Motorhome Overhang Weight Issue

[andyelbac]

A slightly embarrassing ask here, but having reall issues calculating the potential weight issue on our rear axle wheb using the formula found online. I just don't trust my workings and would appreciate someone who has a better grounding in maths provide me with an answer. Basically, I want to know if carrying 150kg in my rear garage gives me a rear axle overhang weight issue or not. Here are the specs:
Front axle plate limit: 1960kg
Rear Axle plate limit: 2240kg
Wheelbase: 4050mm
Front of MH to centre front wheel: 850mm
Rear wheel centre to back of MH: 1850mm
Max permissable load 4,000kg

 

[The Wino]

A slightly embarrassing ask here, but having reall issues calculating the potential weight issue on our rear axle wheb using the formula found online. I just don't trust my workings and would appreciate someone who has a better grounding in maths provide me with an answer. Basically, I want to know if carrying 150kg in my rear garage gives me a rear axle overhang weight issue or not. Here are the specs:
Front axle plate limit: 1960kg
Rear Axle plate limit: 2240kg
Wheelbase: 4050mm
Front of MH to centre front wheel: 850mm
Rear wheel centre to back of MH: 1850mm
Max permissable load 4,000kg

It will depend on how far back from the axle the load is placed and what the axle load is without the extra 150 kg but otherwise fully loaded.
If you fully load the rear axle you can't fully load the front without going over your total weight.

 

[andyelbac]

As further context to this. My current rear axle allowable weight is 2000kg. SV Tech have advised that if I add semi air to the rear, my rear axle limit can be upgrated to 2240kg. However, when I do the maths, the overhang weight appears to be the same irrespective of whether i calculate using the current axle limit or theoretical new one? This seems odd to me. I would have thought, increasing the rear axle limit would reduce the overhang weight when compared to a lower rear axle weight....or perhaps this thinking explains why I never achieved O Level in Maths!

 

[Lenny HB]

As The Wino says it depends how you load the garage the only accurate way is to take the van to a weighbridge.

Having said that 150 kg is a fairly light load for a garage so probably not much chance of overloading the axle at 2240 and a fairly short overhang.

 

[The Wino]

As further context to this. My current rear axle allowable weight is 2000kg. SV Tech have advised that if I add semi air to the rear, my rear axle limit can be upgrated to 2240kg. However, when I do the maths, the overhang weight appears to be the same irrespective of whether i calculate using the current axle limit or theoretical new one? This seems odd to me. I would have thought, increasing the rear axle limit would reduce the overhang weight when compared to a lower rear axle weight....or perhaps this thinking explains why I never achieved O Level in Maths!

If you're calculating the extra load due to the 150 kg in the garage the extra will be the same no matter what the axle limit however if the axle limit is higher it's less likely to take you over the weight limit for that axle. It's unlikely that the extra 150 kg is as far back as the rear motorhome wall if it is stuff in the garage. If it's a towbar it probably is that far back or slightly more if it's a bike carrier it's further back!

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[busbuddy]

I would assume the calculated overhang weight would stay the same whatever the axle weight as you are calculating the weight/force downwards...for example if the 150kg gave a 250kg overhang weight then it would stay the same if you had a 1000kg or 10000kg axle limit, overhang weight is constant because of distance from axle

 

[andyelbac]

This is slightly confusing for me. I can understand that the overhang weight will be the same irrespective of the axle limit, but when
i calculate using the formula I have 69kg coming off the front axle. The formula says to add that to the rear axle limit plus the required additional weight. So: 2000+150+69=2219 kg. An overhang weight of 219kg above legal rear axle limit. When I calculate using the theoretical new rear axle limit of 2240, I get: 2240+150+69= 2459 kg. An overhang weight of 219kg! it just seems odd that having an increased rear axle weight means I am still over the legal limit by the same amount?! On another tack, if I have the vehicle fully loaded, including 150kg in the rear garage and have it weighed on a weighbridge and the rear axle load is lower than the axle limit (whether 2000kg or 2240kg) am i good to go or do i still need to work the formula?

