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Building Class 8 motorhome... Need some opinions

Discussion in 'Trucks' started by Nklpltd, Apr 6, 2013.

  1. Nklpltd

    Nklpltd Member

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    Hey guys and gals...

    Like the title says... I am in the planning stages of building a custom class 8 motorhome.

    So far here are a few of the details.

    It will be max length of 45 feet, per Idaho maximum single vehicle length.

    I want a custom rig, but I am a bit torn on the specific body. Here are the few I'm trying to choose on, a 50's GMC 630 hood and cab on a newer heavier frame, a W900A Kenworth, 60-70's Autocar or a 50's Mack. The diesel will be a Celect + N14 Cummins and the new TC-10 Allison 10 speed trans.

    I know most motorhomes tow a car, but I am planning on mine riding inside the rear garage area. The back will have barn doors with ramps for the car.

    Here is where I need some opinions....

    With a big long rig like this, and a Monster Diesel up front, I'm probably going to need a heavier axle than the typical 12k. I am thinking a 16k or 18k would be safe. I would prefer to not run a 385 or 425 if I don't have to and completely kill my turning radius.

    On the back I am thinking a single drive axle with duals 20-30k, maybe 20k with a 13.5k tag axle. My crazy thought was with a single rig this long, how can I possible make it turn a bit better and not take a football field to turn around in, so why not add a tag steering axle? What do you guys think? I want at least a bogie axle in the back to help with the weight, but having a steering axle seems like a much better idea. Then in my research last night I was looking at drop axles and thought that would be perfect. Have it help steer when I am going forward, and then when I back up, it will lift and I have a single pivot point, therefore helping to turn better in reverse as well.... Thoughts??

    I was planning on finding a salvage truck that the body was smashed but the frame still intact at straight. I have good welding skills and equipment but I'm still a bit uneasy about cutting and stretching the frame. Where the frame will be mated, I am going to weld and bolt them together just to be on the safe side. Also with a newer frame it will be easier to find a matching frame for the stretch.

    My last question is for the rear pintle hitch. I am building a custom rear bumper that is the full 102 inches wide. It will be very reinforced, so do you think I would be alright with a 1/2 inch plate that has multiple trusses tying it to the frame along with the plate itself being welded to the frame?

    This will only ever haul a 16 foot trailer with toys or an additional car so not a ton of weight.

    Any more input on anything would be appreciated.

    Jake
     
  2. tireman

    tireman Senior Member

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    Where do you get the idea that wide base tires affect the turning radius of a vehicle? What affects the turning radius is steer-axle placement (set forward vs. set back) and wheelbase, not tire size.
     
  3. Nklpltd

    Nklpltd Member

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    But wouldn't a skinnier tire give me a better turning degree without rubbing? Thus decreasing the turning radius?
     
  4. tireman

    tireman Senior Member

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    No. With the correct wheel, a wide base tire will not change the steering geometry. That's why they have a different offset.
     
  5. tireman

    tireman Senior Member

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    You could probably get by with something like a 315/80R22.5 - they have a load rating of 9,090 single. They will work on a standard 8.25 wheel, although 9.00 is recommended.
     
  6. johndeere123

    johndeere123 Well-Known Member

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    I dont think a lift axle will be of any benefit if you can get all of the weight with a single axle. If you need tandem axles in the rear I think a lift would be more work than its worth.
     
  7. Scrub Puller

    Scrub Puller Senior Member

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    Yair . . . I think for all concerned the longer this project stays in the "planning stage" the better.

    Cheers
     
  8. Nklpltd

    Nklpltd Member

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    For all those who think I should stop here... I fully intend to complete this project.

    I might not need tandems but I would rather play it safe if I decide to throw a heavy trailer behind it. Rather then regular tandem set, I was planning the self steering drop axle to help improve the turning radius.

    Ridewell Corp has a tandem drive/tag setup (RDS-209). They say it automatically spreads the weight 60/40 with the heavier on the drive axle all the time. My only concern with this system is if I ever take this rig north to Canada or Alaska like I am planning, will 60% of the weight be enough for snow and chains vs a lift where I can pull it up and put 100% of the weight on the drive axle.
     
