Interesting Frame Comparison

Lex · Dec 22, 2009

People often ask, Why should I buy a Factory Five Racing Cobra or Other Factory Five Kit car over some other brand??

There are probably many answers that one could give including value for money, modern design and manufacturing materials and methods, not to mention their overall success.
But for me what REALLY sums it all up is when I look at the Factory Five Frame compared to the other guys frames. Check out the following photos to see what I mean.

This Photo shows the FFR Mk III Bare Frame done up in a black powder coat. Notice the extensive superstructure above the main 4 inch thick wall round tube frame. Of particular interest is the extensive use of triangulated steel which provides incredible strength and rigidity to the FFR Frame. Note also the strong round tube steel foot well protection as well as the extensive steel cage surrounding the passenger compartment

Starting with the bare frame one of the first steps is to glue and rivit the first of more than 40 Panels onto the frame. Every panel that gets added increases the already rigid frames rigidity. This construction method has beem employed by the aircraft industry since its inception and is employed on the Space Shuttle today. Compare this frame and construction method to the other cobra frames pictured below

This is a what we refer to as the "Bed Frame Construction style". Notice on this frame that other then the uprights for the front suspension the frame is devoid of any supporting structure that will provide the torsional rigidity required to keep the wheels on the road and provide a solid handling car.With this method of construction the fiberglass body will weigh upwards of 700 Lbs and is bolted onto the frame in the hope that the fiberglass itself will provide the torsional rigidity that the frame is incapable of. Problem is, fiberglass does not take well to flexing and is a poor material for this purpose. End result is a car handles poorly, Weighs a ton, and provides little or no occupant protection in the event of an accident since fiberglass shatters when hit rather than deforming and absorbing the impact like a steel chassis would do. Over time this Car will develop stress cracks that not only look bad but if left too long can comprimise the cars ability to work properly. Overall this style of build is not a good investment and is definitly not a safe car in the event of an accident.

This is a variation on the Bed frame construction style. Note that this is an improvement over the frame shown above in that this frame at least has a small amount of superstructure above the main frame rails both in front of and behind the passenger compartment.

Still in the event of a side hit this frame is going to crush almost into the center of the car since like Example B below there is nothing but the Fiberglass body to absorb the force of the impact in the passenger seating area, and with no triangulated steel crush zones built into the frame a front or rear end collision will not fare much better.

As for handling due to the built in flex that this style of frame has neither of these cars will handle very well when compared to the Factory Five Chassis.

PSB · Dec 22, 2009

Here we go again...hasn't this subject been beat to death, then beat some, on and on...

Magnus · Dec 22, 2009

Even if the subject has been beaten to death, there might be information that is useful for newbies or for people who are too stupid to use the "search" function, such as me.

I have read several of these threads and there seems to be some new information in each thread.

Hell, this entire forum is a whole dead-horse bash-fest for the over-done subject of building FFRs.

mrmustang · Dec 22, 2009

Lex,

Bed frames such as your center suggestion are a rarity these days, not sure who's kit that is. However, if your strip away the "non structural" 3/4" square tubing from the FFR frame you'll be real close to the SPF frame. Do not allow yourself to be fooled by the 3/4" tubing "birdframe". We won't even get in to the round vs square tube argument as that one has been beat to death and found to be inconsequential when comparing apples to apples crashes of one quality kit vs another.

Also, keep in mind that some manufacturers reinforce their body "tubs" (for lack of a better word at the moment), which are then bolted down to their framing system, where the FFR body is just a shell with no supports bonded in at all.

Edit: the following two links are not meant to start another US vs THEM fight, just offers another view on this subject.

CHASSIS DESIGN LOGIC

and

FFR vs another

There, I've said my piece, here is wishing you and yours a very happy holiday season and a prosperous new year.

Sincerely,

Bill S.

Greg_M · Dec 22, 2009

Hey Lex,

Where did you find those photos?

http://www.worldisround.com/articles/123897/photo100.html
http://www.worldisround.com/articles/123897/photo30.html
http://www.worldisround.com/articles/123897/photo31.html
http://www.worldisround.com/articles/123897/photo412.html
http://www.worldisround.com/articles/123897/photo101.html
http://www.worldisround.com/articles/123897/photo104.html
http://www.worldisround.com/articles/123897/photo102.html

Greg

Don Payne · Dec 22, 2009

Why argue, neither one is a Kirkham!

mrmustang · Dec 22, 2009

Ah yes, my ultimate kit cobra goal :yes:

I've been trying to talk David Kirkham into offering me a "Kirkham in a box" like he did for a very short time several years ago.

Bill S.

hoofa · Dec 22, 2009

I did some Ghetto testing of my chassis:

I wasn't impressed.

tjmotter · Dec 24, 2009

Why?

hoofa said:
I did some Ghetto testing of my chassis:

CobraDVM · Dec 22, 2009

I'm no structural engineer, but it appears that many FFRs that get in accidents have their front and rear superstructures rebuilt and end up back on the road. There was that recent thread with a Superformance that wrecked, and the frame bent like a pretzel. The driver claimed he was doing 30 mph, but others feel he must have been going faster. I don't know what speed he was doing, but I do get the impression that FFRs fare very well in accidents compared to other makes. But this is only anecdotal so take it for what it's worth.

