Small OE spare on AWD vehicles

[yrwei52]

I'd change that to ..."will not cause immediately apparent, catastrophic drivetrain damage"...

Put another way, I guarantee it wasn't an engineer who proposed putting that under-height tire in the spare well of the AWD CX-5.

Yes, I agree. In fact the spec sheet on Mazda website at the time when I purchased my 2016 CX-5 AWD was clearly stated the AWD still gets correct-sized T155/90D18 compact spare. Somehow someone gave up engineering concerns and chose a smaller compact spare to save some pennies.

 

[sm1ke]

The tread depth of a new tire is 10/32” (~ 8 mm). So you want to shave some mm (< 8 mm) off a new tire to match the other 3 partially worn tires, but you’re not worried about using a factory spare which is 56 mm too small on total diameter than other 3 road tires on an AWD CX-5 which will upset AWD and TCS/ABS systems???

That's exactly right.

If I buy a new tire for an AWD vehicle, I would want it to be the same size as the other tires because I would be driving on those tires for as long as they would last, which could be tens of thousands of kilometers.

The smaller spare, if mounted correctly (on the rear), would only be used for a few kms at best because it is a temporary spare tire with a much lower speed rating. Temporary use is not something to worry about, as long as it is temporary and the car isn't driven "normally" (meaning as if it has four wheels that are the same).

Hope that answers your question.

 

[jaycal6]

So, just FYI, the 2020 CX-5 (GTR, at least) comes with a Yokohama 155/90D17 spare. That’s a 28” diameter, while the regular tire is 28.7”. So that’s actually not bad at all.