Wheel Alignment Q&A

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Wheel Mounted vs. Chassis Mounted Lasers – Which is best?

“Best” can be an opinion. If the question were phrased “Which is better for accuracy?”, the chassis mounted laser is the answer. There are two reasons for this. First, the wheel mounted laser is prone to mounting inaccuracies. Even if the hub or spindle adapter is perfect, it’s quite easy to have a burr on the hub or spindle face. For example, a simple piece of silicone .010” thick left on the rear hub face will throw the laser off .332” by the time it reaches the leading edge of the front tire. (120”, based on a 105” wheel base. Math: .010” at 3.5” = .16 degrees; .16 degrees at 119” = .332”) With a chassis mounted laser and wheel fixtures, the fixture can be off, but the laser will not be. For example, if the wheel fixture is mounted with the same .010” piece of silicone under it, that wheel will be off .078”, a lot for sure, but much less than .332”. And only that wheel will be off, because the chassis is the master.

Second, when we mount the laser to the wheel, that wheel now becomes the “master” reference point. To use this method accurately, you first must verify axle tube straightness, before checking rear end placement or wheel alignment. This is true with Real Square RSX systems and all other wheel mounted laser systems. When we mount the laser to the chassis, we’re able to measure axle tube straightness, as well as rear end placement and rear to front tire alignment simultaneously. This saves lots of time. With a chassis mounted laser, the chassis centerline or frame rail (or whatever points you choose) become the master reference points.

Real Square chassis mounted lasers are adjustable. This allows the user to tune the laser to the master reference points (two points on the chassis). Having adjustable lasers eliminate the possibility of a laser being “out of calibration”.

Mounting the lasers to the chassis also enables the user to make suspension adjustments and read the changes instantly. For example, if you decide to adjust a trailing arm or panhard bar, you can watch the rear end location change as you turn the tubes. Your adjustment moves the chassis, which has the lasers attached to it. Once you square the lasers to the chassis, you can make any adjustment to the suspension and the lasers stay square.

It is true with wheel mounted lasers, the further you project the laser, the more accuracy you gain. However, if your mounting surface and adapters are not perfect, you gain more inaccuracy as well.