Read your link tmbubell. With that and other things I've read, I had just about decided with going with 17" over 18s then I got this from Ford Canada in response to an email i sent them the other day (emphasis mine)...
Hi Keith,
My name is Xxxxxx and I am with the Ford of Canada Customer Relationship Centre.
I had the opportunity to read your email regarding your 2013 Ford Edge Limited.
I appreciate the time you have taken to write us and consider our assistance regarding this matter. First, allow me to congratulate you on your purchase of a new vehicle. I understand that you are planning to replace your vehicle’s rims and tires and would like to know if the 17" rims and tires will meet the safety requirements. Rest assured that I have looked into this for you.
Ford of Canada will not replace factory supplied all-season tires with snow tires, as snow tires are not an orderable option for the vehicle. Vehicle handling characteristics, tire load index and speed rating on non-factory installed snow tires may not be the same as factory supplied all-season tires. Snow tires are meant to be operated during winter conditions and may require a higher cold inflation pressure than all-season tires.
In order to meet the safety requirements, snow tires must be the same size, load index, speed rating as those originally provided by Ford. Use of any tire or wheel not recommended by Ford can affect the safety and performance of your vehicle, which could result in an increased risk of loss of vehicle control, vehicle rollover, personal injury and death. Additionally, the use of non-recommended tires and wheels could cause steering, suspension, axle or transfer case/power transfer unit failure. Please consult your Ford dealer for details.
Thank you for contacting Ford of Canada,
Sounds like a dance around the subject to me. Do snow tires have as high a speed rating as OEM All Seasons? Are they saying I can't put snow tires on the car???!!! What about provinces like Quebec where snow tires are mandatory? What does Ford put on a car that's sold in Quebec in Dec or Jan to make it legal when you drive it off of the lot? Are they saying (last bold portion) that if I put anything other than OEM spec'd tires on the car and then have problems with the 'steering, suspension, axle or transfer case/power transfer unit' that I may have problems with warranty?
I've written back to them asking for clarification and to tell me what winter tires will meet their specs.