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Old 01-06-2020, 09:56 AM   #1
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How mich do busses flex?

A big part of our conversion will be some walls that run the 96” from one side of the bus to the other.

One major concern I have is the flexing that occurs as busses drive, and how much wiggle room I should allow for a wall that crosses from one side to the other. If I dont provide any wiggle room, and hit a curb or something else undesirable, will the twisting action smash the walls or perhaps deform the side metal?

I have seen people struggle with bus flexing during roof raises. But that is without the rigidity that the roof provides. How much are we talking in the 96” across? If it is only a 1/4” of flex, I dont think I would worry. But if we are talking 3”, I will need to account heavily in the design.

What do you think?

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Old 01-06-2020, 10:38 AM   #2
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I would imagine very little if at all. The million rivets keep it structurally stable.
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Old 01-06-2020, 10:47 AM   #3
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Quote:
Originally Posted by Truffles View Post
A big part of our conversion will be some walls that run the 96” from one side of the bus to the other.

One major concern I have is the flexing that occurs as busses drive, and how much wiggle room I should allow for a wall that crosses from one side to the other. If I dont provide any wiggle room, and hit a curb or something else undesirable, will the twisting action smash the walls or perhaps deform the side metal?

I have seen people struggle with bus flexing during roof raises. But that is without the rigidity that the roof provides. How much are we talking in the 96” across? If it is only a 1/4” of flex, I dont think I would worry. But if we are talking 3”, I will need to account heavily in the design.

What do you think?
When we cut the roof off of my BB we did not have any issues with flexing. The lower walls moved very little and was easily brought back in line with a piece of C channel and two C clamps.

Keeping everything lined up and square was easy.
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Old 01-06-2020, 11:17 AM   #4
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I really have not noticed any flexing that would be measurable in my bus. The walls built in are staying just fine. A bit more then 15,000 miles so far.

A few pots and pans have jumped out of the dish rack though and landed on the floor after some really bad bumps. However nothing in the walls or cabinets has come out of alignment.
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Old 01-06-2020, 11:42 AM   #5
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Originally Posted by Truffles View Post
A big part of our conversion will be some walls that run the 96” from one side of the bus to the other.

One major concern I have is the flexing that occurs as busses drive, and how much wiggle room I should allow for a wall that crosses from one side to the other. If I dont provide any wiggle room, and hit a curb or something else undesirable, will the twisting action smash the walls or perhaps deform the side metal?

I have seen people struggle with bus flexing during roof raises. But that is without the rigidity that the roof provides. How much are we talking in the 96” across? If it is only a 1/4” of flex, I dont think I would worry. But if we are talking 3”, I will need to account heavily in the design.

What do you think?

I have not noticed any (measurable) body flex at all in any of the buses I have driven. Buses are, structurally speaking, essentially square steel boxes. Any considerable amount of flex would crack/break windows, unseal joints and rivets, and generally cause all sorts of headaches long before we end up with these buses. The suspension is designed to do most of the flexing.


As a professional driver, I've noticed dry-van road trailers flex a lot more than buses do, both the side-walls flexing in/out, as well as the structure "leaning" (out-of-square) on a side slope or going around a corner, or (trying to) closing doors on uneven ground. But then again, road trailers are designed and engineered differently for different purposes (lighter empty weight, more weight and cubic capacity, no need to protect young lives inside), so a little side wall flex is considered acceptable given the nature of the beast.


I have given thought to converting a dry van into my tiny home (a bus simply isn't enough space for my needs, my bus is for passenger hauling) and I would definitely have to take into account the flexing it would be susceptible to. Some diagonal bracing, well attached at each side, would go a long ways toward structural rigidity, as would some appropriate gussets at the back door (which is the structural weak point, given the need/desire for the largest opening possible for loading/unloading freight).


TL;DR version, I don't think you have anything to worry about in a bus.
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Old 01-06-2020, 01:57 PM   #6
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Quote:
Originally Posted by Truffles View Post
A big part of our conversion will be some walls that run the 96” from one side of the bus to the other.

One major concern I have is the flexing that occurs as busses drive, and how much wiggle room I should allow for a wall that crosses from one side to the other. If I dont provide any wiggle room, and hit a curb or something else undesirable, will the twisting action smash the walls or perhaps deform the side metal?

I have seen people struggle with bus flexing during roof raises. But that is without the rigidity that the roof provides. How much are we talking in the 96” across? If it is only a 1/4” of flex, I dont think I would worry. But if we are talking 3”, I will need to account heavily in the design.

What do you think?
Buses don't flex NEARLY as much as the internet believes. Don't even sweat it at all man.
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Old 01-06-2020, 02:18 PM   #7
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Originally Posted by EastCoastCB View Post
Buses don't flex NEARLY as much as the internet believes. Don't even sweat it at all man.
Absolutely!

Folks told me I was nuts when I put ceramic floor tile in my bus. I traveled over 200k miles and managed to crack one tile.

That 12"x12" tile had a 3/4" x 11-1/4" notch in it to fit around a partition. The crack was in the narrow section at the end of the notch.

I had zero issues with partition walls, cabinets or other built-ins.
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Old 01-06-2020, 03:59 PM   #8
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I was driving around for a while with an 8-foot-square section of my floor entirely missing around the rear wheels, with an additional 3 feet of unsupported wall on the driver's side which included a cutout in the chair rail for the side door. No flexing whatsoever.

You don't have to worry about the bus flexing and exploding your inner walls, but you do have to worry about a wooden structure expanding with humidity, so you would want to leave a small gap between your walls and the side of the bus.
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Old 01-06-2020, 04:23 PM   #9
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I was driving around for a while with an 8-foot-square section of my floor entirely missing around the rear wheels, with an additional 3 feet of unsupported wall on the driver's side which included a cutout in the chair rail for the side door. No flexing whatsoever.

