If you’re still on the fence about the validity of performing wheel alignments using strings then it might ease your mind to know that this is the same technique used at the top levels of motorsport including LMP2 as seen here on Jota Sport’s 930kg, 4.2-litre V8 N/A, X-Trac 6-speed sequential ORECA LMP2 race car.
Sure the hardware used is a little more advanced than what we might use at the hobbyist level but the principles behind it are the same. In this case, Jota uses CNC machined setup hubs that sit on top of corner weight scales. This takes away any potential inconsistency that could be caused by the wheel and tire, and with the bodywork removed this also allows easy access for the technician to make adjustments.
The bars that support the strings down each side of the car are also CNC machined and attach to a special fixture that locates directly to the carbon tub at the front and the transaxle at the rear. This takes away the time-consuming job of zeroing the strings before starting a setup. The front fixture also includes a reference plane called ‘Z Zero’ that reference measurements can be taken from to ensure the car is legal.
Having the wheels removed does take away potential inconsistencies as mentioned, but it does also make things a little harder since you do not have the rim to reference. To solve this problem little flags are added to the setup hubs which act as a location to make measurements to the strings. These replicate the diameter of the rims to ensure a realistic measurement.
During the setup procedure, the car is located on a perfectly flat and level setup patch which ensures the measurements are as accurate as possible. This steel plate surface is checked yearly to ensure accuracy and consistency for many aspects of the cars assembly, maintenance and adjustments. Corner weights and camber gauges are zeroed according to this and checked often so that when travelling abroad the team can get as close as possible to a flat surface to work from as possible with a small margin of tolerance allowed and factored into any adjustments the car needs.
The ultimate goal and focus of a dedicated race car at many levels, not just LMP2, is always peak performance rather than the creature comforts and aesthetics that a road car considers more in-depth. In this case, the chassis is so sensitive that the aim is an imbalance of no more than 1 kg across the front axle line and less than 10kg across the rear to ensure even weight distribution and consistent brake performance.
There is no minimum ride height for the car, but instead 25mm skids are fitted which the teams can wear 5mm off during the course of an event, but if any more is measured to be missing the car will be disqualified from the event and as such the height will be adjusted from track to track just as the camber and toe etc is.
Once the car is set up for the track, spares such as the track arms, pushrods and camber shims are also set to match so that in the event a corner of the car is damaged the team can quickly replace everything required knowing the correct setup remains to enable the driver to keep confidence the cars handling and thus remain on pace.