[GTiJohn]

Forgive the ignorance but for my edification: the front brace is across the top of the suspension (under bonnet) and the anti roll bar is somewhere under the engine across the 'axle'?

I know it's not an axle but the word suits my purpose and you hardly hear it these days so felt it needed resurrecting!!

You're correct with both of your comments.

A body brace tries to keep 2 parts body the same distance apart of putting a strut between them. In this case it's the 2 front damper top mounts which, on a Macphereson strut front suspension such as R8 and R3 (but not HH-R), has a major controlling affect on the camber (the in/out lean) of the wheels.
The best design of any strut is straight but unfortunately most enginebay struts have to be cranked slightly to miss the engine.

An anti roll bar (or ARB) is basically a torsion bar between suspension members on the the two sides of the car. Your car can have none, one (usually at the front) or 2 - one front, one rear. They join a suspension member on one side of the car to the same one on the otherside. They are usually cranked to miss the big bits inbetween.
They are used to redistribute the vertical load between the more heavily loaded outer wheel and the less loaded inner wheel during cornering and are basically used to 'trim' the under/over- steer balance of the car.
As the name, suggests the effect is to reduce body-roll which has the beneficial affect of keeping the roadwheels more upright and improving their limit of grip.
The downside is that they make an independent suspension system less independent, as what's happening at one side affects the other. Basically, if the wheel at one side of the car hits a bump or pothole that wheel is less free to move to cushion the input due to the higher combined spring-rate of the road-spring plus the ARB.
If you want your car to understeer less you put an ARB on the front, or increase the stiffness of the one already there. This is usually done by increasing its diameter.

For interest, most R3s don't have a separate RARB as the rear suspension's H-frame performs that function. The cross-section acts as a torsion bar between the two trailing arms and the thicker of the two Maestro/Montego sections was chosen as it has the desired stiffness characteristics. It was the one from the Montego Estate.

[GTiJohn]

... the DC2 front brace (which I discovered by accident) fitted Rover 400s.The Rover chassis had four bolt holes ready drilled with bolts already in situ so it was easy to fit. This has sharpened up my steering considerably.

Something

I have heard of, but not seen, Civic braces that fit inside the front wings that link the damper top mounts back to the A-posts. These, and your brace, are likely to be reducing the mobility of the front-end and so improving feel.
Another alternative is to a a V-shaped pair of struts from the damper top mounts back to the centre of the bulkhead, although there might be a few things you'll need to miss.

All of the above change the crash performance of your car - for better or worse is hard to say - so as always, it would be better if you didn't

[The Origina lNom]

Actually the brace I found is a lower subframe brace. I looked at Rover 400 subframe pics from google images and found that almost all HHR subframes have the four bolt holes.Since i was about to get on the floor to fit the 27mm ARB, it made sense to fit this at the same time. Its made the car a bit heavier but it really feels astonishingly well planted at the front.
Here is brace on ebay:
https://flic.kr/p/2jDh6kq
And here is where it sits. Note the pair of holes on either side.

https://bparts-eu.s3-eu-west-1.amazonaw ... 0if803.jpg

Interestingly, from other photos it would appear that K series engined cars did NOT have the holes for the subframe brace and I cannot predict if it fits the ZS180 cars.
Its not hard to check if you have the brace mount holes once you have a wheel off.


Incidentally, i do use an alloy top front strutbrace made by Weicher.
https://www.ebay.co.uk/itm/Wiechers-str ... Sw2lReeMCE

I am just trying to obtain a rear 24mm anti roll bar which does not currently exist as this would definitely improve the behaviour of the rear end. I have tried to control the rear with preloaded springs by using seats/spacers at the top of the strut which further compressed the springs but this lacked any compliance and was very uncomfortable.

Edit: After talking to the VHS guys as suggested below they suggested changing the springs and whilst this has helped, I still feel a thicker arb would make for faster turn in without using Eibach springs which I have always found too hard for the road.

[GTiJohn]

Interestingly, from other photos it would appear that K series engined cars did NOT have the holes for the subframe brace and I cannot predict if it fits the ZS180 cars.

Ask the VHS guys, they'll know

[The Origina lNom]

I just forked out for a set of H &R springs ( 29994-2 ) from Germany. They require a standard length shock which sellers do not make clear.
. After digging around in the boxes in my lock-up, I discovered an unused pair of Monroe Sens-a -Trac rears which make for an extremely gentle ride which have the rear H&R springs with 10mm spacer on top.and a lightly used pair of standard length KYB Excel Gs fronts which could fit the H&Rs perfectly.

