Glass

The three pieces of glass on the Road Rat are glued straight on to the heavy hollow sections that make up the window frame, and double as a forward roll-over bar. I approached this part of the build with some trepidation. For one, it was really handy to have no glass in the window because this gave full access to the wiring, pedals and steering column without needing any Houdini acts. For another, I was a little unsure about the idea of the glass just held there by glue. I need not have worried on the second count. I made hard-board templates and had Autoglass cut the shapes out of the right sort of laminated glass. They also sold me two tubes of the right sort of adhesive, and gave me small amounts of two other chemicals and swabs needed to do the job. They also gave me a brief tutorial on how to do it right. First off I tried sticking a piece of old steel onto an old windscreen I had lying around. I used a contact area about 25mm square, and minimal preparation. Within seconds it was stuck like the proverbial. Not a chance of moving it. That took away any doubts I might have had, and I proceeded with confidence, using about twice the recommended contact area and generally being very conservative. This is great stuff. I would be happy to stick a whole car together with it. Maybe some day I will. This cost about $350 in materials, and the glass weighed 13kg.

Seats

I made the seats by gluing foam of various densities and shapes onto pieces of plywood and then wrapping the resulting squabs in pieces of brightly coloured vinyl cloth. I stapled the covers on without stitching. The idea I had here was that on occasions they will get soaked with rain, and my experience has been that when this happens, the water gets in through the stitching, so I have tried to make it so that there is no downward path for the water that will lead into the padding of the seats. I did a lot of trial and error work here to get good supportive seats, and they did work out quite well. There is about a 50mm step out for lumber support and about 100mm rise at the front for thigh support. It could have done with more in the thigh area, but I wanted also to be able to stand up on the floor ahead of the seats, to make getting in and out easier, and I was able to achieve this. At this stage the lateral support is very poor, so unless you have a substantial passenger the car is a bit slow round right hand corners. I will see to this inadequacy soon. An added complication to the seat mountings in that the firewall is designed for quick removal (release two clips and out it comes) as this provides the best access to the engine for checking oil etc.

For seat making, I found the best type of foam came from an old latex rubber mattress. This was much denser and more supportive than the various types of plastic foam I had gathered up for this purpose. Weigh-in time

I suspect we all secretly hoped that our cars would turn out a bit lighter than they actually did. I was pleasantly surprised to find that I was almost bang on the nail with my target of 600kg. It weighed in at 585kg ready to drive away. This is a 33/67 split front/rear. Now I look back and wonder where I could have saved a bit of weight. The frame is a bit heavy as I used RHS rather than the thinner walled ERW square tube. This could have saved 40kg or so. The windscreen and frame could have been done without. This would have saved another 30 kg or so. The next saving would have to be in fabricating wishbone suspension and using lighter hubs, brakes, wheels etc. and now we are really talking about quite a different sort of car. But with more of a weight conscious focus, a car like this one could be built under 450 kg without too much trouble or additional expense.

The on-the-road experience

First time out, the term “all-over-the-road” certainly sprang to mind. The initial tech committee drive testers were very brave men. However, after a series of small adjustments to wheel alignment, caster angles, tyre pressures, etc. it has become a much more relaxing drive. A fair bit of this improvement seems to have come from the tyres wearing in. However, it certainly remains a lively car with a very responsive chassis.

With a 2.1m wheelbase and all the weight concentrated at the centre of the vehicle, the polar moment of inertia is very low. This means that there is very little effort required to actually get the vehicle to start turning, and then to straighten up again. Try twisting a large suitcase round by it’s handle compared to say a bucket of sand of the same weight, or carrying a long ladder over your shoulder round corners compared to a sack of flour. So a long car with weight at its ends needs time to transition into and out of a corner. With a car like the Road Rat much more of the available grip on the road can be put into resisting the centrifugal forces during cornering and is not wasted on just twisting the car around.

