Is there anything more simple than just set proper steering lock by yourself? Ultimatelly, you set that to your prefference (and what particular mod requires. There are some that require ridiculusly high steering lock, way too high than you would have in real life). Still, if you want to keep real world steering ratio, you just do a simple math: <total_steering_wheel_lock> divided by <steering_ratio> and then divided by 2 (because steering lock in rF is per side). Let's say, you drive a Carrera GT which have steering ratio 15.7:1 and you set your wheel to 900deg. How much steering lock in rFactor do you need?
(900 / 15.7) /2 = ~28.7. If the mod offer only steering lock changes by 0.5 deg then you choose 28.5 or 29.0. Simple as that (as long as tyre model in that mod is OK ;-) ).