I tried looking online to see how much a 2013 Subaru Impreza would stop and could not find much. I am hoping you have the user manual for yours. If you look in the Brakes section, it should tell you how much weight your car will stop when towing. If there's a towing section, that area
may tell you how much you can tow, which is not the same as stop. Then again, if they don't want you towing, it may not tell you anything.
I did find this, quoted below, here:
http://www.cars101.com/towing.htmlSubaru does not supply trailer hitches for all models. The factory hitch is a class 1, 1 1/4" (1.25"). 2" hitch is not available from the factory.
Note: trailers must have brakes, without brakes lower the capacity below to half or less.
Serious about towing? Get a transmission cooler for the automatic transmission. Be careful not to slip a manual transmission.
The website looks like it was last updated a long time ago as the latest Subaru Impreza was a 2011.
Impreza
Subaru doesn't supply hitches for the sedans or recommend towing and so it is not suggested or recommended and there is no offficial approval. Warranty could be affected by any towing.
Any automatic should be able to tow 1-2000 pounds, with trailer brakes. A trans cooler is always a good idea.
2011, 2010, 2009, 2008, 2007, 2006 2005, 2004, 2003, 2002 automatic trans 2000lbs manual 1000lbs
2001, 2000, 1999, 1998 1997, 1996 1500#
The above reads as though the transmission is as much a problem as the brakes are, as they mention the cooler twice.
I'm guessing that's why you're asking about brakes. If you do decide to build, I would make that build as light as possible. If you look at the thread found here:
viewtopic.php?f=2&t=56787&p=1027920#p1027920 you will see that the weight of the teardrop is heavily dependent upon the builder. If you'd prefer a graph, look here:
viewtopic.php?f=21&t=60392Other than that....Maybe someone with a similar tow vehicle will chime in.