Towing Weight vs Frontal Area Ratings

[charliem]

[font size="3"]Whoofit,

Thanks for this instructive posting: [a href="http://livinlite-owners.com/post/21200/thread"]http://livinlite-owners.com/post/21200/thread[/a][a href="http://livinlite-owners.com/post/21200/thread"][span] [/span][/a]   It's difficult to get the true answer with all the conflicting info out there.

I was thinking of writing something on the towing capability of small TVs with small engines, but your post really highlights the issue. Even though the Escape is rated at 3500# the cross sectional area is only rated at 30 sq. ft. This points out the real limitation of newer small SUVs. Rated towing weight is only a part of the equation. The auto companies are going to smaller and smaller engines in a desperate attempt to meet Government imposed fuel economy standards, but this results in poor performance and limited engine longevity when towing. Unfortunately this is seldom pointed out to the buying public. We are told "It's rated at 3500#, no problem." It's never revealed that towing a 3500# high cross section travel trailer is way different than towing a 3500# boat, popup, or flatbed trailer. For example, the Escort is rated at 30 sq. ft. cross sectional area with the 2.0L turbo Ecoboost engine.  Any of the Camplites, regardless of length or weight, will be almost twice that value (7'x8'=56). I assume the 3500# rating will assure safe braking, but buying a small engined TV for a CL is bound to lead to disappointment and expensive engine/transmission replacement down the road.

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[whoofit]

I agree. Never had a problem towing the 16DB with the Escape other than at highway speeds.

[david]

You are correct Charlie. I believe that the new 2 liter Eco Boost engine is simply too small to tow any of the full height Camplite's. Ford's 30 SF spec (which as you note, everyone disregards) proves it.

I firmly believe that you need at least a 3.0 liter engine to tow a CL 11 or 14, a 3.5 liter to tow a 16, and a 4.0 liter to tow a 21. And those numbers are irrespective of turbocharging. Turbocharging increases peak horsepower but does nothing for ring and bearing wear.

You can tow with less, but you are wearing out your engine faster. As an old hot rodder once said "nothing beats cubic inches". Not so true today in the turbocharged world, but still true for longevity.

Many, many years ago I had a heavy Coleman pop up with a canoe on top that I towed with a 1.6 liter VW wagon, probably 25 SF frontal area. I put 5-10,000 miles on it while towing the Coleman. After 70,000 overall miles it was burning oil and the rings were shot.

David

[charliem]

[font size="3"]Roger that, David. So would you please write Toyota and have them offer a V8 in the Tacoma. I've been unsuccessful so far so I went to the supercharger. Even with the SC or TC, there's no substitute for cubes. Where is the old time tested Chevy 350 CID?  RIP.  
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[tinkeringtechie]

[font size="3"]Roger that, David. So would you please write Toyota and have them offer a V8 in the Tacoma. I've been unsuccessful so far so I went to the supercharger. Even with the SC or TC, there's no substitute for cubes. Where is the old time tested Chevy 350 CID?  RIP.    
[/font]

The Tundra is only a little bit more... plus 2016 Tacomas look weird.

[charliem]

[quote source="/post/21212/thread" timestamp="1463442184" author="@tinkeringtechie"][quote timestamp="1463437961" source="/post/21211/thread" author="@charliem"][font size="3"]Roger that, David. So would you please write Toyota and have them offer a V8 in the Tacoma. I've been unsuccessful so far so I went to the supercharger. Even with the SC or TC, there's no substitute for cubes. Where is the old time tested Chevy 350 CID?  RIP.    
[/font][/quote]The Tundra is only a little bit more... plus 2016 Tacomas look weird.

[font size="3"]It wasn't the cost; it was the size of the Tundra. I originally wanted an F150, but too big for my wife and I sort of agree. I don't like to use a step stool to get stuff out of the back. On the 2016 Tacomas, you may be right. I haven't paid much attention to them yet. [/font]
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[pinstriper]

[fasteddieb]

Let me reiterate that I'm a relative newbie, so take this as simply anecdotal.