 

[Fat Albert]

I have attached an excel copy of a weight calculator that some kind soul took the time to write, unfortunately I don't remember his name but I'm sure it's in the Resources but I couldn't find it. Some do say I couldn't find my own backside at times
It would help to get a front and rear axle weight and fill in the details as per the instruction sheet. I did a down and dirty look at your van details with the load of 150kgs in the garage at 1700mm from the axle and it comes out at a weight change of +213 kgs on the rear and -63kgs on the front. To get your head around that think of a see saw. Hope that helps you

 

[andyelbac]

Thank you. Will give that a go.

 

[funflair]

I think from your workings you have used 1850mm as the distance of the 150kg load from the reaction point ie the rear axle, you would be safer using the mid point of 1850mm and assuming a uniformly distributed load so your 150kg is only going to release around 30kg from the front axle load which yes you have to add to the 150 on the rear axle so the actual rear axle load increase would be around 180kg.

The other important bit of information that seems to be missing is the actual axle loads in ready to go trim, these are the ones that matter.

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[andyelbac]

Thanks for all the advice. in respect of my last question though: the ultimate calculation is the weighbridge weight? If it's below the allowable rear axle limit I am all good?

 

[dunnah01]

The additional 150kg will be felt by the axles as an additional 219kg at the back and a reduction of 69kg at the front and is nothing to do with any axle limits. This assumes all the 150kg is mounted right at the back (on a towball for example) in reality the weight will probably be spread around the garage so any increase at the rear will be reduced and any reduction at the front will be reduced aswell.

 

[Speve]

Thank you. Will give that a go.

Here’s another way to calculate courtesy of freeontour.

 

[andyelbac]

Here’s another way to calculate courtesy of freeontour.
View attachment 704216

Hi, so what you're saying is that I'm making a mistake calculating to the rear of the motorhome. What I actually need to do is measure to the centre of the scooter rack in the garage (it's a scooter I'm wanting to carry) and then to calculate but also, that even if the weighbridge says I'm under the legal weight limit I still have to make sure my overhang weight does not exceed the rear axle limit because wighbridge axle weight and the impact of too much weight coming off tbe front axle (thus affecting handling) are unrelated?

 

[autorouter]

I have attached an excel copy of a weight calculator that some kind soul took the time to write, unfortunately I don't remember his name but I'm sure it's in the Resources but I couldn't find it.

Her name, actually .

Mel B's Spreadsheet to show effect of rear loads on axles

This spreadsheet will let you know if that bike overloads your axles.

www.motorhomefun.co.uk

Here’s another way to calculate courtesy of freeontour.

It may give the correct results, but I'm not convinced when he talks about air suspension and negative shift in the centre of gravity.

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[Lenny HB]

Rather than keep worrying about just load it fully for your trip including the scooter, water, fuel & the mrs and go to a weighbridge. Then you will know exactly where you stand.

 

[funflair]

Hi, so what you're saying is that I'm making a mistake calculating to the rear of the motorhome. What I actually need to do is measure to the centre of the scooter rack in the garage (it's a scooter I'm wanting to carry) and then to calculate but also, that even if the weighbridge says I'm under the legal weight limit I still have to make sure my overhang weight does not exceed the rear axle limit because wighbridge axle weight and the impact of too much weight coming off tbe front axle (thus affecting handling) are unrelated?

Correct, load the scooter as far forward as possible and measure to the centre of the scooter as this is the point that the weight acts around.

 

[andyelbac]

Rather than keep worrying about just load it fully for your trip including the scooter, water, fuel & the mrs and go to a weighbridge. Then you will know exactly where you stand.

Lenny, I think this is what is confusing me. Another reply to a post of mine on this subject appeared to be indicating that the actual rear axle weight as recorded on a weighbridge had no bearing on the results of using the overhang formula (possibly we were both misinterpreting each others posts). So essentially, whatever I may calculate using the formula, if the actual weighbridge weight for the rear axle is less than the allowable axle weight, then I am good to go and I haven't compromised the handling on the front axle ?

