1.51 to 1.60 60fts on stock axles no traction bars and I have broken axles but It usually is just me being stupid and not preloading or raising the 2-step too far ...
For a normal car , not 60ing like mine you should be fine . I never broke 1 axle when I was cutting 1.71's and the like in my Si . Only when I got into the 1.6's .
Your actually less likely to brake an axle with a slick as it lets the tire give
Jap your cutting 1.51 to 1.60 60's? Damn...what size slicks and what tire pressure are you running?