Reversing wheelbase towing rule of thumb? - Fiberglass RV


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Old 05-10-2012, 07:57 PM   #1
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Reversing wheelbase towing rule of thumb?

There is a towing wheel base rule thumb that a 110" wheelbase can tow a 20' trailer and then you can add 1' of trailer for each additional 4" of wheelbase.

I have a 4,000 lb biggar trailer that is 16'6" from bumper to tongue hitch. Is it safe to reverse the rule of thumb and conclude that:

20' - 3' = 17'

So 110" wheelbase - (3' x 4") = 98" wheelbase would suffice.

Which means I could tow my trailer safely with a vehicle with a 104" wheelbase.

Does this seem safe?

Assuming I have antisway and weight distribution towing equipment.

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Old 05-10-2012, 08:19 PM   #2
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Cory, All the things you mentioned play into towing. But first and formost having a tow vehicle that has a tow capacity to pull your Biggar would be the smartest thing. Wheel base, sway bar, weight distrubution are all part of the puzzle.
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Old 05-10-2012, 08:44 PM   #3
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What I have in mind is an older 1970's blazer. Simple to change parts on and most that have survived to today have many non-original parts. So my guess is it could have whatever suspension, springs, and axels necessary. I was just wondering whether there was a wheelbase below which one shouldn't tow and whether 104" is below the threshold for a trailer the size and weight of the bigger.

Right now I tow with an 85 gmc crew cab long box with a turbocharged diesel engine and a 166" wheelbase. Great for cruising while towing but difficult to park downtown when not used tow.

Am thinking of getting a tow vehicle a little easier to park, plus the blazer could be a convertible in the summer.
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Old 05-10-2012, 09:30 PM   #4
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Interesting....Where did you get that Rule of thumb? At first blush it seems WAY too simplistic to be usefull.
If you are going to measure trailer length, shouldn't ball to axle(and number of axles) be as much a factor as overall length?
Think about the variation in trailers of the same length between RVs... let alone Boat, utility, car and cargo trailers and how they are loaded.
Think about variation in tow vehicles of similar wheel base....
Of course there does seem to be an insatiable appetite for "rules of thumb"...(saves a lot on homework)

I like towing my Scamp 13 with my Ranger [shortbox, regular cab 114" WB] and it works great for my open car trailer as well.Both are within the "rule of thumb", but...without suggesting limits on others here, I think trailers above 20 feet are generally starting to cross class lines.

Example...Properly equipped, many small crossovers perform very well towing a 16ft fiberglass trailer like a Scamp. Most vary from +-101" to 109"WB.
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Old 05-10-2012, 09:53 PM   #5
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The only (overly simplistic) rule of thumb I ever encountered spoke to the relationship between the tug's wheelbase vs the distance from the hitch ball to the trailer's axle (or axles).

However, there are many factors to consider - weight of the tug, tires (esp rear tires) on the tug, weight of the trailer, tongue weight of the trailer, etc. There are many factors at play - the tug has to not only PULL it, but CONTROL it in every situation - uphill, downhill, starting, stopping, around corners, in cross winds, slippery roads etc, etc. Wheelbase is a major factor, but so are many others.
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Old 05-10-2012, 09:57 PM   #6
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Quote:
Originally Posted by Cory Lewis View Post
Right now I tow with an 85 gmc crew cab long box with a turbocharged diesel engine and a 166" wheelbase. Great for cruising while towing but difficult to park downtown when not used tow.

I bet! My Dh towed a backhoe with something simular and it was a beast.

From what I have read I think your calculations are correct. But due take into consideration that with a late 70's Blazer, your talking a short wheel base with a high center point. As far as I can tell, depending on the model year your tow cap is anywhere between 4500 and 5500. So your close some model years, but ok if you watch how much gear you take.
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Old 05-10-2012, 10:09 PM   #7
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Quote:
Originally Posted by BCDave View Post
The only (overly simplistic) rule of thumb I ever encountered spoke to the relationship between the tug's wheelbase vs the distance from the hitch ball to the trailer's axle (or axles)..
Never heard that one either, where did you hear it and what were the details?
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Old 05-10-2012, 10:18 PM   #8
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Don't recall what I typed in to find that rule of thumb, but when I type "wheelbase towing rule of thumb" into google it is on several of the top listed sites. Could be someone with little knowledge made it up, posted it once, and it got copied to multiple sites, like this one, I don't know the origin.
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Old 05-10-2012, 10:33 PM   #9
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Same here, LOL but I googled/bing, Tow capacity versus Wheel base and read from there.


