Full-length mudguards are commonly referred to as traditional mudguards, because they’ve been around for many, many years. They are most often a permanent fixture on touring bikes. Due to their length and sides, they cover a large percentage of both wheels and provide the best protection from spray generated by the wheels.
Some full-length mudguards are longer than others. Some have a large rubber flap on the end of the front mudguard. The longer front mudguards really help to stop your feet from getting soaked through. There's a surprising amount of spray kicked up by the front wheel and your feet are right in the firing line. The longer the front mudguard, the more chance of your feet staying dry. Having a long rear mudguard will keep spray from hitting the person following behind you when you're riding in a group too.
The other advantage of these mudguards is that they offer the most protection to the bicycle. They keep all the water and mud away from the rim brake callipers (if your bike has them), which really don't like being dowsed in gritty water, and it's the same for the front derailleur. They also keep water away from a saddle bag and rear light that you might have attached to the saddle/seatpost, so that's another plus for mudguards.
Full-length mudguards are very sturdy. They mount to your frame at the brake callipers, eyelets at the dropouts, and to the chainstay bridge behind the bottom bracket. They can take a bit of time to set up, but once in place they will survive a lot of abuse.
In order to fit full-length mudguards you need a frame with enough clearance under the brakes (if your bike has rim brakes rather than disc brakes) and behind the seat tube. That means the chainstays are a bit longer, lengthening the wheelbase.
If your bike has rim brakes, you’ll usually need long-reach brake callipers, especially if you want to use mudguards with tyres that are 25mm or larger.
The fact that full-length mudguards can only be fitted to frames with the necessary mounts and clearance does limit them, but there are plenty of bikes designed to accept them. Most common are those that fall into the touring/Audax category, with a variety of frame materials including the most common: steel, titanium and alloy. It’s also possible to buy a carbon fibre frame with the necessary eyelets and clearance for these mudguards.
> Check out 11 of the best mudguard-compatible carbon fibre road bikes
Not everyone wants, or has space/money for a second bike built specifically to take mudguards. Luckily, bicycle designers have cottoned on to this and many regular road bikes come with concealed mudguard mounts. Without mudguards a bike like this looks like any regular road racing bike, but look close enough and you'll find mounts that allow it to be a mudguard-equipped winter bike.
The Canyon Inflite, Grizl and Grail also have unique mudguard mounts and Canyon have designed their own mudguards, made by SKS, to be compatible with these mounts, so there's plenty of choice if you look around.