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Chassis Strength

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Hi all,


I have for a while now been looking into areas in which I could improve occupant safety within my 1968 Spitfire MK3.


Now, there are a couple of videos on Youtube showing official crash testing of a spitfire and the end result.


What I have found interesting is a US NHTSA NCAP crash test on a 1978 Spitfire.


The video is here;



If you forward to 3 mins 6 seconds you see the rear impact test from the underside.


It appears quite clearly that there are two extra chassis components extending from the rear of the chassis either side of the differential and extending outwards to the rear overriders.


To my eye this appears to have added some good strength in the event of a rear impact.


Googling for images of a 1978 US Spitfire chassis has proved difficult.


Would be interested to know if this was a full production chassis or, shall we say, just employed for the test.


Anyone with any opinions on this or seen an actual US chassis.

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Standard USA chassis has "boot riggers" just like the Herald and Vitesse.


The chassis "drawings" in the factory workshop manual illustrate both the US Chassis and the Rest of World Chassis.




There are also plenty of photos out on the internet



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Thanks for that.


It obviously adds some strength to the back end.


Though as with all cars, the strength does not mean a lot when a low down car is hit by one with a higher ride/bumper height.


Only curious as it gets annoying when the car travelling behind you has to drive so close in order to read the model designation on the back of my spitfire, then backs off.


My answer, "get your Bl@@dy eyes tested!" and keep back!

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Standard USA chassis has "boot riggers" just like the Herald and Vitesse.

This is correct, but only from the 1974 model year on. I do not know for sure, but I suspect that the rear chassis extensions were added as much for increased rear bumper support as for any other reason. At the time, bumpers on US cars had to be able to withstand an impact of, as I recall, up to 2.5 mph without damage to any safety-related components (notably lighting). Beyond that, I don't believe that the chassis extensions improved rear crashworthiness significantly if at all.


Meanwhile, with or without extensions, that 1973 Spitfire body (at least for its time) did a remarkably good job of absorbing rear impacts without intrusion into the passenger compartment. I happen to know this partly from personal experience of friends who were rear-ended (at a stop light) at a pretty good speed -- perhaps 20-30 mph? -- by a full-size Pontiac. It was a bit of an offset impact, focused more on the right side. Neither of my friends was injured. Notably, the car would still have rolled and driven were it not for the fact that the RH lower rear wheel arch metal had tried to become part of the tire tread! Another friend and I bought the wreck from the insurance company for parts. We were actually able to move that sheet metal a bit and drive the car around the yard...until an axle u-joint snapped. We were convinced that the u-joint had been damaged somehow in the impact. We also later discovered that, despite this particular car predating those chassis extensions, the rear of the chassis was a fair bit out-of-square, an obvious consequence of the impact and how the forces spread.


Oh, and I neglected to mention that both doors still opened and closed!


Moral: As you noted, it's a bit of a moot point with a car as low as a Spitfire, but those cars did remarkably well for their time in terms of occupant protection via absorbing the collision forces before they reach the passenger compartment.

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Something I do like about the Spitfire in regard to rear impact is the location of the fuel tank.


Right above the rear axle and in a low speed incident unlikely to get damaged.


When I think back years ago to my Dolomite Sprint & 1850 with the tank as part of the boot floor I shudder to think what a rear impact would do.


Yes I know that the Heralds are the same to some degree.


Safety is very important, but if we wrapped ourselves up in cotton wool every time we went out we wouldn't go anywhere.

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Make sure you have the spare wheel bolted in place. It forms part of the rear impact protection.


You used to be able to buy the US rear riggers cheaply in the U.K. I have a pair fitted to an old MK3 chassis.


Not sure if you can get them easily now,

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