45 replies to this topic

[A9X]

Thanks for the attachment, it's close to what i'm playing with at the moment.

But lets go back a step or two, you said you have a tubular front end, would you mind sharing some more info?

[ls2lxhatch]

It sounds similar to this.




I don't know how you have managed to build a tubular front end that is 50 - 55 kg lighter than the factory setup.

The factory k-frame weighs 20kg, the upper arms weigh 2 kg each and the lowers weight 4 kg (with bushes and ball joints) each giving a total of 32 kg.

[TerrA LX]

I love the hatch and I like your line of thought, stick with it.

[ls2lxhatch]

You are correct the picture is the McDonald Bros LJ tubular front end, the McDonald Bros LH/LX tubular front end is similar.

Once we have the 4 wheel scales back from the east I can be precise, but the front saving calc is comparing the complete front weight with the Kmac springs/shocks,Hz brakes,calipers etc. Savings in the brakes,hats and aluminium hubs is a fair chunk. Once removed and cleaned/sandblasted our KFrame was not 20kgs. The bare Kframe with no bushes, removed engine mounts. no arms etc was sent to the race shop and it weighed in at 26.25kgs on the freight scales.

My UC k-frame weighs 20 kg. Maybe the LX k-frame is made from thicker steel. The LX control arms are made from thicker steel than the UC control arms.


If you add 6.5 Kg to the stock k-frame then the total weight with control arms is 38.5 kg.
Add the stock V8 springs and shocks at 4.5 kg each gives a total weight of 47.5 kg.
Add the Hopper Stoppers 300 mm kit at 35 kg gives a total weight of 82.5 kg. ( I used the Hoppers kit as an arbitrary example of the weight of brakes )
The VT hubs weigh 2 kg so you could pick up a couple kg for the pair by using alloy hubs. The alloy hats will save around 1.5 kg per disc.

The Axistr/Lenny rack is probably heavier than the stock rack.
The stub axles and steering arms are probably heavier than stock Torana.

I just can not see where you are going to find 50 - 55 kg in weight savings in something that weighs around 82.5 kg.

The pressed steel construction is very efficient in terms of strength vs weight.

Edited by ls2lxhatch, 31 August 2011 - 11:44 AM.

[ls2lxhatch]

If you ring McDonald Bros they will build the LH/LX tubular front suspension. I don't know how McDonald Bros claim their LJ tubular suspension is 40 kg lighter than stock either.


If the heaviest stock front suspension setup including heavier aftermarket brakes weighs around 80 kg then a 50 kg weight reduction by using Chromoly, alloy hubs and hats is not possible. The brake discs will weigh around 20 kg which leaves 10 kg for everything else. (k-frame, control arms, springs, shocks, ball joints, stub axles, hubs).

3m of 2" x 0.12" Chromoly tube weighs around 11 kg.

Chromoly tube will be used to replace the factory k-frame that weigh 20 - 26.6 kg and the factory control arms that weigh 12 kg including ball joints and bushes. If the Chromoly k-frame and control arms with ball joints and bushes come in under 18 kg then you would have to be extremely pleased with the result and will have saved 14 kg over the UC setup.

When the Chromoly suspension is finished you can put it on the scales and let us know how it worked out.

Edited by ls2lxhatch, 31 August 2011 - 01:56 PM.

[ls2lxhatch]

The original statement was that replacing the factory front end with a Chromoly front end saved around 50-55 kg. I think this is impossible because the factory k-frame and control arms weigh between 32 - 38.5 kg. Modifying the brakes should not really come into the equation as the brake modifications could also be done with the factory front end.

It appears the weigh savings estimates were based on the McDonald Bros dubious claim that their LJ tubular front end is 40 kg lighter than the factory LJ front end.

Welby its being built out of chrome moly as we speak. So unfortunately I cant show you some photos at the moment. I will show some once we get a few things together. Although solid mounted it uses the same 6 bolt mounting points that a standard KFrame uses. But it is built for coilovers and is basically two pipes that are mandrel bent into an engine cradle between the 4 chassis rail mounting points. Two chrome moly anchor arms then tie the cradle onto the chassis firewall mounting points. Its a very simple setup, its very light (saves about 50-55kgs) and is much stronger than the bulky standard KFrame.

[ls2lxhatch]

I tell you when we get it all back with the very accurate scales that we uses to balance the car. I didn't sit down a weigh it as it was still in the car. Hence why I asked for the approx weight of a bare Kframe on this forum. I think it may even have been you that said it was 20kgs (Ive never weighed one) besides what freight co said it could be 10kgs for all I know.

Personally I think the front end with HX brakes etc is heavier than 80kg, but that is just a guess. Not even sure the freight scales are accurate enough, but unfortunately our accurate race scales are with another race car, so I can only take the "engineers estimate".

It was me that weighed the k-frame for you. If you want the weight of an UC k-frame with HQ discs, HQ stubs and Harrop steering arms I can weigh it for you as I have one sitting on the bench. The setup with the Hoppers 300 mm brakes comes in at 76 kg, the HQ brakes will weigh less. I also have mild steel 1" x 3/16" tubular control arms, coilover shocks, standard LX control arms, standard UC control arms, LX stubs, HQ car stubs, HZ one tonner stubs and a variety of brakes sitting on the bench.

There are many advantages of the setup you are building however the weight reduction will be the least significant of them.