Once upon a time a typical tunnel car wash featured 20 feet of drip space. Conveyors ran at a balanced pace to ensure sufficient dwell, drip, and drying times before pushing a vehicle out of the tunnel. Somewhere buried deep on my desk, I’m sure I have some charts referencing obsolete best practices for each aspect. Fortunately, advancements in equipment, chemistry, and computer controls have combined to rewrite those rules. Car wash operators are now able to reclaim some of that expensive real estate in the tunnel known as drip space for other purposes. Some have added additional equipment to replace prep labor or increase chain speed to process more cars. Others have added additional pay wax services or friction polishing modules to deliver a superior value to raise their average ticket or improve customer retention. Unfortunately, there is no such thing as a free lunch. Reducing the amount of drip space in your tunnel will make it more difficult to deliver a dry vehicle. That fact cannot be escaped — period.


Over my career, I’ve witnessed the minimum-drip-space requirement drop from 20, to 15, and, more recently, to 10 feet. Lately I’ve watched tunnels pushing the envelope with as little as 5 feet of this precious commodity. What’s worrisome is that the operators most inclined to throw away the minimum drip space guidelines are basing those decisions on learned experience from past failures. To test that theory, I recently asked one veteran multi-site operator how much drip space they recommend when planning a new tunnel. The answer I got was “the more the better, but it really depends.” The truth is that it does depend on numerous factors specific to every wash that I group into what I refer to as the Three Pillars of Drying. Having spent countless hours with that operator diagnosing drying issues over the years, it’s no wonder that trial and error has taught them a certain degree of confidence that they’ll be able to deliver a dry car with nominal drip space. It’s also true, however, that your business depends on delivering a consistently dry vehicle to your customers, and you’d better understand those factors before eliminating drip space or speeding up the conveyor. So, what are the three pillars of drying? Let’s take a look.

Pillar #1: Drying Begins at The Beginning

Most drying issues — and opportunities to reduce drip space — originate at the beginning of the tunnel. It can be confusing, though. First, you cannot dry a dirty car. Second, you cannot clean a car without an alkaline presoak and sufficient friction. Third, most city water is alkaline at a pH of 7 or above, which is done intentionally to protect pipes. The conundrum is that the process of cleaning raises the alkalinity of the vehicle surface. At the same time, it’s difficult to dry a car unless it enters the final rinse with a slightly acidic pH, ideally 4-5. I’ll explain that in more detail in the next pillar, but for now, trust me, you can’t dry an alkaline car. There are several implications to this balance of pH through the wash process in order to prime the vehicle for effective drying. Most obvious is that you will need to work carefully with your chemical supplier to select the pre-soak, priming, sealing, and wax applications that will produce a slightly acidic surface before entering the final rinse. Less obvious is the role your fresh water supply plays in affecting surface pH. There are tools available: Everything from spot-free reject water to conditioning the pH of water before using it to mix with chemistry are all tools you’ll want in your arsenal before reducing drip space in your tunnel package.

Pillar #2: You Must Rinse the Car Dry

Once you’ve achieved a perfectly clean car entering the final rinse at a slightly acidic pH, it’s time to rinse the car dry. First is a freshwater rinse to remove foam followed by a drying agent application to make the surface of the vehicle “hydrophobic,” which literally means afraid of water. Drying agents promote water to pool and break off the vehicle surface and, when used properly, will leave only residual droplets for your drying system to handle. Too little and water won’t break. Too much and water won’t break — plus you can get spotting. Each manufacturer offers multiple drying agents with recommended concentrations for a reason. Although they all use similar raw materials, differing temperatures, conveyor speeds, water quality, and available drip space will call for different products in their lineup.

Some drying agents promote themselves as both a drying agent and sealer wax in one, and many operators use a single product for both functions. The two products are similar, but I prefer to use a distinct drying agent followed by a separate sealer wax that also enhances sheen. Over the years I’ve also changed my thoughts regarding spot-free water. Today, I only promote the spot-free rinse as a feature in my top wash package, but include it on every wash. Some operators will argue that it’s an unnecessary expense. I consider it a form of insurance that my customer will be satisfied with the finished product for days to come.

Pillar #3: You Can’t Dry with Wet Air

Your air-drying system should be designed to use the driest air possible. This starts by using a rinsing system that doesn’t create mist. For years, zero-degree “rain style” manifolds combined with sufficient drip space and blower inlets pulling from the tunnel exit have delivered dry cars at the highest chain speeds. Enter the current trend — to encroach upon drip space with additional equipment — and you may want to consider a physical barrier such as a wall to ensure mist is not recirculated by the blowers.

The next aspect of perfect drying is the proper positioning of your blowers. Various nozzles and flipping actions are available to direct residual droplets off the car and to the ground without blowing them onto the next car. Equally important though is understanding how to adjust blowers to work in conjunction with one another. Sometimes, moving a blower just a few inches can make a dramatic difference on the finished product.

Drying modules — that use spinning brushes with gentle drying materials that flatten out residual water droplets — have become popular with customers and are a great way to distinguish your top package. These units however are designed to enhance the shine and deliver a towel-dry experience without labor. They are not going to solve an issue with your drying system, so make sure you’re delivering a clean, dry, shiny service before investing in one of these machines.


Drying a car is a delicate recipe involving pH, detergent, equipment, temperature, and more. Never assume what you did at one wash will work at every wash. Adding more of one ingredient won’t normally solve a drying problem. Likewise, removing one ingredient won’t work either. It reminds me of the story of Goldilocks and the Three Bears in that everything has to be “just right.” Work closely with your equipment and chemical suppliers and reach out to other operators. With effort, you will be able to deliver a consistent result every time.

Good luck and good washing.

Anthony Analetto has over 35 years’ experience in the car wash business and is a partner at SONNY’S The Car Wash Factory. Before coming to SONNY’S, Anthony was the director of operations for a 74-location national car wash chain. Anthony can be reached at (800) 327-8723 x 104 or at AAnaletto@SonnysDirect.com.