I would have to guess that at least 75 percent of all the road racing in the US, (SCCA Nationals and Regionals) is done on bias ply tires when using slicks, that is all that is available in most classes. I have done it for 30 years on nothing but Bias ply, (goodyears). There is nothing wrong with that technology. I think radials are a better all around choice taking into consideration wet conditions, etc, but bias ply tires by design are not unsafe..