18" on AWD?

[Tyldum]

Got an AWD with the original 18". No problem.

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[ChuckA]

Correct. Tire terminology for this is Section Width. And, to calculate overall diameter without the tire spec sheet handy you can use the above info. like this:

40% (the sidewall profile) * 255mm (section width) = 102mm sidewall height * 2 (sidewall height at bottom and top of wheel) = 204mm, then 204mm / 25mm (25mm in an inch) = 8.16”

Now, add the 8.16” in combined sidewall height to the 18” wheel diameter and you get an overall tire diameter of 26.16”, or approximately 1.6-1.7” smaller diameter than the stock 225/55-18 Select tires, which are 27.8-27.9”.

25.4mm per inch to be exact. Actually Tire Rack shows in their specs for a given tire the rim width that is applicable, and diameter, and revolutions per mile. Very helpful in comparing tires.

 

[ChasingCoral]

Another reason that people often down size rim size for winter tires is because additional side wall results in a longer longitudinal foot print that provides in additional traction in the snow. It is the counter argument against wide tires with narrow side side walls that have a narrow horizontal foot print. The width of the tire is often reduced as wide tires tend to push more snow. However MME factory 18" and 19" tires are the same width and fairly narrow anyway.

One more reason for smaller snow tires is to increase the room in the wheel well for snow accumulation. This can reduce rubbing the tire against the snow/ice buildup.

 

[ChuckA]

One more reason for smaller snow tires is to increase the room in the wheel well for snow accumulation. This can reduce rubbing the tire against the snow/ice buildup.

I would think the smaller snow tires may lower ground clearance. It's a car, not a sled.

 

[phidauex]

Correct!

But correct me if I'm wrong - the red calipers and the discs on the AWD is exactly the samze size as the RWD?

So, the 18" original will fit the AWD just fine? Because I thought that the fitments were different and the brakes/discs would be too big for the 18".

ALL non-GT MachEs have the exact same brake sizes, and will fit the exact same wheels. The GT and GTPE have a larger front rotor, so while all the wheel fitment measurements are the same, they will not work with an 18" wheel.

 

[phidauex]

I would think the smaller snow tires may lower ground clearance. It's a car, not a sled.

There are two ways to interpret "smaller" - most people mean narrower, not smaller diameter. I agree that smaller diameter wouldn't be ideal.

 

[Tyldum]

There are two ways to interpret "smaller" - most people mean narrower, not smaller diameter. I agree that smaller diameter wouldn't be ideal.

The ground clearance with stock 19" and stock 18" is identical. Just more rubber, yes.

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