Automotive Engineers Q&A

[Fozzy325]

I’m looking for advice from an Automotive Engineer.

Subject
I have Identified I would like to use a Lambo door hinge attached to a bumper. With an extension on top of the hinge to mount my spare wheel. The locking device will be a spring pin at the hinge to stop the initial folding before the rotation.

Q1. What stresses should I consider on the hing when closed
Q2. Will Drilling and mounting through the bumper directly will cause stress, should I make a sheath around the bumper and mount the sheath that will have the mounting block on it.
Q3. What grade of metal should I look at using for the tyre mount extension arm.

 

[smritte]

Umm. Cool project. But. Not near enough info to start with.

I have Identified I would like to use a Lambo door hinge attached to a bumper.

What is the bumper made from? Is it stock, how is it tied in, and thickness.

With an extension on top of the hinge to mount my spare wheel

How much does the wheel assembly weigh, How are you mounting the wheel to the hinge, and hing specs needed.

What stresses should I consider on the hing when closed

First we start with above answers.

Will Drilling and mounting through the bumper directly will cause stress, should I make a sheath around the bumper and mount the sheath that will have the mounting block on it.
Q3. What grade of metal should I look at using for the tyre mount extension arm.

and again way more info needed.

An Engineer would help but an experienced fabricator could do the same and build it where the engineer could give basic numbers only.

Looking at the hinge, I'm not sure what you want to do. I'll assume you want a swing out. Ill give you an idea what I built for mine.
My bumper is .250 wall mild steel, My swing out pivot is a 2.250 diameter trailer spindle. It sits partially inside a piece of 5 inch long .250 wall DOM tube. I bored a hole straight down in the corner, welded the DOM into the bumper then welded the spindle into that. Then added gussets to the inside of the bumper to minimize flex.
The swing arm that extends from this is 30" long with the tire mount around 2/3 out on the arm. The arm assy. with tire weighs about 80 pounds. Im just guessing at the leverage but, I have about 140 pound side load on my pivot. With all the gusseting and thick metal, I still get some flex opening it. The issues are not opening and closing but the weight of the tire moving forward and back on rough roads (shaking). That will eventually fatigue my mount.

Looking at that mount and understanding what happens on rough roads, I'm not sure it will work. If you draw out what your looking to build, that would help some.
Im pretty good with steel, not good with aluminum.

Scott

 

[Fozzy325]

Umm. Cool project. But. Not near enough info to start with.

What is the bumper made from? Is it stock, how is it tied in, and thickness.


How much does the wheel assembly weigh, How are you mounting the wheel to the hinge, and hing specs needed.


First we start with above answers.


and again way more info needed.

An Engineer would help but an experienced fabricator could do the same and build it where the engineer could give basic numbers only.

Looking at the hinge, I'm not sure what you want to do. I'll assume you want a swing out. Ill give you an idea what I built for mine.
My bumper is .250 wall mild steel, My swing out pivot is a 2.250 diameter trailer spindle. It sits partially inside a piece of 5 inch long .250 wall DOM tube. I bored a hole straight down in the corner, welded the DOM into the bumper then welded the spindle into that. Then added gussets to the inside of the bumper to minimize flex.
The swing arm that extends from this is 30" long with the tire mount around 2/3 out on the arm. The arm assy. with tire weighs about 80 pounds. Im just guessing at the leverage but, I have about 140 pound side load on my pivot. With all the gusseting and thick metal, I still get some flex opening it. The issues are not opening and closing but the weight of the tire moving forward and back on rough roads (shaking). That will eventually fatigue my mount.

Looking at that mount and understanding what happens on rough roads, I'm not sure it will work. If you draw out what your looking to build, that would help some.
Im pretty good with steel, not good with aluminum.

Scott

Thanks for the info. I will write it out tomorrow and when I can some research.

Issue is, I’m not a welder so I’m trying to deliver something that I can bend, drill, hammer, bolt and drill it into place.

For a swing out it would need to be something like the fore-Runner spare wheel mount for the LR3/4 but then I was thinking if a Lambo mount can hold a door then the weight of a wheel must be less stress. With the hinge in the closed position I was thinking that the bouncing and jarring would be minimal.
But then again I’m not a fabricator or engineer so I can’t give any advice.

 

[smritte]

Were you looking at something similar to the Toyota 4Runner factory mount? I cant remember how those attached.

