If you want to limit the total number of available inventory for a given product line you can do so.

Navigate to the Product Line (PL) in question and set a holdback percentage:

In this example - 50% of the bikes in this product line will be held back when taking online bookings.

This helps you manage any unforeseen circumstances as the day unfolds - late returns, breakages etc.

But of course, it comes at the cost of not maximising your item utilization.