Interesting Frame Comparison

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

Cone Basher said:
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

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....

PSB · Dec 24, 2009

Stinson Pilot said:
Well...if Kirkham does round tube, I'm sold!

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.

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.

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.

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

BS · Dec 26, 2009

Yes, it will. Except in rare instances or a specific design, a welded connection will be much stronger/stiffer than a bolted connection.

trevor · Dec 26, 2009

thomas, the side bars have to be welded to the full width roll bar and 2x3 door hinge frame bar. Also, the bars have to intersect at frame nodes or nothing is really strengthened. So, swinging and detachable stuff doesnt add to the frame stiffness but will definately help protect you. Also, the side bars need an x-brace or something to connect the bottom to the top side bars.
The spec frame has a top and bottom side bar with bars connecting them:

This frame shows a perfect example of all bars joining at nodes (blue heated areas):

289FIA_Cobra · Dec 26, 2009

just my $wooden nickels worth but why do you think modern race cars have moved to monoque chassis instead of staying with ANY tubed chassis, round or otherwise.

I got my car, I'm happy so I don't really care anymore. ... where's that dead horse ...

ROADRACER83 · Dec 27, 2009

VSE monocoque frame

Once upon a time back in the 70's Herb Adams son Matt was building a monocoque C**^% frame that was really stiff. They built maybe only maybe 20 or so but there is a cult that is still talking about that frame and the replicas that were built on that platform.

http://www.vsecobra.com/phpBB3/viewtopic.php?f=1&t=10

I'm not sure if Matt Adams is still building the things or can provide drawings to DIY. They made some of them in steel and a few in aluminum. There is some information on them on the web. Just Google VSE Cobra and get a history lesson.

Ron

2FAST4U · Dec 27, 2009

This frame is superior to all

Interesting Frame Comparison

2FAST4U

Stinson Pilot

PSB

PSB

SloW8

Richard Oben

Art Totten

Richard Oben

raceral

BS

Ron Roth

trevor

mrmustang

PL _RED_COBRA

Thomas W

BS

trevor

289FIA_Cobra

ROADRACER83

2FAST4U

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