For me, it's a roughly 4 foot diameter turning diameter at a slow creep. I know it seems like it would never be enough to get around the track at speed, but when the car is working, this amount of throw is plenty for even the tightest hairpins. I always try to get the chassis working right with this amount of steering throw, if it's not enough I'll go stiffer in the rear or maybe a little softer on front springs or more traction on the front tires.
The idea is to free up the rear of the car enough to work with this amount of throw, not to have to dial in more steering deflection.
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