BMR Tubular K-Member (05-09)

[NA-Stang]

Ok, so I recently was in an accident with my 2005 Mustang GT. Long story short, smacked the front driver corner into a guide rail. The stock k-member, along with other various front suspension parts, was bent. So, I took this opportunity to upgrade to a BMR Tubular K-Member.

Here is my question. The body guy who installed it, and the guy at the shop who aligned the vehicle, both told me that the BMR unit looks weaker than the stock one. Anyone have any input about this? Any experience with them not performing as well as a stock unit?

Now, I have a degree in Civil Engineering. I have had 2 structural analysis classes, and a class in, well, basically metal strength. I believe that the BMR unit looks as if it would be as strong, if not stronger, than the stock unit. I didn't get into it with either of them, because I figured, what's the point. They weren't going to change my mind.

 

[go302]

Lol ya right BMR makes bum shit. Don't listen to anything else those guys tell you.

 

[irishpwr46]

how long has your body shop guy had an engineering degree?

 

[TexasBlownV8]

I can tell you this: mu car was raised up from a single jack under the center crossbar of the BMR k-member; it held the full weight just fine, no bends, nothing. (I wouldn't do that again, it just didnt look right!)

 

[NA-Stang]

Thanks guys.

I was making sure I wasn't crazy.

 

[GT E UPP]

Good choice NA ..they don't know what the hell they are talking about.. that's for sure!

 

[BruceH]

I've had a BMR k member. I'd agree that it's not going to be as strong as a factory unit. However, there have been wrecks posted up involving the BMR and they faired ok.

 

[skwerl]

Mine saved my engine when I totaled my car. Front left wheel was ripped out from under the car and the BMR K member was only tweaked by about 1/3". I took it down to BMR and Kelly had the welder guy throw it on the jig. I probably could have sold it as is but I didn't want to sell anything that wasn't exactly right, and fixing it would have cost as much as a new K member.

If you want to see the gory pics they are posted in my "Skwerl's first hot rod" thread.

 

[go302]

Doesn't make you dumb, just doesn't mean you're smart.

 

[BruceH]

More on the subject, from an engineering standpoint, a tubular setup would likely be much stronger than the factory one. The factory member is what I would guess stamped and then tac welded together. Not a great combo for strength.

The bending and welding of the tubes is a much more involved process, hence why the factory doesn't do it

Have you looked at or installed either one?

 

[go302]

Depends on your definition of "dumb" and "smart," but I'm not going to muck up this thread with that debate.

No, it doesn't depend on any definition. I know two engineers who are downright dumb. Educated? Yes. Smart? No.

 

[skwerl]

Cool story bro. I'm not gonna debate it with you here though. But I already said that... so yea...

You've stated that you didn't want to derail this thread but then make multiple posts doing little more than trying to egg on an argument. Please just stop. You've stated your opinion on the topic and additional multiple posts by you will be little more than trolling for arguments. This is why half the forum hates you.

 

[BruceH]

Yes?

The factory K member is basically sheet metal formed into a frame, no? Same/similar as the body/frame of the car?

The aftermarket ones are welded together from extruded pieces of tubing, similar to how a roll cage is built.

If you were to ask me which I thought was stronger, a roll cage or the body of a car, I would answer roll cage.

A sheet metal frame? No. hydroformed steel plate, yes. You should know what happens when you bend thick steel, it's a very sturdy piece.

The body shop guys were trying to be nice and warn the op of possible safety issues. No need to turn this into an argument, just give your opinion and go. We do ask that your opinion be an informed one, that you have actually seen the parts side by side. My thought was that it wouldn't be as strong as the factory part.

 

[GIG4FUN]

You've stated that you didn't want to derail this thread but then make multiple posts doing little more than trying to egg on an argument. Please just stop. You've stated your opinion on the topic and additional multiple posts by you will be little more than trolling for arguments. This is why half the forum hates you.

took care of it too

 

[Dubstep Shep]

A sheet metal frame? No. hydroformed steel plate, yes. You should know what happens when you bend thick steel, it's a very sturdy piece.

The body shop guys were trying to be nice and warn the op of possible safety issues. No need to turn this into an argument, just give your opinion and go. We do ask that your opinion be an informed one, that you have actually seen the parts side by side. My thought was that it wouldn't be as strong as the factory part.

Sorry, I should have been more specific.

"Sheet metal" where I come from (industrial applications) is anything less than 1/2" thick.

"Plate metal" is anything over that.

So to me hydroformed steel plate is in essence bent sheet metal. It's the same thing though, so this is basically semantics at this point. I'll concede that your description is the more specific of the two.

In any case, I would be interested to see how the differences in the shapes would resist the different forces applied. For a simple force application, a specific cross section is often suitable, where the forces are predictable and applied in a specific direction. Connecting rods are a good example of this.

A vehicle frame however would be subject to far more complex loads... That's why roll cages are so damn complicated lol.

Basically what I was getting at is a round cross section is best for loading in any direction, as it evenly distributes the load regardless of its orientation.

But hey, if anyone has some dimensions, I can always run some FEA on the two and see what happens hahaha.

 

[Dubstep Shep]

Also, I wonder if BMR has already done some FEA on the part? I know Griggs does with their components, so I wouldn't be surprised if BMR did as well

 

[NA-Stang]

Holy shit, what did I miss?

You don't log on to a thread for a day, and all hell breaks loose...

Some messages must have been deleted, because I don't see any that insight an argument...

 

[eighty6gt]

FEA is cheap, I hope BMR uses it but after seeing a swaybar mount failure I don't think they do. Look up "shear lag." It is difficult to make good right angle connections in the middle of a piece of tubing. Tubing is not good at bending loads.

The BMR member is much weaker than the stock piece, but it's strong enough to work.

Good old SHEP!

 

[Dubstep Shep]

FEA is cheap, I hope BMR uses it but after seeing a swaybar mount failure I don't think they do. Look up "shear lag." It is difficult to make good right angle connections in the middle of a piece of tubing. Tubing is not good at bending loads.

The BMR member is much weaker than the stock piece, but it's strong enough to work.

Good old SHEP!

Wait, did you say tubing is not good for bending loads?

So what is good for a bending load then? I-Beams? I can't say I know what k-member is made of I-beams...

 

[eighty6gt]

I think if you look at the factory K member you'll get a good idea of what works. Car unibody. Etc...

Honestly it's an off the cuff thing by me - I think there's a lot of (good) fat in the factory design and the aftermarket stuff takes advantage of this. They can spend a lot more hours building something that's lighter, weaker, and still works, but they don't have nice presses to make custom cross sections.

I'm hoping the BMR guy steps in and says our K deflects this much upon loading this way, etc.. vs the factory one acting like wet paper towels... The factory one should have nice failure modes, though (wadded up aluminum foil,) vs just the ends of tubing tearing off.