As Earl implied, people are creatures of habit. However, new habits can always be formed.
Years ago when I wrote for PC&D, I interviewed Chip Lavigne, owner of Mandeville Car Wash in Louisiana. Mandeville was one of first publicized washes operating with flexible service format.
Mandeville is a multiple facilities carwash with express tunnel (ride-though), several islands with
coin-operated vacuums, large gasoline bar, convenience store, boutique gift shop, drive through coffee/food service, three bay full-service oil change facility and gigantic after-care area (detail canopy).
I asked Lavigne what one thing he would do differently as owner. To paraphrase, he said he would personally work the POS for 90 days straight, shaking hands and kissing babies.
Lavigne said he did this for 30 days and it wasn’t nearly long enough to get customers accustomed to him, his people and process.
Another thing to consider is business model. Yours appears to be out-of-step with current patterns and preferences.
For example, most express tunnels don’t need to towel dry or don’t offer it and those offering it don’t charge.
Since most people like ride-through, 20 percent exterior confirms your assessment; people dislike your ride-through for some reason(s).
So, 35 percent exterior on weekends suggests that full-service is too slow on weekends and customers are opting out for express wash or people who wash their cars on weekends like ride-through.
New York is a big place and carwash markets can be worlds apart (i.e. upstate versus Bronx) so I can’t speak to price.
Biggest thing you haven’t mentioned is goal and objective? People who have made the switch usually see 40 percent or more exterior.
What are you trying to accomplish?