For me I think that number is 8. It's actually 7 or maybe even 6 depending on the 29er experiment but I think "8 Is Enough" I get a lot of raised eyebrows over the number of bikes I own but in terms of hobbies I think I get my money's worth. A single snowmobile, boat or motorcycle could easily approach the $8000 I have spent in bikes over the last almost 30 years. The difference is that those toys take gas to have fun and my toys save me gas. If fact, in the last 5 years my bikes have saved me over $2500 in just gas or about $7300 in vehicle miles. Every bike I own that was bought in the last 2 decades has been used or a closeout. My goal is 50% of retail for any bike I buy and getting technology that is 1 year old isn't really the end of the world.
In order of acquisition and the price paid.
Univega Viva Sport: ($405)
Steel, 12 speed, vintage & sentimental.
Used for: general road riding, long trips, commuting, around town, group rides.
Functionally, this is the bike I could give up. Between the steel cyclocross bike and the carbon road bike this bike isn't really needed. Sentimentally I've been riding this bike for all of my bike riding life and it's worth more to me than anybody else. That and I still love to ride it. Participating in a group ride with a 30 year old bike and hanging with the leaders is just fun. I'll probably keep and ride this bike forever.
Bridgstone MB-3 ($800)
Steel, 21 speed, ridged, sentimental & still highly functional.
Used for: foul weather commuting, family rides, errands.
My only mountain bike for about 15 years turned commuter. This bike and I had a deal, I wouldn't do it any permanent damage in return for the same. We've traded scratches but so-far-so-good. It did send me skimming across the pavement a few months ago but I might have been somewhat at fault there. My road rash has almost totally healed and the new pedals should be on my doorstep.
Scott CR1-Comp ($1200)
Carbon fiber, 18 speed, light, & snappy.Used for: fair weather commuting, fast group rides, races and feeling fast. Truth be told, this bike isn't much faster than the Viva Sport...but it feels faster. The light wheels make it accelerate quicker (and decelerate quicker) and make the climbs a little faster (and the descents a little slower). But it sure feels fast. That said, I don't really feel the need for a lighter road bike. Sometimes enough is enough.
GT Sensor 1.0 ($1600)
Full Suspension, 27(ish) speed, Cross Country Cushy & Fun. Used for: trail riding, trail commuting, winter trail commuting.
A full suspension bike opened up a new level of riding on harsh trails. Taking the Bridgstone through the woods now seems a little barbaric. Of course the fenders clattering away don't help that much. The thought behind getting a full suspension bike was it would be easier on the old bones, now I just ride harder. I'm 100% sold on FS technology.
Surly Cross Check($800)
Steel, 24 speed, comfy & versatile.
Used for: road riding, mixed dirt road riding, light trail riding, touring, commuting, racing (for now)
If I had to settle on just one bike I think this would be it. 100 mile road ride, it will do that. Riding through 4" mud, it will do that. Fast cruising down fire roads, it will do that. Blasting down rocky trails, well maybe not blasting. This bike is the proverbial Jack-of-all-trades. It's not a lightweight road bike, it's not a competitive cyclocross bike, it's not a full suspension mountain bike but it can do them all.
GT Sensor 9er Expert($1400)
Full Suspension, 20? Speed, Cross Country, Comfy & ???
Used for: trail riding, trail commuting, winter trail commuting. (sounds familiar)
When you realize that your most fun bike can spend a month in the shop you go kind of crazy, especially when you were starting to ride it more. When you purchase your mountain bike and the 29er craze goes into full swing you have to wonder what you are missing. This is the bike to solve those problems. Meh, I can see the benefits of the 29er but so far I prefer the nimble handling of it's 26" cousin.
Surly Pugsley ($1450)
Fat Tires, 27 speed, Rolls where others can't
Used for: Winter trail commuting where others fail, maybe some beach riding, probably some general trail riding. It seems like everybody that owns a fat bike loves their fat bike. This evidence can't be overlooked. There are also days that I'd love to ride the trails in late winter when they are too soft to ride on a regular mountain bike. I can't say that I'm going to cast my other bikes aside in favor of this one but it does fit into my riding quite nicely.
Cyclocross bike (TBD)
Cabon fiber, 20 speed, light competitive.
Used for: Racing, Training.
The Cross Check will do it but it's not really a race bike. Besides, stripping the fenders, cages, lights and packs and putting them all back is a pain. If cyclocross racing becomes more of a habit this bike is a must. At once a year the Surly will do. But if one of these crossed my path at a price that cant' be beat I would buy it.
Although it may sound like a lot of bikes there are whole categories I haven't included here.
Downhill & Freeride bike: I don't need to pay to take a chairlift to the top of a hill to break bones on the way down. I can break bones under my own power.
All Mountain: I may trade one of my trail bikes for an all mountain at some point.
Hard Tail: For the trails around here I'd rather carry around the suspension. Again, in the future I could trade one of my trail bikes for a lightweight hard tail but it's not on the radar.
Recumbent: Haven't found the interest yet. They just look silly to me. No offense all you bent riders out there.
Folding: If I were going to go this route I'd probably go with a conversion for a full size steel steed. Since I don't travel with my bike it makes no sense now. If I did travel with my bike it would probably be a mountain bike anyway.
City: I live in the country so I don't need a basket.
Single Speed: I use to have a single speed bike...When I was 12. The hills sucked then too.
Fixie: See Single Speed - Except worse.
Internal Gear: So far my derailleur has kept me going through the snow.
Tri-bike: One CF road bike is enough.
BMX, Hybrid, Track Bike, Freeride, Time Trial, Cruiser, Utility....Nah
Antique Bike: Oops, I guess technically I already own one of those even if it isn't functional - 9 is enough?
Awww Heck. I might as well shoot for a perfect 10!