Choosing tow dollies versus other available towing accessories on the market can get confusing, but the thing to keep in mind is what kind of vehicle you're looking to tow. When towing, the make and model of the vehicle can affect whether it's possible to simply hook it up and go or if you need to make some modifications to it in order to get towing.
The biggest issues tend to crop up if you have a four- , rear- or all-wheel-drive vehicle. In many instances, the vehicle's transmission will be shot unless you disconnect the driveshaft and possibly install other accessories as well. Also, as we noted on the previous page, having a manual versus an automatic transmission will factor into the equation. The best advice to follow is consult the manufacturer for information on your particular vehicle to help you decide if a tow dolly or towing four wheels down is most appropriate for your situation. Some vehicles are good to go as is; some just need a quick, manageable tweak; and others are much more challenging and expensive to prepare for towing. If you're considering the expense of towing four wheels up, these issues can be largely avoided with a tow dolly.
Knowing the weight of the vehicle being towed and the various weight ratings of the tow vehicle and hitch is also fundamental. If you plan on hauling around a little sedan most of the time, a tow dolly might be a good idea. If you want to take a large SUV along for the ride, you may need to keep shopping. This is because tow dollies themselves can weigh quite a bit -- in most cases 500 pounds (225 kilograms) or more. All that weight might put you over the limit, or at least force you to purchase additional equipment such as onboard brakes and other safety features. (For safety's sake, extra brakes and lights are a good idea at any weight.)
Along the same vein, you should be cognizant of the weight ratio between the towing vehicle and the vehicle being towed. U-Haul, for example, advises people renting their tow dollies to keep at least a 750-pound (340-kilogram) buffer between the weight of the front vehicle and the one in back [source: U-Haul]. You must also keep in mind how wide your towed vehicle is because different tow dollies have different maximum vehicle widths that can't be exceeded.
Your best bet is to do some research and carefully consult with the vehicle manufacturers and a towing expert. Their advice can help you choose an appropriate dolly or alternate towing methods that are best suited to your needs.