Doon Buggy Body Tub


WARNING: I am not an expert on cars, automotive engineering, VW Beetles, beach buggies or anything else discussed in these pages. What I have written is my current understanding of the issues involved in building MY buggy. These opinions are based only on my own research in books and on the web. They, therefore, have no basis in fact, may well be wrong and potentially downright dangerous if taken to be gospel truth. If you intend to use any of this information for any purpose other than pure entertainment, then please get its validity confirmed by someone who knows what they're talking about! You have been warned...

This page contains the following Sections:

Chassis Overview

Early LHD Beetle Chassis

The chassis forms the main structural member of the buggy, as it supports the body, front and rear suspensions and the gearbox. The engine is then supported only by the gearbox. The primary function of the chassis is, therefore, to be both strong and durable, i.e. it must not either break or rot away anytime soon! This is particularly important in view of the buggy's proposed off-road use, where the loadings on the chassis will be far greater than under normal on-road conditions. The strength of the chassis will be supplemented by the additional bracing provided by a 6 point roll cage but this should not be relied upon, so the chassis must still be made as strong as possible in its own right.

In order to maximise the off-road performance of the buggy, the chassis must be as short as possible, with the maximum achievable ground clearance. The shortest possible chassis is desirable, as this reduces the possibility of grounding the car whilst traversing obstacles, gives the buggy the best possible turning circle, useful when negotiating obstacles, and increases the strength of the chassis.

The main strength of the chassis is provided by the, 140mm wide and 165mm high, central tunnel, with the sheet metal floorpans, which are fitted on either side, playing only a minor part. The central tunnel flares at the front to form the 'frame head' which the front suspension attaches to, with four bolts. At the rear, the central tunnel divides into two 'frame horns' which provide the mountings for the gearbox and rear suspension. In order to maximise the strength of the shortened chassis, the central tunnel weld should be as long as possible, as far away from the point of maximum loading as possible, not along any potential fracture line, without any sharp angles in it and preferably not through the bottom plate of the central tunnel, as this is the part of the tunnel that is in tension, is most likely to fail and that, therefore, is fundamental to the strength of the chassis.

Beetle Chassis Development

In the UK, prior to 1965, the Beetle was provided with a 'king-pin' front suspension system and a 'swing axle' rear suspension system. In 1965, the front suspension was changed, on all models, to a 'ball-joint' type, to both reduce the maintenance required and to improve the road holding of the car. In 1967, the rear suspension on the 1500 semi-automatic Beetle was changed to a double-jointed 'independent rear suspension', or 'IRS', in order to further improve the road holding of the car. This configuration, arguably, resulted in the best handling Beetle ever produced for the UK. The new 'IRS' rear suspension was also used in all subsequent 1302 and 1303 models (introduced in 1970 and 1973 respectively, which both had McPherson strut front suspension) but the 'swing-axle' rear suspension (and ball-joint front suspension) system continued to be used for all other UK models. Note: All US Spec Beetles from about 1969 onwards had 'IRS' rear suspension and ball-joint front suspension (except the 1302 and 1303).

Front Suspension Type Pros and Cons

Rear Suspension Type Pros and Cons

Swing-axle and IRS Rear Suspension

My Choice of Front and Rear Suspension Type

My ideal combination of front and rear suspension types for an off-road buggy is to have a king-pin front end and an IRS back end, as this would give the best possible off-road handling, suspension travel and durability.

The first and most important choice for me is the 'IRS' rear suspension type, as this is better than the swing-axle both on and off-road and having driven Beetles with both rear suspension types (I have owned a 1500 auto and a basic 1200), I find the IRS to be so much better that I can't really consider using a swing-axle rear end. However, this presents me with a problem at the front end of the buggy. The only way to use a 'standard' VW chassis with an 'IRS' back end and some sort of torsion bar front end is to find a 1500 auto as the donor vehicle. Unfortunately, the chances of finding one of these close enough to home and in the right 'condition', i.e. an MOT failure at a cheap price, are extremely low. All other options involve a more radical modification to the chassis than just shortening it. These options are as follows...