Ive picked up quite a number of spare tire mounts and fuel can mounts off the ground. These mounts didn't hold up to dirt road driving. Broken welds mostly. If you look at whats out there now, you notice a trend. The newer designs are holding up very well. You will notice that their mostly "spindle mounts".
There are some kits out there too. Some are complete and some you buy a piece at a time.
For example (these are just what I came up with quick. I have never bought from these people)
Spindle Kit.
The hard to make parts
Some pictures
What you can do is, get your parts together cut the pieces and have someone weld it together. You can still do some bolting. If you do, anything that can be seen, use stainless carriage bolts. Their strong and they look good.

If you have the room and the money, a small metal saw (hand held), Grinder (if your saw wont switch over), Drill set, square and find a used mig welder. Then U-tube how to use them. I have to warn you though. Once you do that, you will start getting addicted to metal fab. Next thing you know, your wife's expensive car sits outside because you turned the garage into a machine shop. When your not in the garage, your sitting at the computer with your CAD program designing your next project. If you see something made out of wood, you will say "I can do that". Now you have wood working tools too.

Scott

 

[Smileyshaun]

I'm no engineer or a certified fabricator ( I may be certifiably nuts but that's a completely different subject) I would worry about those hinges taking the force of sideloading while bouncing down the trail and with your system completely bolted together you will have to be very diligent about making sure that your bolts are always tight and don't work themselves loose because once a small bit of movement starts in from the both being loose it's easy for them to wear and sheer off.

On the other hand those hinges could work amazingly and be the next step in tire swing out technology so sometimes you just have to be the guinea pig and go ahead and try.

 

[jkxj]

interesting idea... what size tire are we looking at here?

i think you would be able to make it work with time and money anything is possible. i would really be concerned about the loads literally wearing out that aluminum. another concern of mine is those stay struts that would keep the tire open. would those be strong enough to hold that assembly open without falling back on you while you gain access to the cargo area.

 

[Fozzy325]

Thanks all,
So the wheel that will be on it is 8x19J AHE ET 53 with 255/55R19 with Atturo M/T
The kit comes with Dampers and can pitch +90 degrees from closed.
When closed the first motion of 45degree roll will only open when a locking system is open .
So if the thing is setup at +45 degree pitch then the wheel and arm should be out of the way to open the top and bottom back hatch..

 

[Arizona.Overland]

I am studying to be an automotive engineer, I’m in my senior year at Arizona State Polytechnic. I’ve also done internships at a classic restoration shop and a Lamborghini tuning house.
I just joined the forums here and saw this so this will be my first post.(I’ll go back later and do my intro)

Generally car doors are relatively light in comparison to off road tires/rims. If the mount can hold it, the shock wouldn’t probably have the strength to hold it up

Car doors are held in position with several interlocking parts at the door sill and are not being jostled up and down at the endpoints of a vehicle. These endpoints experience more movement over bumps than anywhere inside the wheel base. Thus the effect is multiplied.

They may hold the weight of a tire, but the repeated stresses that would be applied to the mount may over a period of time either rip it from the vehicle, or bend it out of geometry.
The metal used in body panels is much thinner and flimsier than most expect. The rigidity that most panels have is not due to the actual strength but from formed strength. IE. bends in sheet metal make it more rigid.
Mounting with drilled holes, like trying to bolt it to the panels will most likely result in the mount ripping out after the first good bump with significant damage to your rig.

I personally would look elsewhere or see if a fabrication shop would be willing to create what you are looking for. However you will be probably paying quite a premium for a one off custom setup like that

In my experience, and my professors often try to drill this into our heads, K.I.S.S. is the key to success, especially in something that is gonna be beat on, and still needs to get you home.

 

[smritte]

n my experience, and my professors often try to drill this into our heads, K.I.S.S. is the key to success, especially in something that is gonna be beat on, and still needs to get you home.

Very well said. This is a point I hammer into my students constantly. Unfortunately, simple dosent necessarily look cool. I have had to learn this lesson the hard way.

Scott

 

[Fozzy325]

I am studying to be an automotive engineer, I’m in my senior year at Arizona State Polytechnic. I’ve also done internships at a classic restoration shop and a Lamborghini tuning house.
I just joined the forums here and saw this so this will be my first post.(I’ll go back later and do my intro)

Generally car doors are relatively light in comparison to off road tires/rims. If the mount can hold it, the shock wouldn’t probably have the strength to hold it up

Car doors are held in position with several interlocking parts at the door sill and are not being jostled up and down at the endpoints of a vehicle. These endpoints experience more movement over bumps than anywhere inside the wheel base. Thus the effect is multiplied.

