Canadian Disco 2 Build

[Root Moose]

Yes, I'm aware of those tanks. Not a clue what they cost, but I bet it's a lot. And doesn't fuel a dirtbike easy either.

I'm trying to make contact with them. We'll see where it leads...

There's a few of us here (Ontario) that wouldn't mind something like that but it only seems to be available for OBDI XJs. Not sure if it is just because they've never tried installing or if there is a technical reason. I'll find out.

What is nice is that it is an aux tank though. I'm going to guess ~$400 plus shipping. What's a good Jerry can worth these days? $50? $80? Adds up quick.

 

[Cary]

this thread really draws 'em in.


Google my a$$crack - you'll find a free body diagram holding a beer from my time in the physics program :elkgrin: Are we wheelin' a tractor here? I didn't think so. here's an exercise for you - since you seem willing to learn.

Centers of gravity are a 3-axis deal. Keeping it over the tail is a compromise from moving it too high on the Y axis, giving up a bit over the X axis. If the cans are balanced around the spare then Z axis is happy. The truck weighs over 5k lbs, and you're talking about 200lbs of stuff. 2 fuel cans = roughly 10 gallons x 6lbs/gallon = 60'ish lbs. Plus a hi-lift, maybe 30lbs. That's 90lbs plus the weight of the steel in the carrier arm. Maybe we're talking an extra 100~120 lbs over what is already there. Please put together a free body diagram for a static case, and calculate roughly how many inches backward that 100'ish lbs moved the COG on 5,000lb + truck.
We're balancing the cans, so lucky for you that's back to 2-axis diagram. We don't need to consider ground pressure on each tire but each axle, via the tires, are pushing up so that will factor in to your calculation, as you'll need to calculate the torque at the rear axle exerted longitudinally along the chassis due to the unbalanced weight. No need to account for spring rates - just assume they are fixed. there is already a small amount of torque - if you look up the front and rear axle GVW's you should be able to calculate the percentage difference and get a ball-park number. you will also have to "google" the distance from the center of the stock spare tire to the axle center-line in the chassis since I'm sure you don't have a DII, to get an idea of how long your lever is. Now that you have a base case, and you know the weight each axle is pushing up with, and the amount of torque exerted on the rear axle to the rest of the chassis - put the whole deal on a 15% grade and recalculate the forces on the axles pushing back up and compare it to stock. For extra credit, why doncha throw a big ol' winch and heavy front bumper on the front axle and see what that did to your torque on the rear axle by calculating the torque exerted on the chassis by the lever of the front bumper.

It's been 15+ years for me and I'm not digging out the books after a couple beers, but you seem to have spunk and a willingness to learn something via google, as opposed to us poor bastards who had to sit in class. Go on now and come back to us with how much of a difference this really makes, so we can see if Rob is still justified in doing it this way. I have boxes to unpack and and am too annoyed to actually draw this up.

drunk'ish SeaRubi owwwt

You should have just googled.

But to answer your question, even though you do not have all the values to successfully determine the answer to your own question, the "200lbs" of additional weight have moved the D2's COG backwards 4.182". That means the D2's COG has went from 56" to 60" (towards the rear tire). Obviously, to find his new break-over angle we'll need much more information. And, again, obviously, as the front wheels climb, the gravitational wheel base shortens and we need yet even more information.

But here's the simple man's answer to the equation, and it takes much less thought.

 

[LandyAndy]

Is that Hard Labor Creek, I think I saw that design? It's interesting. I'm not quite sure I get it though. Some amount of the weight is still borne on the door?

If all you want to do is move the tire higher, it could be done just by rebuilding a new tire mount off the old mount points, but raise it up. Really easy to do. If I wanted gas on the roof, that's all I would have done.

If all you want to do is raise the tyre up & out a bit for clearence then this will do the job.... available off the shelf from Devon 4x4 in the UK.


Oh.... any chance of getting this thread back to more fun stuff like fabrication..... all these numbers are giving me a right bad head !

 

[R_Lefebvre]

All right, since you asked. :coffeedrink: Closeup of the welding on swing-away mounting stanchion. I've been working hard to improve the appearance of my welds.

I am replacing the plastic corner finishers with metalwork of similar shape welded to the bumper. Get rid of that nasty gap between the bumper and finisher. The swing-away pivot is now mounted in double shear. My plans for the latch are somewhat unique and probably overkill. Will use a paddle latch from a truck/trailer for casual opening and closing, but also have a 1/2" pin that can be installed for long drives, rough roads, etc. just for security. Belt and suspenders.

I'll get more pics later.

 

[RonL]

Let's see more pictures of the design and less talking...

CG does not matter that much, just watch a camel trophy videos!!!

 

[Cary]

COG does not matter? Haha

For all the doubters, here we go:

“X” The Wheelbase Center of Gravity (WBCG)
(1 - (WF / Wt)) * LWB = WBCG location, in inches, behind the front axle.
(1 - (2420 / 6063)) * 100 =
(1 - 0.541667) * 100 =
0.46 * 100 = 59.980 Inches behind the front axle

“Y” The Wheel Track Center of Gravity (WTCG)
(1 - (WP / Wt)) * LTB = WTCG in inches, from the passenger side tire edge
(1 - (2986 / 6063)) * 61 =
(1 - 0.4375) * 61 =
0.5625 * 61 = 30.958 Inches from the passenger side outer tire edge

“Z” The Center of Gravity Height (HTCG)
HFd = HF2 - HF1 = Height difference between front axle level and elevated
HFd = 41.3 – 16.0
HFd = 25.3 inches

LWBn=SQRT (LWB^2 - HFd^2) = Length of the shortened wheelbase when elevated
LWBn=SQRT (100^2 – 25.3^2)
LWBn=SQRT ((100 * 100) – (25.3 * 25.3))
LWBn=SQRT (10,000 – 640.09)
LWBn=SQRT (9359.91)
LWBn=93.599 inches

WRd = WR2 – WR1 = Weight added to rear axle
WRd = 3867 – 3627
WRd = 240 lbs.

