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Old 06-17-2007, 08:29 AM   #1
Goodyear Travels
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Default WD Hitches & Shocks -- Tire Failure Contributors ?

I woke up from a deep sleep with my head spinning with thoughts, feelings, and more questions about marathon tire failures. I wasn't even pondering any of this the night before. Our 2720SL came nicely equipped and we try to be judicious in adding to travel loads. We have an Equalizier 600 lbs hitch that is essential if we are to use our 2001 Tacoma as a TV. The hitch, itself, is physically heavy (80-100 lbs?) but I don't think that its physical weight is as much of an issue as is its weight distribution properties. We load quite a bit of stuff into the bed of the truck and we can see the load compress the springs and lift up the front of the truck. But the WDH remedies this by redistributing the bed load and the tongue weight to the TM's axle and the front axle of the Tacoma. This redistribution would not show up on a GVW scale. I could be wrong but I sense that our setups on our WDH's are putting many of us well over the marathon load limits (especially those of us who are aggressively shifting bed loads). AND --I sense that even with "now level loads" -- our worn, TV shock absorbers are allowing momentary and excessive compressions (from irregularities and dips in the road surface) to be transmitted back to TM's tires and axle -- adding further stresses. Maybe these additional and momentary load blips are factored into the tires' load rating ?? I also wonder if the tire failure rate differs significantly between those folks driving full-sized vehicles WITHOUT WDH's and those driving full-sized vehicles WITH WDH's. We tend to feel that we're in pretty good shape if we stay under gross vehicle weight limits and if we've done a nice job in leveling our loads -- but do you think that our WDH setups (especially as we aggressively level loads) and worn, TV shocks might be real contributors to the tire failure rate? I wish I had a TV that didn't need the assistance of a WDH. Inquiring minds want to know.
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Old 06-17-2007, 08:42 AM   #2
CAmark
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Eric,
You can weigh each axle by finding a CAT scale near you or on your travel route. See http://www.catscale.com/locator.shtml to locate one near you. You can also search my postings for CAT scale for details on how this works. Better to know the answer than guess at it...either you can change your situation or stop being concerned about it....mark
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Old 06-17-2007, 09:00 AM   #3
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Evn though I pull with a full size pickup, I still use a WDH. I did a bunch of weigh-ins at the local quarry while using different chain lengths to find the ultimum setup for our unit. Weigh the front & rear of the TV without the TM, then weigh the front of the TV, combination (needed only once to determine the TM weight), and the axle of the TM using different chain lenghts of the WDH. The rear wheel and tongue weights can be calculated using these figures to find the ultimum setup.

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Old 06-17-2007, 09:31 AM   #4
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Default Inquiring mind here too!

Quote:
Originally Posted by Eric Larson View Post
Maybe these additional and momentary load blips are factored into the tires' load rating ?? I also wonder if the tire failure rate differs significantly between those folks driving full-sized vehicles WITHOUT WDH's and those driving full-sized vehicles WITH WDH's. Inquiring minds want to know.
I have not noticed the signatures of the posts of the folks who have had tire problems to know if there are a significant number of them with WDH's. But I too am curious as you. ( think I will go back and see ) It would seem logical that if the function of a WDH ( and I know only what I read here about them ) is to redistribute the weight among all the axles of the rig then some of that weight would be going back on the TM axle. I understand that for some rigs the WDH is needed. But I would not want any more weight than what was absolutely necessary on the TM axle and tires given the experience of some members and the 1870 lb weight limit ( each ) of my current tires. I tow my TM as light as possible. No fluids in it. Linens, cooking utensils and a few food staples. That is it. I figure with the awning, air conditioner, and LP gas tanks the TM is hauling all it needs to. The heavy stuff goes in the back of Osita ( the truck ) ( Some members have dogs for pets, I have a truck ). It has the heavy duty springs and the LT tires to handle it. Not the TM. But like you, I would like to know if the WDH is a factor. Man! I love this site!
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Old 06-17-2007, 09:38 AM   #5
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Eric -

The redistribution effects WILL show up if you weigh your rig axle-by-axle, but as you note, it will NOT change the total weight of the Tacoma plus TM. The load redistribution is real, and weight will come off the rear axle and be split between the Tacomas's front axle and the TM axle.

