Simplify the following text for a Grade 6 native English-speaking person.
Original: Although Firestone estimates 97 % of the tires were replaced in the 2000 recall concern existed over spare tires that many owners did not think to replace during the 2000 recall .
Simplified: Firestone estimates 97 % of the tires were replaced in the 2000 recall . They are still concerned over spare tires that owners did not think to replace .