By on April 19, 2012

 

Mike writes:

Dear Sajeev,

I have been a fan of TTAC for a while now. I am motivated to write by the recent responses to towing with a 2005 Odyssey. Two years ago I bought a 2008 Toyota Sienna and a 21 foot (actual total length) travel trailer. The trailer has a GVWR of 3500 lb, which the Sienna is rated to tow with its towing package. I had an independent shop install a fluid-to-air ATF cooler, unfortunately, perhaps, choosing the smallest model as it was recommended for a 3500 lb tow. I was concerned about getting too much cooling in the winter. The van already had an ATF cooler in the radiator. I had them put in an ATF temperature gauge (before the radiator) at the same time. The towed weight of the trailer is several hundred pounds below the GVWR, but it has a front profile that is basically vertical. I have towed the trailer about 20,000 km (yes, I’m in Canada) and done what Toyota calls an ATF change three times. That’s actually a drain the pan and refill with 4 L of ATF, not really a change. Of course, I have no way of knowing how accurate the gauge is, but the highest it’s been on the highway is 220 F on a couple of grades in the BC mountains (Coquihalla highway). The temperature went down as soon as the grade did. It went up to 240 F or so for a few minutes while backing up a steep hill and around a bit of a corner into a storage yard. The van had 38,000 km on it when purchased and is now at 82,000 km.

Enough background. I am writing to ask why it is apparently okay to tow a larger trailer (5000 lb rating) with a Highlander but not a 3500 lb trailer with a Sienna. As far as I can tell, the engine, transmission and weight of the vehicles are basically the same. The internet is rife with posters who advise against towing with a minivan but seem to have no qualms about doing so with a SUV, except the very smallest.

What do you think?

Thanks very much for helping me out with this. I can find no answer to my question on the internet.

Sajeev answers:

Wow, you actually put an ATF temperature gauge (among other things) in a minivan?  This is why I love TTAC: our readers do some rather brilliant and enlightened things outside of their computer time.  Well, at least some of you.  I kid, I kid!

There are crucial elements that go into a tow rating: the vehicle’s weight, braking capacity and rear spring stiffness.  The 2012 Sienna is about 200lbs heavier than the 2012 Highlander, for starters.  Who knows, maybe the brakes aren’t good enough for a Highlander sized trailer and the Sienna body.  Ditto the rear springs.

I never had much faith in manufacturer tow ratings, until the Society of Automotive Engineers (SAE) came up with their Surface Vehicle Recommended Practice J2807: which supposedly standardizes these figures.  Is J2807 is be all, end all of towing standards?  Maybe so, but this terribly formatted article gives you more insight.  Definitely cut and paste this one into Word before reading.

While this many not fully answer your question, hopefully this will tow you (sorry) in the right direction.

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry.

 

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23 Comments on “Piston Slap: Crossing over into Minivan Tow Ratings?...”


  • avatar
    mdensch

    There is another factor to consider. The legal and marketing departments have as much input into figures such as a vehicle’s tow rating as the engineering departments do.

    • 0 avatar
      psarhjinian

      +1

      Note that the Highlander retails for more than the Sienna (and the Pilot versus the Oddy, Freestyle/T-X/Flex versus Freestar, Entourage vs Veracruz, etc, etc).

      Crossovers are a great way to get consumers to spend more on a cheaper vehicle (don’t need to engineer those tricky sliding doors!). Why not use something arbitrary like tow ratings to push someone into a higher-margin vehicle.

      Which, of course, ultimately leads to SUVs based on half-ton trucks: cheaper than either a unibody crossover or minivan to make, and yet more expensive to buy. Gross margin FTW!

    • 0 avatar
      Detroit-Iron

      I doubt they were different specs at the time, but the 2003 Focus was rated to tow 2k in the US and 3k in Canada. I think that had more to do with our litigiousness down here than the capabilities of the vehicle.

      • 0 avatar
        Luke42

        I used to think that litigiousness and marketing were the only factors in the towing differences between nations.

        But, when I delved in to the reasons why towing is not recommended with the Kia Soul in the USA, while it’s an award-winning tow car in the UK (http://www.carpages.co.uk/kia/kia-soul-25-09-09.asp), with a capacity of 2800lbs (with trailer brakes) and a tung weight of 114lbs.

