AbandonedTrolley
Member
This reasoning was discussed during the GT5 era, and it is simply not true. If you're that concerned about breaking your thumbs, you should be equally concerned about breaking any part of your hands or wrists - the best option in that case would be to let go of the wheel entirely just before the impact. It's a bad idea to hold the wheel in such a bizarre fashion the entire time just in case of an accident. Typically, race car steering requires significant physical effort, and you need the best possible grip in order to maintain control. In many cases it would be essential to hook your thumbs around the rim simply to gain enough leverage to turn the wheel in a consistent fashion. Gripping the wheel properly means you're less likely to have an accident in the first place.
Search for racing onboards on YouTube - it is extremely rare (and very strange) to see anyone holding the wheel like that. And if you look for onboard crashes, you'll see most drivers don't even let go, and don't end up with broken thumbs.
I'm far from knowledgeable on this, but I did do a rally training day and was advised not to hold the wheel with my thumbs inside do to possible accidents and breaking, Maybe that's just them covering themselves though.