Spacers plus aftermarket crash bar = ?

[HenryMac]

I’ve also see some that were box type but smaller, and if the walls were thicker than the stock ones, maybe they could be as strong.

Highly unlikely.

The moment of inertia of a rectangular section is based on the face width dimension to the 3rd power.

Decreasing the tube size drastically compromises the strength,​

Increasing the thickness has a much lesser effect in increasing strength.​

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[ahha]

@ahha

Duke was kind enough to provide me with some dimensional data on the aftermarket intrusion beams he used. I ran some rudimentary FEA on them. IMO the aftermarket beams are not as strong as the OEM beams.

What does that mean? Impossible to say without crash testing.

If you watch the offset crash test videos, the tire blows out and the wheel is driven backwards and impacts the cab in the footwell area. That's where front seat occupants feet would be. Here's a link: Ford Ranger 2019 | Crash Tests


But all you really need to understand is Ford wouldn't have spent the time and money developing these, if they were not needed.

I found this photo in another thread, is this the Ready Lift crash bar you FEA’d on the right and a stock crash bar on the left?

If so, I find that computer modeling hard to believe, given the differences in thickness of materials. I understand the principle of the rectangular box having inherent strength, but the difference in material thickness seems significant and must make a difference at some point.

 

[HenryMac]

I found this photo in another thread, is this the Ready Lift crash bar you FEA’d on the right and a stock crash bar on the left?

If so, I find that computer modeling hard to believe, given the differences in thickness of materials. I understand the principle of the rectangular box having inherent strength, but the difference in material thickness seems significant and must make a difference at some point.

Yes those are the parts that are modeled.

FEA takes all the guess work out of the conversation.

It has no bias, no ego, no opinion. It is what it is. You draw the parts, assign a material type, constrain the part, and apply a load.

Again, what is not known is how the aftermarket parts perform during a crash test. Stronger may not be better. You want the parts to bend and absorb / dissipate energy during a crash... but not bend to easily such that they don't provide enough resistance.

 

[ahha]

Yes those are the parts that are modeled.

FEA takes all the guess work out of the conversation.

It has no bias, no ego, no opinion. It is what it is. You draw the parts, assign a material type, constrain the part, and apply a load.

Again, what is not known is how the aftermarket parts perform during a crash test. Stronger may not be better. You want the parts to bend and absorb / dissipate energy during a crash... but not bend to easily such that they don't provide enough resistance.

HM, understood on the facts as they relate to the FEA and dissipation of crash energy. I wasn’t suggesting the FEA was somehow inaccurate, just that it was hard to believe given the difference in material thickness.

This discussion has me thinking about crash energy dissipation from a head on collision and the role of airbags. What happens in a head on collision with a heavier steel winch housing bumper, like the Ford performance Arb bumper? Would the elements between it and the cabin be subject to less crumpling and force the airbags to deploy earlier? I’m guessing the speed with which the airbags inflate might need to be slowed down to mitigate shock to the passenger, is that correct?

If that’s true, the crash bars might not need to absorb as much of the shock and crumple. Just wondering if a steel Arb bumper and stiffer crash bars might be more compatible together, and give greater tire clearance…

 

[HenryMac]

I’m guessing the speed with which the airbags inflate might need to be slowed down to mitigate shock to the passenger, is that correct?

If that’s true, the crash bars might not need to absorb as much of the shock and crumple. Just wondering if a steel Arb bumper and stiffer crash bars might be more compatible together, and give greater tire clearance…

Slowed down... I wouldn't think so. A big battering ram of a bumper means the humans inside see more g forces in a crash, and see them quicker because the bumper won't bend nearly as easy as the stock one. So the energy / forces from the crash will be greater and transmitted quicker to the occupants. That increases the shock on internal body organs and would be worse than the stock design. Have you heard of peoples heart being ripped loose? Think about the mass of the internal organs slamming forward when the air bag deploys. Scary stuff.

Again though, without crash testing, it's hard to know and pretty much just speculation.

