Need sound advice on TIRE UPGRADE!

[Beavertractors]

I had my tires mounted today.You do not have to trim for 265-60-18..2 inches away from front cladding corner.They fill the wheel wells nice.Looks like it should have come with this size,maybe a little more offset on the wheels would look a little bit better. Total price with shipping, mounting,balancing,tire disposal,NY sales tax--$403.24 smooth ride and good looks-- Priceless Just in case they are still on sale at Tire Rack

[Raque Thomas]

The 285/55's are 2.6% too slow - when the speedo reads 60, you are actually going 61.6mph. The stock tire diameter is 29.6", these are 30.3". The 285/60's are 6.4% too slow - when the speedo reads 60, you are actually going 63.8mph. These tires are 31.5" in diameter. Check this site for more info:
http://www.miata.net/garage/tirecalc.html

[Moncha]

There's the Miata tire calculator and a couple of other ones listed in the Web Links Section

[tomdietrying]

Yep, the 285/60/18 changed my speedometer about 4.5 miles at 40 mph. Which means when my speedometer says 40 mph. I'm really traveling about 44-45 mph.

Correct me if I'm wrong, but I think the Nitto 285/60/18s require just a bit of trimming. They are just a hair bigger than the Yokohama AVT 285/60/18s which require no trimming.

Peace.
Tom