How is Tow Ratings Figured?

[TrepMan]

OK, was checking out the 30th anniverary addition of Trailer Boats magazine over the weekend. And it started me thinking (now we're in trouble) about how a manufacturer figures out the Max tow rating of a vehicle? The mag noted that in the early years of trailer boats (up to the 70's and later) there were no factory ratings. It even showed an 18ft fiberglass runabout being towed behind an AMC Gremlin! Then I started thinking about my old Saturn SL2 4 cylinder. It was rated (per the manual) for 1000lbs. As I was looking for a wagon last summer I thought, HEY i'll get the new larger V-6 (182 hp) L series Saturn wagon, but low and behold it still only tows 1000lbs.



Can someone give me a layman's idea of how they figure this out? I figured a bigger more torquier motor with larger/heavier frame and better brakes would increase the towing capacity. But then I saw the Hyndai Elantra with a 140hp 4 banger rated at 1500lbs and could not figure that one out campared to a Saturn v-6 with 182hp rated at 1000lbs.



I know either of my current vehicles can tow my boat based on the factory ratings, just don't understand them.



Can you say "i've got cabin fever, i've got cabin fever..."



TrepMan

 

[TrepMan]

David:



Very similar in family vehicles. My wifes Honda Odyessy will tow 3500 and as I mentioned my Mercury Sable will tow 1600. I looked closely at the Legacy wagons, I realy liked the GT model in a 5 speed, but they hold thier value too well for me right now. I only put on about 3-4,000/year working from home and kept my budget to 10K for a used wagon. I've not gotten the hitch put on the wagon yet, as my kids LOVE the sunroof and any time I want to hit the lake my wife has no problem driving the wagon.



Come on Mac, I know you KNOW the answer to this question...

 

[Bill P]

I think it has a lot to do with whether it's front or rear wheel drive. I tow a 3100 lb rig, with a 160 hp v6 Ranger 4wd, and have no real problems. I think the hp rating seems secondary to the suspension, when they rate them. My truck is rated for 6,000 lbs, with the tow package, and 4wd. I know a guy who tows a heavier rig than mine, with a 2wd Ranger, with the smaller v6 ( Of course we both have trailer brakes). I really think the supension, is really what limits a lot of cars, not the hp rating. Cars tend to have soft suspension, compared to even a small pickup, or suv.

 

[Bill McElroy]

Sorry Trep,...I'm clueless on this one,.....I just make sure that whatever i decide to buy or lease,...is powerful enough to tow a 901 or a 929!!..LOL And I make sure it has a Trans cooler on it too!!! Don't know how they determine towing capacity!!!

 

[TrepMan]

David and Bill - Thanks for you input. I like your idea David i'd love to have that job trying!



Hey Mac - Don't I remember you working for GM? Go to work to day and ask someone if they know who knows this answer. Someone in the plant has to know.



TrepMan

 

[Mark Hofman]

Did a bit of research about tow ratings. Here's what I've found so far.



Factors which play into tow ratings include:



Vehicle Wheelbase (wider track is better)

Vehicle Center of gravity (lower is better)

The durability of various powertrain components (powertrain, brakes, steering and suspension systems)



The vehicle manufacturer generally calculates tow rating by deducting the vehicle's curb weight from its gcwr (gross combination weight rating - the maximum allowable combined weight of a tow vehicle and trailer with all fuel, water, supplies and passengers). The weight of additional passengers and cargo in the tow vehicle is deducted from the trailer tow rating.



Does this help?



Mark

 

[Mark Hofman]

That part about the manufacturer's calculation is from an RV web page. For boats, the vehicle's curb weight would be deducted from its gross combination weight rating (maximum allowable combined weight of a tow vehicle, as well as the boat, motor and trailer with all fuel, tackle and equipment. The weight of any people or stuff in the tow vehicle is then deducted from the trailer tow rating.