The only one of the above options which will enable me to use a king-pin front end and an IRS back end, relatively easily, i.e. without having to find a 'rare' chassis, is the 'frame head swap'. However, I can't bring myself to do this as I won't be able to live with a poor quality frame head and two joints in the chassis tunnel. This is the weakest option of the three, in my opinion.

The only other way of achieving a king-pin front end is to find a pre-1965 chassis as the basis for either of the 'cut and shut' or 'IRS conversion' options. The problem with this is that pre-1965 chassis are becoming pretty rare now (I've found less of these available for sale than 1500 autos!) and the ones that are available are generally not in the right 'condition', i.e. they are fully restored and, therefore, very expensive Beetles.

This has lead me to consider using a ball-joint front end, rather than my preferred king-pin option for purely practical reasons. If someone offered me a pre-1965 chassis, in reasonably good condition, tomorrow, I'd do an IRS conversion on it and that would be the basis for my buggy. However, as that's not likely to happen, I've decided to go with the ball-joint front end on the basis that I will gain the following benefits: better on-road handling, parts are likely to be available for longer, lower maintenance and options are available to improve the off-road performance and durability of the ball-joint front end, e.g. long-travel ball-joints, parts from VW Type 181 'Trekker/Thing' etc.

Chassis Options

Having decided on my front and rear suspension types (ball-joint and IRS), I now have further options for how to achieve the desired combination:

Note: I have already discounted the frame head swap option above.

Since the chassis forms such a fundamental part of the buggy and since the cost of a new chassis might not be that much higher than the overall cost of using a donor chassis (when you consider the additional costs required to transport it and repair it to the same standard as the new chassis), provided that I can get a new chassis for under 700 UKP (which I believe I can) then the IRS converted, new chassis looks like the best option to me.

I will, therefore, use a brand new swing-axle/ball-joint Beetle chassis, converted to IRS as the basis for my buggy.

Chassis Shortening Methods

There are several different ways to shorten a beetle chassis. In increasing order of strength and cost...

Whichever shortening method is used, it is essential to maintain the correct alignment of the front and rear sections of the chassis. The best way of doing this is to use a jig, built for this purpose, which bolts to the front and rear sections of the chassis and maintains the alignment. If I was considering shortening the chassis myself, I may be tempted to do it without a jig and to spend a long time measuring to check the alignment at each stage of the process but the extra effort required to do it this way may be more than building a jig . However, since I intend to have the chassis shortened professionally, the design and construction of the jig to be used will be a major consideration.

It's probably not right to classify the various chassis shortening methods into the above four fixed categories, as it's possible to mix and match various aspects of each technique to form a 'new' one. Also, each professional chassis shortener will probably have their own favourite technique which won't necessarily fit neatly into one of the above categories. However, I have seen them referred to using these descriptions elsewhere, with the exception of the 'VolksMagic Cut'. I made this one up (!) because I can't think of another short, descriptive name for it, I've never seen it referred to elsewhere and as far as I know, VolksMagic are the only people who do it this way.

I can't see any technical problems with the VolksMagic method, they have a very well designed and constructed jig, and it seems to be the neatest and strongest way of doing it to me. The only down-side appears to be the significant extra cost, due to the additional work of unpicking the tunnel floor welds.

Again, since the chassis forms such a fundamental part of the buggy, I will use the 'VolksMagic' cut when shortening the chassis on my buggy. This work will, by definition, be carried out by VolksMagic.

