My '05 and '10 Prii have the body stiffening plates sold by Rude person's here on PC. I've heard he got banned and haven't seen him post for quite a while, I've got the TRD rear sway bars on the '05 and '10 also. Both the plate and the sway's have worked well for me. Haven't had time to do anything to the '15 yet, but will be doing the plate and sway bar on it too as soon as I can get around to it, haven't looked into plates yet, so don't know which one I'll get, but rear sway will definitely be the TRD one.
If your car is a touring model the best modification is changing the tyres from 195/55/16/ to 205/55/16. There are no clearance problems and they transform the car. As an added bonus they are also much cheaper in the wider size. John (Britprius)
just bought the trd rear sway bar and juiced hybrid stiffening plate. any thoughts on front sway bar???
IMHO, front bar = nah... However, I strongly recommend a Strut Tower Bar. I had the old BT Tech STB on my 2007 and now have the Cusco STB on my 2012. They transform steering from "mushy" to rails-like stable and very precise. If you are in the market for tires, I also recommend Michelin Defenders. Quiet, stable and grippy, while super-long-lasting.
You can get a front bar from a corolla or matrix '03-'08 (don't forget the frame bushings and brackets) and it will bolt right in. you most likely will need to unbolt the 2 back subframe bolts and loosen the 2 front bolts to dangle the subframe enough to slide the heavier bar in. spray paint around the mounting ears for the rear bolts before you loosen them. the paint line will help you get the subframe right back where it was so you won't need to realign your suspension. tremendous difference in handling, it keeps the car flat in hard corners. anyone who has replaced the front bar loved it. anyone who hasn't replaced it has no idea what they're missing. I was really unhappy with the excessive body roll in these cars, but replacing both sway bars and installing wider tires makes them handle pretty good.
I second 69shovlhed, replace the front sway bar with a corolla/matrix -- Not to steer you one way or the other where to buy parts, but check out TRD Parts: Toyota Parts and Accessories | TRDParts.com That's where I ordered by swaybar, bushings and brackets. Once you swap it out, you will notice a WORLD of difference!