On a street grid with almost no grade, the drivetrain is not doing the job most bicycle marketing assumes it is doing. It is not helping you climb. It is setting one comfortable cadence for a two-mile trip, and it is stopping you at eight intersections along the way, which means the parts that matter most are the ones that tolerate repeated starts from a dead stop with a bag of groceries on the rear rack. A careful reader checks the numbers before checking the badge, and the numbers here are simple enough to work out on paper.
Gear inches, and why the flat city narrows the useful range
Gear inches describe how far the bike travels per pedal stroke, expressed as the diameter of a hypothetical direct-drive wheel. Divide the chainring tooth count by the rear cog tooth count and multiply by the wheel diameter in inches. A common cruiser setup, a 44-tooth chainring and an 18-tooth cog on a 26-inch wheel, gives about 64 gear inches. Swap to a 16-tooth cog and you get about 72. Move to a 46-tooth ring with that 16, and you are near 75. Those three numbers cover most single-speed cruisers sold in the last twenty years.
Sixty-four is a pleasant number on flat ground. It starts from a stop without standing on the pedals and it spins out somewhere around twelve to fourteen miles an hour for most riders, which is a reasonable ceiling for a bike with an upright riding position and a headwind coming off open desert. Seventy-five is faster once rolling and noticeably heavier at every green light. If you are stopping every three blocks, the lower number is usually the better trade, and it is a five-dollar cog change either way.
The coaster brake single speed
A coaster brake is a friction brake inside the rear hub, engaged by back-pedaling. It has no cables, no pads to wear against a rim, and nothing exposed to grit blowing across a bike lane. On flat streets it stops a moderate-speed bike adequately, and the Consumer Product Safety Commission is the federal body responsible for the braking performance requirements bicycles must meet before sale, which is part of why these hubs remain common on entry-level cruisers. The limitation worth knowing in advance: you cannot back-pedal to reposition a pedal before starting, and you have one brake rather than two. A front hand brake, if the fork has the mount, solves that for well under fifty dollars installed.
Three speeds and seven speeds inside the hub
An internally geared hub puts a planetary gearset in the rear axle, sealed away from dust. A three-speed hub typically runs roughly 0.73, 1.00, and 1.36 times the direct ratio. Build that around the 64-inch example and you get about 47, 64, and 87 gear inches: one gear for pulling away loaded, one for everything, and one for a tailwind. A seven-speed hub spreads a wider range in closer steps, landing somewhere near 40 at the bottom and just under 100 at the top from the same chainring and cog. Both shift while stopped, which is the single most useful property in stop-and-start riding.
Derailleurs, and what they ask in return
A derailleur moves the chain across a cluster of cogs. A seven-speed freewheel of 14 to 28 teeth behind a 44-tooth ring gives roughly 41 to 82 gear inches, a range close to the internal seven-speed for considerably less money and weight. The cost is exposure and sequence. The mechanism hangs off the frame where a fallen bike lands on it, and it will not shift unless the chain is moving, so a rider who forgets to downshift before a light arrives at the next green in a gear meant for cruising. On flat ground that is an annoyance rather than a real problem, and riders who shift by habit stop noticing it.
After six months in the carport
Desert storage is kinder than humid storage, but time still acts on each system differently. A coaster brake goes dormant well; the grease inside stiffens slightly and frees up within a block. An internally geared hub does the same, with the caveat that its shift cable and the small indicator chain at the axle want a look and a light lubrication before the first ride. A derailleur is the one that shows the layoff, because cable housing collects grit and dried lubricant, and the jockey wheels stiffen. Ten minutes with a rag, fresh chain lube, and a barrel adjuster usually restores it fully.
Check the cog and chainring stamps on any bike you are considering, do the division, and decide whether you want a fixed number, three of them, or seven. On these streets, all three answers work, and the one you maintain is the one that will keep working.