Just curious what real world ‘undrivable’ behaviour this penalty is reflecting.
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I thought it was that (turning circle), but the penalty applies to rear tyres as well. I think it’s something to do with weight because for a given tyre spec, the heavier the vehicle the lower the penalty.
Behaviour in rain / snow would be my guess then. Wider tires are more prone to aquaplaning.
In a word, friction. The saying that driving is about the balance between grip and slip applies to more than just race nuts.
Since wider tyres have a larger contact patch you could say (all other things being equal) that they also have more responsiveness but that can also means more sensitive. Wider tyres in general are twitchier on anything other than perfectly smooth even surfaces. They’re particularly prone to railroading/ tramlining.
Note of course that you lose drivability if you don’t have enough contact patch for the tyres to produce sufficient friction for the load placed on the tyres by the chassis, which in turn causes problems with cornering ability and braking distance.
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Okay, thanks.
I’ve found that the width at which drivability begins to fall off is lower than I would expect. For a 2016 midsize family sedan it was falling off in the 185-205 range, when real-life sedans tend to have sizes in the 205-225 range.
That just what they put in cars these days, not the best size, but the size people buy.
It might be the best size, Automation in no way can be considered the ultimate arbiter of optimal design choices. 
185 vs 215 hardly is outside the realm of error margins. The optimal size in Automation depends on tire compound, it changes quite drastically between them… so consider that our “average” medium compound in year 2016 is just a little too hard.
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Yup! I’ve got 12.5" wide tires on my tiny little truck, and half the time the tires tell me where I’m going rather than the other way around.