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Old 09-19-2011, 09:27 PM   #11
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thats pretty much what I did, I tried to keep it simple,

I weighed my truck very carefully at the truck scales

I calculated every thing on the 16" centers because thats where my bed crossmembers, the vertical posts, and the roof rafter tubes were located. Then I spit the weight of each sheet of flooring, roofing and wall materials to the nearest 16" point.

You do the same with everything, from the weight of the Microwave, generator, cabinets, inverter and everything else I loaded into my conversion. Long things like a/c and water tanks get divided up into 2-3 datum points.

I used a dial hunting scale to weigh some things, others I held while on a floor scale. some materials can be found in the machinist handbook.

The stuff adds up, even the vinyl for the padded walls, weighed like 60 lbs.

Then its all a function of distance from the front axle x weight, just like your airplane balance.

then you subtract the distance from rear axle, just like High School physics, lever arm rotation equations.

I came out really close. to start with...

once I could drive my truck after the stretch, I weighed it again. pretty close...

After my box was built, I weighed it again, I was surprised to see my figures off a bit, so I had to re-figure to get close after factoring changes the box builder made to my design.

Even after all that I'm way heavier on my steering then I would like, but my truck had only a 7000lb front axle so it was close before I started and the stretch just made things that much harder.

Do to the unique design of my rear bedroom adding more behind the rear axle really wouldn't do much on my interior and would just add to my overall length. I wish I could have added 2-3 more feet for leveraging that front axle.

I'll have to re-upload my charts and drawings to another hosting site...

if your are into reading poor grammar and word structure here is the link to my build...
http://www.rvnetwork.com/index.php?showtopic=73051

blizz
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Old 09-19-2011, 10:12 PM   #12
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That is pretty much the same way I'd do it. if the weights are right and the measurement right, you should be right on.

I've seen some of the bumper pull trucks with lots of truck behind the rear axles and now I'm realizing that is done to get weight off the front axle.

Keep up the good work.

Dick
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Old 09-20-2011, 08:55 AM   #13
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Thanks for the input guys, my king pin will be at the rear most point on the deck behind the toter home box. The trailer i am pulling weighs somewhere in the range of 17,000 and is pretty heavy on the king pin. The twin screw axle locations are not set in stone at this point. I know this is not good logic from an engineering standpoint, but out here in rural kansas guys convert regular over the road tractors to grain hauling trucks with 20' boxes on the rear, hauling 600 bushels of corn * 60 lbs/bu = 36,000lbs + the weight of the bed, with virtually nothing hanging over the rear axles. To my knowledge the front axles are not being upgraded in these trucks??
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Old 09-20-2011, 10:06 AM   #14
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When I was talking with the rep from Renegade the other day at the RV show, he mentioned that If I wanted to supply my own chassis for a conversion, to factor in a few thousand $ to stretch the frame, and a few thousand $ for a 16k front axle. It appears they MFG's are paying more attention to this..

Personally, if able to spec it myself and cost wasn't a factor, on my sketched-up 40' OAL conversion, I'd like a single screw with a retractable tag axle for when I'm towing heavy or up when bobtailing it for best MPG, but that's a lot of work for a minor reward.
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Old 09-20-2011, 02:00 PM   #15
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So here's a question kind of on topic. My truck has a 12k front axle. I scaled it with full fuel and empty water, myself and my son in the front seats. Front axle weighed 12, 060 lbs. Now, I have 200 gallon fresh water tanks and they are completely behind the rear axle line (single rear axle). So, if I filled those with water it might lighten the weight on the front just a few pounds?
Also, I saw a truck/tractor that looked identical to mine but had a much heavier front axle by the looks of the front tires. I located a 16k front axle that looks like it might bolt onto my truck. Is that all it would take, including larger tires for a heavier load rating? Or is there more to it? Think it would improve the ride up front or make it worse? I know the Columbia's have an air ride front axle, I wonder if those are interchangeable with the FL112 frames? Mine is steel springs up front. Maybe I should pay a visit to a truck spring suspension shop and pick the guys brains too?
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Old 09-20-2011, 08:24 PM   #16
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subscribed / following - just checked the door tag on our columbia chassis.
front axle is 17,880 the rear is 22,700 !