The tyres do seem very critical. I would like to experiment with this a bit further. The car currently has wider rims and tyres on the rear than on the front. All tyres are the same profile (60 series). I suspect that a more compliant steering response can be achieved with a car like this (with more weight on the rear wheels than front wheels) by having the rear tyres with a lower profile than the front. This would need a larger rim diameter to maintain overall transmission ratios and ride height.

Ride is very smooth. The torsion bars are quite soft and the suspension has a lot of travel available. Passengers are usually surprised at the comfort of the experience. The car makes a joke of most “speed bumps” which can generally be taken at 40km/hr with no drama at all. Again, the low centralised mass and sitting position means that there is no long period dominant pitching frequency for the speed bumps to excite. The ‘Rat just drives quickly over the little hill.

The car has high sides, with frame members at shoulder level as you sit in the car, and the deep three piece windscreen adds to the cosseted feeling once you have clambered in. Wind and rain are not too much of a problem. At highway speeds the rain tends to blow over the top of your head, but a certain amount of it does drop into your lap from the top of the windscreen. Noise is there too. Once the old air cooled VW engine gets up over 3000 rpm it gets pretty rowdy. And, it’s only about 300mm and one sheet of aluminium away from your kidneys.

Off road it goes well too. Getting first and second at the last two club grass gymkhana events was a lot of fun. Trying it at speed on a really rough track I found the main trouble was keeping my feet on the pedals. They keep bouncing up in the air. On soft sand it gets further than most, but it isn’t quite a beach buggy. The first time I got a bit stuck in sand the car gave me another one of its unique experiences. I put it in reverse, revved it up and dropped the clutch. The whole world suddenly went grey, as these two rooster tail fans of sand came flying up both sides of the car from the rear wheels. Sand everywhere.

Exhaust system

There was a problem to overcome here in that I was keen to get all the pipes into one tailpipe, but there wasn’t a clear path to get the left ones over to the right side of the car (or vice versa) without compromising ground clearance. I was keen to keep a relatively smooth and invulnerable underbelly. So I read up a bit about exhaust systems in the library and learned about the “independence” approach. This effectively uses four straight pipes from each exhaust port into a relatively large volume receiver. This apparently gives the advantages of four “tuned” pipes, but without the “peakiness”. To be effective the volume of the receiving chamber has to be at least 12 (I think) times the displacement of one cylinder of the engine. So I built a six litre chamber across the rear of the car, and fed the four pipes into it, then followed that up with a small Coby muffler. The four straight pipes are about one meter long, dictated by the length of the engine/transmission, which is probably a bit too long for a serious performance improvement, but the system seems to work well. It certainly is quiet and it sounds OK. I have seen similar systems on racing side-car rigs, but with primary pipes about half the length that I used.

Stuff still to do

I got the car on the road with just the bare necessities to make it comply with the legal requirements, and still give me a bit of room to move with further developments. Since then I have smoothed off the rear body work. And I have some more “tidying” like this to do. I also have a newer engine to fit, and a priority still remains to give some attention to the gearshift linkage which is still diabolical. Then there are the seats to improve, inner guards to make for the rear (to keep out the water, dust and grass etc. and reduce the “under the lawnmower” look inside the rear compartment), and possibly some sort of emergency roof.

Looking back

I’m happy with the way the car has turned out. The experience has been very rewarding and the car has turned out to be entertaining, reliable, practical and versatile. However, I would certainly recommend to anyone building something of a similar concept to base it on parts from something a lot newer. Just about any FWD car from the last decade or two is a good point to start. And most have at least twice the power of the old VW.

The thing I would most like to say is to recommend to others who are scratch building to stick to it and get those cars onto the road. The scrutineering system that the club has put in place works very well indeed (thanks very much to the continuing efforts of the dedicated few) and the process for getting VINed certified, inspected, WOFed, registered and let loose on the road works well also. So! Don’t muck about, get out there.

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