You don't have to worry about the bus flexing and exploding your inner walls, but you do have to worry about a wooden structure expanding with humidity, so you would want to leave a small gap between your walls and the side of the bus.
That is excellent advice. I should have known that intuitively from the same concept in hardwood flooring. But I still probably would have made the wood framing butt right up against the walls.
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Old 01-06-2020, 05:07 PM   #10
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Originally Posted by Brad_SwiftFur View Post
I have not noticed any (measurable) body flex at all in any of the buses I have driven. Buses are, structurally speaking, essentially square steel boxes. Any considerable amount of flex would crack/break windows, unseal joints and rivets, and generally cause all sorts of headaches long before we end up with these buses. The suspension is designed to do most of the flexing.


As a professional driver, I've noticed dry-van road trailers flex a lot more than buses do, both the side-walls flexing in/out, as well as the structure "leaning" (out-of-square) on a side slope or going around a corner, or (trying to) closing doors on uneven ground. But then again, road trailers are designed and engineered differently for different purposes (lighter empty weight, more weight and cubic capacity, no need to protect young lives inside), so a little side wall flex is considered acceptable given the nature of the beast.


I have given thought to converting a dry van into my tiny home (a bus simply isn't enough space for my needs, my bus is for passenger hauling) and I would definitely have to take into account the flexing it would be susceptible to. Some diagonal bracing, well attached at each side, would go a long ways toward structural rigidity, as would some appropriate gussets at the back door (which is the structural weak point, given the need/desire for the largest opening possible for loading/unloading freight).


TL;DR version, I don't think you have anything to worry about in a bus.
OMG I had the same idea!

Remember too that the school bus construction is unique in that it is a rigid steel box on a truck frame so the suspension is first going to absorb any predictable stresses and then the I-beam frame is going to resist any extraordinary torsional stress before the body itself is forced to contort out of shape. That would take a significant amount of stress, more than anything I imagine any of us are going to subject on our bus outside of an off-road wilderness trail intended for 4x4s. So as already mentioned, there are environmental factors to consider like humidity but I think you can safely rest easy that body twisting is not a significant factor you need to engineer into your interior build. I would not say the same of box trucks, dry van trailers, or even some motorcoaches based upon their innate design and construction.
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Old 01-06-2020, 05:55 PM   #11
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I traveled over 200k miles and managed to crack one tile.
Thanks for passing along the info. I've been toying with the idea of laying tiles in the stairwell.
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Old 01-06-2020, 06:14 PM   #12
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Thanks for passing along the info. I've been toying with the idea of laying tiles in the stairwell.

The other day I had a slip on the (wet) factory rubber stairwell material. I highly suggest something slip resistant. Fortunately no lasting harm occurred. I'm thinking some sort of industrial/commercial grade carpet designed to be non-slip.
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Old 01-07-2020, 04:10 AM   #13
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Originally Posted by musigenesis View Post
You don't have to worry about the bus flexing and exploding your inner walls, but you do have to worry about a wooden structure expanding with humidity, so you would want to leave a small gap between your walls and the side of the bus.
This is important if you plan on leaving the climate you built in. I built in Central Florida, about a block from the beach. Super humid. Drove to the desert. No humidity. I could see the wood shrinking and causing gaps where things were super tight previously.

Nothing got destroyed, but any seams that weren't covered certainly show more.
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Old 01-07-2020, 03:33 PM   #14
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I highly suggest something slip resistant.
Good point. I, too, have had my fair share of close calls. When I finally break the damn bottle of champagne on this thing, though, I plan on relegating the stairwell to a shoe changing space.
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Old 01-09-2020, 09:07 AM   #15
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One consideration, is that (for reasons that I will bring up in a future post) we will be building the wall framing out of steel square tubing. This will be much more rigid than wood framed walls, and stronger than the side metal. So tolerances will be more important to consider than a wood framed wall would be.

That being said, if there is not enough movement to crack or delaminate tiles as PNW_Steve pointed out, then I suppose it should still not be a major concern.

Thank you for all of the replies.
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Old 01-18-2020, 05:53 PM   #16
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Originally Posted by Marceps View Post
Thanks for passing along the info. I've been toying with the idea of laying tiles in the stairwell.
My Srairwell flexes more than any other part of the bus
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Old 01-18-2020, 07:39 PM   #17
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Decades ago I helped a friend with his wilderness Llama packing business (perk was free guided trips) and we would load 6 llamas into the back of a school bus. He had built a plywood wall across the bus to separate the llamas from the front of the bus. He made the plywood fit very tight in case the 4000 lbs of llamas ever hit the wall. I never saw a problem with the wall and the bus body.
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Old 01-22-2020, 09:46 AM   #18
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Originally Posted by Truffles View Post
One consideration, is that (for reasons that I will bring up in a future post) we will be building the wall framing out of steel square tubing. This will be much more rigid than wood framed walls, and stronger than the side metal. So tolerances will be more important to consider than a wood framed wall would be.

That being said, if there is not enough movement to crack or delaminate tiles as PNW_Steve pointed out, then I suppose it should still not be a major concern.

Thank you for all of the replies.
We've actually repurposed bedframes to do all the building on our bus - cut & welded the beds/storage & our wheel-well covers which are just welded bedframe/plywood boxes filled with foam to cut down on road noise from the tires & it also supports our fridge on one side & our kitchen counter on the other.
Most were bedframes we had lurking about or found dirt cheap - also used 'free' hide-a-beds & recliners for extra metal
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