I just got my 2012 i-Miev and I really like it but I wish it handled as good as my 2002 VW Golf TDI, it feels like a lot of under steer.
So I was looking into options to upgrade the front tires. This thread has some good information, but I want to add my 2 cents, wearing my engineer hat:
Tire width, diameter, wear and pressure being equal, rolling resistance should be within 5% (LRR vs non-LRR). Being in the bone dry part of California, I use heavily worn tires and get great grip and RR.
Wheel weight is also important for ride quality over bumps, energy consumption (range), and handling. I measured the OEM alloy wheels with 30-40% worn Dunlops.
Front 24.7 lbs (calculated 25.1 lbs new)
Rear 28.65 lbs (calculated 29.15 lbs new)
Increasing the rotating inertia (mass) will have a big impact on acceleration, regen deceleration, and a small impact on range in city driving (10-20% energy lost during acceleration and regen deceleration).
The front rear diameter mismatch which causes regen and ASC problems might be correctable with an ECU adaptation. I have a VAGCOM that works great to do all kinds of adaptation on my VW TDI I will try to connect to the obd connector (where is it hidden?) and see if I can do anything other than read codes. Otherwise a MUT3 might solve this issue and allow same size tires or other options than OEM.
I was really interested in 14x5.5 inch Honda Civic HX or Insight wheels but the big problem I also noticed is the strut attachment bracket. If the clearance is only a little too tight, the tabs could be ground down a little with a grinding wheel, or edge bent up to 90 degrees, but this would have to be done carefully in consideration of the structural integrity. Up to a 1/4 inch could be gained by this. Wheel spacers would have to be used bringing out the front tires to a wider track than the steering geometry is designed for, but my gut feeling is that would only reduce grip and scrub the tires in low speed very sharp turns. But the lug bolts would definitely have to be changed to get 10-20mm of spacer... The 14 inch Honda wheel+...tire options are less rotating inertia even if the wheel spaces and lugs add mass overall. The mass near the axle has almost no inertia effect. The prevalence of low profile tires is mostly for marketing and not performance. Notice the Mitsu Mirage is using 14's, also Formula One is holding on to small wheels and big tires for pure performance and efficiency reasons. They might switch to low profile but will take a hit in performance unless they compensate somehow (in wheel motors for example would be good).
So the easiest option which appears to be working with better OEM size front's or 155/60R15.
Looking at the options I found:
OEM front tire size options:
http://www.tirerack.com/tires/TireSearchResults.jsp?width=145%2F&ratio=65&diameter=15
OEM size Dunlop front
http://www.tirerack.com/tires/tires.jsp?tireMake=Dunlop&tireModel=Enasave+01+A%2FS&partnum=465HR5ES01AS&vehicleSearch=false&fromCompare1=yes&tab=Specs
OEM size Conti front, -1 lb, short life rating, same grip rating
http://www.tirerack.com/tires/tires.jsp?tireMake=Continental&tireModel=ContiEcoContact+EP&partnum=465TR5EC&vehicleSearch=false&fromCompare1=yes&tab=Specs
OEM size Yokohama AVID ENVigor front, -1 lb, very long life rating, same grip rating
http://www.tirerack.com/tires/tires.jsp?tireMake=Yokohama&tireModel=AVID+ENVigor+%28H-+or+V-Speed+Rated%29&partnum=465HR5ENV&vehicleSearch=false&fromCompare1=yes&tab=Specs
155/60R15 Kumho Solus KH16
slightly oversize width for OEM wheel (+.5in), good life and very good grip rating, +1 lb
http://www.tirerack.com/tires/tires.jsp?tireMake=Kumho&tireModel=Solus+KH16&partnum=56TR5KH16&vehicleSearch=false&fromCompare1=yes&tab=Specs
155/60R15 ContiProContact
slightly oversize width for OEM wheel (+.5in), good life and very good grip rating, +1 lb
http://www.tirerack.com/tires/tires.jsp?tireMake=Continental&tireModel=ContiProContact&partnum=56TR5CPC&vehicleSearch=false&fromCompare1=yes&tab=Specs
Is 155 safe on a 15x4 inch rim?
Looking here and putting the closest size 15x5, then subtracting 25mm (5in to 4in):
http://www.tyresizecalculator.com/tyre-wheel-calculators/tyre-size-for-rim-size-width-calculator
Minimum
tyre width 155 -25 = 130
Ideal
tyre width 165 to 175 ... 140 to 150
Maximum
tyre width 185 -25 = 160
155 is not unsafe but wear might be less than ideal.