Cardiac · Dec 22, 2009

My Dad's was hit head on in an intersection at about 45-50mph. It's back on the road now after the upper structure of the frame was replaced ahead of the firewall, new lower control arms, a new front half of the body, and a few other things. Most of the car survived just fine and is still in use today.

trevor · Dec 23, 2009

I agree the stock FFR frame is pretty good. Large round tubes definately do a great job in torsion. I read the ERA link and all the stuff he says is true. So, it seems that ERA and FFR have a decent frame design. The Challenge frame is significantly better in torsional stiffness and bending strength - but doesnt look as nice and not ergonomic as the roadster.

The first compasrison photo is junk! That is definatley true.

I have added and will add more tubes to stiffen up my frame. We will soon see if it makes a faster race car or not

Now this is a great cobra frame. http://www.jblmotor.com/JBLchassis.html

Structural/Mechanical Engineer Trevor

saki302 · Dec 23, 2009

All I know is most of our members seem to survive crashes with mild to no injuries with their FFRs. Good enough for me

I was a little nervous about safety, but not so much now after doing the research.

-Dave

DaveT · Dec 23, 2009

Frame 'B' pic date Fed 2004 appears to be a Lonestar. I'm no engineer but that's not sheet metal between the frame rails in those drop pans it's 3/16" steel plate welded in place, seams like in the event of crash that would be fairly rigid.

Dave

Cone Basher · Dec 24, 2009

I looked at all the kits before I bought my Coupe back in 03 and it all came down to the frame. Notice the 4 in tubes that connect the left and right side of the frame together. If you want to build a car that handles start with a rigid frame. If you don't believe me set blocks under the frame at the center line of all four tires that are the same height. Now go set a floor jack under a front A arm and lift that side as you watch. It's not "scientific" but mine flexes very little before the opposite front and rear blocks on the same side as the jack are loose.
CB

PSB · Dec 24, 2009

I can do the same with my awful bed-type non-FFR frame. So what? I've seen comments on this forum about non being able to open doors while the car is partially on jack stands - why? Frame flex maybe? Never had that problem with my Hunter....

Don Payne · Dec 24, 2009

Dude, it's Hoofa, need we say more...

boeing737driver · Dec 24, 2009

I've lusted after a Superformance ever since I realized how authentic looking their bodies are. And the quality of panel fit and paint are very high. Then I had the opportunity to test drive one and found the bump steer and cowl shake were not to my liking. My FFR is much tighter and more refined feeling. So, now I need to redo my body! This really is a disease isn't it? LOL

Bruce

BOB SCHAEFER · Dec 24, 2009

So while we're on this subject, those a Kirkham use a round tube design or are they more like Superformance? If they use the round tube design I would wonder why Superformance doesn't as it would seem the preferred design. What's the reason Superformance doesn't if it's inferior? I mean, those are the ones endorsed by CS. They are either equal or better, or is it they're cheaper to produce? I wouldn't think they're cheaper? Anybody?

Bob

2FAST4U · Dec 24, 2009

Kirkham frames are round tube and nearly identical to original frames

Stinson Pilot · Dec 24, 2009

Well...if Kirkham does round tube, I'm sold!

PSB · Dec 24, 2009

Why do they use a tube frame? It had nothing to do with rigidity, it had to do with replicating the original.

SloW8 · Dec 24, 2009

Round tube frames are a pain in the butt to build compared to a square tube frame. I think that is the main reason most companies have gone to square tube.

Richard Oben · Dec 24, 2009

The frame on the FFR and ERA can not be compared until someone takes both and does an exact test. I notice ERA using the term bending more than anything else. Well bending is for diving boards. Cars like these are never going swimming I hope, but when driven at the limit the car will be put into a twist, I have seen the spec cars lift an inside front wheel, that is a lot of twisting force. The doors do not even move when doing this so the the frame is not allowing any real flex in the chassis.

We built our first FFR in 1998 and the chassis was OK, not as good as now but good. ERA is basing all of their analysis on that chassis. (sorry Bill there is also ERA Koolaid) As the spec racer program came on line, Jim at FFR realized how much better the car felt even on the street. Hence the newer backbone in the MKII. The bad news was the trans was now a PIA to get out. Then the MKIII with the removable mount.

My point being the early MKI chassis are absolutely fine but as the product has developed it has gotten better, much better and much stiffer. From what I remember the backbone added an 83% improvement in torsion which is the difference in how good a car is on the road. JMHO, Cheers Richard.

Art Totten · Dec 24, 2009

Spec Racer doors

Richard wrote: "Cars like these are never going swimming I hope, but when driven at the limit the car will be put into a twist, I have seen the spec cars lift an inside front wheel, that is a lot of twisting force. The doors do not even move when doing this so the the frame is not allowing any real flex in the chassis." A,,,,, the doors are screwed on! (The intrusion bars make doors worthless) And the body may be cut in half. I guess if you twisted it far enough the doors may "fall off". Merry Christmas everone. I love you Richard!