I wouldn't get too concerned about the extra weight that the WDH puts on the TM axle. The increase is nominally 1/3 of the tongue weight, or maybe 150 pounds. While I haven't actually measured the difference, I'm not convinced that the split is really in exact thirds. So maybe 100 pounds. While this is not negligible, it is not a disaster, either, provided that the total weight of the TM is reasonable. And in my opinion, the WDH adds steering-and-handling safety that it is more important than the extra load on the TM tires. Of course I am referring to cars that need a WDH, including my Ford Explorer. Osita, Joseph's pampered Chevy 2500 is a pretty big vehicle, and may not need one.

As for the increase caused by flexing of the springbars as you cross dips and swales, I've had the same question in my mind, and I just don't know the answer. If I understand the geometry correctly, driving through a swale DOES increase the distribution onto the TM wheels. But I have no idea how much. Anyone?

And as for momentary stresses, I'm thinking that one of the worst sources is the rumble strip that seems to be carved into the outside edge of the lane on every Interstate highway. If you drift over for just a couple seconds, your tires will take 50 or 100 hammer-blows before you can pull back into the center of the lane. And in some construction areas, you have no choice but to drive on the rumble strip for fairly long distances. When I encounter this situation, I slow way down, although it doesn't make me very popular.

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Old 06-17-2007, 08:41 PM   #6
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The WDH doesn't necessarily distribute the weight by thirds. Ideally it would, but that would mean the distance from the tires on the TM to the rear axle on the TV would be equal to the wheel base of the TV, or very close to it. This gets into figuring of "moments" which involves the distances from a point to each axle times the weight of the axle. Ideally this would not change once the WDH is "set". However, since towing is dynamic, not static, the actual weight distribution is an ever changing equation due to changes in the road and driving conditions - i.e. braking, acceleration, hills, curves, bumps, swales, curbs, driveways, etc. The best we can do is to adjust the WDH as best we can when static and hope it's "close enough" to absorb the road variations. (Note: It's is possible to put too much weight on the trailer axle if the WDH isn't adjusted properly.)
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Old 06-17-2007, 10:07 PM   #7
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Thank you all for your responses. You've given me still more things to ponder. I, for one, set up my Equalizer hitch without fully loading my TV or TM. In so doing, I redistributed the tongue weight generated by our empty TM. BUT -- then I go and add another 700 lbs or so to the TV (people, dogs, and gear in the bed). Some folks could have even greater loads with 3 or 4 passengers. Wouldn't a third or so of this additional weight necessarily be distributed BACK to TM's rear axle. For this reason, the geometry doesn't seem to change much (empty or with loads) as long as the WDH is being utilized -- from what I've witnessed (both the TV and the TM seem to remain pretty level under load -- because all the additional weight has been distributed to 3 axles). We tend to think that overloading only happens by adding gear to our TM's. But our WDH's work both directions -- don't they? They distribute the TM's tongue weight (forward and back) -- but they also must distribute the TV's passenger and gear weight (forward and back) -- especially if the WDH was set up without all loads being present ??? It kind of makes sense to me but I was watching girls back in high school physics. I wonder now -- if those folks with high rates of tire failures did their WDH setups without full or simulated loads in their TV's and TM's. Maybe all of this might shed some light on some of the axle failures. And Bill -- I'm watching you like a hawk. You and a few others are going to get all of this figured out in the near future. I'm sure of it. Until then -- I'll be driving slowly through the desert and avoiding "rumble strips", "whoop-tee-dos, and the like. Eric
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Old 06-18-2007, 12:07 AM   #8
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Eric