        While marketing undoubtedly has something to do with this particular case, I found a couple of real differences between the US and the UK. In particular:
        1. European rules require trailer brakes in more instances than the than US rules.
        2. European rules specify a speed limit for towing vehicles that’s a around 60mph (or a bit less), no matter what the road type.
        3. The recommended towing capacities have more legal force in the UK and EU than they do here in the USA.

        These are both things that make an actual practical differences between the UK, the EU, and the USA. But, as I said, I went from thinking that the differences in towing capacities were all for “soft” reasons to thinking that there are some real practical differences in road-behavior and driver’s expectations that affect how much I would be comfortable towing.

        Maybe some of The Best and Brightest from the Canada, the UK, and Europe can fill in and correct this.

  • avatar
    BunkerMan

    Before we got our new trailer (29′ inside length, 6000+ lbs) we had a 10-ft tent trailer (not total length) that weighed around 2000 lbs dry. In the beginning, I towed it with a 2002 Mazda MPV with a transmission cooler. It was rated to tow 3500 lbs.

    Even with the tranny cooler, the floor between the front seats would get pretty warm after an hour or so of towing. The real issue however, was the brakes. Since the trailer was just below 2000 lbs unloaded, the manufacturer was not legally required to fit it with brakes. I had to be quite careful towing that thing around town fully loaded with 4 people in the van. Stopping was more of a suggestion and required a lot of planning. Scraping the hitch on the pavement when exiting parking lots and dragging the safety chains was pretty common too.

    We got rid of the van eventually and inherited a 2007 Saturn Vue (with the Honda 3.5 engine). Its tow rating was also 3500 lbs, but the difference was night and day. The higher ride height and larger brakes made it effortless to tow and stop that trailer. The extra 50hp or so didn’t hurt either.

    From this experience, I’d have to say that the ride height, suspension, and size of the brakes has a lot to do with tow ratings. I think the wheelbase plays a part too. That’s why Wranglers aren’t supposed to tow much, even though they appear to be quite capable of doing it.

    Of course if the trailer has brakes and you have a proper weight distribution system, that changes things.

    • 0 avatar
      OldandSlow

      I think you are on to something important with regards to differences in ride height and rear suspensions.

      The last time I rented a mini-van for vacation, I noticed two things. First, the load floor was really low compared to my Mazda Tribute. Second, we took more stuff along than in my Mazda Tribute. The low floor height made that possible – but I’ll bet mandates a rear suspension that is less suited for towing.

      Finally, a good call by the original post to Sajeev regarding periodic draining and refilling of ATF on a tow vehicle far more frequently than the owner’s manual prescibes. I just don’t trust an automatic FWD transaxles to handle the hills without heating up beyond the designed duty cycle.

  • avatar

    For the sake of braking, cooling, and stability (of the rear suspension)I would NEVER push my vehicle to its maximum tow-rating. WHen it comes to travel trailers you should only consider the dry weight as a starting point. Matching a 3500 dry weight trailer to a 3500 lb towing capacity of the vehicle is just asking for trouble.

    My travel trailer is rated at 2500 lb dry. I count on another 1000 lbs of added weight when you include things like passengers in the vehicle and your RV loaded with various equipment. This gives me about 3500 lbs loaded weight that my vehicle is expected to handle.

    Tow ratings are not based on chassis stiffness and “will the hitch break off my vehicle” kind of though, but it’s based on the combination of things. Look at the new Ford Escape as an example. The top tow rating is 3500 lbs with a 4-cylinder engine. To get this rating s a combination of HP/tourque, wheelbase, suspension, engine/trans cooling, and most importanly braking. These considerations are based on many towing variables such as steep grades and extreme heat. So, the Escape can come with a “base” tow rating of 1000 lbs, but with the right equipment can come with a 3500 lb tow rating.

    This isn’t the UK. We take our towing seriously in this country ;)

    • 0 avatar
      OldandSlow

      … and pay attention to tongue weight.

    • 0 avatar

      The other example I wanted to mention, but forgot to do, was regarding my reference to wheelbase.

      I like to use the current Jeep Grand Cherokee and Dodge Durango as an example.

      Both vehicles share the same basic chassis and powertrain. They are built on the same assembly line yet the Durango offers a slightly higher maximum tow rating over the Grand Cherokee. It’s not a marketing gimmick to try and sell the larger Durango, but the fact that the Durango has a slightly longer wheelbase gives it better stability, thus allowing for a heavier tow rating.

      If you look at the equipment on each of the vehicles, you can get them with identical powertrain and equipment.

