Small OE spare on AWD vehicles

[ALafya]

The donut spare tire is significantly smaller in diameter than the regular tire by roughly 3 inches.
Especially on AWD vehicles, but also for FWD vehicles when the spare is mounted in the front, there is a significant difference between the spare and the other wheel on the same axle.
I always thought that even a small difference could cause drivetrain damage. But, here the difference is huge.
The manual says to not drive faster than 50 MPH, but it seems it is mostly for safety reasons. It only lists avoiding obstacles and car washes. No other restriction.
I'd imagine that any damage which can occur driving 70 MPH on such uneven tires on dry roads will happen at 50 MPH as well. However, it is obviously designed for that.

Does it mean that fitting any size tire, which is about the same as the tire on the other axle is safe for the drivetrain (of course, it could be unsafe for keeping traction. Here I am talking only on the drivetrain)?

 

[Mazdiod2]

Good point.

My manual says the temporary spare should be used for "VERY" (all caps) distances...and "NEVER" to be used for long distances.

Thats not very specific. I have read other manuals that specify a particular distance, like 50 miles.

Some people acquire a full size, or at least a larger spare.

I've only had to use a spare once, but if were concerned and felt I might need to drive farther on the spare I might get a full size spare. It would be better for the drivetrain.

 

[meow_man]

The owners manual also states not to use the compact spare on the front (driving wheels).

 

[sm1ke]

Does it mean that fitting any size tire, which is about the same as the tire on the other axle is safe for the drivetrain (of course, it could be unsafe for keeping traction. Here I am talking only on the drivetrain)?

I found this quote on an old ClubLexus thread:

"An AWD drivetrain has a lot of rotational mass. It's easy to upset the balance.

Different size wheels is a definite no-no on an AWD car. The differential would interpret the difference as slip, and route power/torque to the wheels with the least grip."

That said, I wonder if you can change all four tires so that they are the same size all around (i.e. changing wheel diameter from 763mm to 813mm on each wheel). I think people have done that without issue.

 

[RedBaron]

That said, I wonder if you can change all four tires so that they are the same size all around (i.e. changing wheel diameter from 763mm to 813mm on each wheel). I think people have done that without issue.

That would be OK for the AWD aspects, but it would change the measured speed (speedo) and the Odometer elapsed mileage.

 

[jaycal6]

would be cool if you could recalibrate the speedometer/odometer based on wheel size

 

[sm1ke]

That would be OK for the AWD aspects, but it would change the measured speed (speedo) and the Odometer elapsed mileage.

Very true. I left that out as ALafya was asking specifically about the drivetrain only.

would be cool if you could recalibrate the speedometer/odometer based on wheel size

I suspect it is possible for a dealership to do. Ford, Dodge, Jeep, Chevy and Toyota dealers probably do it often for pickups with plus-sized tires.

 

[minnesotaart]

Read all about here: Spare Tire Mod

 

[ALafya]

Read all about here: Spare Tire Mod

I don't think Mazda North America provided us with a spare that would damage the drivetrain. In particular, the manual does not say how far you could drive with the spare on. Sure, the spare is skinny and will not last for very long, but it seems that it will not damage the drivetrain as well.

If all this is correct, then it could mean that people don't need to replace all 4 tires for the sake of the drivetrain, only perhaps to keep traction identical, as slightly different diameter tires (with the difference being << 3 inches, few millimeters) will not damage the vehicle.

 

[murky]

I don't think Mazda North America provided us with a spare that would damage the drivetrain. In particular, the manual does not say how far you could drive with the spare on. Sure, the spare is skinny and will not last for very long, but it seems that it will not damage the drivetrain as well.

If all this is correct, then it could mean that people don't need to replace all 4 tires for the sake of the drivetrain, only perhaps to keep traction identical, as slightly different diameter tires (with the difference being << 3 inches, few millimeters) will not damage the vehicle.

I think that's a dangerous assumption. I think more likely Mazda considers driving with a spare to be relatively uncommon an is unlikely to lead to significant warranty exposure. If it shortens the life of the drivetrain outside of the warranty period, they may be willing to sacrifice that for the money they save on the cheap, or expedient spare.

 

[Avoidin Deer]

The owners manual also states not to use the compact spare on the front (driving wheels).