Richard Oben · Dec 24, 2009

LOL Art, glad to see you out and about.

I know the doors are bolted on but in general you do not see them move around much if at all due to chassis flex. That is how stiff the chassis is.

I have seen cars at run and gun with doors coming open due to chassis twist. On my coupe which is much like the MKII chassis I can lift three wheels off of the ground and the doors still work fine. HTH, cheers Richard.

mrmustang · Dec 26, 2009

Richard Oben said:
I can lift three wheels off of the ground and the doors still work fine. HTH, cheers Richard.

Richard,

Never said their was not Koolaid on both sides of any equation. However, on my current 22 year old ERA, I too can and have lifted all three other wheels off the ground (not on purpose mind you but I did it just the same

. and was able to open and close the drivers door (passenger rear wheel was all that was left on the ground) when I got out (employee was jacking up left front so I could swap out the bolt on wheels for the new Trigo knock off's and was not paying attention :sneaky2

. Again we can go back and forth forever, the difference being I am not biased from one brand kit to another (ok, I'll admit, StreetBeast/CMC sucks due to their own fault) and will own more FFR's, ERA's, SPF's, and hopefully one day a Kirkham or two..........I see the good, the bad, and the ugly with an open eye and mind and call them like I see them.

Here is wishing you a happy and a healthy new year.

Sincerely,

Bill S.

raceral · Dec 24, 2009

After all is said and done... Now what?

BS · Dec 24, 2009

Sounds like it is all a moot point anyway without a true FEA analysis done on both chassis to compare chassis flex and strength.

Throwing the spec racer into the mix really isn't a fair comparison as it is basically a dedicated track car (that can be made street legal). For basic street driven roadsters, either the FFR, ERA, Superformance, Backdraft, Kirkham, etc.... will be more than comfortable to drive and handle just fine.
When pushing to the limits on track days you may find out what your car is made of, but then again, all you may find out is your set up really stinks and you need a good chassis mechanic to help you set it up for track days.

Anybody want to speculate on how long it will be before this dead horse is beaten on again?

Bob

Ron Roth · Dec 24, 2009

I was just looking at a site touting the Hurricane Motorsport 427, while it looks like a nice kit, the frame was a let down. Especially after looking at the F5 and Kirkham offerings.
I tried to upload the file, to large, it is a 3D .pdf file kinda cool, I would like to see F5 do this on their site, anyhow, go here and click on the .pdf of the frame. File can be rotated and zoomed.

http://www.hurricane-motorsports.com/427_roadster/parts/frame.asp

Merry Christmas All...

Ron

trevor · Dec 26, 2009

The bed type frames are fine for the street and cruising. Take that type of car to the track and you are not going to have fun. If you dont go to tracks it doesnt matter.
It is no contest when you add bars enclosing the cockpit area, i.e. spec racer. The open section is the area with the most twist, add bars, diagonals etc and the frame is significantly stiffer in torsion. ERA and SP Im sure orignally started with a square tube frame due to ease of welding, cutting and assy. So, after gerneations of revisions to make the car better, they had to stick with the original sq. tube design to avoid re-designing the whole car. Ive built round and square tube monoque frames. Almost everything is much easier with sq. tubes, welding, making mounting points, cutting the tubes vs. using large end mill machines to cut the curved surface- I could go on for ever.
ERA talks about bending a lot because the rectangular tube is stronger in bending. If you talk about twist or torsion, its better to have a round tube. Looking at the ERA frame, it is very robust, Im sure it weighs quite a bit too.

PL _RED_COBRA · Dec 26, 2009

Hi guys,

The only thing that matter with frame design is testing them.You can have the best concept and the best calculs, it doesn't really matter if you can not test them properly like extensive road test or racing which i think is the best test you can perform because every mecanical and structure aspect is push to the limit and weak spot shows. Thats why i bought an FFR because their frame are race ready and race tested and they did it since the beginning of the company. So as years past, i'm sure they found weak spots and resolve them by adding reinforcement where it was needed to improve their frame.

When a was working in the chopper industry, one of my boss was the old chef engineer of the DS 650 quad frame design (one of the strongest quad frame out there) at Bombardier recreation product. He said to me that they first calculate by hand to get the overall theme. Then they design it on the computer and they made the finite element analysis on Catia which is a Cad program that can do finite element analysis and then they test it on dirt track with jump and every thing. Well the first design wasn't worth a s???t even with the best calculs and the one of the best Cad program in the world. So they tested (jumping table top and trees on the ground...)and breaked and reinforce the frame numerous times until nothing break no more. Thats how they made the one of best quad frame out there and Bombardier is one of the biggest vehicule and transporation company in the world.

I think that FFR have the same working way (with less budget of course) and that's why i trust them.

Just my opinion

Thanks

PL

Thomas W · Dec 26, 2009

This thread got me thinking. I'm planning on installing a full width roll bar with swing out side bars in my Mk II for additional safety on the street and to get hassled less at the track. If I weld in the full width roll bar and have the side bar non swing out, does this add much rigidity to the frame over bolting in the full width bar and having the side bars swing out?
Thomas

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