Here is a general guide to go by but keep in mind that income and expenses vary widely.
https://carwashmag.com/wp-content/uploads/2022/04/2022_self_service_surveyS.pdf
Maybe where you are but depends on local market and there are many variables. We are the most expensive nearby at $3 for 4.6 minutes and many are still $1.50-$2 for four minutes. There is one in the next town up that is $1 for two minutes.
I just ran some numbers and I was slightly wrong. We are down YTD from last year but not much at all. (2.5%) We had some really rainy weather for weeks in April (IIRC) and sales were terrible. We raised our SS prices about three months ago or so and credit card sales are up and cash sales are...
Interesting strategy. Most of the time when looking at washes for sale they have really old equipment (some over 25 years old) so I factor in that extra replacement cost on purchase. The number gets ugly quickly when there are two machines with outdated pay stations so we move on.
Could you reposition them or change the angles of them to be more effective? Are you using a drying agent or something that has it on all wash packages?