How many bikes is it right to own?

In general, if you have somebody else in the house who will question whether you need another bike, then it as well to go into the relationship with a sufficient number that extra ones can pass unnoticed. It helps if you stick to one or two basic colour schemes. If you have 10 black bikes and add a yellow one, it will stand out. If you have 4 black bikes and add another black one, you can probably bluff it out.

In the absence of domestic constraints, the total number will depend on which types of riding you do. For example, if you ride exclusively for the purpose of track racing you probably only need five bikes:

1: Race sprint bike
2: Race pursuit bike
3: Track training bike
4: Summer road bike (can also be used on the rollers for warm ups)
5: Winter road bike

Not everybody is so narrowly focused, though, so you might need to add

6: Road race bike
7: Road TT bike

and then there's the winter to think about

8: CX bike
9: Second CX bike for swaps

but if you're going to ride CX, you might as well do some MTB races for skills improvement

10: XC Race MTB
11: XC Training MTB

That was fun, but now there are other challenges opening up

12: Full-Sus enduro bike
13: SS MTB

And you SS MTB is nice, but it's not quite right on the local six pack, so

14: Dirt jump bike

And you did OK in the MTB class at the BMX track, but those little wheeled bikes seem to be even better

15: BMX race bike
16: BMX jump bike

but your BMX jump bike is good on the stairs and rails, but there are things in the urban landscape you could session if you only had a

17: 20" trials bike

which is all very well, but that hippity hoppity stuff doesn't really flow, so it's not helping you MTB riding as much as it should, so maybe what you need is

18: 26" trials bike

Now that you're going out and playing on natural stuff, picking lines that flow together, perhaps you need to up the ante by hitting them faster

19: Freeride bike

Of course, if you're going to go fast, you have to go faster than everybody else, which means racing

20: DH race bike

and there's no pointing driving all that way to races and then not competing in all the races

21: BSX/4X bike

Obviously, I've pared the collection down to the bare essentials by sticking to sports use and eliminating spares except for CX. Some people also think they are missing out on the full experience if they don't also have a tandem or three

22: shopping bike, probably a flat bar porteur
23: touring bike (expedition)
24: touring bike (audax)
25: recumbulent
26: polo bike
27: some sort of cargo bike
28: grass track bike
29: speedway bike
30: fixed road bike
31: cycle-ball bike
32: acrobatic bike
33: stayer bike
34: 6-day/madison bike
35: fixed TT bike
36: hill climb bike (fixed)
37: hill climb bike (geared)
38: spring classics bike
39: medium gear fixed TT bike
40: "Old Skool" legal TT bike
41: roller racing bike
42: NJS keirin bike, but only if you qualify