 

[ahha]

Slowed down... I wouldn't think so. A big battering ram of a bumper means the humans inside see more g forces in a crash, and see them quicker because the bumper won't bend nearly as easy as the stock one. So the energy / forces from the crash will be greater and transmitted quicker to the occupants. That increases the shock on internal body organs and would be worse than the stock design. Have you heard of peoples heart being ripped loose? Think about the mass of the internal organs slamming forward when the air bag deploys. Scary stuff.

Again though, without crash testing, it's hard to know and pretty much just speculation.

I have heard of terrible shock injuries, I guess I had it backwards in terms of the airbag deployment speed. Thanks

BTW, here’s a quote from Ready Lift about their FEA results: “These new high-clearance anti-intrusion beams are precision engineered and manufactured using heavy-duty laser cut and robot-welded steel and have been verified with Finite Element Analysis to meet the engineering specifications of the factory anti-intrusion beams.”

Any idea why their FEA results are different from yours?

 

[TBR17]

I have read that before. However, they redesigned the knuckles for all of the 2021 Ford Rangers. Someone in marketing grabbed on to that and ran with it. Even to describe it as "Lifted" is a stretch. AND to claim the tires are 32" is rounding up. I have inspected the knuckles on the Tremor and I could not tell that they were any different than other 2021 models. I could be wrong, but if they are different, then it is not by much.

My Tremor is just over 2.25" higher in the front and just over an inch higher in the rear than my '20 FX-4. Tire sizes are what they are, but still an inch larger overall diameter than the FX-4 stock tire. Used to buy a 32x11.50 size for my Jeeps and it was pretty close to 32" +/- depending on brand, but usually a little under 32". Same goes for the 265x70 17 at just under 32" but measured by 70% of 265mm width so it's hard to get the exact 32" . It would have to be a 265x72x17 to be exactly 32" in diameter.

 

[HenryMac]

I have heard of terrible shock injuries, I guess I had it backwards in terms of the airbag deployment speed. Thanks

BTW, here’s a quote from Ready Lift about their FEA results: “These new high-clearance anti-intrusion beams are precision engineered and manufactured using heavy-duty laser cut and robot-welded steel and have been verified with Finite Element Analysis to meet the engineering specifications of the factory anti-intrusion beams.”

Any idea why their FEA results are different from yours?

I'm aware of that. I emailed them in February asking for some sort of signed document to certify what they state in their advertising. This is how they responded.

John,​

​

Yes, that is correct we tested these components and concluded that our Intrusion Beams meet or exceed the strength of the factory intrusion beams. I do not have anything signed but you are welcome to keep this email for future reference.​

That's one reason why I ran the FEA myself. I wanted to verify for myself that their aftermarket bars were as strong as the OEM. As previously discussed, my analysis shows they do not meet or exceed the strength of the factory intrusion beams.

As a Mechanical Engineer, every company I worked for required our vendors to provide a document from the manufacturer, on company letter head, signed by a company official, certifying that the product met the required specifications.

That's where the rubber meets the road. The certification document.

But also, as I stated before, the FEA I did was rudimentary. Perhaps they used a more sophisticated analysis method? Without seeing anything but their words on a marketing document.. who knows?

 

[ahha]

I'm aware of that. I emailed them in February asking for some sort of signed document to certify what they state in their advertising. This is how they responded.

John,​

​

Yes, that is correct we tested these components and concluded that our Intrusion Beams meet or exceed the strength of the factory intrusion beams. I do not have anything signed but you are welcome to keep this email for future reference.​

That's one reason why I ran the FEA myself. I wanted to verify for myself that their aftermarket bars were as strong as the OEM. As previously discussed, my analysis shows they do not meet or exceed the strength of the factory intrusion beams.

As a Mechanical Engineer, every company I worked for required our vendors to provide a document from the manufacturer, on company letter head, signed by a company official, certifying that the product met the required specifications.

That's where the rubber meets the road. The certification document.

But also, as I stated before, the FEA I did was rudimentary. Perhaps they used a more sophisticated analysis method? Without seeing anything but their words on a marketing document.. who knows?

Thanks for asking them and the info!

