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Old 05-18-2009, 05:40 AM   #1
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Re: Towing...

Difficult to read your english a bit. :-/ Not sure if it's a serious question.

I would assume the maximum tow weight is probably going to be 10,000lbs easily, perhaps a bit more with difficulty because thats the weight limit of commonly available rear hitches that aren't fifth wheels or goosenecks. Towing a trailer with any 26k GVWR rated schoolbus will put you over GCWR ratings and require a Class A license i'm told.

Front or rear engine shouldn't matter under 10,000lbs trailer, over that probably means fifth wheel unless you plan to put one on the frame rails over the tires meaning a serious shortening of the bus and the single rear axle wont pull enough weight on top of what a schoolbus weighs to make that conversion worthwhile.

Articulated busses have two separate bodies joined by an accordion like section if thats what youre asking, so do trains, some kind of pass through could probably be improvised based on that design if really necessary.
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Old 05-18-2009, 07:10 PM   #2
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Re: Towing...

I would think just having a thick canvas curtain of some sort like used for boat sails would be tough enough to withstand any weather and prevent water/rain/snow infiltration into either cab with the door open. That's what i'd try.
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Old 05-27-2009, 10:23 PM   #3
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Re: Towing...

Thought i'd add something to the thread for future readers...


A rule of thumb in the past was you could tow a trailer up to the weight of the vehicle hauling it with reasonable safety and more if it's made for towing. Since most busses are in the 20,000lb and up category by that standard you should have enough reserve to haul anything you can possibly get a hitch for, which tends to max somewhere in the 10,000lb to 14,000lb range without a fifth wheel or gooseneck. Heavy hitch trailers can be a little squirrelly but that's because you have a 5000lb pickup hauling 12,000lbs behind it. Even with adequate brakes the weight mismatch is just a physics issue. A bus should have the reserve to deal with any load you can reasonably tow by heavy duty hitch. You probably wouldn't even feel 5000lbs. One reason they suggest medium duty trucks for the heaviest travel trailers in the 6-8 ton range is that if the brakes on the trailer goes out the truck has enough weight and braking reserve to bring the trailer to a safe stop. (though I wouldn't want to tow an unbraked 8 ton trailer, that's more of a one stop issue)

Also RWD vehicles are better towers than FWD because the weight presses the drive axles down and there's no sensitive CV joints to worry about. So personally I wouldn't have any fear putting 7 tons behind in a trailer since in some busses you can put 7 tons INSIDE it, even if it's over the GCWR a bit because they dont rate modern vehicles for towing by the old rule of thumb that worked for years but it's still probably doable.

There are three main questions or problems i'm aware of for any heavy tow:
- Starting torque. Can you start the vehicle fully laden on an uphill grade? This is often the reason for having very low gears in a 1 ton truck. It can start far more on a flat road (i've pulled 33,000lbs with a half ton - stupid, but I did it, didnt know what it weighed, it was a favor for a friend) but you dont want a stall out if you have to stop going up the mountainside! The low gearing of many busses probably doesnt make this much of an issue.
- Braking. This is obvious! But even 13,000lbs of trailer behind a 26,000lb bus is not an impossible increase in load if your speeds aren't excessive, slowing from 75mph unladen is probably harder on brakes than slowing from 50mph totally loaded.
- Transmission. This could be the killer! Literally. Heat kills transmissions and pulling heavy loads overworks transmissions, especially if you add hills and such to the mix. Although the "half again" trailer load behind a bus should not be excessive, if you had a real old or tired bus or real hot conditions it could add to the problem. I'd definately get a transmission cooler for anything over a 5000lb trailer if it doesnt' have one already. Automatics are killed more by towing than manuals, with a manual there's nothing to worry about.

Hopefully this is useful to somebody.
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Old 05-28-2009, 10:46 PM   #4
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Re: Towing...

I tow my Jeep around behind my Thomas Pusher, the Jeep has a listed Empty weight of 3500#, and that bus doesn't even know it's back there. I've towed the Jeep 4 times so far, the last was a trip to Cape Hatteras and back for a total of 250 miles...

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Old 05-28-2009, 11:57 PM   #5
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Re: Towing...

I wouldn't have a problem loading up 20,000 lbs behind my bus. It is going to handle the load just fine...except for one component. The transmissions used in our buses just aren't rated for that kind of load. An MT643 might be a little better, but an AT545 pretty much tops out at 30,000 lbs GCW. Heat is a killer and transmission heat is generated almost exclusively by the shearing of fluid within the torque converter. Locking the converter helps this a lot..provided your converter even has a lock up feature. On an MT643 I would certainly consider wiring in a switch to be able to manually force converter lock up, much the same as 700R4 owners have done for years to help their transmissions live under towing conditions.
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Old 05-29-2009, 09:33 AM   #6
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Re: Towing...

Quote:
Originally Posted by the_experience03
I wouldn't have a problem loading up 20,000 lbs behind my bus. It is going to handle the load just fine...except for one component. The transmissions used in our buses just aren't rated for that kind of load. An MT643 might be a little better, but an AT545 pretty much tops out at 30,000 lbs GCW. Heat is a killer and transmission heat is generated almost exclusively by the shearing of fluid within the torque converter. Locking the converter helps this a lot..provided your converter even has a lock up feature. On an MT643 I would certainly consider wiring in a switch to be able to manually force converter lock up, much the same as 700R4 owners have done for years to help their transmissions live under towing conditions.
This is good to know. If the 545 tops out at around 30,000 GCW, what would the 643 top out at?

