Tires: Upsizing/downsizing options for Altima 2002, northern ontario canada, altima 2002

Question
My 2002 Altima 2.5S (with ABS) currently has Bridgestone 205/65R/16 Turanza all season tires. I am considering buying 4 new winter tires - with separate rims - as I wasn't totally happy with the traction last winter. For one thing, the wheel wells fill up quickly with slush/ice and, secondly, I anticipate much more snow this winter up here in Northern Ontario, Canada.
 Now, my "problem" is that my choice of winter tires is limited to two companies in this size of tire: Bridgestone & Toyo. My dealer says not to put on any other size, whereas, a local tire dealer says that a 225/60R/16 will "work." In fact when I "play around" with the various calculators out there I can get 225/65R/15's to work!
 The big issue for me is the limited choice I have in tire sizes (along with the attendant prices), but am more concerned with saftey/handling/warranty issues, than the overall cost, should I decide to undersize/oversize/zerosize - things I don't pretend to understand at all.
 Thank you,
Alan Wilson
Elliot Lake, ON Canada

Answer
Alan,

When given the opportunity, it is better to use a narrow tire for snow traction - pushes more easily through to the pavement.  Pavement always has better traction than snow.  The exception to this is where the road stays completely snow covered with no chance of getting to the pavement, then wider is better - float on the snow.

Rule of thumb:  If you go wider by 10, go down in aspect ratio by 5.  Example:  P205/65R16 = P195/70R16 = P215/60R16.

The limiting factor is the rim width.  My book is not up to date, but I show Altima's with 16" wheels having 6" wide wheels.  The maximum width you can put on there is 225 - the minimum is 175.  That would seem to be where the one recommendation came from.

The recommendation for the same size is based on the idea that the vehicle manufacturer is in the best position to size the tire for the vehicle and he provides sufficient room in the fender well for this size plus a bit for chains etc.  I think this is a good recommendation as a blanket statement, but presonally, I prefer to juggle the size a bit to get the type of performance I want.

I hope this is enough info to help you make your decision.