Spring Rates with BC coilovers.

Jamesk350

Jamesk350

Club Member
Morning All.

I am just about to order some BC coilovers for my 76 280z they offer various spring rates and as its going to mainly used on the Road I'm not sure what spring rates to go for. The car is already polybushed but otherwise the suspension is standard.
BC offer these spring rates
5/5 kg.mm
4/4 kg.mm
4/3 kg.mm
5/6 kg.mm
4/6 kg.mm

I am thinking on the softer side as I've read BC's run quite firm to start with. I have seen a few people mention swift springs work well, does any one know the rates they are compared to the BC options?

Engine wise i will be aiming for 180 wheel once i've rebuilt the engine etc.
 
Wally

Wally

Club Member
I spoke to a few guys who tarmac rally the 240z on a semi regular basis. They recommended the softer 4/4kg springs which is what I've gone for. The 280z is marginally heavier though.
 
Rob Gaskin

Rob Gaskin

Treasurer
Staff member
Site Administrator
I can't recommend a metric rate but 200lb spring rate should be ok. So anybody got a conversion?
 
Albrecht

Albrecht

Well-Known Forum User
Wally said:
I spoke to a few guys who tarmac rally the 240z on a semi regular basis. They recommended the softer 4/4kg springs which is what I've gone for.
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Are they tarmac rallying with BC Racing dampers?

Ideally spring rates need to work in conjunction with damper bump and rebound rates. A spread of 3kg/mm between spring rates on the same damper bump & rebound rates is rather on the wide side. Its a difference of 168lb/in.

Whenever I've enquired, nobody has been able to tell me the damper rates for the BC Racing coilover kits that are supplied for these cars. I'm always curious to know what they might be.
 
Wally

Wally

Club Member
Albrecht said:
Are they tarmac rallying with BC Racing dampers?

Ideally spring rates need to work in conjunction with damper bump and rebound rates. A spread of 3kg/mm between spring rates on the same damper bump & rebound rates is rather on the wide side. Its a difference of 168lb/in.

Whenever I've enquired, nobody has been able to tell me the damper rates for the BC Racing coilover kits that are supplied for these cars. I'm always curious to know what they might be.
Click to expand...
One of the guys was using BC coilovers, yes.
 
Woody928

Woody928

Events Officer
Staff member
Club Member
You'll never get the full info from BC on their coilovers however they do their job very well for the price point.

I've got 4kg/4kg fitted to my 240Z which despite all my TTT rose jointed suspension is still very compliant, honestly I wish I'd gone a little stiffer on the rear if anything. 4kg/5kg is their recommended default option and probably best for all around use (JohnnyMD has that on his ratty car I believe). While I'd probably have gone a little stiffer, it depends on your usage. My car is setup for fast road usage but I also tour in it so its a difficult balance to strike and there's always a trade off to be made.

If my budget was higher I would honestly explore some of the other offerings that I have been discussed on the forum.
 
johnymd

johnymd

Club Member
I’m running 4/5kg on 2 cars. Both feel different in ride quality and most of this is related to the amount of sticktion in the bushes and how much the cars are used. From my experience a full rose jointed zed (my blue car) has a far superior ride quality from one with bushed. This is due to the suspension being able to react to bumps much quicker when to joints have no resistance to movement. The dampers can then do their job properly.

My advice on suspension upgrades and installing poly bushes: with the strut disconnected make sure all control arms will fall under their own weight so have very little resistance. If they don’t fall then you need to look at the bushes and regressed in the correct areas until the arms move freely. With rose joints there is virtually no resistance to movement.

the springs and dampers can only then do their job properly and unrestricted. This was all learnt by doing the poly bushes wrong and wondering why the ride quality was so bad the first time around.
 
Texasroadrunner

Texasroadrunner

Club Member
Long ago I had a '72 Datsun 510. The previous owner had installed Datsun Comp springs and shocks. It would only handle well on perfectly smooth tarmac. It rode very stiff and was a jarring ride. I installed a set of Interpart brand springs and shocks and kept the big sway bars. What a difference that made. I was then able to tackle any mountain road with lots of tight curves and bumps with confidence. That is when I realized that medium rate springs and big sway bars are the way to go on the street. Now I wish I had that 510 back again, thinking about how fun it was.
 
Jamesk350

Jamesk350

Club Member
yellowz said:
What is your opinion on the 4/4 set up?
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My car is only a road car as it will never see a track but it will be driven hard on back roads.
I have the lowered by 30mm all round and the shocks are set half way ie 15 clicks on the wheel.
I have poly bushes all round too, I find the car rides smoother and turns in much quicker. Body roll is well controlled with a small amount of lean when cornering quickly.
Over all I am very happy with the set up I have and grip levels are good but the engine is stock for now.
 
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