When checking tweak on a rubber-tired touring car, using standard rubber tires typically gives non-precise and non-repeatable measurements. Rubber tires are never perfectly rounded, so when checking tweak one tire can lift earlier than another but this does not always indicate a tweaked car. Tire roundness and insert weight is different from one tire to the next.
When checking tweak on a foam-tired touring car, the differences between tires are even greater than with rubber tires. Each foam tire has a different diameter after each run due to tire wear, making it impossible to check for tweak because the tires can give very misleading results. In this case the alu set-up wheels are the best tool for checking tweak.