The Definitive CR-Z Tire Size Guide
Disclaimer: Neither CR-Z Forum, nor myself, are liable for any damages or injury that occur as a result of selecting an incorrect tire size. Vehicle manufacturers have recommended tire sizes for many reasons, and tire retailers recommend you do not go beyond 3% of overall diameter of the factory tire size, for many reasons as well. The reasons, sizes, and everything in between will be explained in this thread.
This is not a tire fitment thread. Tire fitment choices should come only after selecting a properly sized tire from all the tires that fall into the category of 'recommended' for the vehicle (tires that are within 3% of the factory overall diameter). In all honesty this thread should have been created a long time ago.
What this is:
This is the definitive list of tire sizes that can be used on the Honda CR-Z. I have been seeing a lot of people selecting tire sizes that are outside the recommended overall diameters, so I decided to make a comprehensive, easy to read list, along with explanations, of all the tire sizes from 14" to 21" diameters that can be used on a CR-Z, and a complete list of all the tire sizes that should not be used on a CR-Z.
There are very real, very serious reasons as to why you do not want to go outside the recommended range of tire sizes. The reasons range from very serious safety concerns, to increased mileage readings on the odometer and excessive vehicle and component wear, as well as reduced performance in terms of acceleration deceleration ride quality and suspension wear. Once again, neither myself, nor CR-Z Forum are responsible for any damage or injury that occur with improper tire size use.
Where to start: The factory tire size.
When selecting tire sizes yourself using one of the many available and free tire size calculators, you always need to input and compare the tire sizes to the factory tire size. The factory tire size being the size that the car comes with when it is 100% OEM as it rolls off the assembly line.
For reference, the factory OEM tire size for the 2011-2013 Honda CR-Z is: 195/55/16.
Tire sizes: The measurements.
There are three measurements that make up a tire size, this number is almost always molded into the sidewall of the tire. The tire size numbering follows the ISO Metric Code for tires. The primary set of numbers to be concerned with regarding tire size is the three-digit number followed by the forward-slash, the two-digit number followed by another forward slash (or sometimes a hyphen), and another two-digit number. This series of numbers and forward slashes is the tire size. For example the factory CR-Z tire size is written as: 195/55/16.
The first number set (195 for the factory tires) is the nominal tread width, or section width of the tire (measured in millimeters).
The second number set (55 for the factory tires) is the aspect ratio (sometimes called 'profile'), this is obtained from taking the sidewall height of the tire as a percentage of the overall tire width.
The third number set (16 for the factory tires) is the diameter of the wheel, in inches, for which the tire will fit.
The most important tire size specification when selecting a tire size is the overall diameter, which can only be calculated by using all three sets of numbers from the tire size. The overall diameter is not molded or printed on the tire. This calculation can be done yourself, or you can simply input the tire size into one of the many free online tire size calculators to get the overall diameter of the tire.
Tire Size Calculators:
Overall Diameter: The reasons explained.
The overall diameter of the stock CR-Z tire is 24.44", or 620.90mm.
The overall diameter is the most important consideration for tire sizes as changing this dimension too dramatically in either direction can affect the speedometer and odometer readings, acceleration and gearing of the vehicle, revolutions per mile or the wear and tear on the engine drivetrain and other components, handling, and the most important and serious aspect that can be affected: braking.
Tire Rack, Discount Tire, 1010 Tires, and most other reputable tire retailers have disclaimers about the overall tire diameter, and recommend that one not deviate beyond 3% of the overall tire diameter.
The reason you do not want to go beyond the recommendation of staying within 3% of the overall factory diameter is because most of the major mechanical components of the vehicle were designed around the factory tire diameter. From the gearing of the transmission, to the size and distribution of the braking system, the entire suspension and wheel-rate from the shocks and springs to the stiffness of the bushings, and even the engine power-band and revolutions per minute are all taken into account and tediously calculated and balanced for the vehicle around the factory tire size.
Going with a tire that is too small (in overall diameter) will increase the mileage that is registered to the odometer. You won't actually be driving any further, you will just be increasing the rate of accumulated mileage on the odometer and mechanical wear on every mechanical component, more than someone with the same CR-Z and properly-sized tires. With a smaller tire the brakes have to work harder as the wheel rotates more times per minute than a properly sized tire, this can lead to excessive brake-wear, excessive brake heat and possibly brake failure.
Going with a tire that is too large (in overall diameter) will reduce the acceleration of the vehicle, in effect making all of the gears in the transmission seem longer or taller. This usually results in a loss of efficiency and miles-per-gallon. Once again with a tire that is too large, just as too small, you can experience issues with increased brake wear, excessive brake heat and possibly brake failure.
With either of these (going too large or too small) the suspension system will be affected as well. The entire suspension is designed around the factory tire size and chaining this size changes the wheel-rate. The suspension will not feel the same, may not ride as good and the shock absorbers can be overworked in addition to not being valved properly for the new wheel-rate as a result of the improper tire size. This can lead to shortened suspension/shock absorber life, poor handling, poor ride quality and poor overall performance of the suspension. The same holds true for aftermarket suspension systems as well, as the good suspension companies calculate the wheel-rate and all other measurements around the factory tire size.
The List: And explanation.
Ok so you skipped to the end and just want to read the list. Here it is below.
The tires are broken up by diameter, and then broken down by section-width. Clearly labeled as "good" or "bad". The tires that are labeled as good have been cleared as being within 3% of the overall factory diameter for the CR-Z. All the tires sizes listed as "good" have their overall diameter listed as a percentage change from the stock factory diameter, a -0.3% is 0.3% smaller, while a 0.3% is 0.3% larger, take note of the negative or positive values.
The tires labeled as "bad" are grouped into short lists of approximately 4 bad sizes each. The reason for this is to save some space and time. There is no reason to go beyond a certain point when calculating these tire sizes, as once the 3% overall diameter has been passed, it will only get worse. The 4 sets of bad tires represent either end of a good tire size. So you can find the "good" tire size, fits right in-between it's corresponding "bad" sizes.
As an example: 225/50/16 is a good size. The bad sizes in that section-width and diameter group are: 225/35/16, 225/40/16, 225/55/16 and 225/60/16. There is no reason to list the 225/25/16 or 225/65/16 (they are not listed) as the other tires in the bad list that would come before those sizes are already way passed the 3% overall diameter. Going any further, ie a 225/20/16 (-16.4% over) is way passed the 225/35/16 which is already over 3% (it is -9.2% over). So there is no reason to list all the bad tires past a certain threshold.
The groups of 4 bad-list tires represent two tire-sizes in either direction of a good tire size.
Regarding section width and wheel diameter: Certain sizes are calculated to show the good/bad status, but are not necessarily recommended for the CR-Z. For example, I would not personally recommend going any narrower in section-width than 195mm. Similarly a 255 section-width is quite excessive and will likely harm gas milage, but some K-series track-goers may desire it. With regards to wheel diameter, I'm not sure how many are planning on down-sizing the wheel diameter to 14" or 15" (14" probably won't clear stock brakes, but some 15" wheels do, at least two 15" wheels confirmed fit), but it was calculated, just as I wouldn't personally recommend going with a 21" wheel, but it is represented here nonetheless.
One last disclaimer, unfortunately not all of these tire sizes are real. Most of them are, but a few are not. Just because they can be calculated on paper doesn't mean they are actually made by a tire manufacturer, so not every size listed here is actually produced. Nevertheless this is a full list of what would work, based on the overall diameter.
And finally here is the list. Good tire sizes are in black, bad tire sizes are in red.