  9. johndeere123

    johndeere123 Well-Known Member

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    That looks like a pretty rough riding setup. For an RV which would be built for comfort, anything but all air ride seems pointless. An air ride rear and an air ride lift axle seems alot more practical. Although if you plan on going places you need chains, maybe full tandem drives are worth looking into.
     
  10. Nklpltd

    Nklpltd Member

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    Well I do plan to have air suspension for all 3 axles...

    I don't know how often I will need chains, but i do plan a full tour of Canada and Alaska, and I just want to be prepared.
     
  11. Tiny

    Tiny Senior Member

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    A steerable drop axle is pretty sweet to use compared to a fixed one and it does help turning radius on our 4 axle tractors . Only warning I have is they will counter steer in reverse . Ours have reverse dump switches hooked to the backup lights so the axle dumps the load and clears the ground . Might be what your looking for . :)
     

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  12. Nklpltd

    Nklpltd Member

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    That is my exact thought, have the axle lift when in reverse.
     
  13. tireman

    tireman Senior Member

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    Steerable lift axles steer to improve tire life by preventing the scrubbing of the tread. I suppose the reduced drag will help get the full available turning radius the truck is capable of, so if you want to call that an improvement you can. However, they WILL NOT give you any tighter turning radius than you would have without that axle touching the ground. It's geometrically impossible. Only if the axles behind it (drives) also counter - steered (like a stinger steered trailer or one of those cranes like is on Tiny's float)would an improved (tighter) turning radius be possible. I don't mean to be an a$$, but some folks could get the wrong idea from reading these claims, then go waste a bunch of money on false hopes.
     
  14. Nklpltd

    Nklpltd Member

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    Tireman... Are you under the impression the drop axle would be in front of the drives? I was planning putting the drop axle behind the single drive axle.

    I don't see you as being an a**. I want differing opinions that are helpful in figuring out the best setup for my project.
     
  15. tireman

    tireman Senior Member

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    Yes, that was my impression. Sorry for the uptake fail. Still not gonna shorten your radius. You'll wanna go with a set back front axle for the shortest possible turning radius. Set it back as far as you can get away with.
     
  16. Nklpltd

    Nklpltd Member

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    I will try and do that. That will help me figure out what body I should use.
     
  17. markshr151

    markshr151 Well-Known Member

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    I am forwarding this to a friend ( more like a brother) who has years of experience addressing all of these problems.he can tell you what he thought would work but didn't and vise-a-versa.
     
  18. johndeere123

    johndeere123 Well-Known Member

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    The turning radius of a vehicle 45 feet long is going to be big whatever you do. The rear axles will have to be back almost to the rear because most of the weight will be in the rear because of a vehicle and a bumper tow trailer. The gains you get from adding the setback axle and the lift axle may not even be noticeable.
     
  19. Scrub Puller

    Scrub Puller Senior Member

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    Yair . . . As I see it 45 feet is 45 feet and a set back steer and steerable arse end would help but it is only fidleing around the edges of a geometric fact . . . I drove an Oshkosh for a while with an extreme set back steer and you still needed room to get that nose around.

    Cheers
     
  20. Nklpltd

    Nklpltd Member

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    Determining where to place the rear axle(s) is my biggest focus right now. The car going inside will only weight about 3500 lbs.

    I am making a list of everything that will be going inside and in the toolboxes to determine how much added weight on top of the structure itself, and how it's positioned front to back.

    One rear axle would be great, but the few concerns I see are... A- I haven't been able to find a rear single axle air suspension over 30k pounds. B- Even with a 30k rear, I am concerned with a heavy trailer that I would overload it.

    Yes, but inches are inches and gaining a few inches on turning could be the difference between making it or hitting the curb.

    I plan to hit all 48 lower states, Canada and Alaska with this rig and I want it to be able to go as many places as possible, that allow a rig this size. So it might not be a huge gain, but like I said, inches are inches and I want to make it the best it can be.