[Mystake]

(11-27-2010, 10:14 AM)SVT-WGN Wrote: I use Michelin X-Ice on all our vehicles over winter. For those that like the look of their aluminum wheels, consider this. The SVT wheels to be installed on SVT-WGN (Focus wagon) next spring are 17". The correct size tire for this rim is 205/45-17 at $148 per tire. Instead over winter, I use a fifteen inch rim with a 195/60R15 tire which cost me $93. Add in the $15 to mount, balance the tire in the fall, and then again to switch back to summer tires in the spring, and considering my previous X-Ice lasted four winters, means my total cost for vanity is $55 (difference in tire price) + (4 years x $15 per changeover x 2 times each year/season) or a total of $175, or more than what a nice aluminum wheel costs on the used market.

Add in the following benefits. A higher profile tire (would we call this Minus-Two?) is better able to cut through the snow (look at military vehicles - none of them use wide, low profile tires) and have more resiliency when hitting a pothole (very low profile tires mean you will inevitably dent your large vanity rims on that very first pothole), not to mention the possible corrosion because of the salt.

My recommendation? Buy the smallest diameter rim that will clear your brakes/rotors and install the highest profile winter tire you can. You will save money, aggravation, and your car will thank you.

Some tire/wheel combinations for the Focus:

18 inch wheels (largest diameter wheels recommended for Focus). I would never run a 35 profile snow tire.
215/35R18 (23.93 inches in diameter)
225/35ZR18 (24.20 inches in diameter) $199 Pilot Sport PS2

17 inch wheels (SVT)
205/45R17 (24.26 inches in diameter) $148 X-Ice $185 Pilot Sport A/S Plus
215/45R17 (24.62 inches in diameter)

16 inch wheels (newer Focus)
195/55R16 (24.44 inches in diameter) $118 X-Ice
205/50R16 (24.07 inches in diameter) $132 X-Ice

15 inch wheels (older Focus)
195/60R15 (24.21 inches in diameter) $93 X-Ice $106 HydroEdge

14 inch wheels (old Escorts, Contour/Mystique)
185/70R14 (24.20 inches in diameter) $82 X-Ice $97 HydroEdge

Finally, may I suggest you test your speedometer for accuracy. Most new speedometers and odometers are accurate. Older vehicles are sometimes as much as 10% out. Use or borrow a GPS. On an empty stretch of highway, set the cruise on your car to exactly 100 km/hr. Then check the speed reading on the GPS. If it also says 100, then just match your existing tire diameter to maintain accuracy. If however, the GPS reads under 100 (usual, rare to read over) note that value.

Use the following formula to determine your optimal tire diameter (works for all speeds):

For example one of my former cars, the GPS read 95 when the speedometer said 100. So plugging these numbers into the above equation (100 divided by 95 times 24.21 inch old tire diameter) gives 25.48 inches for the corrected tire diameter. In this case I would go from the 195/60R15 tire to a 205/65R15 to correct the speed (larger diameter tire). Using an oversize tire like this should fit, but always check.

Better still, go up one size of wheel to a 16" and use a 215/55R16 tire.

The formula to determine overall tire diameter looks like this:

All of that can be summarized with
http://www.miata.net/garage/tirecalc.html