Originally Posted by
Mark
I doubt your 1976 Colt had ABS brakes, traction & stability control features. Radius is just half of diameter. All tire sidewall flex some. Radius may be a good indicator of increased ground clearance & not much more. An increase in tire diameter increases tire circumference. A change in tire circumference changes tire revolutions/mile. Changing revolutions/mile changes your speedometer/odometer readings. All these things are related. That why tire comparison sites are so wonderful. They allow you to match up two tires of different sizes and compare. It allows a person to make a more informed decision. Even with all that information, we aren't looking at all the factors involved with change. For example, increased torque needed to get a larger, heavier tire in motion.
I highly doubt any Tour de France competitor would consider adding wider, heavier tires to his bike in hope of achieving greater racing performance. If I owned a CVT Mirage, I would be even more hesitant of all this (especially if I value my warranty & want to keep my Mirage for a long time).
Adding a substantially larger tire to an over powered sports car or Jeep Wrangler (blessed with clearance) is different than adding somewhat larger tires to relatively low hp economy car. I don't have to list all the possible negative outcomes, because you already did above. I am not being critical of Mirage owners trying different size tires. I just question going overboard on it & ask what are the benefits then?
I think different tire sizes can be explored, but the smallness (size & power) of the car somewhat limits the range of those possibilities. I feel 165/65-14 tires are the perfect size for the Mirage. My only gripe is the lack of tires available on the market. My 1990 Ford Festiva used 145SR12 tires. By comparison, the Mirage tires seem huge! In today's market, the Mirage tires seem tiny compared to everything else. I just accept that as part of the Mirage's charm!
I feel 165-185 wide tires that are within a 3% diameter variance (22"-23" diameter) is a good reference point for those considering other tire sizes. Most tires within this range are not going to have clearance issues, have need of an different rim offset, or create much of an added strain to the powertrain.
If you use those guidelines, 5-6 tire somewhat more popular tire sizes fall within that range. It's just a good starting point for new members. I still like reading/hearing about those who try to go beyond that, too.