At first glance touring bikes looks just like a racer due to the dropped handlebars. Then you notice the mudguards, the rear carrier, a third chainring, bigger rear sprockets, cantilever brakes, slightly wider tyres … remove or change some of these and what you have is not very different – only the frame must be a bit stiffer and the back wheel stronger, since they need to support the weight of luggage in addition to the rider.
Contrary to what some may allege, those features do not make the touring bike that much slower. Between racing bikes and the sportier touring bike variants, known as audax bikes or fast tourers, such differences virtually disappear.
Compared with the trekking bike or hybrid, the obvious difference is a dropped handlebar. You’ll also get a slightly slimmer tyre (commonly 28 or 32mm) that's more efficient on tarmac but still usable on gravel, an equally stable but often lighter (since more expensive) frame, but same wide-range gears and powerful brakes – although the latter are not quite so easy to operate from dropped handlebars.
Dropped handlebars put the handgrips further from the saddle, bringing a bit more bodyweight over the pedals and slightly reducing wind resistance without even using the dropped part. The riding position is like that of a dropped bar fitness bike, making it easier for you to work a bit harder - which is useful on climbs - whilst the choice of hand positions relieves fatigue over long distances.
Unfortunately, the combination of dropped handlebars with sensible tyres, mudguards and a rear carrier is something the marketing folk can’t quite get their heads around, so touring bikes are rarely flavour of the month.
You’ve got to be well into bikes to appreciate these features, so there isn’t a lot of choice and none at all in the lower price brackets.
In many shops you’ll not find a single tourer on show and you may be persuaded to buy something else. That’s a shame, because this is a tremendously useful and versatile kind of bike. If you’ve room for only one, this bike will haul shopping as well as touring loads, handle mild off-road surfaces as well as tarmac and go almost as fast as a racing bike when stripped for such action!
So much for the racy, audax bike end of the touring bike spectrum. At the other extreme, an expedition tourer may be more akin to a mountain bike. Indeed, early mountain bikes were often fitted with luggage carriers - some also with dropped handlebars - for long trips into remote places on unpaved roads.
Since any kind of bike could be used to explore, just as any kind could be pressed into service for the journey to work, it’s hard to say that such and such isn’t a touring bike. A trekking bike is essentially a flat bar, shorter-distance, more relaxed touring bike variant.