Open Roads Forum

Print  |  Close

Topic: Observation About WD Hitch Shank Length

Posted By: jjinatx on 08/30/12 10:34am

I was about to shorten the length of the shank on my WD hitch thinking a smaller moment arm from drive axle to ball would reduce the effect of tongue weight. But, I looked (for the umpteenth time) at the "WD Hitch - How it Works" sticky and decided not to.

If you look at the calculations for how much weight is distributed to the front and rear TV axles, you can see that decreasing the ball overhang will result in a DECREASE in the amount of weight lifted from the drive axle and a DECREASE in the amount distributed to the steer axle. For example, decreasing it by 5" results in 11# less being distributed. So it seems it's best NOT to shorten a WD hitch shank, or if nothing else, a total waste of time and effort.

-jj


Current Rig: 2017 F350 Crew Cab Short Bed 4X4 Powerstroke, 2018 Grand Design Reflection 29RS. Dearly Departed: 2003 GMC Sierra 3500 Dually, 2002 Bigfoot 25C10.6.



Posted By: TomG2 on 08/30/12 12:17pm

The rear axle is the fulcrum. Shortening the distance from the rear axle to the ball will reduce the amount of lift applied to the front axle by the application of tongue weight. Look at it this way. If the "Stinger" was eight feet long, it would lift the front tires right off the ground when hitched up. Shortening it reduces this tendency.


Posted By: jjinatx on 08/30/12 12:53pm

TomG2 wrote:

The rear axle is the fulcrum. Shortening the distance from the rear axle to the ball will reduce the amount of lift applied to the front axle by the application of tongue weight. Look at it this way. If the "Stinger" was eight feet long, it would lift the front tires right off the ground when hitched up. Shortening it reduces this tendency.


True with a weight carrying hitch, but with WD hitch, according to Ron's formlae, not so.

-jj


Posted By: gijoecam on 08/30/12 01:18pm

TomG2 wrote:

The rear axle is the fulcrum. Shortening the distance from the rear axle to the ball will reduce the amount of lift applied to the front axle by the application of tongue weight. Look at it this way. If the "Stinger" was eight feet long, it would lift the front tires right off the ground when hitched up. Shortening it reduces this tendency.


Indeed... with a weight carrying hitch. With a weight distributing hitch, the fulcrum point is the ball and coupler intersection. The shorter lever arm in front of the ball, the more weight the same load on the bars can transfer.

Now, is shortening it 5" enough to make a measurable change? Possibly... But IMHO, if you're that close to your limits where 5" makes a difference, it may be time to consider a new tow vehicle...


Posted By: TomG2 on 08/30/12 03:23pm

Okay, if an extra long stinger would lift the front tires off the ground, then why wouldn't you want the shortest possible stinger to eliminate some of the lift? By doing this, the WD hitch will have less work to do since it will not be at such a mechanical disadvantage . I realize that it is not hundreds of pounds, but any and all things that improve towing are good with me. It is actually pretty simple mechanical engineering. I am NOT saying that it is going to be noticeable, just a small adjustment that can only help. I drilled mine with a home drill press in less than thirty minutes.


Posted By: skipnchar on 08/30/12 03:30pm

You DO realize that the weight transfer is greatly adjustable so if you end up not transferring enough you simply readjust it so it does. You are correct that the amount transferred would change UNLESS you changed the settings on the hitch.


2011 F-150 HD Ecoboost 3.5 V6. 2550 payload, 17,100 GCVWR -
2004 F-150 HD (Traded after 80,000 towing miles)
2007 Rockwood 8314SS 34' travel trailer

US Govt survey shows three out of four people make up 75% of the total population



Posted By: TomG2 on 08/30/12 04:01pm

Okay, I will try to explain. If the ball is eight foot from the rear axle and four hundred pounds are removed from the front axle, shortening the shank will reduce this amount slightly. Right? Therefore, the WD hitch will not have to be quite as aggressive in its setup. I would rather depend on the WD hitch for less instead of more. Not that complicated or important, but a small improvement.


Posted By: LarryJM on 08/30/12 04:10pm

I'm really not sure 6" one way or another is going to have much effect, but I admit I haven't done the math.

Larry


2001 standard box 7.3L E-350 PSD Van with 4.10 rear and 2007 Holiday Rambler Aluma-Lite 8306S Been RV'ing since 1974.
RAINKAP INSTALL////ETERNABOND INSTALL



Posted By: TomG2 on 08/30/12 04:24pm

You probably can't gain 6", but lets say you could. Given a typical tongue weight of 600 pounds. 600 pounds acting through a lever arm of 6ft results in 3,600 foot pounds of torque (600 X 6.0). Change that to 6.5ft and the force grows to 3,900 foot pounds. Not a lot, but it is something. Long bed, short bed, the actual numbers will vary but not the idea.

