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Kitcar and Replica

Kit tips and advice



A kitcar without integral inner body panels is a pariah in the industry. Some have worked for years to weed out those companies that slip by and give the customer a half-finished body.


All combined, doors, hood, and trunk inner panels, shouldn't add much more than 20 pounds. They don't need to be thick and heavy. It takes work and a lot more expense for a manufacturer to include inner panels. First of all they must pay for the design and "tooling" and it is costly. (The people who do this work are talented artists.) Plus the cost of extra molds, bonding jigs, and the extra labor is expensive and time consuming.

The established industry standard for over 30 YEARS for ordering fiberglass bodies and parts requires you to specify whether they are for street or race. The race version is lower in cost, has no inner panels, and is thinner than it's street counterpart. The race versions are not intended for street use.

If you buy a kitcar for everyday use that has NO inner panels, you should be paying a lot less, a LOT less than the kits that have integral inner panels.


Compared against bonded FRP inner panels, plywood or FRP covered plywood or balsa, the aluminum interior panels or facade, do nothing to reinforce body or frame. The aluminum tranfers heat and noise very efficiently. The aluminum will have to be insulated or carpeted to overcome it's inherent qualities. Corrosion should also be taken into consideration. It is acceptable to use aluminum in the engine compartment or the trunk area lining. But it would be covered over in the interior, so the ornamental aspect is lost. Better utilized in a show car or race car interior, aluminum is not the best material for a comfortable, quiet ride on the street.


Some kit companies are mis-applying the nomenclature and calling their frames by these names,

thinking that you will be fooled into believing their frames have qualities of the type.


A ladder frame is just that, it looks like a ladder without all the rungs. Also called "twin-tube", it's main purpose is to hold the suspension and mechanicals to isolate the works from the passenger compartment. This provides a smooth and quiet car. Whether round or rectangular section tubing is used, frame torsion or twist is a major weakness of this type if no other reinforcements are strategically added. The original AC Cobra frame is called "twin tube" and has a skeletal superstructure to mount and support the soft aluminum body. It does little if anything to add strength to the frame as it is not triangulated. The AC frame was not designed for racing or for high power applications. If no other corrections or additions are applied, the frame remains quite flexible in torsion. However, if too many braces are added, weight becomes a factor and another frame type should be considered. Most of the kits on the market today utilize this type of frame.



A backbone frame has a big and usually a monocoque or some other form of a strong and stiff tunnel down the center of the car and this serves as the MAIN center of strength, hence the name. Want to see a real backbone frame? (It's also a good example of the space-frame technology) Go to, that's the Gardner-Douglas Cobra. Colin Chapman's Lotus Elan is a well-known example.



A space frame is such that it would remain sturdy and strong even if swivel/ball joints were placed at each joint. This is because the construction places all of the loads in tension and compression, NOT "bending". The top rails of a space frame are in compression and should be larger or thicker than the bottom rails to prevent collapse or buckling. A space frame is made up of a series of square shapes with diagonals, forming triangular structures. A construction crane is a space frame, a radio transmission tower is a space frame, the old "tube and rag" airplanes are space frames covered with fabric.



The method of frame reinforcing by shear plate, is where a metal plate is attached in a planar position, taking advantage of the tremendous strength available in shear. This has the dual purpose of providing a usable surface and a very stiff brace. Shear plates can be added to nearly any type of frame, but if you add too much of it to a ladder frame, for example, there will be redundancy. A good example of the utilization of shear plates [designed from the ground up to take full advantage of the concept] is at Look at the chassis page. Notice the torsional rigidity figures. Ask your prospective kitcar company if they have such figures available.



A unit body, "unibody", is also a form of monocoque. Called "stressed skin", a monocoque is a body made from thin sheets, commonly steel or aluminum. The aluminum aircraft you fly in is a monocoque example. This type has no frame rails as such, the whole outer skin forms the frame [with sheetmetal "bulkheads" and "stringers" used to hold the shape]. This is usually the lightest and stiffest of the types.

There are a few more types of frames that defy categorizing.


is a combination of many forms and materials. The new materials are being tested and developed by the formula car teams and the manufacturers who supply Indy/CART type cars and they do not regularly publish their discoveries. Right.

This overview is to help you recognize quality engineering or the lack of know-how of the kit manufacturer.

If you are building your car for street cruising, do not try to duplicate the suspension setup of a bona fide race car. Race cars do not give very much consideration for creature comfort. They ride hard, transmit vibration to the driver, and are hot and noisy. This may bring on considerable fatigue on a long drive. It is equally difficult, and maybe more so, to design and build a smooth, quiet, and comfortable car.

Though production car technology is going in a different direction than race car design, the study of race cars is a good place to learn the hows and whys of auto design. On a race car we discover what works and what doesn't right away. On a street car, we may never know how the car may react in a given situation because of so many variables. It may take years to discover a major fault in a design.

Automotive Frame Graphic


You are paying a lot of money for your kit, are you getting the quality you deserve? Or will you have to keep convincing yourself you did OK, even though you're not so sure. How can you know? Trust the magazine advertising? Trust the person who wants your money? Face it, if the American public demanded better cars from Detroit 30 years ago, they would have built them then. Only now, after the Japanese took basically European design, then added reliability, and put together the best cars on the planet, Detroit finally responds with some acceptable cars. Detroit had you pegged for a long time, they knew you didn't know the difference, so why should they build a sophisticated and comfortable car? The same is true now of the kitcar companies, they know you can't tell the difference between frame types and other design considerations. If you smarten up they will respond with the kind of products worthy of the name custom made, hand-crafted. And the industry will once again be going forward instead of backward. Learn some simple facts about car construction, it's really not so hard, then you can make a difference!

Travelling? Buying a new car? Searching for low gasoline prices? This is really big!

Mother's Day 6

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Kitcar FAQ


Automotive Frame Graphic

Send comments or contributions (literary) to 3rdParty [Att: Todd Dixon] at

What has been presented could be easily found by anyone interested in learning. There is no information that is off-base, odd, unprovable. Nothing here is anything secret. The truth is out there if you want it. No company endorses or encourages this endeavor. If you wish to discuss in a civil manner, any area related to any of the above, you are welcome to email.

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