According to Consumer Reports, in their MS review, with the 21" tires the car stopped quicker and handled better but the ride was less comfortable. One of the reviewers specifically said that if he bought a MS he would not get the 21" tires. Why?! The biggest advantage of larger bicycle tires (29") is a smoother ride on rough surfaces due to theit larger circumference. NOTE: I am posting this in the MX Forum because I think that it is an issue that people who are configuring their cars might want to be aware of.