Hey guys. I put after market wheels on my truck with 275-55/20 tires. My stock tires were 265-70/17. My question is if I get a flat can I use one of my stocks for an emergency spare? By using a tire size calculator these tires are almost the same height. When my speedo says 100km/hr Im doing 99km/hr. Or will I have to get a 275-55/20 spare?

 

I'm no tire expert, but my understanding is that the overall outside tire diameter is the most important factor for spare tires on vehicles with drive systems that are sensitive to individual wheel RPM. If your current spare is truly very close in diameter then you should be fine to use it.

Not all tires are sized accurately though. You may want to take actual measurements to confirm.

Rob

 

I did this exact tire swap on my last 2009 2wd. Check out this site. http://www.miata.net/garage/tirecalc.html. You will find that those two tire sizes are almost identical. I didn't bother recal my speedo because it was so close. The biggest thing you need to watch for when your changing tires is overall diameter. That is if your concerned about your speedo. Width is important if you are concerned about hitting the knuckle.