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Techniques Winching - Recoveries - Chainsaw Safety - Proper aproach to 4wding etc

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Old 08-07-16
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Default Weight Distribution and Transfer

I recently did a post about WDH and the effects on axle loadings, and I got small part of this wrong, thanks Mundy 55 for pointing this out, all corrected now. So I thought I would do a thread on weight distribution and transfer, rather than it being a theoretical math exercise I decided to do a visual display. Hopefully it will get the message across and will be a benefit to some.

Be patient and let the give you the background. I want to give a visual demonstration of what happens as you load up your 4wd. I used 2 scales, a 300mm steel rule and some nuts and nut plates that I used for weights.


I weighed the nuts at 5.4g each so for the demonstration consider these as weighing 54kgs.



I weighed the nut plates at 10.1g each so for the demonstration consider these as weighing 101kg.



I then set up the steel rule and balanced it on half saddles on each scale at 150 mm spacing to simulate a 3000mm wheel base between the axles. I then placed weights over the axle centres to give a Tare weight of 220.8 x 10 = 2208kg which is about the average tare weight of a mid size 4wd. I choose 55% front and 45% weight distribution as this is typical so the front weight was 1220kg and the rear 988kg. Gross weight of 2208kgs.



I then added 16g half way between the front and rear axles to simulate a driver and passenger totalling 160kgs. This load is spread evenly between the front and rear axles and we can see this by the increase readings on the scales but does not change the weight distribution.
Front axle load 1220kg + 80kg = 1300kgs WD 55%
Rear axle load 988kg + 80kg = 1068kgs WD 45%
Gross weight 2368kgs.



I then added 15.5g over the rear axle to simulate 2 rear seat passengers totalling 155kgs. This load only effects the rear axle loading and not the front axle loading. For some reason the rear axle weight did not increase by 155kgs, 1068kg + 155kg = 1223kg but my scale only showed 120.7g so that converts to 1207kgs, 1.6g / 16kgs out for some reason that we will ignore since the error is very low as a percentage.
Front axle load 1300kgs, unchanged. WD48%
Rear axle load 1207kgs indicated (1223kgs theoretical) WD52%
Gross weight from 2368kgs to 2507kgs.



I then added 20.2g, 40mm rearwards of the rear axle to simulate 202kg of load in the cargo area 800mm rear of the rear axle centreline. Because the weight is behind the rear axle this "200kg" load and the rear axle load is now greater than the front axle load, the "200kg" actually puts 260kg of load on the rear axle as 60kgs of load is transferred from the front axle. This also results in a change of weight distribution.
Front axle load 1300kgs - 60kgs = 1240kgs WD 46%.
Rear axle load 1207kgs + 200kgs = 1467kgs WD 54%.
Gross weight from 2507kgs to 2707kgs.



I then added 15.5g, 70mm rearwards of the rear axle to simulate 155kgs of tow ball down load at 1400mm rear of the rear axle. Once again because the weight is rear of the rear axle and there is more weight on the rear axle than the front axle so this adds 155kgs + 81kgs of weight transferred from the front axle so that is an extra 236kgs applied to the rear axle. This further change in weight distribution will effect the steering and braking.
Front axle load 1240kgs - 81kgs = 1170kgs WD 40%.
Rear axle load 1467kgs + 236kgs = 1703kgs WD 60%.



It is easy to see how easy it is to not only exceed the vehicles GVM but also the front or rear axle loads limits. Fitting a WDH will help correct this problem but WDH's are not recommend for use on rough roads or off road. I have not worked a way out of simulating the effect of a WDH as this is more complicated. I would need 4 wheel scales and perform a full weight check of all wheels, the tow ball down load and the effect of the WDH.

It should be possible to format a calculator in Excel that calculates what happens when loads are applied for a specific vehicle. You would need to know the front and rear axle weights empty, the wheel base, position of the front and rear seat within the wheel base, the centre of the cargo area and the distance of the tow ball rearwards of the rear axle centreline, and but this into the spreadsheet to get the calculations or you could do it old school with manual calculations (bring out the slide rule old timers).

cheers, OJ.
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Old 08-07-16
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Nice graphical demonstration OJ. Certainly food for thought. I think you have weigh (pun intended) too much time on your hands
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Old 08-07-16
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Thanks Steve, consider it a form of redemption for posting incorrect information. I had worked out the theoretical but one lunchtime this week I decided to do a mockup test to prove the theory.

OJ.
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Old 09-07-16
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Wow OJ that is awesome. Makes it easier to understand.

Would love to see you simulate a WDH somehow.

Thanks for sharing
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Old 09-07-16
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Good stuff Jack. Makes things easier to see. Still amazes me people still insist on towing bloody great vans with the car loaded up and god knows what else in the van. One day, yes one day, the authorities are going to have to do something about the amount of obviously over loaded vehicles on the roads. In Cairns at the moment you see many wonderful and weird contraptions on the roads driven by the mexicans. Some sweet outfits and some , well, lets say they shouldnt be travelling anywhere off road.

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Old 09-07-16
envee envee is offline
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Great explanation Old Jack, thanks for taking the time to post.
Are there specific points at which use of the weight distribution devices become necessary? Or is it more a case of if the weight over the front axles becomes less at all, then they should be used? Your unladen starting weight on the front axles is 1220kg and at the finish after loading is 1170kg, a difference of 50kg. Does this have enough of an effect to make their use necessary?

It is something that I have often wondered. At the moment we tow a Camprite camper behind our NW with stock suspension. There is just the 2 of us, normally a 60l fridge in the back and not much else and a tow ball weight of about 150kg. We are looking to put some draws in the back and do intend to upgrade the suspension in a couple of years.

Cheers again for your post.

envee
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Old 09-07-16
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Fantastic explanation OJ many thanks, lost count of the number of times I've tried to explain this principal to other people who insist on throwing in everything including the kitchen sink.

Now to try an get the missus to understand it.
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Old 09-07-16
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Sticky time mods..Appreciate your time to do this OJ
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Old 09-07-16
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Stickied
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Old 09-07-16
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Very nice Demo OJ, I found it very interesting.

We tow our 1100kg Van with our NT & we have a EazLift 600 WDH. When I hook up the WDH, you can see the back end of the Pajero come up nice & level.

It may not be absolutely essential with such a light van, but I had it when we towed the van with a Commodore & that was essential.

The other think I have noticed is how well the van tows. There is never any swaying when a truck goes by the opposite direction, & it corners like a spots car. Extremely stable.

One last point I want to make is how easy it is to hitch up. I have a very bad back but putting the load on the EazLift WDH is so easy and painless. Not like the old days when I used to help dad hitch up his WDH.

I think it's worth having a WDH even on a small van like ours, but It's worth getting a good quality one.

Steve
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