I see questions where people want a bike to commute, road ride, and take on trails. Not one bike will do it all. When do I need more than one bike. How many bikes is enough?
If you have n bikes, n+1 bikes is the right amount of bikes to have. ;)
Realistically, I think 2 or 3 is adequate - a cyclocross or non-racing road bike can do the first two tasks (road ride + commute) provided it has rack and fender mounts, and one mountain bike is likely good enough for the trails in one's area (if you go somewhere else where another type of mountain bike would do very well, say a fat bike in the snow versus your hardtail which is adequate for your area's trails or whatever, rent it for the trip). A third would be a winter beater (an old rigid mountain bike, most likely) or something to take to the shady parts of town.
Of course, enthusiasts can always justify more bikes (much like with lots of hobbies).
[There is also the community of monster cross'ers, who build beefed up cross bikes which you can take on lighter trails, so if the trails are light enough, you could do it all with one bike!]
Too many would be when it starts affecting parts of your life which you're not okay with,e.g. too much money in bikes, not enough space, not feeding your kids for a new bike, etc.
Aside from (n+1), the other honest answer is: as many as your spouse will tolerate, often written as (s-1).
At the time I wrote this answer, I had six bikes (two road bikes, one mtb, two folders, one English cruiser). I had met the spousal tolerance factor. After this, I can only replace, not add. So if I really wanted that Brompton, one of the folders had to go. You can click my profile to see what I currently have.
Now, your question doesn't also get to another important question:
- How many bikes can you hide / disguise from your spouse by breaking them into individual components (frame, wheels, etc.). I think I could build another bike or two from spare parts in my garage, but don't tell my spouse.
I won't give my own question the check.
I have a few bikes and I see a bike I want and I am going through the can I justify to myself.
How many is too much?
- If you don't have room to store them safely and sheltered then too many.
- If you are not going to maintain them then it is too many.
- You can't afford it.
When do you need more than one bike?
Range of conditions
A bike can be pure road - speed.
Or road and light trail.
Or heavy trail.
Cannot expect a pure road bike to handle heavy ruff trails.
You don't want to leave your expensive bike locked on the street. Pretty easy to justify a cheap second bike.
Ramble around town, shopping, training, racing, or touring.
Justify your next bike
What type of riding do you want to do that you are just not equipped for? Will you actually use the bike? If you will use the bike and will exercise more then go for it.
Can you upgrade an existing bike to satisfy the need?
Would a second set of wheels let you bridge the gap. Like a set of road wheels for cyclocross.
Is it such a good deal that you could sell it for close to what you paid for it?
For me that is the easy way. Watch for used bikes.
The equipment on a current bike is outdated. It is not worth replacing any major components. Like my cyclocross is not disc. I am going to ride it until it dies but I am not going replace any major components. It takes a really outdated bike to justify retiring a working bike - but if you are just plain not riding it because it is outdated and you would ride a new bike then go for it.
Could be as simple as tired of trading out pedals. I had have mountain I used for walking the dog and actual trail riding. I saw the mountain bike I wanted at great price and just retired the current to dog walker and short city rides with full time flat pedals.
Will it save you money?
Can you avoid paying for park. Gas you don't need to buy for the car. Can you go so far as no car?
Not the same as another bike but a nice set of lights lets you extend a bike from day time use to day and night.
I want a gravel racer for exercise / speed in town but it is not enough different from by cyclocross to justify. And I put new wheels on the cyclocross two years ago and I will never wear them out.
But if you have road bike and if you had mountain bike you would ride just one more day a week then go for it. It does not need to be an expensive bike.
Some times you get first time buyers that want a bike the will do everything. Pick a bike that will do your primary task and don't break the bank. Start with a mid range bike. I see questions of I want in my first time bike and not sure how I will use it and I have a budget of $2000. My reaction is buy an $800 bike. Don't spend $2000+ on bike until you know exactly what you want.
As for a max. Unless you are a competition rider it would be hard to justify more than 5.
My collection and how I justify/use from oldest to newest
- Trek 1500 road
Not much use as it is 7 speed down tube
Currently on loan to a friend riding it to grad school
- Bianchi Cyclross Concept
SPD pedals and 35 mm tires
Was used for training, road, and light trails
Starting racing cyclocross and now this is my racing bike
- Specialized Tricross Singlecross
Used great price No longer primary commuter but a great backup bike
- Salsa Vaya
All round - shopping, leisure, touring, and commute when I can lock inside
If I had to keep only one this would be the bike
- Orbea Lonzo
Single speed mountain with Niner carbon fork and downhill pedals
Walking the dog and knocking around town
Used great price
My 7 speed Bianchi Grizzly just was not hacking it - the Concept was better mountain bike and the Vaya a better shopping bike
- Niner Air Nine Carbon
Single speed mountain with Niner carbon fork, tubeless, and spd pedals
I like single speed and fixed fork for learning technique
The price was so good I could not pass it up
Would sell the Orbea Lonzo but I just put new tubeless wheels on it
Started racing cyclocross and use this as my training bike on flat pedals rather than beat up clip shoes
- A month ago I added a titanium Sala cyclocross that I got used for great price. It quickly took over as my daily commuter. Yes I take a risk that a more expensive bike will be targeted and stolen but I am riding a bike I enjoy (more) and it is easily to turns my commutes into a workout on a nice day. I could live with this my Niner and Concept.
I'd say n (or n + 1) where n is the number of riding styles you are currently and actively pursing is reasonable. The +1 formula is optional for people who race fairly seriously. So if you like to ride cross-country mtn occasionally, but seriously race road and commute, I'd say your n was 3 with the +1 option of an additional road bike for racing. I recently sold a full downhill rig because it hadn't been used in two years and I didn't see myself getting back to shuttle running crowd in my area. n = n - 1 for me. I have a nice full suspension all mountain rig that may go the same way at the end of next summer if it doesn't see any use.
When I started leaning toward a serious collection years ago, I thought an ideal number was 7. I actually had that at one point, but have now realized, having some really nice ride hanging around that I haven't used in two years only depresses me. On the spousal front, it's much easier to justify a new bike when I can claim that I rode every bike I own within the last year. I obtain a brief period of joy every time sell an unused bike (or two) and turn it into a new bike that I will ride.