That is just one of the reasons that fifth wheel trailers tow better. The tongue weight is very close to the rear axle, which results in very little lift to the front axle of the tow vehicle.

* This post was edited 08/30/12 04:38pm by TomG2 *


Posted By: husk on 08/30/12 05:16pm

shortening the shank from receiver pin hole to ball, would move the tailgate of your truck closer to the jack on the trailer...I had to reposition my electric jack in order for the tailgate to open fully...I was looking at buying a longer stinger until I found I could move the jack......

just another thing to consider...


Posted By: jerem0621 on 08/30/12 07:11pm

Pretty happy with my shank length, it helps increase my turning radius.

Thanks!

Jeremiah


TV- 2011 Chevy Tahoe, 2WD, Hayden transmission cooler
TT - Zinger 270BH
WD Hitch- HaulMaster 1,000 lb Round Bar
Dual Friction bar sway control
Tekonsha Voyager brake controller (Great Brake Controller)

It’s Kind of Fun to do the Impossible
~Walt Disney~



Posted By: Ron Gratz on 08/30/12 07:14pm

jjinatx wrote:

If you look at the calculations for how much weight is distributed to the front and rear TV axles, you can see that decreasing the ball overhang will result in a DECREASE in the amount of weight lifted from the drive axle and a DECREASE in the amount distributed to the steer axle. For example, decreasing it by 5" results in 11# less being distributed. So it seems it's best NOT to shorten a WD hitch shank, or if nothing else, a total waste of time and effort.
Assume a Suburban with 130" wheelbase, 65" ball overhang, and a trailer with 195" coupler to axles' midpoint.
A 1000# load would cause 500# to be removed from the steer axle.
To restore the 500# to the steer axle via application of WD would require that 250# is transferred to the trailer's axles.

If the ball overhang is shortened to 60", the 1000# TW would cause a load of 462# to be removed from the steer axle.
To restore the 462# to the steer axle via application of WD would require that 235# is transferred to the trailer's axles.

Shortening the ball overhang by 5" (7.7%) would reduce the WD bar loading by about 6%.

Shortening the ball overhang by 5" also would improve yaw stability.
The lever arm which allows the TT to "steer" the TV would be shortened.

Ron


Posted By: mkirsch on 08/31/12 09:25am

The OP said, "11#."

Eleven pounds is not even worth thinking about, let alone losing sleep over.

Of course as Skip says, the hitch is ADJUSTABLE if eleven pounds bothers you that much.


Putting 10-ply tires on half ton trucks since aught-four.


Posted By: TomG2 on 08/31/12 10:33am

Nobody said it was a major change. It is just a minor improvement, and I like to improve as much as I can. As a full-timer, I see some pretty weird rigs going down the highway being driven by people that don't care, as long as it gets them where they are going. In Ron's example, it would make a five to ten percent change in the amount of force that the WD hitch would have to deal with. Nothing to lose sleep over, but why not get it as good as you can?


Posted By: Coyotecprs on 08/31/12 03:30pm

A shorter shank length helps a little in reduce sway affects too but i would still rather be able to open the tailgate or door on suv.


2005 Dodge Ram 2500, 5.7 Hemi
2007 Jayco Jay Flight 30.5 BHS


Posted By: Coyotecprs on 08/31/12 03:32pm

A longer shank is useful for bike racks that attach over the shank


Posted By: christopherglenn on 08/31/12 04:16pm

I changed the 2" shank (with adapter) to a 2.5" shank about a year before I traded my TT. The longer shank made no weight or handleing difference I could see. The slightyl longer shank ~4" made the trailer track slightly better at low speeds (backing and moving in a campground). Full to empty on the gas guage makes far more difference then a few lbs on front and rear axles.


2007 Chevrolet 3500 CC/LB Duramax/Dually 4X4 Mine r4tech, Reese Signature Series 18k +slider, duratrac, Titan 62 gallon, diamond eye, Cheetah 64
2011 Keystone Fusion 405 TrailAir & Triglide, Centerpoint, gen-turi, 3 PVX-840T, XANTREX FREEDOM SW3012, G614



Posted By: TomG2 on 08/31/12 04:20pm

Longer shanks are required for many Truck Campers who want to tow.


Print  |  Close