Bikes
are pretty common in Guatemala and cycling is a popular sport, so you'll be well received and should be able to find a repair shop in most towns. Though cycling is the most exhilarating way to see Guatemala, the country is very mountainous and roads are poor. Most buses will carry bikes on the roof if it all gets a bit too much. You can rent
mountain bikes
in Antigua and Panajachel: see the relevant listings.
Motorbikes
can also be an excellent way of getting around and since many locals ride them it's not too hard to locate parts and expertise. There are rental outlets in Guatemala City, Panajachel and Antigua, charging around US$25 a day or US$120 for a week.