They may hold the weight of a tire, but the repeated stresses that would be applied to the mount may over a period of time either rip it from the vehicle, or bend it out of geometry.
The metal used in body panels is much thinner and flimsier than most expect. The rigidity that most panels have is not due to the actual strength but from formed strength. IE. bends in sheet metal make it more rigid.
Mounting with drilled holes, like trying to bolt it to the panels will most likely result in the mount ripping out after the first good bump with significant damage to your rig.

I personally would look elsewhere or see if a fabrication shop would be willing to create what you are looking for. However you will be probably paying quite a premium for a one off custom setup like that

In my experience, and my professors often try to drill this into our heads, K.I.S.S. is the key to success, especially in something that is gonna be beat on, and still needs to get you home.

Ok thanks; this what I was looking for. As money is an issue it looks like the front-runner system is what it’s got to have to be for $2.5k

 

[Anak]

Generally car doors are relatively light in comparison to off road tires/rims. If the mount can hold it, the shock wouldn’t probably have the strength to hold it up

I am going to have to disagree on that point.

I can pick up a tire/rim combo without much trouble, but picking up a complete door is not so easy. If you think car doors are light, park on a good slope such that the doors have to open up or down hill. I think you will notice the increase in effort that is required to open/close them. And you still are not dealing with the full weight. Remove a door from its hinges and try to carry it around. You will soon find it is not such a light component. It only feels light when you are swinging it in a horizontal plane and thus doing no actual work.

As to the Lambo hinges, that is an interesting idea. I agree that someone will have to be the guinea pig in order to figure out if it is a workable idea.

 

[Arizona.Overland]

I am going to have to disagree on that point.

I can pick up a tire/rim combo without much trouble, but picking up a complete door is not so easy. If you think car doors are light, park on a good slope such that the doors have to open up or down hill. I think you will notice the increase in effort that is required to open/close them. And you still are not dealing with the full weight. Remove a door from its hinges and try to carry it around. You will soon find it is not such a light component. It only feels light when you are swinging it in a horizontal plane and thus doing no actual work.

As to the Lambo hinges, that is an interesting idea. I agree that someone will have to be the guinea pig in order to figure out if it is a workable idea.

Having installed many doors in many different vehicles, they can be extremely light and extremely heavy, it’s dependent on a lot of things. And vehicles have reinforced mounts specifically for door hinges, if you put that same door anywhere else it would probably rip off...

From my experience, large off-road tires are extremely heavy.

From 4wd.com -

A stock 275/55/15 can weigh up to 30 pounds, that’s before mounting. Mounting on steel rims can bring that to almost 50
A 33/12.5/15 can be almost 60 pounds mounting on steel can make it over 80 pounds...
What about 35s or bigger?

A car door can be between 30-200 pounds depending on the vehicle and what door it is... most newer doors are less than 100lbs

So sure the mounts may be able to carry the weight, but I’m doubtful they could take the abuse of holding a tire off-road. They may work for a while but may eventually fail.

I’m honestly less concerned about the mount itself and more concerned about actually mounting the mount. The thin sheet metal on the tailgate is definitely not going to take the abuse. Maybe with some BIG washers and some sort of guard for the hole.

Most carriers are bolted to frame, replace the rear bumper, or sit on the hitch, this is not necessarily due to the sitting weight but more for what happens when that weight is jostled up and down.

 

[Fozzy325]

Having installed many doors in many different vehicles, they can be extremely light and extremely heavy, it’s dependent on a lot of things. And vehicles have reinforced mounts specifically for door hinges, if you put that same door anywhere else it would probably rip off...

From my experience, large off-road tires are extremely heavy.

From 4wd.com -

A stock 275/55/15 can weigh up to 30 pounds, that’s before mounting. Mounting on steel rims can bring that to almost 50
A 33/12.5/15 can be almost 60 pounds mounting on steel can make it over 80 pounds...
What about 35s or bigger?

A car door can be between 30-200 pounds depending on the vehicle and what door it is... most newer doors are less than 100lbs

So sure the mounts may be able to carry the weight, but I’m doubtful they could take the abuse of holding a tire off-road. They may work for a while but may eventually fail.

I’m honestly less concerned about the mount itself and more concerned about actually mounting the mount. The thin sheet metal on the tailgate is definitely not going to take the abuse. Maybe with some BIG washers and some sort of guard for the hole.

Most carriers are bolted to frame, replace the rear bumper, or sit on the hitch, this is not necessarily due to the sitting weight but more for what happens when that weight is jostled up and down.

My idea was to extend a block from the inner bumper and mount it to that. I was thinking of having to sandwich the inner bumper by clamping it and trapping the mounting block which would extend through the plastic part of the bumper