Analyzing Towing Troubles - 12/02/2009

A reader recently wrote: Can you please explain the physics and mechanics as to what makes a car/SUV-capable of towing a certain weight? I have a Hurricane Sundeck 19 ft. (about 4,000 lbs) on a 4-wheel trailer and a Jeep Liberty (rated at 5,000 lbs). This summer it started to fishtail and forced us off the road. Luckily only a tie rod broke. People (supposedly in the know) are claiming that it had to happen as the car has too short a wheel base to tow a boat. What is happening here?

Towing Trouble
Sometimes there are towing problems that just escape solutions. Sometimes not.

Capt. Steve Says...

It’s hard to play Monday morning quarterback on something like this when I wasn’t there, but what you’re describing sounds an awful lot like the problem is with the tow itself, rather than the tow vehicle (we’ll assume the tie rod broke as a result, rather than cause).

If the balance of the boat on the trailer is too far forward, and you have excess tongue weight on the trailer hitch/ball, you’ll typically get the results you describe, and they get worse as speed increases down the road. Prop the tongue of the trailer on a heavy duty scale, or combination of scales, to get the amount of weight being forced down on the hitch. It should be within 10% of the entire weight of the boat/trailer combination. If it’s more, which I am suspecting, then the boat needs to be further back on the trailer.

Go to the local landfill or city trash collection depot and drive the trailer and boat onto the scales to get an accurate measurement of the total weight. Then you’ll have an idea of what the tongue weight should be. Keep it within 10% of the total weight.

A Simple Example...

Look at it this way. If you put a load of heavy boxes on a hand truck, you can still walk down the hall if they’re all balanced right on the wheels. If you tip the hand truck too far forward, then you lose control and the load becomes hard to steer. If you have the hand truck too far back, or towards you, it gets too heavy and, again, hard to control.

You need the same balance with your trailer, and it doesn’t take much of an imbalance to screw things up. Moving the boat forward or back to achieve this balance should solve your problem.

A Tow Vehicle Isn’t Enough

As for your vehicle, make sure you have a tow package. Just because the vehicle is rated to tow a certain weight, doesn’t mean it’s equipped to. You appear to be at the maximum of the rated tow weight and that can cause damage in the long run to the vehicle itself if it’s not set up to carry that much weight (oil cooler, beefed up suspension, stronger engine …etc.). That would be the second place I’d look.

Check the Axels

The third place I’d look is on the trailer axles. You have two, so are they aligned properly? Having one out of alignment with the other will have them fighting each other for control with neither winning and the vehicle taking the beating. This is rare, though, as they usually leave the manufacturer pretty well set up. Some dealers just put the boat on and send them away.

I hope all this helps.