Hi, yeah same old question, but couldn't find an answer in any of the threads.

I have 205/65R15s, will 215/60R16s be:
a: legal
b: accurately reported by the speedo?

I had thought that 205 and 215 meant the rolling diameter, but different things I've read seem to say otherwise. If it is rolling diameter, going from 205 to 215 would put the speedo out by about 5% by my (quick) calculations?

a. yes, it is legal
b. i don't know :doubt:

Actually, forget it, I don't have time to make an informed decision (ie. within the next few minutes), and realistically I don't need new wheels, would like some mags, but probably should worry about other things.
If you are wondering about the abrupt about-face, I only just found them on ebay, and looked like the best bet I've seen for quite some time, but I haven't had time to fully suss it out.
Ce la vie.

PRE-POST EDIT: Hehe, just checked the auction again, looks like it's gonna do a last minute surge anyway.

205 and 215 (mm)are the width of your tyres, 65r and 60r (mm) are the profile of the your tyres and 15" and 16" are the size of your rims. So the profile + the size of your rims = the rolling diameter (roughly).

And from what i have been told from 2 friends who have both worked in tyres places is that the difference in rolling diameter between 15", 16" and 17" rims hardly changes so there is almost no change in speedo readings.

Going 18" and up does affect your speedo though.

Just to finalise:
So, if you have 15" with 65 profile, the radius of the wheel would be 7.5" + approx 2.5" = 11", and 16" with 60 profile would be 8" + approx 2.4" = 10.4"?
If so, rolling diameter would actually be a little less on the 16", so if anything you'd be going slower than your speedo says?

Any ideas what the range of width is legally for 2nd gens? eg. 195 - 225?

PS. The mags/tryes went for $330 (for 4) in the end. A bit more than I'd spend on a spur of the moment thing I knew little about, but at a different time, and if I was sure they were suitable, not a bad price at all for what they were.

i was under the impression it more worked out like a ratio.

http://www.miata.net/garage/tirecalc.html
using 205 or 215 will be legal as i think the max you can change your diameter is 1 inch and yours comes in at about .7 for 215 and only .2 for 205, % wise only a .8% for 205 or 2.6% for 215.
I think you'd be pretty safe with those tyres :).

Also saying the speedo will be ok on 14/15/16 tires is wrong, it depends on the rubber! And you can have 18's that are correct, just need really really low profile, which are probably illegal lol.

The tyre size change guidelines are different from state to state so check with your motor registry!

Also check with your insurer too because sometimes they can be more strict