For our Flex with 3.5l boosted V6, Ford lists 40 sq ft frontal area limit (together with a 4,500 lb limit with wd hitch and 450 lb max tongue weight).

I figure the frontal area of our 21BHS is about 63 sq ft (9*7).

I also know our tongue weight exceeds Ford's limit, but we did at least have the hitch reinforced.

Again, only anecdotally, 2+ years and about 10,500 miles of towing and no issues. Yet. We do usually limit our speed to 55mph, both for safety margin and fuel consumption.

[gnies]

So does that mean that with my Escape and my 13QBB I am pushing it?

[charliem]

[quote timestamp="1463496373" author="@paul" source="/post/21241/thread"]So does that mean that with my Escape and my 13QBB I am pushing it?[/quote][font size="3"]Paul,

Assuming you have the 2L Ecoboost I think it depends on your habits. The issue is wind resistance which is proportional to the square of velocity (speed). You will be stressing the engine trying to maintain 60 mph (~100kph) and/or climbing the Canadian Rockies. But, as I believe is your case, your CL spends most of its time in your seasonal site, the added wear is minimal. Just don't push it on the way home and you'll be OK.
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[david]

Paul:

First a bit of tutorial on towing, off the top of my fuzzy head!

Frontal area is the biggest component of drag, probably 75% of the total at 60 mph. Rolling resistance is the rest. So at a level, steady state speed of 60 mph, a CL 11 might require 40 hp, a CL 13 a few hp more, a 16, a few hp more and a 21 roughly 10 hp more. It doesn't change much because the biggest component of drag, frontal area is the same for all four units.

But hp for acceleration and hill climbing are directly related to weight. The CL 21 weighs almost double that of a CL 11, so it will take double the hp to accelerate or climb at the same rate. But the climbing or the acceleration rate is the important parameter. If you want to climb a 6% grade at 60 mph, it will take a lot of hp. But if you slow down to 40 and shift to a lower gear it will take only 2/3 of the hp. It is just like getting a bigger engine if you slow down while climbing.

For my own experience while climbing, I can watch the dashboard fuel consumption data (which is fairly accurate) and see that starting at a flat fuel burn rate of 13-14 mpg at 60 mph, it drops to 8 or so while climbing a 6% grade at 40 mph. If I goosed it up to 60 mph it would drop through the basement. MPG is inversely proportional to fuel burned in gal/hr which is almost directly related to hp used and engine stress.

Hill climbing puts stress on the engine and the only way to deal with that is to slow down or get a bigger engine to reduce the stress.

I based my rule of thumb above (a 3 liter for a CL 11 or 13, a 3.5 liter for a 16 and a 4 liter for a 21) on my own experience towing a 16 with a 3.5 liter as well as some feedback from others here, and adjusting upwards or downwards for CL aize and weight.

So, back to Paul's question, you have a 2.5 liter Escape towing your CL 13, right? So yes I think you are marginal. Nothing immediately bad is going to happen however. The engine will just wear faster than a 3.0 liter and if you stay away from the mountains, or slow down but stay in a lower gear and let the revs go up while climbing them, you will be fine.

David

[gnies]

[quote timestamp="1463496373" source="/post/21241/thread" author="@paul"]So does that mean that with my Escape and my 13QBB I am pushing it?

[font size="3"]Paul,

Assuming you have the 2L Ecoboost I think it depends on your habits. The issue is wind resistance which is proportional to the square of velocity (speed). You will be stressing the engine trying to maintain 60 mph (~100kph) and/or climbing the Canadian Rockies. But, as I believe is your case, your CL spends most of its time in your seasonal site, the added wear is minimal. Just don't push it on the way home and you'll be OK.
[/font][/quote]Yes most time my trailer is at my seasonal site, but I go out about 4 or 5 times during the summer. This year my longest trip will be 900 kms (558 miles) round trip and my other trips will be less than 200-300 miles round trip. I participate to some Geocaching event around the province that's why I go out often with my trailer :-)

[gnies]

Paul:

First a bit of tutorial on towing, off the top of my fuzzy head!