I agree with you, I don't think my bus will have any serious problem with pulling almost anything, but I do worry about frying a transmission. One of my many mods I plan includes full instrumentation to monitor all the important (and much unimportant) information about the operation of the driveline. I prefer to know well before things reach critical if a problem is developing. That includes a few transmission temperature sensors.

jim
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Old 05-29-2009, 08:52 PM   #7
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Re: Towing...

AT545=30,000 lbs GCW, 235 hp, 445 ft lbs of torque. All those numbers are maxes and by reducing your GCW, for example, you can up your max input torque. This is how Allison 1000 series (on par with the AT545 in terms of strength) can hold up in a Chevy pickup with 650 ft lbs of torque. My bus has an AT545 with a 30,000 lbs GVWR (not that it's actually that heavy), 474 ft lbs, but only 185 horsepower.

MT643=up to 73,280 lbs, 250 hp, 640 ft lbs. I'm not sure how they arrive at the 73,280 lbs GCW because the MT643 is rated more specifically by vocation, but I think it suffices to say that you're not going to damage it with any load you're going to hook up behind your bus.
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Old 05-29-2009, 10:10 PM   #8
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Re: Towing...

Not knowing what you are trying to tow, I can only go with my own numbers. My Thomas has a GVW of 30,000# and an empty weight of 19,000#. When you add my 3500# Jeep to the buses empty weight I come up with 22,500#... that leaves a lot of room for cargo!! I don't carry much gear with me, so I'm sure I'm way under the 30,000# figure...
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Old 05-29-2009, 11:05 PM   #9
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Re: Towing...

GVWR is only affected by the tongue weight of the trailer. GVWR refers to just the single vehicle, not the combination. GCWR refers to the maximum weight both can weigh together. Now in the case of an AT545 the numbers are one in the same, but that is a rarity. A person must look at ALL the various ratings to decide if something is safe. I'm going to use my truck as an example only because I know the numbers off the top of my head.

GVWR 7200 lbs, curb weight of about 5200 lbs
MTWR 7000 lbs
GCWR 13000 lbs
GAWR (front) 3600 lbs
GAWR (rear) 4800 lbs


GVWR=gross vehicle weight rating, the maximum weight the vehicle as a whole, including cargo, occupants, etc can weigh

MTWR=maximum trailer weight rating. This WILL affect your totals for calulating GVWR, but is not directly related to GVWR

GCWR=gross combined weight rating. This is like GVWR, but is for the whole combination of vehicle, trailer, cargo, etc

GAWR=gross axle weight rating, the maximum amount of weight that can be put on a single axle. GAWRs are given separately for the front and rear. Added together they may add up to the GVWR or in many cases, more than the GVWR, but never less.

Ok...first we must note some oddities here. For instance, if you add my GAWRs together you get 8400 lbs, a full 1200 lbs more than the GCWR. This is because there is some tolerance for uneven loading. Second, it should be noted that my GVWR plus my MTWR exceeds my GCWR by 1200 lbs. Why? Because the engine and transmission can only be expected to do so much. You get your choice between filling the bed, pulling a trailer, or any combination in between that stays within these guidelines. For instance, I could not have a 7000 lbs trailer (which results in 700 lbs of tongue weight) and then throw another 2000 lbs in the bed of the truck. Sure, I'm within my MTWR, but I will exceed my GVWR and my GCWR. In fact, even if I deduct the 700 lbs for the tongue weight and only put 1300 lbs in the bed I will still be over my GCWR. Chances are I will NEVER touch the GAWR in the rear and still be within the other limits. That semifloat 14 bolt rear end is a pretty stout piece...

I could, however, pull a 7000 lbs trailer with 700 lbs of tongue weight with my truck and still even throw 800 lbs of stuff in the truck (fuel, me, a friend, whatever) and still be within my 7200 lbs GVWR (I'd be at 6700 lbs) and be at my 13,000 lbs GCWR, all while still avoiding exceeding the 4800 lbs of rear GAWR. It's all a balancing game. You cannot be at max GVWR and max tow weight rating because your max tow rating puts weight on the truck, for example.

Ok...maybe it's getting a bit complicated, but the point is that you CAN exceed your GVWR when you add the weight of your tow rig (bus) and the trailer legally and safely provided another factor (like the limits of the AT545) don't get in the way.

*edit* I should also add, just for you, Gone Camping, that flat towing a vehicle will affect GCWR calculations and MTWR calculations, but not GVWR, save for the weight of the hitch I suppose. This means that you potentially still have 11,000 lbs of payload capacity left for your tools and "stuff." Yes, this is 100% legal and safe provided you do your math correctly. If it wasn't you wouldn't see 8600 lbs GVWR pick up trucks pulling 10,000 lbs stick n staple fivers around.
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Old 07-23-2010, 09:44 PM   #10
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Re: Towing...

I have built exactly as you would like. a slide out that connects the 2 vehicles when parked, I call it the 72' motorhome. Might I warn you it is a tremendous amount of work and money. Just know what your getting into when you start cutting and building. I have taken it on several long hauls through some of the steepest mountian ranges in nevada and never overheated or had any issues at all. trailer whight 11,000lbs. bus 36,500 gvwr cummins 5.9 slow on the hills but it will get ya there
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