Weighting during alignment

[D-O]

Now that the vincebar and skins are in I need to have the car aligned. I see that the TIS calls for 68 kg in each front seat, 14 kg in the trunk, and a full tank of gas. Is this just BMW's best guess on the average load the car will carry, or is there more to it than that?

I figured I would just put my weight in the driver's front seat, have a half tank of gas, and skip the rest of the weight. Am I outsmarting myself?

Jesse

[Tbonem3]

Your weight and a half tank sounds right to me, unless you often carry other weight in the car? Most alignments don't have any weight in the car besides gas.

It's not a huge deal. You're not squeezing every tenth out to win races and put food on the table.

[01SG]

I think modern alignment racks can compensate for the ballast. However, I am doing my own string alignments, and in that case I followed the weighting procedure.

[discoelk]

It looks like you're in the Atlanta area. GTE, in Chamblee, will sit you in the car while they do the alignment. Arguably no better place in the area to get one anyway. They know these cars well and pricing is very reasonable.

[Casa de Mesa]

If you can put weight in how the car is normally driven, do so. If you normally carry a passenger, plus luggage, BMW tries to mimic your car's normal state when doing alignments. But as Tbone said, it's not a huge deal if you can't do it.

[Arith2]

Weight in the front seat and half a tank sound like the most accurate way to do it. If I know customers driving conditions I'd try to mimic them. No weight is not going to mess up your alignment though. Unless you have something readily available to weigh it down, don't go out of your way. Suspension all stock?

[George Hill]

*Edit, I'm rewording this.... The answer to this question depends on whether you are you using BMWs or CUSTOM specs.

[D-O]

It looks like you're in the Atlanta area. GTE, in Chamblee, will sit you in the car while they do the alignment. Arguably no better place in the area to get one anyway. They know these cars well and pricing is very reasonable.

I have heard good things about them, but I have access to an alignment machine and will be doing it myself (with a little supervision).

Weight in the front seat and half a tank sound like the most accurate way to do it. If I know customers driving conditions I'd try to mimic them. No weight is not going to mess up your alignment though. Unless you have something readily available to weigh it down, don't go out of your way. Suspension all stock?

I am on coilovers. Just a little lower than stock (13.5" / 13")

*Edit, I'm rewording this.... The answer to this question depends on whether you are you using BMWs or CUSTOM specs.

I am planning on going with the BMW recommended specs for now. Please elaborate.

[George Hill]

I am planning on going with the BMW recommended specs for now. Please elaborate.

Weighting the cars is to make sure that every car is exactly the same. BMW doesn't weight cars to simulate the drivers use, they weight them to make them all the same ride height. All cars have varying ride heights, that just how it is, so if you align all cars to the same specs at various heights then make the ride height the same now those cars will have a different alignment from each other and thus may drive or wear tires differently.

Depending on your alignment machine, when you set it up, there will be a ride height spec. You will add weight to the car to achieve the ride height in the spec and then align it to BMWs numbers.

A very general example would be car A at 13.5" and B at 13" if you set both of those cars to -1.5* and then lower car A to 13" it will now have a different camber number than car B at 13". BUT if you weight car A and its now 13" and set both cars to -1.5* they will be the same. That's why BMW weights cars.

*Also note that when I was doing alignments we just about never get the rear camber on E46 M3s to come into spec and so we would overweight them by 5mm and that would allow the camber to come in.

[Arith2]

*Also note that when I was doing alignments we just about never get the rear camber on E46 M3s to come into spec and so we would overweight them by 5mm and that would allow the camber to come in.

I have this problem with mine. Even with Eibach Sport springs it sits at only 1 degree of camber. The trunk is fiberglass, the muffler weighs 11.2 lbs and I removed all the carpet and spare kit nonsense so there's even less weight.

[George Hill]

I have this problem with mine. Even with Eibach Sport springs it sits at only 1 degree of camber. The trunk is fiberglass, the muffler weighs 11.2 lbs and I removed all the carpet and spare kit nonsense so there's even less weight.

Are you aligning to BMW specs and using their ride height spec? If you aren't setting the car to ride the ride height you might as well be using your own numbers.

Personally for stock street cars I use BMW, then lowered cars I use Dinan specs and racecars are 100% dependent on the car.

[Arith2]

Are you aligning to BMW specs and using their ride height spec? If you aren't setting the car to ride the ride height you might as well be using your own numbers.

Personally for stock street cars I use BMW, then lowered cars I use Dinan specs and racecars are 100% dependent on the car.

I can't remember ride height because it's been a while but I'll have to use that since it does seem reasonable. Typically, where I'm at, my demographic is not the one for E46s but lame Z cars and M8s. We've had more M8s in the shop in the past month than all M3s and M5s, to include PDIs, combined.

[George Hill]

I can't remember ride height because it's been a while but I'll have to use that since it does seem reasonable. Typically, where I'm at, my demographic is not the one for E46s but lame Z cars and M8s. We've had more M8s in the shop in the past month than all M3s and M5s, to include PDIs, combined.

My recommendations are not M3 specific, it's what I would do for any BMW.

[bigjae46]

If you ever take corner weights with and without a driver, you're talking about 2% to 4% difference in weight on a particular corner. Also, if you slide the seat forward and back, you will get different weight distribution. On my car, I saw increases of LF - 1.87%, RF - 1.53%, LR - 3.4% and RR - .1%. Keep in mind, my car weights 2600 lbs. On a street car, these increases will be much less on a % basis. So I don't think weighting the car makes much of a difference for the alignment and handling unless it is for performance reasons and the car is significantly lighter.

Now that my car is driven at 2900 lbs with driver and fuel, the car handles significantly worse with a passenger and is much more sensitive to the alignment being off.

[01SG]

I see that the TIS calls for 68 kg in each front seat, 14 kg in the trunk

Are you sure that applied to M cars? I have not been able to check for the e46, but this TIS PDF for the E36/e38/e39 says that there is an exception to weighing cars with the M suspension. It says it is not required except as needed to level ride height.

Just to reiterate what was well explained above, ride height is the key. I experimented myself on my e36. First I followed the Bentley procedure of adding the full 500 pound ballast. That did not come out right. Then I aligned it with no weight at all. Still off. Finally, I used only as much weight as was needed to level the ride height to within 1mm, which was three sandbags over the driver side rear. That showed my camber was uneven by .3 degrees. It had read even without weight. That alignment came out perfect.

With all the weight, you will have too much camber, and it will be uneven. Without the weight, it will be too little, and it will be uneven. With just enough weight in the right place, I got excellent results. This is essential for anyone trying a string alignment.