to me the most important thing would be the trailer’s brakes. as for your other concern, “underpowered” is relative; people were towing that much in the '90s with F-250s which had only 200-240 horsepower, and you have 380. and it really isn’t about how powerful the engine is, but making sure it stays cool.
There are three weight limits to consider, and they all need to be met.
GAWR - Gross Axle Weight Rating - This is the maximum weight that can be placed on the axle. Especially important with a fifth wheel as a considerable portion of the trailers weight is carried by the rear axle of the tow vehicle (unlike a tag trailer), along with the weight of the trailer hitch.
GVWR - Gross Vehicle Weight Rating - The maximum weight that can be carried by the truck itself. This may be less than the sum of the two axle GAWRs, since the truck’s frame is also a factor. Again, a fifth wheel’s weight on the truck will impact here.
GCWR - Gross Combined Weight Rating - The maximum amount that the truck plus trailer can weigh.
Also, towing capacity is usually calculated by truck manufacture’s by taking a stripped down truck (no cargo, no fifth wheel hitch, and no passengers) and subtracting the weight of that truck from the GCWR. You need to weigh your truck, fully loaded as you would on a trip, and including the fifth wheel hitch weight, to find out what your towing capacity really is (and as long as you do not forget the weight ratings described above).
Be wary what your trailer dealer “expert” tells you. I once pulled in with my Ford F150, and was told that I could tow everything that he had on his lot. Right.
Towing overweight does not mean an automatic vehicle failure. What is does mean is that damage can occur that might not be evident until much later. Another words, cursing the truck because it completely self destructs at 100,000 miles, instead like your neighbors whose truck lasted 200,000 miles.
Another thing to consider: If you are involved in an accident, and are found to be towing over-weight, you could be setting yourself up to loose the inevitable law suit, even if you are not at fault.
Ok - Let’s take a quick look, using a market I’m familiar with (disclaimer - I do some work for a partner of BMW)
BMW X5 30d / 16.1km per litre / 560 nM torque / $382,800
BMW X5 35i / 11.8km per litre / 400 nM torque / $336,000
That’s a 14% price differential for a 40% torque differential for a 36% efficiency differential.
From here
Let’s use the pricing as $2.32 for gas and $2.78 for diesel. (gallon)
Convert to litres we get 73.5 cents and 61.4 cents respectively
Convert that to fuel cost per 100 km and we get —
$4.56 for diesel and $5.20 respectively
Take the difference of 64 cents per 100 km and you get 125,000 km (78,000 miles) to make back your $8,000 cost differential.
If instead of the 35i we compare the oil burner to the 50i
The 50i gets 9.5 km/l with torque of 650 nM
In this case the cost differential per 100 km is $1.90
So to make back the $8k difference is 42,000 km - 26,000 miles
Of course - the mileage figures for the combined cycle aren’t going to be anywhere close to what you get while towing a 5th wheel - but it does put some perspective yes?
Somebody with more time than me might be able to look up some consumption comparisons while under load, as well as truly matched engines in terms of torque - but for me, if there were a $8k price differential between the 35i and the 30d -
I’d sure be going for the 30d - every single time.
A quick search found two more closely matched models
The Cayenne GTS and the Cayenne Diesel
The GTS has torque of 600 while the diesel is 580 - a difference of just 3%
The economy figures (combined cycle) are 9.8 litres per 100 km vs 6.6 litres per 100 km
So…
Cost per 100 km for the GTS is $6.02 vs $4.85
I tow a 7500 lb bumper pull RV trailer with my Tundra, equipped like yours, and it handles it very well. It is definitely not underpowered. In about 8000 miles of trailer hauling, through coastal California, the Sierras and southwestern Rockies, I’ve only found two grades that I couldn’t pull at the speed limit. The main concern for a fifth wheel is bed size. My truck is a Crew Max 4 door with a 5’6" bed. When I researched a fifth wheel for it, I discovered that Toyota does not recommend towing any fifth wheel trailer with a Crew Max. Unless you buy a very expensive sliding hitch–and maybe not even then, the trailer can bend the corners of the cab on tight turns. My brother in law has a short bed Dodge diesel and did just that, so I’m a believer.
