If testicles are exposed to trauma or biking will infertility follow?

Possibly. Severe damage or highly stressful training certainly could cause fertility problems from stress or damage, but this is not common. Fertility problems would only follow severe stress like training for a major sporting event. Routine bike riding is not a problem.
Uncommon. If there is trauma to both testicles and the trauma is severe, then sperm counts may be decreased. Although cycling more than 50 miles per week has an association with lower sperm counts, it is certainly not the norm. Long distance cycling is the only exercise that has been shown have an effect on sperm counts.