Front to Rear weight ratio of M1078.

[coachgeo]

Looking at options on mounting my Ambulance box more seriously now and talking to welder/Fabricator. Question about balance. Has anyone checked their front to back weight ratio or in a position to do so? Put up on scales at a truck stop with front axle only on scales ..... followed by back axle only on scales to see what each end carries? Id do it but seller had already removed my spare etc. so it won't be as informative.

Seems to me the truck is front heavy and if that is the case then might move up the air tanks or something up in place of the spare.... and move the spare to the back with the motorcycle as many Overlanding trucks do anyway. What are ya'lls thoughts? Granted I'll have the heavy Power Divider Box on the axle but that is unsprung weight so not as much of an equation in this.

 

[Awesomeness]

I've wondered the same thing, but I haven't tested it. My truck is missing the data plate from the passenger door, but the plate has information about the theoretical center of gravity, that you could use to calculate the load on each axle. (And I've been looking to get a data plate for mine, so if anyone reading this has one off a parts truck, please PM me.)

 

[cheepsk8]

At most truck scales, there are separate pads to park on. Just make sure your front and rear tires are on separate pads and you will get front, rear, and total weights at once.

 

[Jbulach]

Dont these trucks have the empty and loaded axle weights on the data plate? Might not be exact, but your trucks already missing parts, so another trucks weights aren’t going to be exact either.

 

[tennmogger]

I have not weighed my truck either so am also interested. Wouldn't any data plate load ratings be maximums, not actuals? A tire's weight won't make much difference compared to the 18000 lb truck. The position of your ambulance box and all its support hardware will be significant, and we do not have that info.

 

[wheelspinner]

The center of balance is supposed to be directly between the front and rear sling points for lifting.

 

[Awesomeness]

Pictures that I have seen of the data plate from the passenger door show that it has dimensions, location of the center of gravity, and a bunch of other information. (Again, my truck is missing the plate, so I've never seen one in person.)

 

[Jbulach]

Sorry about the poor resolution... found it on the gooogle machine under “M1078 load data”

 

[TNriverjet]

There you go... The row labeled "curb" is unloaded weight. The row labelled "gross" is total evenly loaded. It's even broken down by front axle, rear axle and total weight.

 

[Awesomeness]

The diagram is fairly unreadable, but if you look closely there is an icon in the middle of the truck that is a circle with two opposing quadrants colored white. That's the center of gravity symbol. So if you can get a good look at a real data plate, it looks like it has actual dimensions (labeled A and B) on exactly where the center of gravity is.

 

[coachgeo]

Thanks for the info. Not being a mathematician not sure exactly how COG helps me. Now if it was COG's relation to rotation (flip) and Twist.. or multiple of each like the gymnast I deal with daily that would be different lol.

Weight on each axle will help though. As to a previous mention of moving tire to rear not making much difference..... well when you add a 400lb motorcycle, maybe second spare tire and the lift to raise and hold those up... then it starts to add up and make a difference. Working on getting weight of box and info on its front and rear weight as well. I assume it is balanced in weight but one should never assume.

 

[Awesomeness]

Center of gravity is the "balance point". That's why I kept mentioning it. It's exactly what you were looking for, no calculations needed.

 

[coachgeo]

Center of gravity is the "balance point". That's why I kept mentioning it. It's exactly what you were looking for, no calculations needed.

I know what COG is and what it represents. Deal with COG hands on everyday for last 45ish years..... but when calcu...estimating changes that will occur think the axle weights will help me more. Will play with numbers some. How much ya'll think the spare tire carrier weights?? Spare tire? lets say all together with , motorycle and lift..... 1000lbs. If my Ambo camper box was mounted same as Bed... and assumed just for ease of math only, the box weighed same as bed (its all aluminum) then that would swing it thousand lbs heavier at rear axle and probably move COG back a little. hmmm


COG image does seem to point out the ratio is front heavy and numbers support that. For Shiats and Grinz the Front to Back Weight Ratio is 63% front and 37% rear of a Cargo/Troopy M1078. Above #'s mentioned would move that closer to 60/40 front to back ruffly. Not huge change but little better...

