okay, this is probabaly a stupid question, but I just switched from 215/55/16's to 225/50/16's (Dunlop SP5000's... so far VERY nice).... should there be any miscalculation with my speedometer?

Thanks in advance,
Randy

 

You lost around 0.40" in overall tire/rim diameter, which will equate to a 1.8% decrease in Speedo reading - you'll see 60 mph on the speedo when the car is actually going 58.9 mph (assuming your speedo is accurate to begin with)

1 mph difference isn't too much to worry about.

 

check out this spreadsheet:

www.glue.umd.edu/~nauman/tire.xls

 

Also try these:
http://www.miata.net/garage/tirecalc.html
http://members.aol.com/agspeed/tiresize.htm

 

COOL... Thanks for the info guys...

-Randy