Rail/ladder chassis

[cbreez]

Here is an extreme example of why you can't get too serious regarding a Backdraft Cobra on the track, the exception is a Factory Five. It doesn't matter what shocks or springs you use, the basic frame is very similar to this. Antique technology...This is why most modern race frames are triangulated, caged structures. Go just have fun with these for what they are...a fast street toy. The biggest factors in your track day fun will be tire choice and right foot!
[ame]https://www.youtube.com/watch?v=LOflUwwz9Dw[/ame]

[cycleguy55]

The original Cobras had ladder frames that were, by some accounts, pretty flexible. I believe I've seen a quote somewhere where Carroll Shelby said the frames were part of the suspension!

A couple of Cobra frames which are not 'ladder' frames:
West Coast Cobra frame: Cobra Chassis Information
Factory Five MK4 frame: Design - Factory Five RacingFactory Five Racing

[GLS-BDR226]

Not saying a Backdraft is the ultimate track car but this doesn't look similar at all to a Backdraft frame. A G. body Monte Carlo frame. Really?

[jimbo01]

The frame on my Backdraft car will make that GM frame look like a piece of ****. No flex on my frame. Are you trying to blow smoke up someone's ass?

[itstock]

I guess I understand your overall message, but comparing the torsional rigidity between the backdraft frame and that frame is completely irrelevant and meaningless. You have a jack, you couldn't do this with your example, but the backdraft does well.

This is toward the front right corner jacked up on the side frame rail, which jacks the right rear corner frame 2", and drops the front left frame 2" lower then the front right, basically using the left rear and front right as perfect pivot points with zero flex. This is not scientific by any means, but move it around at different balance points and check for deflection. The frame is certainly quite rigid and nowhere near your example.

[cbreez]

The point is to keep it real regarding the track capabilities of a rail chassis. Just have fun with these cars for what they are and don't waste a ton of $ and time on an old design. They all flex, that is why most race cars Indy, sprints, midgets, stock cars and yes sports cars went to triangulated space frames many, many years ago. A good discussion is contained in the old Herb Adams book.

[cbreez]

Originally Posted by itstock

I guess I understand your overall message, but comparing the torsional rigidity between the backdraft frame and that frame is completely irrelevant and meaningless. You have a jack, you couldn't do this with your example, but the backdraft does well.

This is the front right corner jacked up, which jacks the right rear corner frame 2", and drops the front left frame 2" lower then the front right, basically using the left rear and front right as perfect pivot points with zero flex. This is not scientific by any means. The frame is certainly quite rigid and nowhere near your example

Actually it is relevant. Who uses rail chassis anymore?

The point is not saying the MC chassis is JUST like a BD, but the principle is the same. The BD has quite a bit shorter of a WB, plus you have a plastic body bolted on to help to help. These examples also have no G-Force loads which will enhance any twist further.

[scottj]

We kept going stiffer on spring rates for the track. Eventually the chassis began to behave like a kart chassis. This resulted in pinching the passenger door in the body opening and splitting the inner to outer door panels. That's quite a bit of chassis flex...

Compared to any race car or current high performance production car standard these chassis are wet noodles.

[itstock]

Originally Posted by cbreez

The point is to keep it real regarding the track capabilities of a rail chassis. Just have fun with these cars for what they are and don't waste a ton of $ and time on an old design. They all flex, that is why most race cars Indy, sprints, midgets, stock cars and yes sports cars went to triangulated space frames many, many years ago. A good discussion is contained in the old Herb Adams book.

Originally Posted by cbreez

Actually it is relevant. Who uses rail chassis anymore?

The point is not saying the MC chassis is JUST like a BD, but the principle is the same. The BD has quite a bit shorter of a WB, plus you have a plastic body bolted on to help to help. These examples also have no G-Force loads which will enhance any twist further.

I don't disagree with the premise of your argument but your example was piss poor. Your example couldn't possibly be any more irrelevant.

[Morris]

Originally Posted by scottj

We kept going stiffer on spring rates for the track. Eventually the chassis began to behave like a kart chassis. This resulted in pinching the passenger door in the body opening and splitting the inner to outer door panels. That's quite a bit of chassis flex...

Compared to any race car or current high performance production car standard these chassis are wet noodles.

Scott

I agree with you regarding all of these short wheel base Cobra's.....

That's why we spent all of the time developing the chassis on KMP259. Our chassis is built to reduce the torsional twist from the suspension input. After we enhanced the chassis.....the bottom plate bolted to the frame rails from the front of the chassis to the rear of the chassis was the icing on the cake. On the track we could raise or lower the chassis one turn on a corner and see the results in the tire temps immediately ......

The national championship cars we built over the years, all started with a well thought out chassis first..... Then on to the suspension.....

Morris

[scottj]

Originally Posted by Morris

Scott

I agree with you regarding all of these short wheel base Cobra's.....

That's why we spent all of the time developing the chassis on KMP259. Our chassis is built to reduce the torsional twist from the suspension input. After we enhanced the chassis.....the bottom plate bolted to the frame rails from the front of the chassis to the rear of the chassis was the icing on the cake. On the track we could raise or lower the chassis one turn on a corner and see the results in the tire temps immediately ......

The national championship cars we built over the years, all started with a well thought out chassis first..... Then on to the suspension.....

Morris

Hi Morris,

To anyone who followed the KMP259 build thread it was obvious that you were the man with a plan... and the results proved it! I was more of a novice with a dream... lol. But, our track performance exceeded all our expectations and we learned a lot. More importantly, we made a few friends and had a lot of fun...

[MJC]

Originally Posted by Morris

Scott

I agree with you regarding all of these short wheel base Cobra's.....

That's why we spent all of the time developing the chassis on KMP259. Our chassis is built to reduce the torsional twist from the suspension input. After we enhanced the chassis.....the bottom plate bolted to the frame rails from the front of the chassis to the rear of the chassis was the icing on the cake. On the track we could raise or lower the chassis one turn on a corner and see the results in the tire temps immediately ......

The national championship cars we built over the years, all started with a well thought out chassis first..... Then on to the suspension.....

Morris

Is the Kirkham chassis similar to the Backdraft's? Any links to this thread? Interested in stiffening the chassis up over the winter for track days next year.

[Cashburn]

Originally Posted by MJC

Is the Kirkham chassis similar to the Backdraft's? Any links to this thread? Interested in stiffening the chassis up over the winter for track days next year.

There is zero similarity other than 4 wheels.

[Zeke]

Does anybody have info/photos of a Backdraft chassis? I'm considering purchasing this car but have no idea other than it has a BMW rear IRS. Thanks in advance.

[Cashburn]

Originally Posted by Zeke

Does anybody have info/photos of a Backdraft chassis? I'm considering purchasing this car but have no idea other than it has a BMW rear IRS. Thanks in advance.

Backdraft Racing - Custom Shelby Cobra Kit Car | Backdraft Racing

and click on "Chassis"...