So what would be the difference between the Focus and the Mazda 3? Both use the same engine(s), and I'm wondering if they share the chasis? CR has given the Mazda 3 high marks. I like the styling of the 3 5-door; looks better (to me) than the 4 door.

 

There's no relationship between the Mazda3 and the U.S. market Focus. The Mazda3 shares a platform with the current European Focus and small Volvos, but Ford North America opted out of that project because of the expense.

The engines are related, but here again the Mazda gets VVT while the Fords don't. So the horsepower rating is higher in the Mazda. That said, the Focus ST engine felt better to me than the Mazda3s engine, stronger midrange and more character somehow.

The Focus isn't priced far below the Mazda3, but tends to carry a $2,500 rebate and sell at a larger discount. So you'll pay much less for the Ford.

You can compare these with and most other cars here:

TrueDelta vehicle price comparisons