I just ordered a vehicle that comes with all-season 21" wheels and tires. I live in the mountains in Utah, and we get a lot of snow in the winter, so I always have a different set of winter wheels & tires for our vehicles.
I’ve read that smaller wheels and tires perform better in the snow. Tire Rack has a page on this and I’ve seen it mentioned elsewhere too. I’m just wondering how significant this difference is, especially on a car with AWD and great off-road/snow performance already.
I prefer the look of 21" wheels/tires, but I’m considering sizing down to 20" for the winter wheels/tires for this vehicle to get better traction/performance in the snow.
Downsizing to 20 inch wheels for your car will not help traction. The wheel diameter itself doesn’t matter at all. What matters is the tire size, not what wheel it is mounted on.
Looking at Tire Rack, the winter tire selection for your car in 21s versus 20s, the width and aspect ratio, which do matter, barely change. The width doesn’t change at all and aspect ratio changes by 5 points. Basically, no change.
The biggest concern with downsizing the wheel is brake clearance. A smaller wheel may not fit over the brakes. If your car came with 20" wheels as stock and your 21’s are an option, and it doesn’t have optional brakes, then you would probably be OK.
A lot of people get a set of steel wheels to mount their winter tires on, that also may not be an option with you because of the brakes, even if there are 21" steel wheels.
You will either have to deal with the hassle and expense of remounting tires to your wheels twice a year or get a second set of Porsche wheels, which will not be cheap. You could look to after-market wheels of the same size but if you do, be sure to get wheels with the same hub diameter and offset or you will have issues.
I’d go with 20", better rim protection with the higher sidewall. A set of tires plus alloy rims (I don’t think steel are available) was around $4500, all-in, on Tirerack.
As mentioned above, you’re confusing two different issues.
A tire that’s a bit narrower will be a bit better in snow. However, a narrower tire might have a lower load index, so you have to make sure it’s sufficient.
Going to a wheel with a smaller diameter and a tire with a correspondingly larger aspect ratio will help absorb the shock of hitting bad winter potholes, possibly protecting your wheel from damage. Also, you’ll probably find a better selection of winter tires available at a lower price. You’ll give up some high-speed cornering performance, but most people don’t care about that in winter.
I could be wrong, but I do believe that tire rack’s website sells what will fit on the vehicle within the specs of the manufacturer. If 20" is the smallest they offer in ters of diameter, then 19s might be too small to clear the brakes.
Configurator shows 19" as standard with the 21" and 20" being optional. As long as this doesn’t have the optional Cermaic brakes a set of 20" wheels will fit.