Bikes and panniers are more fluid than, say, a car and a golf bag. It's easy to know if the golf bag will fit in the car, but not always so easy to know if the panniers will fit the bike as readily.

Ankle clearance is the most common problem of all panniers. Space becomes a premium with bigger panniers on a smaller bike, or with people with large feet.

One of the best ways to know beforehand if you'll have the clearance necessary (short of trying it first hand) is to see if there is an overlap between your ankle and where the panniers will sit on your rack. Each of our pannier models has a blueprints page with pannier and hooks dimensions available. Use these to draw the outline of the pannier on a piece of cardboard and tape that cardboard on the side of your rack, as far back as the position of the hooks will allow. Hop on the bike, backpedal and have a friend check to see if there's an overlap.

It's that easy, and very precise too!

If it doesn't fit, what can I do?
The following parameters have most influence on the fit on a bike, in order of importance. Some you can change, other you hardly can:

1. Pannier size: shapes play a big role. When all else fails, resorting to a different shape of pannier may be the only solution.
2. Wheel size: Smaller 26" wheels also make for shorter chainstays thus shortening available space. Of course one can't change the wheel size on his/her bike, but it can bring the question if another bike wouldn't be best suited for the task at hand.
3. Rack type / brand: Some racks sit higher and further than others, allowing you to slide back the panniers and dramatically improve the clearance. This is the easiest fix and it will suffice over 95% of the time.
4. Chainstays length: Touring bikes usually have the longest stays, with racing bikes the shortest and mountain bikes somewhere in the middle. But even then there are lots of variation inside the respective fields. Again, like on point #2, it means changing the whole bike to achieve the goal. Not always easy.
5. Shoe size: It's obvious, bigger feet take more space (can't do much here, eh?)
6. Crankarm length: typical touring cranks are 170mm long while mountain bikes are 175mm. Sometimes, when spacing is a question of very little, changing cranks to shorter ones can just about do it.