I’ve spent quite a bit of time towing a 5th wheel with a half-ton. I’d like to point out a few things you should consider.
For starters, aa6vh covered the basics of GCWR/GVWR/etc. very well. You will likely find your limit is either the GCWR or the capacity of the rear axle. A word of caution on weights; If you’re using the trailer manufacturer’s published weight for your trailer, you should probably add at least 1200 lbs to it. This ends up being about right for me, once I take the loaded trailers to the CAT scales and get an accurate weight. You may find that the published “curb” weight for your truck is also very optimistic. I don’t know about Toyota, but the listed weight is often the weight for the lightest version (single cab, short bed) and it’s up to the owner to find the actual weight.
For example: The published weight on my trailer is 7200 lbs. Loaded (2/3s water) it shows 8300 lbs on the CAT scales at the truck stop. Ditto my truck; IIRC the weight showm on the docs is 5200 lbs. Actual weight at the truck stop scales is 5850. All told, this is 1750 pounds over what the manufacturers would lead me to expect. I also took axle weights with and without the 5th wheel. Manufacturers brochures say 800 lbs pin weight. Scales say 1100. My little truck only has 1370 available to add to the (unloaded) rear axle so this severely limits what can be carried in the bed when towing. My tow rating (GCWR) is 15,050, and with both trailers in my setup, I’m right at the upper limit. It tows, handles, and brakes just fine. IME, trucks will tow at their max tow rating without any problems, but you need to weigh everything to be sure.
Now (if you’ll tolerate it), a bit more advice. In this thread about pickups, I told my experiences while shopping for a replacement truck (to pull my 5th whl, doubles rig). I found that the Toyota was unsuitable for 5th wheel towing due to the height of the bed walls (or “depth” of the bed, if you wish). I couldn’t get adequate bed-rail clearance on either an RBW or Curt 5th wheel hitch. Even at their max height adjustment, there was insufficient room to account for normal rocking motions of the trailer itself. This is based on the manufacturers minimum clearance. You might want to investigate this by measuring your pinbox (dist from bottom of trailer) and the max height of your planned hitch. Compare this to the depth of the Toyota bed, and you may discover it to be incompatible with the trailer.
I hope it all works out, but I thought I’d toss in the warning. Just my $0.02
Disclaimer: The weights given above are for a different trailer than that in the pic.
I realize this is drifting into GD terrirtory, but here is a GQ:
I always thought that diesel had an inherent advantage in producing torque, especially low end torque (important for towing/hauling/pulling) because of its ability to run at very high compression ratios (Wiki says 15-20, but I thought it was usually 16).
I am not aware of any normal application* where gas gets even close to that- 12:1 is pretty high compression in the OTR world; 10-ish is the highest I have seen in any consumer vehicle since the 60s.
If all that is correct, then it does represent a real capability difference between diesel and gas. If gas were to perform equally at the same compression ratio, but operating gas at that compression ratio isn’t possible or practical, then that (IMO) is a meaningless hypothetical.
I am open to having my ignorance fought.
*I am excluding exotic applications like purpose-built race cars; I’m talking about an OTR vehicle that any consumer or business could walk in and buy
Since you keep talking about an $8000 price differential I’m assuming there’s a typo in there somewhere. I see a $46,800 price differential.
no. the high compression ratio (and subsequent high expansion ratio) contributes to the diesel’s superior efficiency. But an engine’s torque potential relies almost entirely on its displacement and the peak BMEP (Brake Mean Effective Pressure) it can generate. peak BMEP is lower in a diesel compared to a gas engine (on a like-for-like comparison.) So (again) all else equal, a diesel will have lower torque output than a gas engine of similar displacement. The reason diesels have acquired a reputation for being “torque monsters” is because people have been almost always comparing turbodiesels to normally aspirated gas engines. now that turbocharged gas engines are common they’re running away from diesels.
case in point; the 2.0 TDI in VW/Audi cars puts out 150 hp and 236 lb-ft of torque. The 2.0 GTDI in Ford cars puts out 240 hp, 270 lb-ft of torque. GM’s 2.0 GTDI has 250 hp, and 260 lb-ft. The diesel is not the torque monster here.