My Dh had a simular chart he used years ago with work trucks towing, loads, etc. So it made sense to me when I read it. Actually read it a couple different places with different posters. So, ?
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Old 05-10-2012, 10:38 PM   #10
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Seems like I saw that on rv.net forum some time back. Where they got it, I dunno.
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Old 05-10-2012, 10:42 PM   #11
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Originally Posted by floyd View Post
Never heard that one either, where did you hear it and what were the details?

Awww gee - now I gotta look it up again - and I had it a couple of days (daze?) ago, too!

I know the wheelbase had to exceed the distance from hitchball to axle(s) but I cannot remember by how much - something like 1.25 times or something like that
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Old 05-10-2012, 10:51 PM   #12
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Here's one place I read it. Davidsrvtips.blogspot


But here is some of what Cory and I are talking about and what Dave was saying. You can read more on this guys blogspot.



You'll need 2 measurements, the wheelbase of your tow vehicle, and the total length of the trailer you are pulling (or intend to pull). That length is from the coupler to the back bumper.


The First Guideline
(This guideline was first used by the RV Consumers Group rv.org)

For the first 110" of wheelbase, this allows you 20' of trailer.

For each additional 4" of wheelbase, this gets you 1' more of trailer.

Wheelbase / Trailer length
110" = 20'
114" = 21'
118" = 22'
and so on


The Second Guideline
The distance from the coupler to the rear trailer axle should be no more than twice the wheelbase of the tow vehicle.

Why this second guideline? I think this second guideline applies more to non-RV trailers, like boat or flatbed trailers with short (less height) loads on them. Those types of trailers usually do not have the large vertical surfaces (exterior walls) that would be susceptible to wind. You've probably seen a small SUV or pickup pulling a very large boat, right?



If you look at some of the physics and geometry inherent to travel trailers, you might see why length is an important factor to consider. Ever try to carry a full sheet of plywood (or something similar in size) by yourself, on a windy day? It can be pretty difficult to maintain control. But how about carrying a couple of 2 by 4's on that same windy day? Not so hard, is it? That's because the 2 by 4's do not have the same surface area to catch the wind as the sheet of plywood does. So, in a way, that travel trailer is just like a sheet of plywood for catching the wind.

The next thing to look at is how far the coupler is from the trailer tires? The greater the distance, the lesser the impact it will have on the tow vehicle and the less sway it could create. You will see travel trailers of the same overall length with the axles in different locations. This is probably due to the floor plan or layout of the trailer in order to balance the overall trailer, as well as to provide enough, but not too much, tongue weight.

Finally, the ball, or hitch location. How far is it from the tow vehicle's rear axle? The farther away it is (known as rear overhang), the more leverage the trailer can apply to the tow vehicle and create the possibility for more sway. A Jeep or a Hummer would make great tow vehicles because they have very little rear overhang compared to most pickup trucks and SUV's. Another example of this would be in comparing a 2003 Chevy Tahoe to a 2003 Chevy Suburban. The wheelbase of the two are different, but their wheelbase to rear overhang ratios are almost identical. Therefore, both vehicles should be able to handle the same trailer with similar results as far as length is concerned.
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Old 05-11-2012, 02:37 AM   #13
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The Blazer would be fine, I towed with one and dad has towed with his 75 AWD one just fine, the track width and heft helps keep things on the straight and narrow. As long as there are no lifts added to the suspension.

I have seen a mid 80s fullsize blazer go off the road with a 22ft sticky, everything stayed upright and straight.
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Old 05-11-2012, 07:30 AM   #14
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Great off road vehicles but the old Blazers were never know for their towing prowess. Do you have an alternative?
A buddy had a trailer like yours (3,500 lbs) and towed it with a Blazer. When the Blazer was sold he thought he would try his Mini Van. To his amazement the Mini Van felt a lot more stable towing the trailer than the Blazer.
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