IMO you may have less of a problem than you think because you are towing with a pickup. As I've said before, most rear-wheel-drive SUVs have close to equal weight on their front and rear axles sitting empty while pickups have several (varies) hundred lbs more on their front than rear axle when empty. You can therefore add whatever your difference is on the rear axle and still start even with the SUVs. There are overhang and other differences however so it won't be exactly the same situation but close. I agree with whoever said you need to weigh your Tacoma loaded and go from there. We have a 600lb Equal-i-zer and I agree they are not as easily adjusted as the chained ones because you have to loosen and raise/lower the "L" pieces -- but once you do that you are set -- assuming you travel with a similar load each time. If you are carrying a 1000lb ORV in the back of your truck some times and not others then you will have to adjust more often. I also agree with your assessment that distributing that kind of weight may overload your TM axle and I suspect you will be better off to let the Tacoma remain low in the back and distribute only part of the weight -- not a good situation but sometimes there are no good choices. Then again, your 600lb WDH is possibly only capable of distributing maybe 200lbs to the TM's axle regardless of what you do so you may be safe anyway. We started out with a 400lb WDH when we were towing our 2619 with an Odyssey minvan for this very reason but once we traded for the Tundra and my wife started sneaking in more books etc the 400 would no longer lift the tongue to fully level. Weighing everthing loaded should clear up much of this. Just my $0.02. I might add that we will be traveling for the next three weeks and probably off the net so enjoy my absence.
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Old 06-18-2007, 07:03 AM   #9
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OK, here goes my $.02 worth also.

As I wrote a post previously in this thread, I think it is important to weigh your TV and TM to see how the WDH works your setup. Even though I tow with a 1/2 ton pickup, I wanted to get the geometry back close to an "partial bed load" for my truck. Ideally, if you load a truck, the weight center should be immediately in front of the rear axle.....that is why they put the hook-up for a 5th wheel trailer just in front of the rear axle. Most of the weight is taken by the rear axle, but a little is taken by the front axle also, to keep the geometry of the vehicle somewhat proportionally the same. Because of a trailer is hanging behind the back bumper, the WDH will act to get this back to a "compromise postion".....putting some weight back on the front axle and the TM axle.

In my case, with a 480 lb. tongue weight (that includes ~65 lbs of WDH), my front end is only 80 lbs. lighter (vs. 220 lbs. lighter without the WDH), my rear axle is 440 lbs heavier, and the TM axle is 120 lbs heavier (now at 3040 lbs. loaded, but without water) than without the WDH. I have the front axle near the empty weight, most of the weight is on the rear axle (as it should be in a truck), and a little more weight on the TM axle. I feel this is a good compromise. When I add camping gear to this setup, I load the heavy stuff in the front of the pickup bed, again to add a little more weight to the front axle, with most of the weight still being on the rear axle.

Again, just had to add my $.02 worth.

Chap
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Old 06-18-2007, 07:55 PM   #10
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Quote:
Originally Posted by Eric Larson View Post
Thank you all for your responses. You've given me still more things to ponder. I, for one, set up my Equalizer hitch without fully loading my TV or TM. In so doing, I redistributed the tongue weight generated by our empty TM. BUT -- then I go and add another 700 lbs or so to the TV (people, dogs, and gear in the bed). Some folks could have even greater loads with 3 or 4 passengers. Wouldn't a third or so of this additional weight necessarily be distributed BACK to TM's rear axle.........snip......
Depends, methinks. If the TV load is distributed such that the TV's Center of Gravity(CG) stays relatively close to the unloaded CG, then there would be nearly zero effect on the trailer axle. The TV would settle, but it's pitch attitude would remain nearly unchanged.

OTOH, if the additional weight were biased toward the rear, then the TV would drop more at the rear axle. The vehicle attitude change would be seen to be a pitch up. In this case, the spring bars of the WDH, where they insert below the hitch ball, would rotate exactly the same number of degrees as the pitch change of the TV. Additional down-force on the trailer frame would be minor, the increased load on the trailer's axle resulting from a slight bending of the spring bars. The angle (measured from a hitch reference line) between the trailer frame and hitch would also increase slightly.

Suppose we were to connect the WDH after the TV loading is complete. Connect the spring bars such that the rear axle and front axle of the TV squat nearly equally ( up to 1/2" more squat for the rear axle). My hunch is that one or two additional links would have to be dropped, compared to connecting before loading the TV! Performing just such a comparison test could easily prove the hypothesis either T or F.

Point: I don't think that loading the TV after WDH hook-up will increase the load on the trailer axle nearly as much as loading the TV before WDH hook-up (assuming aft CG movement) and leveling!


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