Ideal goal??? hmmm good question? sports car days it was 50/50 front to back. An AWD truck caring a camper on back ... when thinking of up hill climbs or down hill ascents and other offroad twist and turns? Should there be a biased to front or back.... or still 50/50?? My guess is still 50/50.

PS my dataplate attached

 

[Awesomeness]

Here's a better picture of the data plate from an A1.

 

[coachgeo]

Maybe?? answering my own question after little search.... seems maybe 50/50 front to back ratio is still the goal? Looks like Dakar Kamaz went for that. Few articles just read mentions them pushing some things back (Tcase) to improve weight balance..... while other article shows front axle weight at 4800kg and rear axle 4700kg.... which seems to show they shot for the 50/50 goal.

 

[Jbulach]

Thanks for the info. Not being a mathematician not sure exactly how COG helps me...

Your welcome. It doesn’t really.

What you need is the COG of your box, loaded and ready for the trail. Go to a farm supply store and buy a round 6” wooden fence post, jack the box up, roll it under, and experiment with the position until the loaded box teeters on the post. That position is the measurement you are looking for.

Now you need someone with a stock truck to give you a measurement where their bed centerline, front to rear is in relation to the axle. This is the point where the addition of 5000lbs, plus the weight of you missing bed will give you the “Gross” numbers on your data plate.

I’m not sure how modified the weight of your truck is, but if it has just mainly had the bed removed, you could take your truck to a truck stop and get your axle weights and total weight then subtract that from the total curb weight on your data plate, this will give you the approximate weight of the original bed.

Then your going to have to get your box and extras weighed somehow, guessing and assuming will cost you in the end! Once you get all that, there are a few good truck load distribution calculators on line, that you can plug your weights into and move them around to see how they affect your axle weights.

 

[Awesomeness]

Your welcome. It doesn’t really.

I know you guys think you "aren't mathemeticians", but I'm going to help explain. CG is exactly what you need to know, and it's exactly what that 63%/37% split is that Coach just calculated. The info about the "centerline of your bed" is right on that data plate too! I know FMV owners are an eccentric bunch, but sometimes we really make things harder than they need to be.

The data plate shows the CG is 110" from the front of the truck, the front axle is 53.7" from the front of the truck, and the distance between the axles is 153.5". So we want to know how far the CG is between the axles (or from the front axle). That's 110" back from the front, minus 53.7", which equals 57.3" (110 - 53.7 = 57.3).
What's that balance ratio? Easy. 57.3" out of the whole 153.5" between the axles. You can already see that's about 1/3. 57.3" back, divided by 153.5" total, equals 37.3%. (57.3 / 153.5 = 0.3732).

Want to know what happens when the truck is fully loaded with 5000lb in the bed? It moves the center of gravity back to 124". Do the same calculation... ((124 - 53.7) / 153.5 = .4579) ... 45%

The bed is 12.5' long (~150"). CG on the empty bed 110" from the front, and the whole truck is 254.5" long. (254" - 110" = 144") So the CG is 12' from the overall back of the truck, or about 8" from the inside front of the bed.

You can calculate (with simple math again) "What happens if I put 2000lb about 2' from the rear of the truck?" too.

 

[Jbulach]

Worthless if your guessing at weights...


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[coachgeo]

what about M1079. curious SStevens approach to front/back weight ratio for those

 

[Ronmar]

I have a m1079 let me look at my door panels which are off in the back of my garage, to see if I have the weight and balance placard...

IMO your goal should be near a 50/50 axle weight distribution on a 4x4 for a couple reasons.
1. Tire wear with CTIS. It applys 1 pressure to both axles, Which will give you different footprints and wear patterns front to rear with different axle weights. Unless you are trailering it everywhere, it will consume most of its tire rubber on smooth pavement...
2. Balanced traction. In the eco offroad post since they had no weight on the back, they were not getting as much tread contouring as they could have on the rear going uphill because the weight was well forward of the midpoint and the shift to the rear was not very significant. Going downhill they almost didnt have enough front axle pressure, as they almost compressed to rim contact coming down some of those steps, but they had tall solid lightly loaded rear tires at the same pressure...
3. Still balanced traction, say in sand or snow. As the lighter rear axle will have a taller/narrow tire profile at a given pressure, along with less downforce, so will tend to spin/dig more easilly, especially in AWD as it directs twice as much torque that direction.