Winch bumpers themselves add around 100 lb or so...less than a passenger typically...would you upgrade the suspension if you joined a car pool?
The weight is foward of the wheels though, so there is more polar moment than for an equivalent passenger...but thats a handling not a load capacity issue really.
Adding a winch can almost double the weight if its a big one with steel rope and a roller fairlead, etc...
Anyway - Better shocks will help control the extra polar moments, etc...and you can always crank the t-bars if you notice a bit of front end sag.
I didn't see a huge difference on my '01 when the bumper went on, but I went with synthetic line and an Al fairlead to cut half the winch weight.
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- TJ
2001 Xterra '03 VG33, SE 5 spd, 305/70/16's, Revolvers, UBSkidderz, Doubled AAL's, 3"SL/2"BL, winch/bumpers, skids, sliders, OBA, Snorkel, pine stripes....
Friends don't let friends drive stock.
http://www.gifsoup.com/view/501230/tj-tackling-crawlers-ridge-o.gif