A trailer isn't part of the load rating, except for the downward force on the hitch, which usually isn't a lot...

 

No, by law it cannot. If you were to cause damage that was proven to be caused by towing too heavy of a load, then they could deny warranty coverage for that particular damage. There is nothing you can add to your car that will "void the warranty".

Sorry, this is just not true. Toyota approves the xD (Toyota Urban Cruiser in the UK) to tow up to 1,900 pounds. I'm sure the larger, more powerful xB is rated to tow even more. See my explanation below for more info on why they don't rate it to tow in the US.

(Sorry for the cross post... but it relates to this post as well)

Toyota does not rate any of their cars for towing in the US. The reason is that Americans are lawsuit-happy. They don't want anything falling off the back of a car (bike rack, trailer, etc.) that could cause damage or injury that they might be liable for. If you look at the same cars in other countries, they are rated to tow. For instance, the xD manual says the same thing about not towing anything... but in England, they rate it to tow 1,900 pounds. Frivolous lawsuits basically don't happen in the UK.

In Europe, they'd be hard pressed to sell a small car that isn't rated to tow. When I was in the Czech Republic a few months ago, I counted the trailer hitches and one out of every four cars on average had a trailer hitch. Their hitches are for trailers only, not bike racks. I saw many people towing small trailers with subcompact cars... including ones with 1.1 to 1.4 liter engines (less than 100hp).

In the US, people think they need a truck to tow a 1,000 pound trailer... and the car companies don't want them to know otherwise! I tow all the time with my xD. The heaviest load I had was about 1,600 pounds. That was an enclosed 4x8 Uhaul trailer filled with furniture and books. It towed this load with no problems. Braking wasn't an issue. I had to downshift to 4th a few times on long uphill grades... but that was in the hills in PA.

It is perfectly legal to tow, so long as you have the right equipment and watch your state's laws regarding brakes. In Maryland, a trailer doesn't need brakes unless it is over 3,000 pounds (which is more than I'd tow with my xD, anyway). It is also perfectly safe to tow up to the hitch's rating. Just keep in mind the leverage that a cargo rack or bike rack puts on the hitch. If your tongue rating is 300 pounds, you can have a trailer with a 250 pound tongue rating and you're okay... however, if you have a scooter rack that weighs 50 pounds and a 200 pound scooter, you may be over the limit because of the amount of leverage with the scooter a foot or more behind the receiver.

I don't know for sure about the xB, but if you have open springs on the back, you can install AirLift1000 bags in them. I used them on my VW Golf for towing and they were awesome. You inflate them when you need them and deflate them when you don't. In my opinion, they work a lot better than those rubber spring helpers. They're only about $75 for a set. I haven't installed them on the xD because the TRD springs don't compress much.