HTCG = HF1 + ((WRd * LWB * LWBn) / (Wt * HFd)) = Your CG Height
HTCG = 16 + (( 240 * 100 * 93.599) / (6063 * 25.3))
HTCG = 16 + (2,246,376.0 / 153,393.9)
HTCG = 16 + 14.64
HTCG = 30.64 Inches above the tire patch

COG on a stock D2 is:
59.98 Inches behind the front axle
30.96 Inches from the passenger side outer tire edge
30.64 Inches above tire patch

If Rob wants to volunteer his rear door contraption information we can figure out the negative affects it has on his D2 in terms of COG. Based on 200lbs, and not knowing exactly where it's centered, we can guess it would be 64.08 inches behind the front axle, or 35.92 inches in front of the rear tire; and of course the COG above the tire patch is going to go up, too.

In other words, yes, 200lbs will severely impact your COG, which in return affects your vehicles off-road ability. But hey, it's going to look good, right?

 

[LandyAndy]

All right, since you asked. :coffeedrink: Closeup of the welding on swing-away mounting stanchion. I've been working hard to improve the appearance of my welds.

You really should be ashamed of those welds.... the weld pools are clearly not the same size and pitch.... I suggest that you grind it all out & start again

 

[R_Lefebvre]

I'll weigh the thing on the weekend. It's not 200 lbs. And don't forget to account for the 200lbs on the nose.

Interesting numbers there, I'm curious where they came from. Somebody scaled their truck? I'd like to know the details on the truck used as 6063lbs is way over the published curb weight. The NHTSA lists the curb weight as 4741 with a CG 52.4" behind the front axle, and a nominal weight of 5189 and CG 53.7".

I was curious where you got those equations because I know you didn't come up with them on your own. Pretty easily found. Seems like a pretty decent paper, actually.

http://www.scribd.com/doc/3981600/Center-of-Gravity-and-Roll-Over

I already started this myself but with a lot of unknowns. Based on your WAG of 200lbs and CG provided, and my WAG of 45" behind the rear axle, and a truck weight of 5000lbs my FBD shows the CG moved back 3.4" to 59.4". Not too far off your numbers.

Now, adding 200lbs to the nose, I figure 40" in front of the axle, bring the CG back up to 55.7"... actually better than your 56" starting point.

And, just to demonstrate my point about the racks... When traveling a 30° slope, and roof rack with a CG 7 feet off the ground, the CG shifts back 48". I figure the CG is about 10" in front of the rear axle, so going up the slope, it's now 38" behind the rear axle. At 45° slope, the CG of the rack now shifts 74" behind the rear axle!

 

[Cary]

And, just to demonstrate my point about the racks... When traveling a 30° slope, and roof rack with a CG 7 feet off the ground, the CG shifts back 48". I figure the CG is about 10" in front of the rear axle, so going up the slope, it's now 38" behind the rear axle. At 45° slope, the CG of the rack now shifts 74" behind the rear axle!

That's not entirely correct because you going from a 30.64" measurement to a 84" measurement without actually running the numbers.

The vehicle actually weighed in at 5962, with driver. I used 6063 as that's the advertised GVWR of the D2, and it was close to the actual measurement. The D2 did, however, have wet snow and ice sticking to it from last nights storm. So I now the numbers are not going to 100% dead-nuts on, but no two trucks are going to weight the same, either. I could not get a side load weight because the scale we used had rails along the sides - so I used an educated guess. For the WRd measurement, I used the actual weight difference and applied that to the advertised specs of the D2. It might be off a shade, but not enough to really worry about as you're only taking fractions.

 

[R_Lefebvre]

What equipment is on this truck? 1300lbs is a lot of snow!

 

[Cary]

Besides LR running boards, grill guard, and BFG AT's, it's bone stock.

 

[R_Lefebvre]

What size AT's, as it affects the CG height. Just curious as I'm comparing some things.

I guess somebody should notify the NHTSA that all their calculations done after the Firestone tire recall are off since the Nominal Vehicle Loads were... anti-sand-bagged.

http://www.nhtsa.dot.gov/cars/rules...r/NonConf_SOJan22_LandRover_051503-NoVINs.xls

Not to mention the empty trucks are very close to their Axle Weight Ratings. You've got a front axle weight of 2420 to a GAWR of 2640. And a rear axle weight of 3542 to a GAWR of 3960. Couple more passengers and a bit of luggage, and you're done.

 

[muskyman]

sorry adding a roof rack does not move the COG to 7'...LOL

 

[R_Lefebvre]

sorry adding a roof rack does not move the COG to 7'...LOL

That's not what I said. Go back and reread.

 

[muskyman]

And, just to demonstrate my point about the racks... When traveling a 30° slope, and roof rack with a CG 7 feet off the ground, the CG shifts back 48". I figure the CG is about 10" in front of the rear axle, so going up the slope, it's now 38" behind the rear axle. At 45° slope, the CG of the rack now shifts 74" behind the rear axle!

sounds llike it here.