Jon's Tech-Talk
Thoughts on High Performance Summer Tire Replacement
(posted 10/25/2014) - Bought a 2014 Ford Focus ST this summer. Really enjoy the car... the OEM 235/40R18 Goodyear Eagle F1 Asymmetric 2 tires, mounted on 5-108 18x8 wheels, provides fantastic traction when putting down 200+ horsepower to the front wheels (ST rated @252 BHP).
Here in the mid-west winter temps arrive beginning in November. I found that summer tires are hazardous when temperatures drop into the 30 F degree range. It's called the 'glass transition' temperature. The summer rated rubber compound turns from grippy to glass-like when it gets cold. The result is that even on cold clear days you've lost most of your traction and the car becomes hazardous to drive. How hazardous? Actual tests indicate 20X increases in stopping distances between winter and summer tires in cold weather!
Most cars come with all-season tires that are fine for non-performance driving demands. The Focus ST is a "hot-hatch" designed to adhere to the road at close to 1G cornering forces -- so the summer tires make sense; in the summer....
But from November through April when average temps are far below the design criteria for summer compounds what is the best solution? One could fit high-performance all-season tires on the OEM 18x8 wheels; but that gives up 20% of what the summer only tire provides in warm weather and 30% of what the winter only tire provides in cold weather. This is why performance oriented drivers call all-seasons 'no-season' tires.
One could buy winter-only tires and mount them on narrower, smaller diameter wheels to get the best possible traction in slush, snow, and ice conditions. The problem with winter only tires is that when temps get above 50 F the rubber compound wears much faster than all-season compounds. I often drive to Texas in the December time-frame and the 2500 mile round trip would produce unacceptable wear in winter-tires.
I chose to mount high-performance all-season tires on my car in November. I bought custom Platinum E-twine 17x7.5" wheels with 225/50ZR17 General G-Max AS-03 tires mounted and balanced, along with new TPMS transponders, -- delivered to my door by UPS through the TireRack.com website. I highly recommend these folks -- they make the whole matching and ordering process painless. My philosophy is that I use the all-seasons till May then put the summer wheel/tire-set back on. I get decent handling for cold weather and the best possible handling for the summer. I also get the best possible tread-wear because I'm using the tire-sets in their best temperature ranges.
An Addendum: Lots of folks worry about the Tire Pressure Monitor Sensors not wirelessly registering themselves with the car's PCM. In my experience the key is to mount the new wheels, make sure they are at the recommended PSI, then take the car out for at least a 20-minute drive at road speeds (50+ MPH sustained). This should result in the new TPMS transponders being detected and auto-registered.
The Ford TPMS reset tool I bought is probably only necessary if there is a problem in auto-registering. I did not need it! Again, my experience is only with my Ford Focus ST (built 8/2014), your mileage may vary.