Interesting. Here are the tire diameters in play:
25.1" for the 165/70-16 emergency spare
25.1" for a Crossfire 225/40-18 front tire
26" for a Crossfire 255/35-19 rear tire

Although this emergency spare has a decal saying "max 50mph" the tire itself has a 'P' speed rating, which means the tire itself is rated for continuous travel at up to 93mph.

I once saw someone who had emergency spares mounted on all 4 wheels. It was a unique look to be sure, so he accomplished his goal of standing out!!