      • 0 avatar
        BuzzDog

        In my opinion, an even better example is the comparison of the Jeep Wrangler Unlimited (four-door) to the “regular” Wrangler (two-door).

        Other than the wheelbase and curb weight, they’re basically the same…but the Unlimted is rated to tow up to 3,500 pounds, versus 2,000 for the two-door.

  • avatar
    grzydj

    My rule of thumb for towing a trailer is never tow near your vehicles capacity. If your max tow rating is 3500 pounds, then only tow up 3000 especially if you have an automatic transmission, even with an auxiliary cooler.

    I’ve always ignored my own rule of thumb for pickups with manual transmissions that I’ve used for towing because heat isn’t a problem with the gearbox and ample use of engine braking down long hills limits heat build up on the brakes. I learned this rather quickly by being about 20% over the towing capacity of my Toyota Hilux towing through the Smokey Mountains.

    Do as I say, not as I do.

  • avatar
    gslippy

    Two years ago I towed a U-Haul on a cross-US camping trip with our 09 Kia Sedona, which is rated for 3500-lbs towing. I estimated that we were actually towing about 1800 lbs, but with the car filled with 7 people and stuff, our total road weight was about 7300 lbs.

    Results – no problem with brakes, V6 engine, or transmission, but I was careful. Average speed was about 70 mph, and we averaged about 12 mpg due to the extra weight. Don’t let people tell you that highway mpg is only about aerodynamics. Vehicle weight (friction) has a lot to do with it.

    I was glad to not be towing the full 3500 lbs, however. I think total road weight should be a consideration when towing, but I don’t think most mfrs publish recommendations about that.

  • avatar
    phlipski

    I’ve towed a boat that with gas/trailer you’re looking at almost 3500lbs for about 5 years now. I currently use an old 89 suburban, but previously used a 97 explorer (v6) and a 98 ml320. Even though the suburban is bigger, has more torque and a longer wheelbase then the ml or explorer, I’d say the ML was the better tow vehicle. Why? Brakes. Engine power is probably the least important factor in towing – as long as you’ve got enough to pull the boat out of the water. I don’t think you can ever have enough stopping power – and the tiptronic auto in that ML made engine braking a breeze. That said maybe my burban needs a brake job….

  • avatar
    DC Bruce

    Considering the rather marginal braking performance of some of these vehicles (e.g. the Honda Pilot, which I own) as shown by buff book tests with a basically empty vehicle, the idea of filling them up with people and stuff and also pulling a ton or more behind them with no additional braking capacity (i.e. no trailer brakes) is just plain scary to me. Forget about blowing your tranny, forget about cooking your brakes and/or your autobox on long downgrades. What about stopping in a hell of a hurry in an emergency? That’s just not gonna happen. . . or it’s gonna spin the towing vehicle if the emergency braking happens to be on a curve.

    70 mph towing a one and a half ton trailer with no brakes of its own? You gotta be kidding.

    • 0 avatar
      don1967

      I don’t think any CUV in North America is rated to pull 3500 pounds without trailer brakes. The fine print in the owner’s manual typically sets a lower (ie: 1000-2000 lb) limit for non-braked trailers.

      Based on my experience with a Nissan Quest and a Santa Fe, I’d argue that the old 50% rule of thumb is a reasonable one. A 4000-pound minivan or CUV should be able to safely stop a 2000-pound non-braked trailer, with a bit of added care from the driver of course. Exceeding this limit, however, virtually guarantees overheated brakes and/or train-like stopping distances.

  • avatar
    redmondjp

    One solution that hasn’t been brought up yet is to ADD trailer brakes. Most trailer axles can be easily retrofitted with either hydraulic (surge) brakes or electric brakes (with a brake controller mounted below the dash) for $500 or less in parts (per axle).

    I have a Demco tow dolly without brakes, and it gets dicey when hauling any vehicle over 3K lbs. Surge brakes would make a huge difference and I have been looking into adding them.

  • avatar
    Toad

    Crazy idea: RTFM and follow it. If the company that spent many millions of dollars engineering the vehicle components gives it a specific tow rating not to be exceeded, don’t exceed it. Better yet, don’t exceed 75% of it. Just because your engine has a maximum RPM of 6500 does not mean you would drive with the engine spinning that fast all day. Why treat your brakes and suspension with equal disdain?

    Engineers are actually pretty smart, and they have a pretty good idea about the overall limitations of the vehicle they designed. If you don’t think they knew what they were doing when they designed your vehicle you should not have bought it in the first place.

