Choosing A Bike
Use-Case and Tire Clearance
When I purchase a new bike, I always start by determining the "use-case"; that is, why am I buying this bike and what features am I looking to have? To put it another way, ask yourself "what do I want to use this bike for?" Is this a 2nd or 3rd bike (or a 25th) being purchased for a specific purpose? Will this be your "dream bike"? I think that folks sometimes feel they can buy a gravel bike that they can use for everything - both road and gravel. While this is true to an extent, a gravel bike with narrow tires will not be as fast and handle as well on the road as a specific road bike, and vice-versa. Of course a gravel bike will do just fine on roads, but if you are looking for a real performance advantage on the road…buy a road bike. Conversely, if you plan to be riding on some really gnarly terrain with rain, mud, and rocks look for a pure gravel bike with clearance for really big tires and progressive geometry…and don't plan on riding such a bike on the road.
I think the biggest driver these days for bike purchases is tire clearance, as in the examples above. Tire clearance affects so much of the bike such as wheelbase, handling, and other factors of bike design. If we had to pick one factor that determines the type of bike, it would be tire clearance. Keep in mind most frames are optimized for a particular size wheel/tire combo. For example, a gravel bike optimized for 40mm tires, will not handle the same with 28mm tires installed. On the other hand, let's take a bike with clearance for up to 35mm tires for which the frame design is optimized for 700c x 28mm tires. Why would a frame be designed like this? Perhaps they intend the rider to use 28-30mm tires with full fenders, hence the extra clearance. So theoretically, you can swap out to 650b wheels and use, say, 42mm tires mounted on the smaller rims. This would give about the same total rim + tire diameter and so the handling would approximate the 700cx 28mm combo. It is a good idea to consider all the possibilities related to both tires and wheels when purchasing a multi-surface drop-bar bike.
In frame design there is always a tradeoff between maximum tire clearance and handling characteristics. I try to determine what size tires the designer intended for the bike - which is not always obvious. Certainly if a particular frame won't handle the maximum tire/wheel size that I intend to use with it, then that frame is no longer a contender. Keep in mind some frames have so much tire clearance that a front derailleur and/or double chainrings will simply not fit - the FD (front derailleur) will hit the rear tire, or the chainstay is too close to the crank to run two chainrings. In other words, some bikes come with a 1x drivetrain installed, but can be converted to 2x later. Other bikes can be only set up 1x. Once I determine my desired tire clearance, the next thing I personally look for is what type of mounting points the bike has. If I am purchasing a bike strictly for fast road riding or racing, I might not expect more than two standard bottle cage mounts on the seat tube and downtube. If I am buying a triathlon or time-trial bike, I might only need a single bottle mount plus a top tube mount or some other integrated hydration system. For any bike I expect to ride in foul weather, I look for full fender mounts front & rear. A bikepacking bike might have three bottle cage mounts, top tube mounts, fork mounts, plus mounts for racks & fenders. These are just a few examples; the idea is to think about what types of mounts you might need to attain your riding goals and use that to help narrow down your options. If you are on the fence, buy the frame with more mounts. Although there is some measurable weight penalty for carrying around mounts you don't use, the amount of extra weight is small.