“What are the formulas….to evaluate a prospective car wash site and an existing car wash site?”
Analogue-based approach uses performance of existing sites to evaluate prospective ones. Example is checklist method used by OEM’s to develop pro forma for quotations. Some are online, free. Issue - most OEM models haven’t been updated for over a decade.
Gravity model (retail gravitation) predicts share of customers that a site attracts or probability of patronage as function of distance to customers and competing sites. Requires statistical knowledge or commercial service.
Discriminate analysis is another method for site location. Here, technique is to identify those variables that best explain the difference between pre-selected groups of stores. Some OEM’s have models. Issue – models haven’t been update for decades. However, DIY is possible.
Spatial analysis is another approach where mathematical model and gravity model are combined. Very complicated, much more expensive than gravity model.
Another approach is intuition or as Earl described “seat-of-the-pants.”
As Earl infers, analysis of demand/supply balance would be incomplete without qualitative assessment as reasonableness check of the conclusion. Issue – seat-of-the-pants judgment takes years of experience just like modeling does.
This is why it is unwise to rely on only one simple formula (i.e. capture rate) to judge site location.