    On the bright side people not towing properly provide lots of fun on YouTube.

    • 0 avatar
      don1967

      That doesn’t explain why European vehicles consistently get higher tow ratings than North American vehicles of the same design. Unless one believes that Europe has less gravity, of course.

      • 0 avatar

        I’d be shocked if Euro and US (SAE) towing standards are using the same measuring stick. Not to mention that us ‘Mericans in the flyover states tend to drive (well) over 70 MPH while towing on a regular basis…and most roads in Europe make that impossible to duplicate.

        That is a LOT of inertia to stop, and it doesn’t exist in Europe.

        I blame the US Interstate system and our love of buffets. (kidding)

      • 0 avatar
        Luke42

        “That doesn’t explain why European vehicles consistently get higher tow ratings than North American vehicles of the same design.”

        I did some reading about this, and I found that Europe has a towing-speed-limit that’s under 60mph (maybe even closer to 50mph), no matter what the road type. So, if you’re towing a trailer on a European equivalent of an Interstate, you’re Expected to lumber along at 50-60mph, no matter how fast the other traffic is going.

        The European rules also favor different types of trailer braking systems, and they’re required on more/smaller trailers.

        Then add in the marketing differences (it’s easier to talk an American into an F-150 that they don’t really need), and the litigiousness, and I think that’s sufficient to explain the differences between the US and the EU/UK rules.

        “Unless one believes that Europe has less gravity, of course.”

        [Pedantic didactic screed on the differences between mass and weight, as well as how weight creates traction, has been deleted for the sanity of all. Look in any physics FAQ for a discussion of weight vs. mass for the details.]

    • 0 avatar
      bikegoesbaa

      Great idea!

      One thing – can I pick which manual I want to read?

      If so, I pick the European one that says my car is rated to tow 1,000+ pounds as-is; rather than the US one that says the very same car isn’t able to tow anything.

      I’m confident that the engineers knew what they were doing when they designed the vehicle. I’m not confident that the marketing guys and legal eagles are setting different tow ratings for different markets based on sound technical reasons.

      • 0 avatar
        Luke42

        Ever notice that many World cars even have threaded holes for mounting a trailer hitch, even when towing is Not Recommended?

        But, as I said above, the differences go beyond just marketing and legal reasons. Trailer brakes and speed limits (for combination vehicles) are different between the US and Europe. So, if you promise to drive your car the way a European drives his car on a European road, then you can use the numbers in the European manual…

        Still, using artificially low tow-ratings for marketing purposes does hurt buyers here. For instance, I’d have bought a Kia Soul if the manual said I could tow 1200lbs with it. The UK version is rated to tow 2800lbs, and towing is contraindicated in the operations manual of the US version — so, I bought a beater-Escape instead. In other words, I settled for a car that’s less-well suited for my purposes so that I wouldn’t have to prove to dealer service departments and/or cops who want to give me a rough time that my vehicle is capable of towing some very modest loads that the Soul’s sheetmetal, suspension, and drivetrain really is capable of handling.

  • avatar
    fatehunter

    My car is a 2003 Audi a4 wagon with a 1.8 L turbo. The tow rating is 2000lbs and I tow 2000 lbs (pop-up trailer). Mind you, there are electric brakes on the trailer. Longest drive is from Prince Rupert in BC through the coast mountains down to Vancouver, BC. I also tow 1500 lbs of boat (+ trailer). No brakes on the boat trailer so I keep it below 110 km. I love the looks on faces when I use my audi to launch my boat (16 ft cabin fishing boat). My audi is my beater truck when it tows my full size utility trailer. a yard of dirt weighs near a ton so that trip is nice and easy from the dirt yard to home.

    You can tow if you stay with-in the capabilities of the equipment. Ask for more and you are not going to get it. However, here in NA we love to blame others for our own lack of fore-sight, in other places they say you can do it, but follow the rules. I have experience (lived in Holland for 7 years).

    With regards to the audi, The RV dealer was very surprised when the 150 lb tongue weight only dropped the back end of the audi by one inch. I think the suspension on this car make a big difference, as many minivans just drag with weight in the back.

    bottom line I think is that some vehicles are better suited just because of their basic construction standards.

    In reality my audi is a piece of shit, new(er) engine at 180,000 km because of a cracked head, all kinds of other shit including a steering rack adding up to $10000 (not including engine) over the last four years. I hate the ****ing car to maintain, but I sure love to drive it. Came from Subaru’s, don’t want to get another Audi, what do I do?


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