 

[Jim]

https://www.motorhomefun.co.uk/foru...et-to-show-effect-of-rear-loads-on-axles.266/

 

[Lenny HB]

Lenny, I think this is what is confusing me. Another reply to a post of mine on this subject appeared to be indicating that the actual rear axle weight as recorded on a weighbridge had no bearing on the results of using the overhang formula (possibly we were both misinterpreting each others posts). So essentially, whatever I may calculate using the formula, if the actual weighbridge weight for the rear axle is less than the allowable axle weight, then I am good to go and I haven't compromised the handling on the front axle ?

Yes that is correct however the load on the front axle will have reduced a bit but you are putting a fairly light load in the garage and your overhang is not that long so the effect on the front axle won't be a lot.

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[andyelbac]

For all of tose who contributed to trying to answer my query, thank you very much. I think I may have comfused things with my own stupidity! I posted this question after looking at the overhang formula on the Horton Common website. Having looked at all your answers again and gone back to the original formula, I think I should be using the starting point for each axle NOT as the axle load limits as stated on the plate but the ACTUAL weight over the axles as determined by a weighbridge or some of the spreadsheets that some have posted on here, i.e. my rear axle plate limit may be 2000kg but if the weighbridge weight is (for example) only 1700kg over the rear axle then I use 1700kg as the starting point, not 2000kg, then add my 150kg into the formula for weight carried behind the rear axle. I then compare the result against the plated limit (2000kg) to see if I have a potential overhang issue?

 

[The Wino]

For all of tose who contributed to trying to answer my query, thank you very much. I think I may have comfused things with my own stupidity! I posted this question after looking at the overhang formula on the Horton Common website. Having looked at all your answers again and gone back to the original formula, I think I should be using the starting point for each axle NOT as the axle load limits as stated on the plate but the ACTUAL weight over the axles as determined by a weighbridge or some of the spreadsheets that some have posted on here, i.e. my rear axle plate limit may be 2000kg but if the weighbridge weight is (for example) only 1700kg over the rear axle then I use 1700kg as the starting point, not 2000kg, then add my 150kg into the formula for weight carried behind the rear axle. I then compare the result against the plated limit (2000kg) to see if I have a potential overhang issue?

If you've already done the calculations for the extra load just weigh the rear axle add onto it what you've calculated and see what the number is. If you have a fair bit left you could guess the extra you're going to add when fully loaded and see if you're ok before spending on upping your plated weight.

 

[autorouter]

Looks like you've worked out how to do the calculation now. You can repeat it for different weights of scooter, different positions inside the garage and on a rack at the back, etc. It may be a pain to do these calculations but it's a lot better than buying the wrong scooter and finding it will take you over the limit.

The advantage of using a spreadsheet is it's easy to change the figures and see the result immediately. It's always best to check one of the spreadsheet results with a calculation, just to be sure the spreadsheet works.

 

[Revolvor]

I have attached an excel copy of a weight calculator that some kind soul took the time to write, unfortunately I don't remember his name but I'm sure it's in the Resources but I couldn't find it. .......

It was me that originally posted the spreadsheet! I was just about to post a link when I saw your post! Please contact me if you have any questions about how to use it.

Edit: I was a bit late posting this. andyelbac , glad you have got it sorted

Motorhome Weight Calculator

The aim of this Spreadsheet was to allow me to add or remove items from my MH, once I had been to a Weighbridge, but to still know the actual axle-weights. Although I am confident that I have sufficient Payload, I wanted to know accurate Axle...

www.motorhomefun.co.uk

 

[Fat Albert]

It was me that originally posted the spreadsheet! I was just about to post a link when I saw your post! Please contact me if you have any questions about how to use it.

Edit: I was a bit late posting this. andyelbac , glad you have got it sorted

Motorhome Weight Calculator

The aim of this Spreadsheet was to allow me to add or remove items from my MH, once I had been to a Weighbridge, but to still know the actual axle-weights. Although I am confident that I have sufficient Payload, I wanted to know accurate Axle...

www.motorhomefun.co.uk

Thank you for producing the spreadsheet. It's very intuitive to use and I keep my copy up to date. My local weighbridge is only a mile away and not surprisingly the vehicle figures are very accurate.

