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Yea theres a lot in suspension setup and the application it's setup for. My VR has 225/60/15 tyres and rides a little riugh and handles quiet well for a standard car. It's interesting what happens when people lower cars and the affect on roll centre location. Some good some bad.

There certainly is. The red VP when I bought it only had Pedders shocks up front and nothing else done, a bog stock car throughout. It handled very well and I thought there was more done to the suspension but that was all I found.

Here’s the vy springs rate and stuff ect. Would be good to get all the info like this for all the commodores plus sway details ect.

Wow!! that's great info!!! Where did that come from? I'd love to get that info for my VS Grange to be able to turn it back to stock.

That is from the factory service manual.

I can add those pages from VT and VX. Unfortunately I don't have VS.

There are links on the JC forum to download the various factory service manuals.

If it helps, my VP S with FE2 has the front bar 92041500. ID code CG. 25mm. I am sure the rear is 20mm, but I will need to double check and report back if there is any labels on it with above details.

Looks like I'm going to search for a rear bar from a SS model VX as the rear bar should be 2mm larger than mine.

This the VR info

I checked all my cars that aren't modified with the bars.

All are 19mm rear, stock front is 26mm and the FE2 is 25mm front, but remains the 19mm rear. Not sure where I got the 18mm stock figure from.

So this rear 20mm bar I have, no idea what model it came from, but I bought it as an FE2 one. So really, all I need to do is get a smaller one up front and that should help the front grip more and not lose grip on the rear by sticking to stock, upgrading the rear to thicker will change the balance but probably reduce grip overall.

The stock/FE2 rear bar's PN is 92036388.

So looking at the maths of bar thicknesses etc... I eventually found this calc where I use an arbitrary number top and bottom as constants and look at the result vs the diameter.

It's a lot more complicated than you'd think and simply doubling the diameter is not double the torsional force. The maths suggests that the smaller the bar, the larger the difference in force per mm of size change which make sense given there is a lot to do with circumference and also cross-sectional area, not diameter alone.

So a mere 1mm reduction from 26 to 25 went from a figure of 4.48, down to 3.83 which is like 15% reduction in stiffness.

To complicate things further, strut mounting vs control arm mounting is an increase in leverage for the control arm version by 50% or a reduction is stiffness to 66.67% going to the older arm version mounting for the same bar.

So to get an equiv bar to the stock 26mm that is on the strut, you need a bar of 29mm on the control arms. This is a bees dick over the stiffness of the former. (Side note that my red VP is 31mm on the arms, set to the softest setting, this aligns with my results not feeling much different to stock)

A 28mm on the arms will give you approx exactly the same as the 25mm on the struts.

The common 27mm after market arm based bars ended up being something like running a 19mm front bar if mounted the same way on the strut as VN-VS do. So the 27mm upgrades are super soft.

I thought that was very insightful and thought I share this.

https://calculator.dev/physics/torsiona ... alculator/