The best type of bike for exercise depends what level of rider you are and whether you would rather ride on trails or on the road. There is a type of road bike that is called a “Fitness Bike,” and features a lightweight frame and narrow tires, but do not have a drop handlebar. This may be the best type of bike for someone who intends to ride regularly and strenuously on the roads. If you plan to do a lot of trail riding, the best bike for exercise would probably be a mountain bike. For a person who uses bikes for transportation and exercise, but doesn’t go off-road, the hybrid bike build is a good type of bike.
A plastic garbage bag, or $2 disposable poncho:  Just in case of an unexpected downpour or getting caught out after dark.   More than once, I’ve gone for a ride on a beautiful day with a perfect forecast, not taken a jacket and had the weather go south on me.  Being able to cover up can mean the difference between just mild discomfort or a freezing cold, shivering ride home!

It has some useful information for basic repairs... not so heavy on the maintenance side but there is some in there. The pictures and drawings are in black and white, but mostly visible. Only a few are difficult to see. However, they are in 2-dimensions and they don't show you HOW to do the thing, they only show you the general area and the part you want to manipulate. The phrasing in the instructions can be hard to follow without a good visual reference unless you're already a master bike mechanic (which you aren't if you're thinking about buying this). So, buy this for general reference and rely on Youtube for video. The two together are better than either one alone.
The fabric attachment system is low-tech, but that seems to be helpful, as it can adapt to seat rails of different widths. One fancier option you might see on more expensive seat bags is a quick-release mount that you install under your saddle. But those have a fixed width, and therefore can fit under seats with only those exact specs. Brooks saddles, for example, are too wide for these mounts.
Friction gear systems are a lot simpler to adjust, because the movement of the derailer cable can be modulated as you ride, every time you change the gear- they require less cycle maintenance. Modern index shifting systems are a little more complicated because each ‘click’ must release the exact right amount of cable to allow the derailer to move the correct distance to move the chain from one gear to another. Setting up and adjusting a derailer is not difficult and requires only basic tools, but there is a methodical procedure to follow.
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