For bar sizing, bigger is better to a point. Not meaning to ruffle anyone, but going oversized is good- too oversized will result in the following:
1. When adjusted to the correct tension for that size bar- if too large, stiff almost board like ride.
2. Too stiff of spring bar can actually work against you for control.
3. Too stiff of spring bar can potentially damage the A-Frame on some of the lighter weight trailers- check the A-Frame for any disclaimers- for example my Jayco has a placard that states specifically NOT to use a bar with a greater than 1000lbs rating or damage to the frame may occur.
4. If you loosen the spring bar off enough to get the proper ride and handling, you may find that you are losing some or all of the anti-sway benefits.
Just some tidbits that may help
In my opinion, look at your tongue weight loaded. Use 15% of GVWR for a good guess, but also consider the weight that you will have behind the axle or use a portion of the weight you may carry in the box to give you a good estimate. Then, size the bar accordingly. For example, I have a 680-770 lbs tongue weight with roughly another 100lbs in the box. The options I had were a 750lbs, 1000lbs bar or a 1200lbs bar. Went in the middle- I have a great ride, great sway control and have a little cushion for weight if I need it. 1200lbs would have been overkill and would likely cause damage since I have an ultralite frame.
In your case with a 900lbs tongue weight- I would run a 1200lbs bar. 1000lbs would be cutting too close. 1400lbs bar would be acceptable too- you may just have to slack it off a bit or adjust the head.
Did you get that new TT?