Chassis Shortening Tasks

New chassis at Volksmagic ready to be shortened

Since I will be starting with a brand-new South American Beetle chassis, the shortening tasks will be a little different to shortening an older chassis for the following reasons: The chassis will initially be left hand drive and will have to be converted to right hand drive. The chassis will have several additional brackets for mounting fuel injection and engine management components which will need removing. The chassis will have dual fuel lines for fuel injection which will need removing. The seat mountings will not be the usual 'runners'. Although the chassis will be for swing-axle rear suspension, the South American chassis looks like it started life as an IRS chassis and was then converted to swing-axle. This will make the IRS conversion easier as the cut-outs in the frame horns already exist, but are blanked off, and the profile of the frame horns is already correct to accept an IRS gearbox.

The shortening of the chassis and associated work will involve the following tasks:

The buggy will then be 'dry built' on the chassis whilst it is still in its factory primer. This will enable any additional brackets or further modifications to be made without affecting the final finish on the chassis. Once the buggy has been completed, it will be fully disassembled and the chassis will be finished with some, as yet undecided, coating.

Chassis Shortening Photos

Chassis after being shortened by Volksmagic

Click here to see a slide show of the chassis before, during and after the shortening process.

Doon Kit Photos

Body tub as delivered by Doon Buggies

Click here to see a slide show of exactly what you get in the Doon kit, as delivered.

Body Lift Kit

Body lift kit made by ZaNNetec Motorsports

In order to maximise the ground clearance of my buggy, I need to use wheels and tyres with the largest diameter possible (I'm aiming for 30 inch front and 31-33 inch rear tyres) and in order to maximise the amount of suspension travel the wheels must be free to move both upwards and downwards as far as possible (I'm aiming for about 12 inches of suspension travel at both the front and rear). Since the Doon Buggy is designed as a roadster, there isn't as much clearance between the wheels and the arches as I need and when the suspension is fully compressed the tyres foul the arches, especially at the front, even with 27 inch tyres fitted.

In order to increase the clearance between the tyres and the body at full suspension compression a body lift kit can be used to raise the body in realation to the chassis of the buggy. The body lift kit is a spacer that sits between the body and the chassis and is attached to both.

In addition to raising the body in relation to the chassis, the body lift kit also has the following benefits:

The down sides to a body lift kit are that it increases the weight of the buggy as well as the cost and can spoil the lines and propotion of the buggy if it's not done well.

Body lift kits are available off-the-shelf from several suppliers in the USA but are of widely varying quality. The consensus of opinion seems to be that most of the pre-fabricated kits are of poor quality, with the possible exception of the kits made by Up-Yer-Bug:

Up-Yer-Bug body lift kit advert

In addition to the problems associated with the poor quality of off-the-shelf body lift kits, another problem is that no two shortened chassis are exactly alike and no two buggy bodies are exactly alike either. In fact, on my buggy, the fit between the body and the chassis is not great at all and an off-the-shelf body lift kit is likely to make the problem worse, rather than better.

The easiest way to overcome these problems is to fabricate a custom body lift kit specifically for my buggy that is a compromise in fit between the chassis and the body.

The body lift kit for my buggy was made by Zane Llewellyn of ZaNNetec Motorsports and is made from 80 x 40mm box section (3mm thick) for the main side rails with fabricated front and rear sections made from cut down box section, 40 x 3mm flat bar and 3mm sheet, all TIG welded in mild steel. The body lift kit is attached to the chassis by bolting up through the normal VW body mounting holes into welded M10 captive nuts in the underside of the body lift kit. The body is also attached down onto the body lift kit using M10 bolts and welded captive nuts. None of the bolts pass right through the body lift kit. Only four bolts hold the body down initially, although more will be added when the roll-cage is made and the location of the mounting points is known. In addition to the bolts coming up through the chassis, the body lift kit is attached to the chassis front cross member by bolting through four vertical tabs and to the outside ends of the rear torsion bar housing using bolted brackets.

Click here to see a slide show of the 80mm body lift kit made by ZaNNetec Motorsports.

Once the roll cage has been fitted, along with the side bars and seat mounting frames, i.e. when no further additions or modifications are required, the body lift kit will be powder coated in matt black.

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