ill be weighing mine this week - ive weighed it before but the scale i used wasnt multi-axle, i know fairly well loaded i was right at 30k (where my gvwr is 36580 & my gcwr is 40k)
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Old 09-21-2011, 10:43 AM   #17
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Quote:
Originally Posted by Bob86ZZ4 View Post
So here's a question kind of on topic. My truck has a 12k front axle. I scaled it with full fuel and empty water, myself and my son in the front seats. Front axle weighed 12, 060 lbs. Now, I have 200 gallon fresh water tanks and they are completely behind the rear axle line (single rear axle). So, if I filled those with water it might lighten the weight on the front just a few pounds?
I'd bet ya it wouldn't take much water to get you under your 12k limit, since any weight behind the axle will help lever weight off the front. just guesstimating, (it could be calculated if needed), but I'd bet 50 gallons of water would get you under.

Quote:
Originally Posted by Bob86ZZ4 View Post
Also, I saw a truck/tractor that looked identical to mine but had a much heavier front axle by the looks of the front tires. I located a 16k front axle that looks like it might bolt onto my truck. Is that all it would take, including larger tires for a heavier load rating? Or is there more to it? Think it would improve the ride up front or make it worse?
This I can't say for certain, but I'd bet a 16k front axle truck would have 16k springs, as well, be they air or leaf. This would seem to make the ride harsher, but if you go from a 12k leaf to 16k air, hmmmm.
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Old 09-21-2011, 11:34 AM   #18
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Quote:
Originally Posted by bushpilot View Post
subscribed / following - just checked the door tag on our columbia chassis.
front axle is 17,880 the rear is 22,700 !

ill be weighing mine this week - ive weighed it before but the scale i used wasnt multi-axle, i know fairly well loaded i was right at 30k (where my gvwr is 36580 & my gcwr is 40k)
Wow, that's great you've got a 17,880 front axle. I've got the same rear axle as you. I'm kind of confused though. Wouldn't your gvwr be 40k with those two axles added together? And isn't the gcwr closer to 80k? Does gcwr = gross combined weight rating, meaning combination of veh. and any trailer? I thought gvwr is gross veh. weight rating, which is the maximum amount the manufacturer says can be on the single veh. itself?

Is your 17,880 front axle an air ride or steel springs?
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Old 09-21-2011, 12:11 PM   #19
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Quote:
Originally Posted by Bob86ZZ4 View Post
Wow, that's great you've got a 17,880 front axle. I've got the same rear axle as you. I'm kind of confused though. Wouldn't your gvwr be 40k with those two axles added together? And isn't the gcwr closer to 80k? Does gcwr = gross combined weight rating, meaning combination of veh. and any trailer? I thought gvwr is gross veh. weight rating, which is the maximum amount the manufacturer says can be on the single veh. itself?

Is your 17,880 front axle an air ride or steel springs?
good ol' fashion leafs up front

Oh CRAP - i made a typo last night ! the Front is 13880, not 17880

so the GVWR (13880+22700) is 36580 (which i think i said before)

im going by what the drivers door tag & the tag inside the kitchen cabinet says combined (loaded coach and trailer) is 40k.

i WISH i was 80k rated (im single screw-ed) - ive got no plans to pull a stacker <mental note: play the lotto>....but if im not careful i could be OVER weight - pulling a simple little jeep (ill just leave that topic alone).





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Old 09-21-2011, 02:51 PM   #20
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Don, that can't possibly be correct. I think somebody made a mistake there. A 5k lb. max trailer?! No way. I think what they meant was a 40k lb. trailer. Your engine and trans are certainly made for an 80k lb load, all day every day. I think somebody at Showhauler mixed things up. Is there a gcwr rating on the original Freightliner sticker?
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