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[bigtwin]

I then compare the result against the plated limit (2000kg) to see if I have a potential overhang issue?

Yes.

However, it is not a potential overhang issue, it’s a potential axle weight issue.

The formula merely calculates how much a given load adds to the rear axle weight when that load is placed a certain distance from the axle. The result will always be greater than the load added (due to the leverage effect).

Ian

 

[andyelbac]

I've been giving all the advice I kindly received on this post some thought over the least week or so and confident I now understand how the whole axle load/overhang/pivot weight point thing works and many thanks for those of you who supplied various spreadsheets; they will come in handy. I've just had SV Tech uprate the Burstner to 4,000kg GVW and up from 2t to 2,240kg on the rear axle. (semi air just having been fitted). According to my calculations, I can carry the Honda SH mode in the rear and all our other gear (it's just me and my partner..no dogs or kids) and I'm calculating I will be 45kg under the front axle limit and 80 kg under the new rear axle limit (even allowing for the additional rear garage load caused by the weight behind the rear axle). All that remains is a trip to the weighbridge in fighting weight to check that I am legal in reality and not just in my dreams. One final question though, and excuse me if I am being dense: I understand that placing weight behind the rear axle adds more than the actual weight added due to the pivot effect. I get that. But there is also the issue of weight being taken off the front axle as a result. What I don't understand is...how do I know what is good or bad is in respect of weight coming off the front axle? I can see how the rear axle calculation shows definitively what is good or bad (over the axle limit=BAD, under the limit = GOOD!) but what about the front?

 

[funflair]

If your calculations and then actual weight tell you that you are 40kg under the front axle limit then it certainly isn't too light or too heavy I would say if it were too light on the front the steering would be very light so you would know.

 

[The Wino]

I've been giving all the advice I kindly received on this post some thought over the least week or so and confident I now understand how the whole axle load/overhang/pivot weight point thing works and many thanks for those of you who supplied various spreadsheets; they will come in handy. I've just had SV Tech uprate the Burstner to 4,000kg GVW and up from 2t to 2,240kg on the rear axle. (semi air just having been fitted). According to my calculations, I can carry the Honda SH mode in the rear and all our other gear (it's just me and my partner..no dogs or kids) and I'm calculating I will be 45kg under the front axle limit and 80 kg under the new rear axle limit (even allowing for the additional rear garage load caused by the weight behind the rear axle). All that remains is a trip to the weighbridge in fighting weight to check that I am legal in reality and not just in my dreams. One final question though, and excuse me if I am being dense: I understand that placing weight behind the rear axle adds more than the actual weight added due to the pivot effect. I get that. But there is also the issue of weight being taken off the front axle as a result. What I don't understand is...how do I know what is good or bad is in respect of weight coming off the front axle? I can see how the rear axle calculation shows definitively what is good or bad (over the axle limit=BAD, under the limit = GOOD!) but what about the front?

I think the issue would be if you were really heavy at the back and really light at the front if it's a front wheel drive van you would most likely really struggle to get traction on some surfaces. The weights you quote sound fine although not a lot of spare for wine!

 

[BouncyBoatFolk]

Hi, we have trod the same path. Our scooter [ Honda Wave 120kg wet ] sits in the [ garage] up against the front bulkhead, which is the best way for travelling in any case as it tends not shift in transit from there. Look at the all the other stuff you would normally carry in the garage, how much of that could be moved moved forward when travelling. Behind the passengers seat is normally where we locate some square flexi tubs of items, and a 20ltr tub of water. The sqaure tubs can also be sat on any forward facing seats with the seat belt around the tubs, probably a good 150kgs[ = 2 x passengers @75kg each capacity to utilised there]. We have tubs of kayaking, and other gear sat there when travelling. Spreading the load over both axles is the key. Overloading the front axle is really quite difficult. Yes, it's a bit more work, but it saves having to contemplate a different van of 4500/5000 kg.
Mike.