This is one of those things - you will either know immediately what we're talking about here, or you won't care!
It all really depends on how much space you have relative to your inventory size.
- More bikes than space - leading to piles or stacks of bikes. Hence "back of pile" problem.
- Plenty of space - meaning you can 'pick out' individual bikes.
'Piles of bikes' kind of shop
Take a look at this image, does it look familiar?
If this looks at all familiar then you will understand this statement:
"I have so many bikes I would never dream of searching through piles of bike just to find a particular one. I just need to know I have enough of that kind of bike to take the booking. I then give the customer the first from the pile."
In which case you will want to make use of the powerful BRM feature: 'GBAL'; Generic Book', Allocate Later.
'Neatly racked / accessible bikes' kind of store
If however you are spoilt for space relative to your inventory size you may be more familiar with this kind of thing:
You can pick out individual bikes.
This is definitely easier to handle. Customer books. Allocate an actual bike. Give to the customer, Track that bike.