There should not be a problem as long as you keep the rolling circumference the same. What size fronts are you keeping on?

I have Michelin latitude 275/40-20 in front, and 315/35-20 in rear. I am ready to purchase the Bridgestone Dueler Sports for the rear. I am not sure if the rolling circumference is the same between the Duelers I want and the latitude's I have now.
Thanks.

There's nothing wrong with going different brands front/back, provided you maintain the proper sizing required by your model. ie: Mine are 285 45 19 back and 255 50 19 front.

Quick formula for getting diameter of different tire sizes:
First # in tire size (I.E. 255) x Second Number in decimal % (I.E. .55 for 55) x 2 + Diameter of Wheel in mm (18" wheels = 25.4mm x 477.2mm = 18") / 25.4mm for inches.

You want to keep these VERY close. I wouldn't stray to far from the front set-up. As you see in earlier excerise, the differing tire sizes front ot back have the same Diameter, thus same circumfrence.

I just scored a nice set of 18" style 57's from Ebay and am putting on 4 Blizzaks to handle the Central Oregon winter. But will put some sporty tires on my 18" Y spokes next spring and have been playing with above formula on different tire sizes to find something close to OEM Diameter to keep the wheel wells semi-filled.
Good luck.

There will be less sizing difference between brands than there would be between a new tyre and an old tyre of the same brand. You have nothing to worry about, the car will comfortably accept a small difference and 2 tyres specified the same will be near as damn it, the same.

Thanks for all of the input. I guess it is time to pull the trigger on these.