The H & Rs are meant to lower -35mm but I dont think they would lower anywhere near that, we shall see
The Spax really needed a standard length shock too (16"x 6.5" and tyres 205/50/16 . Incidentally, a 205/45/16 set of tyres would have been just about okay with the Standard shock - Spax combination but not if you carry heavyweight friends in the rear of your car
The Bilstein B6 with shorter springs would be perfect if I ran standard 15" wheels but I seem to like making things more difficult for myself.
I have also found a MGZS180 std front spring in the lock-up which is the same as a 420D HHR so I will try that as it looks much beefier than the H&R front and should protect my tyres from hitting the under wing plastic due to the ZS180 brakes.
Fitting is next.

[The Origina lNom]

I have come to a conclusion regarding my suspension.
The 2021 HHR 416 is about to fitted with stock ZS180 front springs complete with 10mm spacers on top of Bilstein B6 front shocks .

I had tried so many variations to get what I wanted but the limiting factor was always my 16" Hairpins and 50 profile tyres.
To keep my tyres unscuffed I had to retain the standard shock length or use a heavy duty spring on the front to prevent the tyre catching on the inner wheel arch liner. i might have escaped most clearance problems but my ZS180 front brakes needed the matching springs to stop the front of my car making bad noises tearing out wheel arch liners when braking hard.
It will probably take a year or so to soften up the front springs but I think it will be worth it in the end.
I still think a 24mm rear anti roll bar would make this car steer a lot faster but lockdown and most importantly price has prevented this from happening.

Edit:
The front rides very high compared to the rear with the spacers in but as I live in an area with many speed bumps, this helps smooth the ride.
I will leave it for a few months looking high at the front to see if it 'settles'', before I think about removing the spacers. I think it will be level without the spacers but dont want to risk tyre contact with my arch liners.

[redandwhitE]

Interesting stuff. Keep the info coming as I am keen to see what works and then perhaps adopting some (or all!!)

[The Origina lNom]

I have been experimenting to improve the front headlights and have found that 'Nighteye' H7 Led give me the best combination of light, whiteness and upper cut off to stop glare to oncoming drivers. I tried Philips Racingvision +150% before that and although they gave me vision ten yards further ahead, the light spread and seeming brightness was not as good as the Nighteyes.
I also learnt that you should change both headlight Hi and Lo bulbs together if you plan to change to Led or similar as when the leds were adjusted to suit , it threw my H1 Hi-beams into owl spotting mode.
The Nighteye H1s i tried were pathetic and swiftly junked.
I have just received some reduced price Wontolf H1 Leds from Amazon USA and with a quick hotbox removal am hoping these will prove more suited and work with the Nighteye H7s

[The Origina lNom]

At last, the Wontolf H1 LEDs proved to be hugely unreliable due to overheating issues and were promptly junked. The best bulbs I found for me were legal, Philips Whitevision Intense Xenon Effect. https://www.youtube.com/watch?v=TmZSsysjTLg

The final piece of my handling jigsaw came together when I added a secondhand Dark Ice Designs upper rear strutbrace which seriously increased the rigidity of the back which seemed to be slowing the steering. In my previous experimentation, I had used spacers on top of the rear spring to make the rear end almost rigid which gave me very fast steering indeed but it was murder on my back.
The rear strutbrace is very heavy but it stops most of the body roll from the rear of the car enabling me to accelerate all through most corners, I am now wondering whether to fit a lower rear strutbrace.
The engine is still 216sli D16 SOHC Honda but with a few ponies freed up due to K & N panel filter, 4-2-1 Impreza D16 manifold and very slightly 52mm oversize exhaust tubing.
Its now quite fun to drive down country lanes without shaking my aged body apart
, steering accurately with minimal body roll.
Its not a fast car but at least it goes around corners well whilst still being able to take speedbumps at 20 mph.
I am currently debating whether to have the ecu tuned but that probably wont happen until next year.
This project has taken me a good few years. The exhaust modifications were most time consuming and painful as I had to get on the floor and wriggle under the car from my wheelchair and most of what I had previously read on other forums had disappeared together with the forums themselves so info that I thought was accessible proved to be missing.
Many thanks to those who offered advice and encouragement.
My next daily driver will be an electric car in a few years time and hopefully that will accelerate and handle well from the getgo.
I have to admit the modification that made the most difference for lowest price was the rear upper strutbrace followed by the ZS180 brakes but springs and shockas needed to be upgraded. I had improved the car's handling with assorted front suspension mods but the rear upper strutbrace was the thing that immediately made itself felt.