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Old 01-06-2008, 07:09 AM   #1
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TV wheel base ?

We were discussing the issue of stability in towing with a short WB vs a long WB.

I think the long WB will be better as far sway with tractor trailers passing (wind buffeting) and be more stable braking, resisting jack knifing etc.

Do you agree if so why?
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Old 01-06-2008, 07:30 AM   #2
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Hi Bob

In all our testing we have found that you cannot look at the wheelbase in Isolation, you need to compare it to the rear overhang. So a vehicle with 100" wheel base and 30" or 30% of overhang is actually better than a vehicle with a 120" of wheelbase and 40" of rear overhang or 33%. You have to take this measurement from the centre of the back tires to the ball not the end of the bumper. One way to dramatically improve this ratio sometimes is to move the ball closer to the bumper by shortening and redrilling the shank.

The one downside to an excessively long wheelbase is the lack of maneuverability when trying to get into tight campsites. This is not important to some people but a bigger factor for others. I can park a 31' in a tighter spot with our shorter vehicles than I can park a 25' with a long one.

The most common mistake when trying to compare tow vehicles however is looking at just one factor such as wheelbase and focusing on just that. The type of suspension, tire and wheel combinations, Centre of Gravity, Shock control vs spring rates and steering feel are all important as well.

Andy
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Old 01-06-2008, 07:39 AM   #3
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Andy, are you the fellow at Can Am?

If I take your two examples of the 30 and 33 percent, and now I apply a side force to the rear of the TV which will have a greater resistance?

Hope you follow my question.
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Old 01-06-2008, 09:46 AM   #4
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Quote:
Originally Posted by LI Pets
We were discussing the issue of stability in towing with a short WB vs a long WB.

I think the long WB will be better as far sway with tractor trailers passing (wind buffeting) and be more stable braking, resisting jack knifing etc.

Do you agree if so why?
At face value I would agree with that statement, but consider that I towed the the rig in the pic three years with a Hensley and never experience any sway. As Andy T said, when it comes to sway WB is just one factor that must be considered in combination with a lot of other things.

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Old 01-06-2008, 11:36 AM   #5
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Quote:
Originally Posted by Andrew T
Hi Bob

One way to dramatically improve this ratio sometimes is to move the ball closer to the bumper by shortening and redrilling the shank.

Andy
For sure.
When we were putting our first TV together we initially were going to go with an "out of the box" adjustable ball mount with a typical shank. It could have looked something like this...


Instead we used the principles outlined by Andy. We used the welded ball mount which we already had and Andy's people redrilled and reduced the shank length. Instead of the ball being 12+ inches from the back bumper of our van the distance was reduced to a mere 3 1/2 inches from the back bumper. In the end it looked like this...


This vehicle had a 112" wheelbase. The redesign reduced the rear over hang by 8" (roughly 20%). If the theory holds true this vehicle when towing (by contrast) now thinks and reacts as if the wheel base is somewhat longer. The wheellbase to overhang ratio has been improved. This explains why TV's with a reduced overhang tow better and are more stable than ones with the longer rear overhangs.

The added bonus is that you still have a vehicle with a short wheel base which has advantage in many cases. There is also far less stress on hitch and receiver parts with the shorter distance.

Andy...please correct if this information is not right.
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Old 01-06-2008, 12:20 PM   #6
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The one with the 30% overhang will have less resistance to sway if all other factors are equal. A good example is a 4 door Tahoe vs a Suburban. They both ride on the same chassis with the same suspension tires and wheels. The overhang and wheelbase are both longer on the Suburban if you calculate the overhang percentage they are almost identical. If you connect them to the same trailer with the same hitch system the handling is also almost identical.

For many a welded ball mount will be hard to find and even harder to have someone weld. However if you have one of the cast iron hitch shanks that projects the ball so far out you can switch it to a Eaz-Lift Shank as the bolt spacings are the same. The eaz-lift shank can be redrilled to allow it in as close as possible.

Just to prove it to myself that it matters I once had a shank with two holes in it 3" appart so I could change the overhang without changing anything else. The wind effect was noticeably more and we lost 3 kph in the slalom. It also took a 3/8" bolt in the chain to get the same weight distribution.

Andy
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Old 01-06-2008, 01:46 PM   #7
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If "They both ride on the same chassis". Then how could the suburban have a longer wheelbase?
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Old 01-06-2008, 02:12 PM   #8
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Good point.

I should have explained that. The only difference between the two chassis is that Suburban has longer frame rails between the axles and out to the back bumper. Otherwise they are the same, the front and rear suspensions, the ride height, tire size, shocks are all identical. The Tahoe has slighty lower spring rates but just in proportion to the weight difference.

Andy
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Old 01-06-2008, 04:45 PM   #9
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Very interesting thread. Andy, I'm glad you're posting. I think your perspective adds great value to the forum, and I hope you can continue hanging out with us.

So, this compelled me to go out and do some measuring on my TV...139" wheelbase, and about 40" from the rear axle to the bumper. So that's "good"...about 30%. But when I add the length of the hitch/shank to that, its another foot, which puts me at 37% I think that could be shortened, but not by much, as its a Reese, and has a bracket welded between the horizontal and the vertical shanks for reinforcement. I need this large shank so I can get enough drop in the ball height. (4x4 sits up high).
I have to admit, also, that I actually like it being this long, as I can turn the vehicle 90 degrees to the trailer, without bumping the trailer body with the truck's bumper...gives me room to lower the tailgate easily when hitched up, etc. I've never noticed the slightest hint of instability in the combination, either...perhaps because the wheelbase is so long, and also because the trailer isn't that heavy. Anyway...still interesting.

I'd like my next tow vehicle to be an SUV with a shorter wheelbase, because I have needs other than "towing". (imagine that: a life beyond airstreaming!! gasp!! ). So many here disparage anything lighter/shorter than a GE Diesel/Electric Locomotive...particularly anything "short". Seems to me that most SUVs have fairly short overhangs, as it maximizes interior space, but its not something that is listed in many "specs". I'm thinking "Durango" (Hemi!!) might be a good choice. The picture in my mind has the wheels pretty far aft...
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