Hey guys I know this has been said a hundred times but what is the diff in handling in the stock rear arms and the flat rear arms thanks Jimmy..
Flat arms are "firmer" than the kit gull wing arms. The biggest difference is how they roll less in the corners and allow you to corner harder. If you are on a track that has anything resembling traction, you want the flat arms. IF you are constantly on low traction, the kit arms may be better.
On our track, most of us use flat arms. I've tried both and honestly it just feels like you're running a much lower roll center if you run the kit arms. It's just a tuning aid.
The reason the arms do this (in my view) is the difference in progression. Gull wing arms are like laying the shocks down, flat arms are like standing them up.
If you want to run the flat arms (UM521-1), you will need to run the short shock eyelet end and ream out the 'hinge pin capture' on the outside of the arm with a reamer. Takes like just a few twists and it's done. Then use 2mm spacers on each side of the outer hinge pins before the nuts. Alternatively you can purchase the right hinge pins for those arms and get some 1.5 head capture screws, but that requires you buy stuff, so nobody I know does that.
Wayne