How many cars can you actually take in a day?
Four lifts and three techs doesn't mean what the schedule assumes it means, which is why the same book produces a calm Tuesday and a disastrous Wednesday.
Bays are not capacity
The natural way to book is against physical space. Four lifts, so four cars at a time, so however many that works out to across a day.
The flaw shows up the moment a car occupies a lift without being worked on. Waiting on approval, waiting on a part, waiting on a customer to call back. That lift is unavailable and no capacity calculation accounts for it.
A shop with four lifts where two routinely hold cars waiting on something has two lifts of real capacity, and a schedule built on four.
Hours aren't capacity either
The next attempt is booking against available labor hours. Three techs, eight hours, twenty-four hours of capacity, book to about eighty percent.
Better, and still optimistic, because it assumes hours are interchangeable. They aren't. A tech who does the diagnostic work is a different constraint from one doing brakes and tires, and booking four diagnostics into a day with one diagnostician creates a queue no amount of total hours fixes.
It also ignores that the advisor is a constraint. There's a number of estimates one person can write properly in a day, and past it the estimates get thin and approval rates fall.
Find your actual constraint
Every shop has one thing that runs out first. Worth knowing which, because adding anything else is wasted money.
- Diagnostic capacity. One or two people can do the hard jobs and everything queues behind them.
- Advisor throughput. Cars sit written-up but unquoted, or estimates go out thin because there wasn't time.
- Lift availability , genuinely, once you subtract the ones holding waiting cars.
- Parts turnaround. Work is approved and nothing can proceed.
- Alignment rack or another single piece of equipment that a third of jobs pass through.
The test that finds it
On your worst day in the next fortnight, at the moment it feels most out of control, write down what everyone is waiting for. Not what they're doing. What they're waiting for.
That's your constraint, and it's frequently not what the owner would have guessed. Shops that were sure they needed another lift often find three of four lifts are fine and the whole day is queued behind one person or one piece of equipment.
Mixing job types is what makes a day survivable
A day of five diagnostics is fragile. Any one of them running long takes the day with it, and they all compete for the same person.
A day mixing two diagnostics with a set of known-duration jobs absorbs a problem. When the hard job goes wrong, the rest of the shop keeps moving.
This is a booking decision, and it can only be made if you know what's coming in before it arrives. A slot that says "9am, Johnson" tells you nothing. One that says a 2016 crossover with an intermittent electrical fault tells you what kind of day you've booked.
Leave a gap on purpose
A fully booked day has no capacity to absorb the car that turns out to need three hours more than quoted, and there's one of those most days.
Booking to about eighty percent feels like leaving money on the table and generally isn't. The gap absorbs overruns, takes the emergency from a good customer, and means the shop finishes on time rather than pushing two jobs into tomorrow and starting the next day already behind.
The alternative is a book that looks full and a shop permanently one day in arrears, which is worse for everyone and shows up as overtime.
Adding capacity in the wrong place makes things worse
This is the part that costs real money. A shop that feels stretched buys another lift, or hires another general tech, and six months later feels exactly as stretched with higher fixed costs.
It happens because capacity added anywhere except the constraint just moves the queue. Another lift in a shop whose real limit is diagnostic time means more cars waiting in more places. Another general tech in a shop limited by advisor throughput means more inspections completed and more cars sitting written-up but unquoted.
Worse, the new capacity often makes the constraint tighter. More cars flowing in means more estimates to write, which is exactly what the advisor didn't have time for.
Before adding anything, be able to say in one sentence what runs out first and how the purchase relieves it. If that sentence is hard to write, the purchase is probably wrong.
The number worth tracking
Not car count. Hours actually billed against hours available, and separately, how much lift time went to cars that weren't being worked on.
The second number is the one nobody has and it's usually the one with the most room in it. Fixing that is capacity you already own and are paying for.