Strava has great volumes of activity data uploaded by athletes, and should be able to use that data to calculate / predict race results. 

There are some simple online calculators, but not very accurate. Strava might take into consideration the following (but not limited to):

• previous race results
• athlete's recent training volume / mileage, and other parameters of the training quality (speed sessions etc)
• for long distances (e.g a marathon), also percentage of sufficiently long runs 
• athlete's attributes such as gender, age, weight (there's already an existing feature request to sync this), VO2max (dtto)
• and if a prediction turns out to be off, use that to adjust future predictions accordingly 

Athletes should be able to get their predictions for any distance (the feature can include the most usual distances by default but let's not limit to those, people should be able to add custom distances), but also time (e.g. prediction for a 12 mins run for the Cooper test, 1 hr run and such). At the same time, athletes could see a recommended pace for each distance - that's extremely helpful if the athlete plans to race on that distance for the first time.