Dunno about the K3, but on my old libra (& I’m guessing the weight won’t be too different) I followed the thread on here which had all the calculations on. So when i bought the Protech shocks, i went for 215 front & 325 rear. It rode like my Renault scenic!! Soft, wallowy & rolling round the corners! I ended up (after trying about 3 sets of springs) with 225 front & 400 rears. This was for road use. The original builder (Dave Boud) used 450lb rears but was more track orientated.
At the end of the day, you can do all the calculations you want.... but its how it feels & handles that matters. I personally wouldn’t recommend going softer at the rear.

Thanks Sven, that's very helpful. I have read most of the Libre threads regarding spring rates etc and yes I think they'd be similar weight wise. I was thinking I might get a few quid back for the 9 inch springs but I'm tempted to lop an inch off each one and see how the car sits even though that will increase the spring rates a bit more.

Be careful comparing spring rates between Libra and K3. Although weights are similar the units are at a steep angle in the Libra set up and more or less vertical in the K3. The angle in itself isn't necessarily an issue but the movement ratio might be and steeper angles often suggest a different movement ratio. You need to measure how much the spring will compress for a given vertical movement of the wheel. If the movement ratio is similar then you can safely refer to data from the Libra but not sure if it is.

Yes I understand the Libre rear suspension is very different to the K3.

Sorry for the late reply. I kept getting logged out last night and I gave up in frustration

Haven't done anything about the springs yet. However the wiring needed tidying up so decided to get on with that instead. The coilover bracket on the passenger side front touches the heater box even after trimming the casing right back so some metal had to be taken off the bracket to allow the cables to pass through.

Nice work
I will have to check out this on my car
And see if I have the same problem when i get round to changeing my k3 over to coilovers i have the brakes gust need to get it done

I could have just dragged the cables over the top of the coilover but it would look a mess. There's no issue on the drivers side as there's nothing on the bulkhead there. The inner wheel arches need cutting back some to clear the top mounting bush too. On the plus side all the lights work as does the heater and wipers and the dashboard. I finally got the fuel gauge hooked up and found the tank is nearly full! It might be a bit stale now so I'll take out a gallon at a time and bung it in my Suzuki as its too dear to waste I really would like to get rid of the Metro fuel tank but that's a job for next year.

I might have the same problem on the drivers side I whent and put in some cable's for the radio on that side.

I don't think you'll have an issue on the drivers side. This pic isn't very good but it might help. I'll take a few more next time I go to the workshop.

Went to start her up in prep for moving her to my mates garage and she wouldn't start. I buggered around with the wiring for three days to no avail. The circuit diagrams in my Rover Metro manual are close but not close enough but I finally tracked down the correct circuit diagram on the Lotus 7 and Caterham Club site. Problem traced to a bad solder joint in the loom where it was extended. I tidied the loom up a while ago and wrapped it with fresh tape and I must have stressed that joint somehow. Anyway problem solved and she cracked up a treat. Next year when the sub frames come out for replacing I'll have a new loom ready to go in.

And here she is in my mates paint booth ready for some tlc.

It’s been a while since I last posted here. Not long after I took my car to my mate’s garage he suddenly decided to retire and the garage was sold on. Whilst I know the new owners I don’t have the same relationship with them so the car was moved back to my workshop until I had time to sort things out. After joining the GTMCC last week I decided it’s time to get my K3 back on the road and yesterday I made a start. I’ve replaced the front springs as the nine inch springs I originally fitted were just plain wrong. I’ve also decided to fit the new plywood floor sections myself and I’ve removed both doors to give me better access. The plywood sections are cut and the floor has been roughed up and the car hoovered out ready for work today. The floor dipped in the middle so I’ve supported that on some 3 x 4s.

Apologies folks. The pics went in the right way up but for some reason they ended up upside down.

Another pair of springs ordered. Same rate, 250lb/350lb but 8 inch long this time. Also bought the parts to convert the clutch to hydraulic.

I’ve modified the clutch pedal and installed the clutch master cylinder. Now I have to work out how to do the gearbox end. I’m struggling to get the pin out of the clutch release arm so I might just cut it off leaving half an inch or so and weld a piece of flat bar to it instead of making a whole new arm. If I have to take the gearbox out I might as well go for a PG1 box.