Just bought a used 2003 P5 and, living in Michigan, my thoughts are already turning to winter driving. I have a set of nice 205/60-16 snow tires from my old vehicle with one season on them sitting in my garage. Here's the question: is it at all possible to mount them on the 195/55-16 P5 rims and use them without upsetting the computer and/or speedometer? Thanks in advance for any advice.

 

Your 205/60-16 is a lot taller than the stock tire. Your speedo will be off reading slower than actual.

 

Go to: www.miata.net/garage/tirecalc.html

 

yes it will be SLIGHTLY off, not enough to make enough of a difference tho, and if you take it into a tire shop they can fix that, the tire WILL fit on the rim because they are both 16" tires... just slap'em on and have at it, i'm also a michigander and winters SUCK here, having snow tires helps a ton,

 

your heights is 5mm off, i doubt you will see any difference in your speed, your aspect ratio going from 205 to 195 will make the tire look alot narrow'er, once its mounted.
but, a good investment though for winter. I'm here in Columbus, OH and bought my car this past april, i won't even thinking of taking it over winter with those damn Dunlops, i'm looking into the BF Goodrich Traction T/A's at this moment, but, school, rent, bloody bills.... AHH, its a never ending story. .. the saga still continues..

 

The aspect ratio is the 60 on the snow tire TGC listed. The 205 and 195 is the tread width. So he'd be switching to a taller and wider tire. The stock tire is 195/50R16 not 195/55R16 as mentioned in the initial post. This will make the difference in tire height (diameter) about 51mm or 2". The sidewall would be an inch taller, so the car would be an inch higher off the ground. The extra height would be good for getting that extra clearance, but the width of the wheel may be questionable. Usually, you don't want to go with a tread width more than an inch wider that the wheel. The thread width on a 205 is 8.07".

This increased diameter will create a 8.5% error. If the speedometer is reading at 100kph you'd be travelling at 108.5kph or if reading 60mph actual would be 65.1mph.

Back to the initial post: You could mount them and use them. You shouldn't have any clearance issues. No issues with the computer either, however, the speedo will by off.