How important is it that tires match?

[sdifox]

On FWD?
That's not a good idea.
Having no traction to get going is really annoying, and at least you can power out of over steer.
With under steer, you just go straight off the cliff...Especially because the rears will have less traction during a braking maneuver anyway.

Losing your tail is a lot harder to correct. Especially when you are trying to stop.

 

[Rifter]

In a AWD vehicle they must match 100%

In a unlocked(open diffs) 4x4 it doesnt matter as much, they should but not 100%.

In a Locked 4x4 (locked diffs, such as a detroit locker) they must match 100%

In a FWD or RWD front to back matching is not essential unless you push you car to the bitter edge on a daily basis, even then just be aware where the stronger tires are and drive accordingly.

 

[railer]

OP - If your racing your truck around Watkins Glen International Speedway tomorrow, then I would suggest that your front tires match.

If not......keep the used tire on the pass side, and enjoy your life. Buy some ice cream sandwiches tomorrow with the money you saved. I love the mint chocolate chip ones myself.

It makes no difference whether the brands are the same front to back or even side to side. The truck will handle fine, stop fine, manuever fine, etc.

EDIT: And the people that are saying that the tires should or must match, I assume (I hope!) are referring to the size of the tire matching - i.e 275/70R17, and possibly the type of tire (summer, or all season, etc). I assume that your used tire is the same size and type, but just a different brand.