Joe wants to support his claim that dirtbike Grayson can be dangerous. He found these sources a June 2020 blog post by 18 who completes competes in dirt by racing a 2018 illustrated article by a retired Doctor Who treated head injuries and athletes a 1990 ad with diagrams from the manufacturer of dirtbike helmets Which ones are expert unbiased and supported claims

Based on the provided information, the expert, unbiased, and supported claims could be inferred from the following sources:

1. The June 2020 blog post by an 18-year-old who competes in dirt bike racing.
2. The 2018 illustrated article by a retired doctor who treated head injuries in athletes.

Both of these sources seem to have relevant expertise or knowledge in the field of dirt bike racing and its associated risks. The blog post by the 18-year-old athlete could provide subjective but experienced insights, while the article by the retired doctor could provide objective information based on their professional experience treating head injuries in athletes.

However, it is important to note that a definitive answer cannot be provided without actually examining the content and context of these sources in detail.