I just ordered two tires but only one was sent because the company ran out. Now I have options. I currently ride 28's and wanted to give 25's a try. The front 28 is in pretty good shape and has quite a few miles left on it. The rear is showing much wear (the reason I'm replacing the tires). Well now I can either send the lone 25 back and just place a new order for something different, or I can mix the tire sizes using the good front 28 and the new 25. They are the same tire, just different sizes.

Should I mix or send it back?

If I mix, should I go with the larger tire on the rear or front? I ride 50% nice highway shoulder with a few patches of rocks and debris on the road and 50% city with a few potholes and deep cracks. I only cary about 10 lbs. in a messenger bag and like to go for speed when I can.

What do you think? Mix? Wide Rear/Narrow Front? Narrow Rear/Wide Front?

My bike has a 2.125" wide front and 1.90" rear. Crap...thats the bmx.

On my road bike I was running 700x25 in the front and a 700x23 rear for months without an issue. If anything you'll notice an increase of speed because of less rolling resistance.

I usually have the larger tire up front and the narrower in back (greater traction for stopping and turning, less rolling friction from the rear).

Sheldon Brown (R.I.P.) discusses the issue on his website: https://www.sheldonbrown.com/tires.html about 2/3 of the way down, under 'mixing/matching tires'

I'm not sure why you'd think this is a problem. My tires are always different sizes. Expensive tough tire on the rear and cheap on-clearance-this-month-for-$5 tire on the front.

I would stick your slightly larger tire on the front. You shouldn't have any issues with this. If the 28 has better puncture protection you may want to keep that on the back though. I do presume you bought "better" tires than your current ones. If that is the case keep the 28 on the front and roll the 25 in the back.