 

[LoneRNGR]

Tire sizes are what they are, but still an inch larger overall diameter than the FX-4 stock tire.

Tremor tires are 31.6" diameter and 10.7" width. My stock FX4 tires are 31" diameter and 10.6" width.

 

[OFC Ranger]

Any modification runs the risk of unintended consequences. Even installing a 2" level.

There is no way for a company to crash test a car or install safety devices against all possible outcomes. Think of it this way; if your truck crashes into a lower mini-cooper, a stock height F-150, or 3 foot lifted bro-truck the end result is all going to be different. Probably combinations in the millions between different size vehicles and different impact points.

The only correct answer regarding safety is to make no deviation from the factory installed components.

But thats not how the human race works, ie; motorcycles are a good example. To me, why anyone would get on a 2 wheeled contraption with zero impact protection is outside my realm of interest.

But its not my place to tell them if they get on one their chance of dying increases greatly vs. a standard vehicle.

My first safety concern has always been in the cabin.

1. No loose items to become missiles.

2. Nothing blocking bag deployment zones.

Everything else I will play the cards where they fall.

You'll see people on here blather on about modifying crash bars, yet they completely alter their suspension specs or other components. Or worse yet you see a picture of their cabin and there are a hundred items lying around to go sailing through an eyeball or bash their skull in the event of an accident.


That of course makes zero sense to a logical person.

 

[P. A. Schilke]

Any modification runs the risk of unintended consequences. Even installing a 2" level.

There is no way for a company to crash test a car or install safety devices against all possible outcomes. Think of it this way; if your truck crashes into a lower mini-cooper, a stock height F-150, or 3 foot lifted bro-truck the end result is all going to be different. Probably combinations in the millions between different size vehicles and different impact points.

The only correct answer regarding safety is to make no deviation from the factory installed components.

But thats not how the human race works, ie; motorcycles are a good example. To me, why anyone would get on a 2 wheeled contraption with zero impact protection is outside my realm of interest.

But its not my place to tell them if they get on one their chance of dying increases greatly vs. a standard vehicle.

My first safety concern has always been in the cabin.

1. No loose items to become missiles.

2. Nothing blocking bag deployment zones.

Everything else I will play the cards where they fall.

You'll see people on here blather on about modifying crash bars, yet they completely alter their suspension specs or other components. Or worse yet you see a picture of their cabin and there are a hundred items lying around to go sailing through an eyeball or bash their skull in the event of an accident.


That of course makes zero sense to a logical person.

Hi Jack,

You make informed decisions...many folks do not... The touted FEA crash bar analysis of a Manufacturer has no credibility for crash analysis which is non linerar unless they run very sophisticated software. I will bet that they did a stress analysis. Okoy...what were the boundary conditiions. I bet they spc'ed the frame...not true...should be a spring element. Besides, to my knowledge, Radios is still in use for crash analysis. Maybe there is more cutting edge software, but a co worker now retired is still using this nonlinear software. So the manufacture claims need to be backed up by the analysis data. A Radious run on one of two Cray Reseach C90s we had at the time took all night to deliver results. Very complex. Maybe times have changed, but my co worker disputes this for non linear analysis... No interest in digging more into this.

Best.
Phil Schilke
Ranger Vehicle Engineering
Ford Motor Co. Retired
Ranger Vehicle Engineering
Ford Motor Co. Retoired

 

[TBR17]

Tremor tires are 31.6" diameter and 10.7" width. My stock FX4 tires are 31" diameter and 10.6" width.

FX-4 tire is shy of 31" as is the Tremor tire short of 32". There is an inch overall diameter difference in the two. Neither appear to be an exact round up to the inch based upon the measurement.

 

[LoneRNGR]

FX-4 tire is shy of 31" as is the Tremor tire short of 32"

My stock FX4 tires are 31" diameter and 10.6" width. They are Hankook Dynapro ATM LT265/65R17.

 

[TBR17]

In that tire you are correct if you have the C load range. I didn't so mine were 30.7. Interesting how the load range changes the tire specs slightly.

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