Direct-injection diesels typically have compression ratios in the range of 15:1 to 18:1. The indirect-injection (pre-chamber) engines used in the '70s and '80s ran about 19:1 to 22:1.
the compression ratios on gas engines are creeping up, too. Direct injection provides a charge cooling effect because the gasoline evaporates inside the cylinder (cooling the mixture) instead of in the intake runner. So now we have turbocharged gas engines which still can have 10:1 or 11:1 static compression ratios, and Mazda’s SkyActiv engines in naturally aspirated form are at 14:1.
The prices I quoted are Singapore prices - the $8k comes from an earlier post as being mentioned as the US difference between a diesel and a petrol -
Round here we have a lot of taxes on vehicles
Vehicle OMV ARF Rate
First S$20,000 100%
Next S$30,000 (i.e. S$20,001 to S$50,000) 140%
Above S$50,000 180%
OMV is open market value - otherwise known as price from manufacturer
On a side note: A lot of people tow without having a braking system in place because they don’t want to spend the money on it. It’s required by law in most - if not all - states, whether you’re towing a car or a trailer. As you say, if you’re in an accident and found not to be in compliance, it probably won’t matter if you were at fault or not. Seems like a foolish bet to make.
But don’t we also need the RPM at which peak occurs, as well as the flatness of the curve, to complete the picture?
no, because those are characteristics of a specific engine (e.g. bore/stroke, cylinder count) and not the underlying thermodynamic cycle.
You forgot one measure there. Verano and Focus with their companies’ 2.0L GTDI engine get 24 and 26 combined MPG respectively. The 2.0L TDI in a Jetta gets 36. The diesel is still a torque monster for that level of fuel consumption. The other thing you’re missing with these cherry-picked comparisons is that even though you’re railing against the higher cost of the diesel, all these hot-as-snot GTDI engines you’re pointing to as examples also command a pretty hefty price premium. The TDI is about a $4k option, but the GTDI motors only come in the top trim levels which are going to set you back about $3k-6k versus a comparably equipped version with a more pedestrian gas engine.
My question to you is if diesel has no real advantage as you claim, why have they been building them for decades and decades? Your theory that people are comparing turbodiesels to NA gas engines doesn’t really work because diesel’s reputation for high torque and high efficiency long pre-dates TDI motors.
I think you may be right that gasoline direct injection technology will reduce diesel’s advantage over spark ignition engines considerably as they work out the kinks, but we’re not really to the point that they’re matching diesel on all three performance, price, and efficiency quite yet. Saying that the “conventional wisdom” on diesels is wrong and always has been is simply untrue. GTDI engines might overturn that conventional wisdom in the future, but they haven’t yet.
I’ve already said multiple times that diesel engines have an efficiency and economy advantage. If this is going to descend into constructing strawmen then I’m done here.
How exactly do you compare two engines if you’re not talking about efficiency and economy though? It’s not a particularly profound observation that for any given diesel engine, you can build a gasoline engine with more torque by simply making it a thirstier higher output engine. If it takes a massive 8.0L V10 that gets about 8 MPG to match the torque produced by a 6.0L diesel that gets 18 MPG, that tells me that there IS an inherent torque advantage to a diesel. Sure you can overcome that advantage by throwing fuel economy out the window, but that only really works in markets that have US-style fuel prices.
Your comparison of 2.0L engines earlier is a little misleading because even though those are the same displacement engines, the gas versions are designed to be high-performance engines (with low fuel economy to match) whereas the TDI is pretty much a regular economy car engine. The fact that the humdrum TDI makes the same torque as those two hot hatch engines is further evidence that the diesel torque advantage does in fact exist.