What limits tow ratings for unibody vehicles?

[IndyIan]

I'm with the anti-towing conspiracy guy, most modern cars have the the old full frame sloppy jalopy of years past beat in every way, with better brakes, better designed cooling systems, and better suspension with better tires. A solid rear axle is nice in that you can have it riding on the bump stops and still have good wheel alignment, but a mac strut rear suspension isn't going to get to out of shape either
Watch a few clips on this site, Can-Am RV :: Intrepid towing Airstream It's amazing what a well setup hitch and trailer can do.
I suspect our silly low tow ratings today have more to do with lawyers then anything else.

 

[Just Bill]

Cars used to tow those weights all the time but they also did not travel at the speeds we do now days and were sitting on a full frame. New cars are about the same weight but use many weight saving techniques to allow for all the goodies to be put in like power seats, gps, ac, power windows, ect. Look at a new car and they hold less coolant, tranny fluid, oil, ect. This lessens the heat dissipation.

Chris

What speeds do we travel at today that is different?
Every Interstate I ever drove on until 55 was mandated by the feds was at least 70 as was a lot of other roads.
Plus there wasn't a cop around every curve in the road so there was a lot of cheating.
A big difference was that automatic transmissions were a lot stronger and vehicles geared better for pulling not gas mileage.
Most engines back then held 5 qts with a filter change, do they hold less now?
Probably biggest difference is unibody , front wheel drive , light duty trans , and terrible gearing all to get better gas mileage.

 

[CompactTractorFan]

I purchased a 1985 LTD Crown Victoria with the factory towing package and drove it until 1996 and stored it away in my barn. It had the 302 (5 liter) V8 and was rated to tow 5,000 pounds with the proper WD hitch, although it weighed only about 3,800 pounds with a driver and full tank of fuel. My '04 Lesabre weighs about the same, develops greater horsepower, yet has a measly 1,000 pound tow rating. The ultimate American tow car in recent years would be the body-on-frame 1994-1996 Cadillac Fleetwood, with the Corvette-derived 260 hp. LT-1 engine and the available factory towing package it was rated for a full 7,000 pound trailering capacity.

I bet you will NEVER see a 7k tow rating on a sedan again.

 

[CompactTractorFan]

I'm with the anti-towing conspiracy guy, most modern cars have the the old full frame sloppy jalopy of years past beat in every way, with better brakes, better designed cooling systems, and better suspension with better tires. A solid rear axle is nice in that you can have it riding on the bump stops and still have good wheel alignment, but a mac strut rear suspension isn't going to get to out of shape either
Watch a few clips on this site, Can-Am RV :: Intrepid towing Airstream It's amazing what a well setup hitch and trailer can do.
I suspect our silly low tow ratings today have more to do with lawyers then anything else.

I can tow that with my Intrepid???

 

[IndyIan]

I can tow that with my Intrepid???

Its almost scary to watch but it goes to show what a properly setup trailer and hitch can do. In Canada and I believe in the US, you can legally ignore the tow ratings of a vehicle if you are towing an RV trailer with a bathroom. The key though is to have the hitch setup for the particular car and trailer.

 

[JDgreen227]

Its almost scary to watch but it goes to show what a properly setup trailer and hitch can do. In Canada and I believe in the US, you can legally ignore the tow ratings of a vehicle if you are towing an RV trailer with a bathroom. The key though is to have the hitch setup for the particular car and trailer.

Back about 1996 or so when I did a lot of towing our travel trailer, there was a really costly hitch available that was made by a company near Davison, Michigan about an hour's drive from where I live. The hitch setup was called something like the Hensley Arrow and they made a video available that shows something like the link provided by Indylan. It is still a mystery to me, however, how a unibody car can possibly have a hitch strong enough to tow a heavy trailer without tearing the thin sheet metal apart. IndyIan, I towed travel trailers from '94 thru 2005 and have never heard of that "ignore tow ratings if the RV has a bathroom".... well my Lesabre doesn't care about legality it just wants to know how to handle the 800 pound tongue weight of my center bathroom equipped Jayco that weighs 6500 pounds loaded.....:laughing:

 

[3930dave]

I'm thinking that the OP is confusing the "bathroom" exemption with commercial trailer compliance. Where I am, if you have a 10,000# utility trailer/float you will end up in deep doodoo if you don't have a valid commercial annual inspection sticker on it.

"Bathroom" comes in if you have a 10,000# travel trailer - it doesn't need a commercial sticker. But, you can't legally tow a 10,000# travel trailer here with a Smart car, or for that matter JD's Buick.

I'm in Canada, not Europe, but have even seen Smart cars towing (OK, tiny by TBN standards) trailers here.

I prefer a heavy metal approach to towing, just makes sense to me for the long haul - pun intended.

