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Weight of a K3 
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Joined: Thu Nov 22, 2007 10:31 am
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Post Weight of a K3
Hi,
Any of you guys know why a Coupe weighs 610 kg, a Rossa 700 kg, a Libra 695 kg and a spyder 790 kg whilst according to GTMOC history a K3 weighs in at a meaty 820 kg? - much heavier than a spyder!
I know there must be a bit more glass and therefore a bit more resin to make up for the chassis not being steel like the Coupe but 30 kgs? - that's a hole lotta resin.
I would have expected 790 kg or less given the flexability of the tub (per Dudley).
Cheers


Thu Jan 10, 2019 6:24 pm
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Post Re: Weight of a K3
My k3 weighs 850 kg but i did add a lot of weight with a rollbar and fuletank
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paul
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Thu Jan 10, 2019 8:48 pm
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Post Re: Weight of a K3
I have lost the exact numbers for all of the bits that go to make up a k3, due to a great filling system that you put things in and they disappear exactly when you are looking for them.
However from memory the bare subframe used front and back weighs in at well over 20 kg each. The libras I believe don't use the subframes so should have a big weight saving. The coupe uses a mini subframe which is a bit lighter than what is in the K3, less complicated suspension system and a fair amount of aluminium.

The next area I would be looking at is the GRP strengthening and layup. Most companies working with GRP get very good at cutting back on the amount of layup and resin they use. A change from a plywood core to a proper GRP core material can save a huge amount of weight.


If you look at GRP boats from the 60`s and early 70`s they had solid layup in the hull ranging from 25mm to 10 mm, the boats were very heavy. By the 80`s the builders understood the material better and had developed better core materials. Boats now had 2mm outer skins 20mm balsa core and 2mm inner skins.

This gave the same boat a massive saving in weight, about a 1/3 lighter, along with more strength.


So the weight of the cars could vary for a lot of reasons, mechanicals used, construction used, builders choice and knowledge of materials it would be difficult to work out without a close study of all the cars.


Your weight question may be along the lines of when I looked at getting rid of the subframes in my K3 when I found how heavy they were. I have a post discussing my thoughts it may be worth looking up.


Fri Jan 11, 2019 1:08 pm
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Joined: Thu Nov 22, 2007 10:31 am
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Post Re: Weight of a K3
Hi Techead,
So it looks like the excess weight is mainly down to the complexity and therefore weight of the subframes and the glass/resin in the tub.
Do you have a drawing of the tub construction? I believe it was made up with a number of boxes bonded into the tub to add stiffness.
You talk about aluminium in the Coupe and apart from the mini gearchange, I don't remember any?
I'll look up the thread on subframe. Thanks

Hey Catsam,
Was the 820kg before of after the tank and roll bar?
cheers


Sat Jan 12, 2019 11:07 am
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Post Re: Weight of a K3
The aluminium in the coupe subframe suspension is the trumpets. The metro or MG subrames have a far more complicated and therefor heavier all steel suspension system. I have a 3d model made in autocad inventor of an idea for a front subframe. It was not proved as I got side tracked on other projects. If you find my post you will see I had been looking at an engine change to electric. There was still a lot of work needing to be done. I have only recently thought about going back to the k3 as I have found a drive system which would give 150 to 200 hp 266lbs torque. The whole drive system is 77.4kg plus batteries and a few other bits. this would be a massive saving in weight in the car.


Sat Jan 12, 2019 6:21 pm
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Post Re: Weight of a K3
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Hey Catsam,
Was the 820kg before of after the tank and roll bar?
cheers

Hi my car is 850 kg with the roll bar and tank i did not get it weiged with out the tank and roll bar

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paul
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Sun Jan 13, 2019 10:10 am
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Post Re: Weight of a K3
695kg for a Libra?

I think that's optimistic. Maybe an early car with a 1400cc engine, lightweight seats and none of the interior trim panels etc.

I seem to remember most VVC cars came in around the 750kg and the Spyder 800kg plus. One particular Spyder was 1100kg! That was with a little 8v engine too!


Sun Jan 13, 2019 6:34 pm
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