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Zx6rrdan, interesting observations you make.

My 2015 with the 16-inch factory tires also result in a lower-than-actual speedometer reading, by a factor of about 2%, and this applies to the odometer too. It 's the first car I remember doing that from the factory; usually, the speedometer reads a bit fast.

Mazda's changing the tire size and not adjusting for it must be the reason, alright.
 

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This is really a non issue. The difference is minimal.
WRONG again, the difference between 16 and 17 inch wheels is not minimal and does effect speedometer, odometer reading and engine calibrations, this is WHY Mazda IDS has an adjustment setting for changes in ECU/PCM for different wheel size use, which can ONLY be altered by a Mazda Dealer or IDS owner.
 

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WRONG again, the difference between 16 and 17 inch wheels is not minimal and does effect speedometer, odometer reading and engine calibrations, this is WHY Mazda IDS has an adjustment setting for changes in ECU/PCM for different wheel size use, which can ONLY be altered by a Mazda Dealer or IDS owner.
Wrong.
Do the math. 16" rims use different size tires as do 17 and 18 inch rims. Overall height should be very close if you choose the correct tire size. Of course, if you choose tires that are way to tall or short, you will have some speedometer error.

Here is an example posted in another thread, and do try to follow along

Thats not true at all. For instance, the Continental DWS 06 is fairly popular on this forum. In 225/50-17 that tire is 25.9 inches overall diameter, . The Michelin Pilot Sport A/S 3 is the same, as is the Firehawk Indy 500.
215/45-18 tires are actually slightly smaller, not larger. Overall diameter is 25.6 inches, making for ~1.2% circumference difference and less then 1 mph between the two sizes.
You need to use actual measured installed heights to figure circumference. You can't add up rim diameters and sidewall heights. Those are not accurate references by any means.

The formula for circumference is C = πd.

So, 25.6 x 3.14159 = 80.42
and 25.9 x 3.14159 = 81.37

That being said, the percent difference is

|80.42 - 81.37| / (80.42+81.37)/2 x 100

= |-.95| / 161.79/2 x 100

=.95/80.895 x 100

= .0117436 x 100

= 1.17436% difference
 

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this is another useful site if u are trying to compare tire sizes (stocks being 215/45r18 and 205/60r16)

https://tiresize.com/comparison/

you can find more tire options if u dont mind going slightly shorter or taller with your tires, your speedo will be off a little and this page will show the difference

i just went with 225/50r17s which is making my gearing a little taller (~81 mph at 80 indicated)
 

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this is another useful site if u are trying to compare tire sizes (stocks being 215/45r18 and 205/60r16)

https://tiresize.com/comparison/

you can find more tire options if u dont mind going slightly shorter or taller with your tires, your speedo will be off a little and this page will show the difference

i just went with 225/50r17s which is making my gearing a little taller (~81 mph at 80 indicated)
You do need to remember though that the actual installed size of the tire may vary from the industry standards provided by most tire manufacturer. For instance, the 205/50-17 Continentals I have are said to be 25.1" tall. The 205/60-16 Dunlops I had previously are 25.7" according to spec. However, the Continentals, despite being listed as .6" smaller, are the same installed height.
 

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You do need to remember though that the actual installed size of the tire may vary from the industry standards provided by most tire manufacturer. For instance, the 205/50-17 Continentals I have are said to be 25.1" tall. The 205/60-16 Dunlops I had previously are 25.7" according to spec. However, the Continentals, despite being listed as .6" smaller, are the same installed height.
The Tire Rack clearly states on this page the possibility of encountering an unexpected variance in one or more tire dimensions: https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=7

"Warning: These calculations (and those provided by all online tire dimension calculators) only reflect nominal tire dimensions, which are often subtly or substantially different than the tire's actual physical size and/or the dimensions provided by the tire manufactures."
 

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Go min for 17", looks great
Question. So I had a 2018 Mazda sport and traded it for 2017 Mazda touring. Both hatch. I’m pretty sure my 2018 had 16s and my 2017 came w 18s. I just got 17s fof my 2017 but I think that the 16s look fine on the 2018. Is there any difference in suspension or anything? Or do they have the same wheel gap/area?
 

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