I have a harbor freight tubing bender, it tends to kink the roll bar tubing, any methods or suggestions to bend the tubing? Thanks

 

I had one of those before I got my mandrel bender. Bend it a little, move it a little, repeat process. Sweeping bends are less likely to kink. You can also cap the ends and fill the tubing with sand if you want to go old school.

 

saw a guy on youtube with one of those benders that said you need to trying using a size smaller mandrel to get it to not kink

 

Made for industrial pipe, that's not the same dimensions as chassis material.
The dies are not machined to prevent the kinks....
We use the JD2 w/ air/hyd assist. No issues w/ being "kinky"..

 

The machine complexity & necessary characteristics required to bend tubing increases as you get tighter in radius assuming the wall stays the same. If you are trying to bend something like a 6-8*Diameter radius, you can probably do it with a torch and a lever. 4-5*diameter require a single shot or crush style bender. Once you get below 3*Diameter, you start needing a mandrel, and when you get below 2*diameter you need a mandrel and a wiper. To get to 1.5*diameter requires mandrel, wiper and pressure die assist. Below 1*diameter, requires mandrel, wiper, pressure die assist and carriage boost.