Intended Usage
When living in a van, I primarily intend to use bike(s) to access distant climbs, run errands, and for low-impact recovery excersize between hard climbs. I plan to live and ride in variety of locations, ranging from off-road places (Moab slick rock or South Platte), to suburban places (e.g., Squamish, BC or Boulder, CO).
I do not plan To do: competitive racing, uberlong tours, or aggressive downhilling.
Bike preferences
I have tried to list my general bike preferences, in order of high to low:
1. Off-road worthy tires / low risk of flat tires
2. Low stress on back and forearms
3. Energy efficient (but do not require specialized bike shoes / clothing)
4. Compact (easily stored)
5. Low cost
6. Low maintenance
Specific Questions
1. Better to have a quiver of 2 more specialized bikes or 1 all-around compromise?
2. What "type" of bikes do you recommend?
3. What are the best online review sites for the types of bikes you recommend?
4. Are there an specific brands or models that you would recommend?
To answer your specific questions:
1. Space is at a premium for you. While specialized bikes are awesome if you're actively pursuing a particular sport (mountain bikes aren't a first choice to cycle a hundred km on paved roads, road bikes aren't going to handle serious off-roading with 2+ ft drops very well), most bikes are pretty general purpose. I think you would be far better off getting a single bike that does most of what you want.
2. You've said the following are important to you:
a. Off-road worthy tires / low risk of flat tires
Generally speaking, the bigger (wider) the tires you get the lower pressure you can run them at. Lower pressures mean you get better grip going around corners and they give a softer ride (acting like a suspension). Lower pressure tires also tend to be less likely to puncture. There's a trade-off though. Big, wide mountain bike tires are heavier. You'll feel that weight every time you accelerate and every time you climb a hill.
Tires with an aggressive, knobby tread pattern will dig in really well to mud, snow, and sand off-road. They suck on the road though . . . they not only slow you down (you will have to pedal harder to go the same speed), but you'll find that the knobs actually cause the tire to squirm and give you less grip when cornering on a hard surface.
I've found that a 32mm tire with a bit of tread pattern on a 700C wheel is a decent compromise . . . it works well for hard packed off-road trails and singletrack, as well as on the road. You can also get 1.5 inch tires with minimal tread patterns for the typical 26 inch mountain bike wheels that work about as well.
b. Low stress on back and forearms
This depends on your flexibility and how comfortable you are with a bike, how you ride, and how you set it up. I can ride my road bike in a very bent over position for five or six hours well over a hundred km and be pretty comfy. My wife would be miserable on a similar setup after an hour.
c. Energy efficient (but do not require specialized bike shoes / clothing)
You can put regular flat pedals (better are studded downhill type pedals - your feet don't slide around much, but you can wear any shoes with them) on any bike. Efficiency comes from weight and aerodynamics. You are the least aerodynamic part of a bike, so wearing tight clothing, and hunching down (like in the drops of a road bike) helps this the most. Weight is really only a big difference when you're going up a hill.
d. Compact (easily stored)
Pretty much all bikes come with QRs these days, so it's not too bad to pop off the front and rear wheel if you really need to jam everything down to save space. If you're really worried about this you could look into folding bikes which are designed to be space savers first and all other bike related stuff second.
e. Low cost
A decent bike is going to run you in the 4-800$ range new. If you're willing to shop for a used one you could probably get one for half that. Under that range you tend to get bikes that are poorly built, way too heavy, and use crappy components that will break and be hard to keep adjusted.
f. Low maintenance
Bikes all require maintenance. The type of maintenance that's required really have more to do with how and where you ride as the bike you get. If you ride in the wet and the mud, if you grind the pedals rather than spin, if you regularly cross-chain, if you land hard after potholes and bumps vs absorbing the impact in your knees and arms . . . these are the things that will determine how long you can go between maintenance. Fortunately most bike maintenance is pretty simple (grease, lube, replace chain / true wheels) and can be done on your own without too many special tools.
If you're planning on riding mostly flat packed trails without jumps off-road, but will do a fair amount of riding around paved areas too . . . my suggestion would be to look into hybrid type bikes. The Giant Escape, Specialized Sirrus, Trek FX are all in this category. They have eyelets for mounting a rack (pretty handy if you ever need to carry stuff) and fenders (if you decide to ride in rain regularly). They have wider tires (32 mm) with a little tread on them that will be heavier than road tires, but lighter than mountain bike tires. They don't have suspension, which is a big bonus . . . cheap suspensions suck and are heavy, good suspensions are expensive and only really needed if you're doing very aggressive off-road trials with jumps/drops. This is a pretty good all-rounder.
Other styles I'd consider based on what you've said:
- Cyclocross bike
- Hardtail mountain bike (26 or 29er)
3. I don't really use any specific single site. Once you pick a type of bike, just google around for reviews and comparisons of the most popular models in that style.
4. Any of the big bike brands should be fine. Giant, Jamis, Specialized, Trek, Cannondale, Fuji, etc.