This^^

From the 2019 model year manual:

Do not install the temporary spare tire on the front wheels (driving wheels):
Driving with the temporary spare tire on one of the front driving wheels is dangerous. Handling will be affected. You could lose control of the vehicle, especially on ice or snow bound roads, and have an accident. Move a regular tire to the front wheel and install the temporary spare tire to the rear.

I believe others here have commented that it's impossible to mount the spare on the front axle because the front caliper is in the way of the spare's smaller wheel. I'm pretty sure I read that here.

 

[erhayes]

My CX5 has a full size spare I believe.

 

[mactire.rua]

I found an OEM wheel and made my own full size spare for my 2016.5. you will need to build up the sides of the cargo area so the cargo for will shoot level though and you will lose some vertical cargo space.

For me it was worth it and nice piece of mind having a full size spare when I'm out knocking around the middle of nowhere. An additional benefit is it extends the time for the replacement because you will need to rotate your spare to keep tread depth equal. I got 40k on my OEM tires. I'm getting new tires Saturday but probably could have pushed the tires another thousand miles or so.

 

[yrwei52]

This^^

From the manual:
⋯
I believe others here have commented that it's impossible to mount the spare on the front axle because the front caliper is in the way of the spare's smaller wheel. I'm pretty sure I read that here.

No, for CX-5 you can mount smaller 16” factory compact spare with T145/90D16 106M tire on the front unless you have a 2.5T which comes with bigger dual-piston front brake calipers.

As for the statement from owner’s manual that “do not install the temporary spare tire on the front wheels (driving wheels)”, I’d take it like many other questionable info in the owner’s manual, such as no maintenance schedule on ATF and brake fluid, and wrong fluid capacities on engine oil、rear differential, and wrong bulb spec on rear turn signals.

If I have a flat at front on the highway, I definitely will put the compact spare on the front and drive my CX-5 to a nearest tire shop to get the repair. Changing the tire once on the highway shoulder is dangerous enough, especially with those 18-wheelers constantly passing by!

 

[ALafya]

This^^

From the manual:



I believe others here have commented that it's impossible to mount the spare on the front axle because the front caliper is in the way of the spare's smaller wheel. I'm pretty sure I read that here.

Well, actually, I mounted my spare temporarily on the front wheel, but then went through a long process of putting a full size wheel on the front and the spare on the back, only with the kit available in the car.

I fully agree it is dangerous to put it on the front, because it will be harder to control the car.
Even on the back, I slowed down before any left turn, where the weight of the vehicle went on the spare. It definitely performed worse with the spare in the back. I cannot imagine how bad it would have been on the front.

 

[Avoidin Deer]

I keep forgetting to qualify my manual references with "2019 CX-5 Manual"

As yrwei52 stated, you physically cannot mount the spare on the front of a 2.5T. That was what I was (sort of) remembering.

As others have said, it sure would be a pain in the butt to be stuck in the middle of nowhere are go through 2 wheel changes for a flat tire.

 

[MyFirstMazda]

It is retarded that Mazda gives us the wrong sized spare tire. Has anyone driven their AWD with the spare tire?

 

[murky]

I keep forgetting to qualify my manual references with "2019 CX-5 Manual"

As yrwei52 stated, you physically cannot mount the spare on the front of a 2.5T. That was what I was (sort of) remembering.

As others have said, it sure would be a pain in the butt to be stuck in the middle of nowhere are go through 2 wheel changes for a flat tire.

I did the 2 wheel changes in a parking lot. It wasn't a big deal, but dumb to have such a discrepancy in tire diameter when the spare cavity is clearly designed to accomodate the correct diameter. The CX-7 spare is the correct size and will fit. The rubber is just too old by now.

 

[bTwix]

Using Sottozero run flats on my 2019 Sig to avoid the spare tire issue and to free up trunk space (ditching the spare to make room for upgraded sub).

 

[yrwei52]

I did the 2 wheel changes in a parking lot. It wasn't a big deal, but dumb to have such a discrepancy in tire diameter when the spare cavity is clearly designed to accomodate the correct diameter. The CX-7 spare is the correct size and will fit. The rubber is just too old by now.

The 18X4 spare steel wheel on gen-1 CX-9 has correct size too with Dunlop Space Miser MKIII T155/90D18 103M compact spare tire. The one I got is from a 2015 Mazda CX-9 which has newer date code than my factory 16” spare.