One thing that became rapidly obvious looking at a day’s travel time is just how good bicycles are. It ran against my assumptions about horses being an obviously ‘better’ form of transport on the grounds that the horse is doing a lot of work for you. That assumption doesn’t play out for several reasons.
Firstly, from what I’m told, riding a horse is itself quite tiring. A slower horse trained to have a more comfortable gait were used in the past but by their nature they didn’t travel very quickly. The net effect is there are limits to how far you can comfortably travel by horse.
The horse itself has limits on how far it will travel in a day. Horse based distance transport has historically required systems for a regular change of horses. The same limitation applies to coaches. They can go quicker and travel further if there are regular horse changes. Horse drawn wagons heading off over long distances without places to change horses (e.g. 19th century American wagon trains of settlers) went slowly – basically walking speed.
On foot humans and horses are surprisingly well matched and even more so for longer distances. I was sort of aware of this famous (and slightly silly) race in Wales which is a competition between horses and people (https://en.wikipedia.org/wiki/Man_versus_Horse_Marathon ). Over a distance of 35 km (22 miles) the horse usually wins but the times (just over 2 hours usually) are comparable between human and horse.
Humans are quite good at going long distances by foot and over an extended period. When Tolkien sets his main part of adventurers off on foot, it’s not a stupid choice. People can walk great distances and if you don’t have access to a regular change of horses, walking is probably the most reliable way of getting from A to B. A testament to that is the vast network of foot roads established by the Incas up and down the spine of South America. Donkey’s or mules for carrying gear make sense but riding has limitations.
The bicycle though takes that human advantage of bipedalism and puts into work by pedalling. Range and speed increase markedly. I freely confess that my numbers are far from perfect but modern bikes appear to easily match ye olden times horse travel and may exceed it.
The major obstacle to have your party of adventurers hop on a bike to cycle their way to Castle Macguffin is simple: the non-existence of bicycles until the industrial age. I’ll come back to that. What else is there?
Bikes certainly operate a lot better on smooth, level, well maintained roads. Horses (and walking) is less impacted by terrain. However, so long as there is something road-like, a modern bike can cope with rougher roads and dirt paths. What the impact is on distance, speed and fatigue, I don’t know because a lot depends on the terrain.
Carrying gear is an issue as well but I’ve seen bikes with trailers and all sorts of bag carrying schemes (eg https://road.cc/content/buyers-guide/195494-beginners-guide-cycling-luggage-how-carry-stuff-your-bike ). A pack animal can carry more but a cyclist can carry at least as much as a walker and more if they have good equipment.
So the hard limitation is technology. A post-apocalypse is surely perfect for cyclist heroes. There are roads, abandoned bike shops and supermarkets to loot on your way thus saving you the effort of carrying a lot of gear.
A bicycle looks out of place in high fantasy and adding one might seem comical but what are the actual limits? Ancient roads in magically good condition are not uncommon in fantasy (relics of the lost civilisation). Amazingly advanced metal work is practically de rigueur for fantasy. Tolkien’s mithril (super light and strong and non-brittle) would be a perfect material for a bike if it wasn’t for the fact that it is so valuable that you’d need a very, very good bike lock to stop your steed being stolen.
Highly skillful metal workers and cunning but simple mechanism are also hardly forbidden by the standards of high fantasy. It’s aesthetically weird for a magical dwarven smith to craft a bicycle but there’s really nothing there that is out of keeping with the kind of exceptional technology that appears.
However, ‘exceptional technology’ is insufficient. A sustained bike trip needs people along the way who can fix a bent spoke or a twisted wheel. Rubber tyres is a level of material technology that is really out of keeping to a fantasy setting.
And yet…how much of a stretch is it to wave a magical pretext for bicycles to exist in your fantasy world? None at all if we can have sentient harps or walking statues or rings of invisibility. What prevents our fantasy heroes from cycling to Mount Horrible is that bikes just scream “modern” in a way that our fake medieval setting won’t accept.
[Note 1: I am not a cyclist and my bike riding capacity would be best described as ‘marginal’. If I fall through a wardrobe to Narnia, then I’m walking]
[Note 2: I’ve been trying to think of fantasy examples of bike riding and I can think of examples with modern world collides with magical worlds but even then not many. I vaguely recall the kids in Alan Garner’s Weirdstone books riding bikes around Cheshire at some point. Any other examples?]
[Note 3: I should have mentioned Steampunk fantasy obviously. Bicycles fit perfectly into that setting.]