My car is unusual when compared to most 7s in that the suspension design requires considerably stiffer springs than say something like a Westfield. it is however a very hard ride and I'd like to soften it up to get some more road compliance. My current set up is:

Front - 1.9" ID x 8", 600lb
Rear - 2.25" ID x 6", 550lb

I don't really know what poundage of spring I should be fitting to get the desired softening so I was wondering if anyone had some springs either going cheap or if you're near (I'm in Brighton) that I could trial fit? I guess I'm looking to start out in the region of 400-500lb?

Cheers, Russ.

Is it a RR SR2? If you have some photos of the suspension setup, I would be able to give you some ballpark figures to try if you like. You can use shock angles and leverage ratios (of wishbone and any rockers) to work back to a wheel frequency, which then gives you the spring rate required.

I think I have some spare 500s but they are 8" from memory.

It is an SR2 yeah. It's hard to demonstrate the exact geometry in photos as the wishbone pickup points on the chassis are buried some way inside the bodywork. Essentially the bones are long, the leading edge of the front lower wishbone is at least 50cm.






Here's some pics from the RRR facebook page.


Just to be clear mine has OUTBOARD front suspension but the wishbones are the same.


[Edited on 21/10/15 by russtik]

Cheers for that! You do have VERY high wheel rates in that case.

I'll do a few quick sums at lunch and jot down what I reckon would be a ballpark spring rate... hopefully others will be able to chip in with their experience too.

To check - is the car all road, road / track or just track? Any anti roll bars? Ta.

I probably have some springs suitable for the rear in the right sort of range, will take a look.

BTW in my non-expert opinion, your front ride height looks a bit low, I believe normally you should aim to have the line between the two pivot points on the bottom wishbone no further than parallel with the ground as a starting point (or outer pivot point lower than inner point). Although obviously having a low centre of gravity has benefits too, there's a trade off to be made.

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Originally posted by AdamR20
To check - is the car all road, road / track or just track? Any anti roll bars? Ta.

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Originally posted by rodgling
...your front ride height looks a bit low, I believe normally you should aim to have the line between the two pivot points on the bottom wishbone no further than parallel with the ground...

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The car does look pretty low, all the SR2s I've seen look a bit 'wrong', but if the suspension is designed to be run at this ride height it's no problem. There is a little more to it than just lower wishbone angle, but that is a good 'starting point' for most double wishbone systems to have them level, especially for road-going cars.

Here's a bit of light reading related to wheel frequencies - www.optimumg.com/docs/Springs&Dampers_Tech_Tip_1.pdf. In short you probably want to be around the 1.7-1.9Hz sort of range from my experience / testing, with slightly higher (10-15%) frequency at the front. This is what I would call 'soft' compared with most kit cars, but it gives good compliance and confidence in the car.

Looking at the pics and taking some angles / lengths from them, plus guesstimating corner weights (using the ones from my CEC Westfield), you will probably need to be around 450-500lbs at the front and - weirdly - 200ish at the rear. It would be useful to get some dimensions and angles from your car (happy to provide details of how / what to measure) to confirm these, but that's what my calculator is saying... The main factor seems to be how much the front shocks are 'laid down'.

To note, you may need to raise the car a touch to prevent it bottoming if you reduce the wheel rates.

The other alternative would be to try something softer on the rear - 250 to 300 would match the front springs you already have, but give higher wheel rates overall. The rear is where you feel most of the 'jarring' given where you sit, so this could be a good port of call. I think I have some 300s or 275s in 7" if they would be of use.

Cheers,
Adam

[Edited on 21/10/15 by AdamR20]

Just as a bit of an update one this... I've finally gotten round to taking some rough measurements. It's hard getting a tape measure to it as there's things in the way so these aren't as accurate as I'd like but they should at least be a good enough ball park.

Can anyone help me work what wheel rates/frequencies I currently have and where I need to go to get it more towards the ideal?

I've not had my car on the scales but I've seen a figure published before for a caged SR2 with fluids at 560kg and I suppose I'm about 80kg. I weighed one front corner unsprung and it was 31kg.

Thanks

Guesstimating 52% rear weight distribution, and 35kg unsprung mass at the rear, with your 600 / 550lb springs the wheel rates come out to 2.12hz front and 3.25hz rear (!).

Changing the rears to 200 and leaving the 600s up front will get you somewhere near. Alternatively, something like 500s up front and 160s at the rear will be a little better overall for road driving.

Personally I'd just change the rears for now so you can appreciate what a difference it will make to the car. It's easier and cheaper, too!

[Edited on 6/2/16 by AdamR20]

Thanks for your response Adam. I have managed to pick up some second-hand 300lb springs and fitted them on the rear. I've only completed a couple of short test drives so far but it's made a big improvement in the ride quality as you might imagine. I've yet to assess what the impact is in cornering ability as that will take longer and I also suspect it may bottom out on some bigger bumps and higher speed. The shock platforms have yet to go back to their original positions as a C spanner is in the post.

Undecided whether I will do anything at the front, may try a 500lb spring but they're somewhat harder to come by second-hand. More testing...

Cheers.