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Any logic to the OEM wheel sizes?

1674 Views 3 Replies 4 Participants Last post by  Viffermike
Let’s take the 20s as an example:

20x8 and 20x10
235/35/20 and 265/35/20

If you look at replacement tires on Tirerack (including OEM replacement) you will see that the fronts are designed for 8-9.5” rim sizes, and the rears are designed for 9-10.5” wheels.

So the front wheels are at the narrow end of the spectrum, and the rears are pretty close to the wide end?

Some of the optional wheels are 8.5/10.5” respectively.

Just seems odd to me, it would make sure sense IMO to have 8.5 or 9” in the front.

Any thoughts?
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I think a wider tire in the front could equate to more traction in the front thus greater chance of oversteer during aggressive or high speed corners??? Just a guess.
Maybe I misunderstand, but I think it would be the same tire on a slightly wider wheel to be more consistent with the dimensions at rear...

It's primarily looks, combined with effective economies of scale since most OEM tires that come on the 718 have specific design adjustments for the car model. IOW, it makes MUCH more sense to use the same tire size on multiple wheel widths because Porsche can order more (thus making them less expensive in a larger bulk order) and doesn't have to invest R&D in those model-specific 'adjustments' for more than one size.

The tire sizes are the same even as you go from the 18s to the 19s to the 20s, as well. There will be a slight contact-patch benefit between the 18s, 19s and 20s simply because the tire's aspect is slightly larger as one goes upward in diameter. In my mind, however, that advantage is offset by the increased unsprung weight that a larger-diameter wheel and tire will almost certainly have. A lighter tire/wheel will handle better even with slightly skinnier rubber on it, and the hub forces (acceleration, braking, turn in, etc.) will be quicker with a lighter unsprung setup.
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