OKAY...

Looking for everyone's thoughts and input (and I am comtemplating posting this over at GMI).

I will be taking delivery this week of my Bu' however it will have the 18" wheels on it. Now being that I am up in Canada one of the things I do is put winter tires on (in the winter of course) however I have P225 60R16 winter tires and am looking at buying a set of steelie rims for them so I can just do a quick swap in the winter. (Also looking at buying Heather's rims they are 16's also).

However my past experiences tell me that when you make such a size downgrade it throws off the speedometer....Now I am getting mixed responses from people. Talked to my dealer and he talked to his "service manager" who says "Nope shouldn't make a difference" however I know a lot of guys in the racing field and they are saying it will make a difference.

What are everyone else's thoughts? I don't want to do this if ends up messing up the speedometer.

Anyone got some more detailed insight?

Thanks,

As long as you upsize or downsize by keeping the same width/sidewall ratio, the speedo should be accurate.

I'm not sure about the 18" wheels size, but I know the LS comes with 215/65/16s. If you upsize 1 to 225/60/16, you still have almost the exact same rotating diameter, and your speedo should still be just about dead on (+/- 1mph).

You should be fine becuase the car was made to accomidate 16in to 18in rims. Heck I got 17in rims on my 1997 that originally had 15in rims on it and everything is fine. If you went way over sized then you would probably have problems.

I'm no rocket scientist, but I did spend the night at a Holiday Inn Ex..... nevermind! :D

Most online tire sites will give the number of rotations per mile of any given tire size. Compare the number of rotations per mile of the LTZ tire size vs the tire size you want to use for the winter. Then calculate the percentage of error and see what you get. It may be insignificant.

DOA, use this tire calculater to see the diff in the tires ;) gives you a lot of info and a side by side graph of the tire diameter and widths :D
http://www.miata.net/garage/tirecalc.html

Malo - That is exactly what I needed to see....Thank you very much!

let me know how it works out. I also live in the northeast and although I plan to drive with the 18 s , if I found a set of 16 s local I may grab them for the snow. I had the same tire, but 20 s on my truck and they weren t bad in the snow.

cerbomark - Problem I am having is finding winter steelies in 18" size...that's why I am having to look at 16's....maybe have a look around in your area and see if you can come up with 18 winter steelies.

try you local dealer too, they have people who swap them out when the car is new and the dealer sells them at a fair price.

I have found 2 18" snow tires that will fit the stock rim, one is the Bridgestone Blizzak and the other a Michelin Xice Xi2 (brand new this year). Haven't seen any pricing yet on the Michelin (looks like a better tire), but figure it will be roughly the same as buying 4 rims, 4 tire pressure monitors and 4 new tires...