Frontal area is the biggest component of drag, probably 75% of the total at 60 mph. Rolling resistance is the rest. So at a level, steady state speed of 60 mph, a CL 11 might require 40 hp, a CL 13 a few hp more, a 16, a few hp more and a 21 roughly 10 hp more. It doesn't change much because the biggest component of drag, frontal area is the same for all four units.

But hp for acceleration and hill climbing are directly related to weight. The CL 21 weighs almost double that of a CL 11, so it will take double the hp to accelerate or climb at the same rate. But the climbing or the acceleration rate is the important parameter. If you want to climb a 6% grade at 60 mph, it will take a lot of hp. But if you slow down to 40 and shift to a lower gear it will take only 2/3 of the hp. It is just like getting a bigger engine if you slow down while climbing.

For my own experience while climbing, I can watch the dashboard fuel consumption data (which is fairly accurate) and see that starting at a flat fuel burn rate of 13-14 mpg at 60 mph, it drops to 8 or so while climbing a 6% grade at 40 mph. If I goosed it up to 60 mph it would drop through the basement. MPG is inversely proportional to fuel burned in gal/hr which is almost directly related to hp used and engine stress.

Hill climbing puts stress on the engine and the only way to deal with that is to slow down or get a bigger engine to reduce the stress.

I based my rule of thumb above (a 3 liter for a CL 11 or 13, a 3.5 liter for a 16 and a 4 liter for a 21) on my own experience towing a 16 with a 3.5 liter as well as some feedback from others here, and adjusting upwards or downwards for CL aize and weight.

So, back to Paul's question, you have a 2.5 liter Escape towing your CL 13, right? So yes I think you are marginal. Nothing immediately bad is going to happen however. The engine will just wear faster than a 3.0 liter and if you stay away from the mountains, or slow down but stay in a lower gear and let the revs go up while climbing them, you will be fine.

David

Hi David, thank you for your post. Yes I have the 2.0 liter turbo Escape. I am a bit concern about the wear and tear I put on my Escape and also safety. I also often bring bikes on my roof which I am sure does add to the drag! I am thinking I do no more than 2500 miles a year with my trailer.

[daplumbr]

It's a shame helpful and important information like in this thread (and others) is not routinely available. I agree with Charlie the buying public is not well informed. I know Honda rates the Pilot differently for towing a boat vs towing a camper due to the frontal area (aerodynamic) differences and that car manufacturers have put a lot of design time into improving the "slipperiness" of vehicles. 

As a relevant aside, I wish all RV retailers had scales for tongue weight, trailer weight and vehicle weight. It could improve safety on the road if the buying public knew those numbers and kept things within specs. Some of the rigs I see on the road now were clearly the result of an overly-enthusiastic salesperson and an ignorant buyer.

[gnies]

[quote source="/post/21249/thread" author="@sandroad" timestamp="1463507164"]It's a shame helpful and important information like in this thread (and others) is not routinely available. I agree with Charlie the buying public is not well informed. I know Honda rates the Pilot differently for towing a boat vs towing a camper due to the frontal area (aerodynamic) differences and that car manufacturers have put a lot of design time into improving the "slipperiness" of vehicles. 

As a relevant aside, I wish all RV retailers had scales for tongue weight, trailer weight and vehicle weight. It could improve safety on the road if the buying public knew those numbers and kept things within specs. Some of the rigs I see on the road now were clearly the result of an overly-enthusiastic salesperson and an ignorant buyer.[/quote]Yes I wasn't aware of this! I am all worried now, I don't like to be over the limit. I am trying to convince my wife that we need to buy a truck now