IF I was going to push the boundaries towing with a unibody car, aside from the common sense items (all brake and fluid maintenance done) I'd upgrade or add a transmission cooler, and get something like a Scangauge II for displaying Trani fluid temperature.

Without a trailer, just take a regular sedan and load it with people and luggage - I think many people would be surprised how hot Trani fluid gets, even with a driver with a light foot. Rolling hills or stop/go traffic are a tough load, as the trani is always shifting - every shift produces heat.

IMO, a trani temp gauge is critical for towing (any automatic equipped vehicle), and with todays OBD ports on the cars and $150 plug'n'play meters available, there isn't much excuse for not using one. In many vehicles, by the time your coolant temp gauge is showing a major deviation, your trani is well on it's way to baking.

It's no fun breaking/wearing out basic mechanical items (bearings, brakes, springs, or tearing the floor out of your trunk), but at least they are way less spendy to repair than a transmission.

Rgds, D.

 

[toppop52]

A lot of people are right, part of it is warranty claims, part liability, a lot has do with individual vehicle crush zones, mounting area strength, drivetrain strength, cooling capacity and sometimes it's as simple as they prefer to sell a different model due to profit margin, so beyond its basic intended use, they steer you toward higher profit models. The gear ratio has a Lot less to do with it now than in the 70's/80's before overdrive became the normal and fuel injection allowed car to be way more efficient and powerful. Transmissions, transaxles and rear axles in many cars are a lot lighter duty than in the past, while truck units have gotten stronger in recent years. Then there are the tire sizes, ratings, etc...
Just as a side note, every time you go up an inch in tire height, you correspondingly lose a proportionate percentage of overall gearing ratio. If you have a truck with 3.73 gears and 31" tires is would be roughly equivalent to the same truck with 3.50 ish gears if you go up to a 32" tire.

 

[IndyIan]

I'm thinking that the OP is confusing the "bathroom" exemption with commercial trailer compliance. Where I am, if you have a 10,000# utility trailer/float you will end up in deep doodoo if you don't have a valid commercial annual inspection sticker on it.

"Bathroom" comes in if you have a 10,000# travel trailer - it doesn't need a commercial sticker. But, you can't legally tow a 10,000# travel trailer here with a Smart car, or for that matter JD's Buick.

I'm in Canada, not Europe, but have even seen Smart cars towing (OK, tiny by TBN standards) trailers here.

I prefer a heavy metal approach to towing, just makes sense to me for the long haul - pun intended.

IF I was going to push the boundaries towing with a unibody car, aside from the common sense items (all brake and fluid maintenance done) I'd upgrade or add a transmission cooler, and get something like a Scangauge II for displaying Trani fluid temperature.

Without a trailer, just take a regular sedan and load it with people and luggage - I think many people would be surprised how hot Trani fluid gets, even with a driver with a light foot. Rolling hills or stop/go traffic are a tough load, as the trani is always shifting - every shift produces heat.

IMO, a trani temp gauge is critical for towing (any automatic equipped vehicle), and with todays OBD ports on the cars and $150 plug'n'play meters available, there isn't much excuse for not using one. In many vehicles, by the time your coolant temp gauge is showing a major deviation, your trani is well on it's way to baking.

It's no fun breaking/wearing out basic mechanical items (bearings, brakes, springs, or tearing the floor out of your trunk), but at least they are way less spendy to repair than a transmission.

Rgds, D.

I was thinking of the RV commercial exemption, which in ontario is 4500kg GVWR for both the truck and trailer combined. There was a whole thread on an Ontario motorsports forum about towing and it is a confusing mess. Rules change for an Excursion vs. an F150, etc.... So confusing that one guy carries around copy of the highway traffic act to inform the police of the rules that allows him to use his tow setup.

 

[3930dave]

Agreed Ian - I'm lost in ON land too, in terms of making sense of the trailer regs here..... but I've done enough ranting on that subject in other threads.

Suffice to say that the Green Bears (MTO) here should understand the regs, but I'm pretty sure most LEOs here don't. Not disrespecting LEOs - if we brought Hunter S. Thompson back to life, and he did a "Trailer Tales" movie with Tim Burton and Johnny Depp, it couldn't get much weirder than what passes for reality at the moment.

So... back to the thread...... here (Ontario), if it is a "shades of gray" in terms of what somebody should be towing, I suspect most LEOs would either let it slide, or call MTO for an assessment.

OPP (our provincial police) does tend to target major 400 series highways, along with MTO, for good reason this time of year. Plenty of "borrowed Uncle Bob's 30 y/o falling apart trailer to take a pile of stuff to the cottage" folks heading out locally - in many of these cases, the towing capacity of the vehicle is a lesser problem.

Pull safe. D.