Any and all opions are appreciated.

[MN6WS6]

There's a subframe up front, and a subframe out back, but there is no frame in the middle.

In case you don't know, camber is the angle that the tires roll perpendicular to the frame of the car. For instance, as we all know, the late 80's models of the 300ZX had a bad camber problem. The insides of the tires were on the road, but the outsides of the tires seemed not to even touch the pavement. It's the same thing ricers get when they lower their car. Camber is used to make a car turn and keep the tires flat on the pavement. It's also used to keep consistent pressure on the bearings so the tires don't "rattle" side to side. Most street car camber ratings are 2 degrees or so up front, 1 degree out back (if adjustable).

Caster is hard for me to define, so I'll use examples. On American Chopper, all their bikes are "raked", where the front forks come out at a 30 degree angle from the frame. This makes the bike stay straight, but hard to corner. A sportbike though has little rake in it. This makes it easier to turn, but requires more effort to keep it straight. In car terminology, drag cars have a lot of "rake" or caster; you don't want them to turn, you want them to stay straight. F1 or IRL uses less caster, that way the car is easier to turn. Caster also has an effect on body roll, but that is way too technical for this discussion.

To not be able to get the caster and camber in spec "in unison" then he has to know what he's talking about. That's a pretty significant lick to cause that problem, because what has happened is that either the front suspension is tweaked or the frame is tweaked. He's trying to pull in camber more than likely and the vertical wheel axis is rotating, probably backwards (towards zero caster), causing the caster numbers to not match on both sides of the car. That causes steering problems.

As much as I hate to say it, the car probably needs to go on a frame machine to see if the measurements are in spec. If they are, then you know it's a suspension issue. That's a lot cheaper than having the frame pulled back straight.

If that's not an option, you'll have to tell him to redneck it. Now obviously you want the camber in spec, because if it's not, it will cause excessive tire wear on the edges. To compensate for that, he'll either have to put more or less caster in it to get everything to match. Caster doesn't hurt anything, all it does is cause the car to either turn easier but harder to keep straight, or keep straight but harder to turn. These are EXTREMES though, so he will probably be able to get it close enough to spec so that you don't even notice it.

The real question is, is it so far out of spec that he can't even do that for you.

If it were my car, it would be first of all getting a second opinion. Then it would be measured on a frame machine so that I would know what I was dealing with. But it's your car, so it's up to you.

No, I am not an alignment man. All my knowledge comes from my dad who sold Hunter alignment machines for about 10 years. So if I'm wrong, oh well. I know what caster, camber, toe, and bounce toe are, what 2 wheel, thrust, and 4 wheel alignments are, and how many thousands of dollars these machines are and what all they do, but it's easier for me to draw it out on paper than to try and explain it in words.

[Joe 1320]

Originally posted by MN6WS6

If it were my car, it would be first of all getting a second opinion. Then it would be measured on a frame machine so that I would know what I was dealing with. But it's your car, so it's up to you.

Bingo......

I've seen an alignment done on a car that once it rolled off the rack, you could visually see it wasn't right. I second the second opinion.