Spring Rates...Little bit of advice needed.

IbanezDan51

IbanezDan51

Well-Known Forum User
Hi everyone,

I finally sent my struts off to GAZ this week to have the coilover treatment!

Question is...what spring rates?

My car will have a V8 in the front that is set quite far to the bulkhead. Fiberglass wings, doors, bonnet, hatch etc... Fully caged (front to back) and seam welded where necessary.

I intend to use it for the occasional drag race/track day with lots of fast road use (sensible fast road use!).

I was thinking of 330lb front and 280lb rear but I might be able to get away with higher? Or does the 240Z handle better with a stiffer rear?

Any help appreciated!
Cheers,
Dan
 
Alphabettispaghetti

Alphabettispaghetti

Club Member
how much does the engine weight compared to the standard L6? Whats the standard spring rates? For fast road I don't think you'd want too stiff as it won't grip as well due to lack of compliance, also factor in what size ARB's you're running?

Gaz should help you get in the right ball park. When I get mine done i'm only going 12% up on standard as a start point with better ARB's front and rear. Oh and old man rubber bushes too ;)
 
IbanezDan51

IbanezDan51

Well-Known Forum User
Thanks for the input Franky,

I would assume there to be little (maybe even less) weight over the front end than a standard car.

As for standard rates...I have no idea? I think around 180/160?

I will be running upgraded ARB's when funds allow...which will be before the car is on the road anyway Gaz did make a suggestion but I dont think he quite new the extent of my modifications.

I'm not particularly bothered about a comfortable ride but I do want it to grip well...
 
Alphabettispaghetti

Alphabettispaghetti

Club Member
What did they suggest? You need enough 'spring' that you don't have to use dampening to stop the soft feeling, this will allow the dampers to do their job.

Its a total package so work out what you're going to have when your finished then go for that. I'm not bothered about having a limo ride but on the road you'll get more grip with compliance. Also think about what size sidewalls your tyres will have as that'll affect everything too.
 
IbanezDan51

IbanezDan51

Well-Known Forum User
Sounds like a good base to start from Rob.

I've enquired again to GAZ telling them my set up. The struts will be ready assembled with a choice of springs so I won't need them off of you Rob but thanks!

I know keeping soft springs on the rear is desirable for drag racing...but its completely useless to do that on a track car so something 50/50 will be good.
 
Alphabettispaghetti

Alphabettispaghetti

Club Member
IbanezDan51 said:
Sounds like a good base to start from Rob.

I've enquired again to GAZ telling them my set up. The struts will be ready assembled with a choice of springs so I won't need them off of you Rob but thanks!

I know keeping soft springs on the rear is desirable for drag racing...but its completely useless to do that on a track car so something 50/50 will be good.
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Let us know how you get on with GAZ, I'm pretty sure that's what i'm going for, seems to be the best 'bang for buck'.:thumbs:
 
johnymd

johnymd

Club Member
I can't remember the rates they supplied on mine but if you ask them, they may have the details. If you also mention how mine handles they may tweak the rates.

Mine has virtually unlimited front end grip with no sign of understear. When pushed up to and past the limits on the track the back end starts to slide with no loss of front end. This is not just under power. I had planned to talk to them about adjusting the rear springs to improve this but didn't get round to it.

The rear does deal a little soft so I may increase the rear rates before Spa.
 
Ian

Ian

Club Member
I run 7kg/mm front and 5kg/mm rear in the Civic (390lb/in and 280lb/in unless I got my maths wrong) The ride is not too stiff for the road and it rides the bumps well and this is in a lighter car than the datsun.

I'm going to try 6kg/mm front and 5kg/mm rear springs to start with in my 260Z, I really can't see them being too stiff.
 
Albrecht

Albrecht

Well-Known Forum User
Ian said:
I run 7kg/mm front and 5kg/mm rear in the Civic (390lb/in and 280lb/in unless I got my maths wrong) The ride is not too stiff for the road and it rides the bumps well and this is in a lighter car than the datsun.
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You can't transpose the values for the Civic straight onto the S30-series Z. They have completely different suspension layouts. It's meaningless.

Ian said:
I'm going to try 6kg/mm front and 5kg/mm rear springs to start with in my 260Z, I really can't see them being too stiff.
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I can. With a stock ( nearly 40 year old ) body, those spring rates are high enough to make the body of the car act as the fifth spring. There will be certain situations where the body becomes the softest spring in the whole setup, and a few too many of these deflections will eventually take a toll on the monocoque....

6kg/mm is 336lb/in, and 5kg/mm is 280lb/in. That's really too stiff for a sensible road car setup. Pretty much everyone seems to go too stiff on spring rates these days. You'd be better off with a lower spring rate, some fancy damping and some beefier anti roll bars.
 
B

bigblock

Well-Known Forum User
What engine(iron heads or ally) box and diff have you ended up with.Are these items installed and any pics/measurements of engine setback.
 
Ian

Ian

Club Member
Albrecht said:
I can. With a stock ( nearly 40 year old ) body, those spring rates are high enough to make the body of the car act as the fifth spring. There will be certain situations where the body becomes the softest spring in the whole setup, and a few too many of these deflections will eventually take a toll on the monocoque....
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My car is a late 260Z so its only around 33 years old which will help. I can't see those spring rates being a problem, The car will be seam welded in the vital areas, it will have stiffer chassis rails front to back which will also be connected to the rear subframe, it has front and rear strut braces and I'll also be considering a half cage setup.

You are probably right for an older 240Z with a less stiff body from the factory and higher milage then those could well be too stiff. And good point about not being able to compare spring rates beetween my Civic with its double wishbone setup and my Datsun with the Mcpherson Strut setup.





6kg/mm is 336lb/in, and 5kg/mm is 280lb/in. That's really too stiff for a sensible road car setup. Pretty much everyone seems to go too stiff on spring rates these days. You'd be better off with a lower spring rate, some fancy damping and some beefier anti roll bars
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You might be correct, but I'm going to try it and if its not right I'll change it.

Shouldn't the damping be matched to the spring rate? Therefore you can have a fancy damper setup but its always going to have to be related to what spring rate you are running.


I disagree about those being too stiff for a road car (depends on the car though) but my civic has a pretty comfy ride and doesn't skip over bumps and it handles very nicely on track so I don't see those spring rates being bad for the road.
 
Albrecht

Albrecht

Well-Known Forum User
Ian said:
Shouldn't the damping be matched to the spring rate? Therefore you can have a fancy damper setup but its always going to have to be related to what spring rate you are running.
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Correct, but most of the bump and rebound data you will find for the S30-series Z usually relates to 'race' setups. A lower spring rate with correctly-matched bump and rebound rates in the dampers is going to be better for an all-round car that gets used on the road.

Ian said:
I disagree about those being too stiff for a road car (depends on the car though) but my civic has a pretty comfy ride and doesn't skip over bumps and it handles very nicely on track so I don't see those spring rates being bad for the road.
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Again, the Civic spring rates DO NOT transfer like-for-like to the Civic. What's the wheel rate on the Civic, and what's the motion ratio on your Z?
 
racer

racer

Club Member
My HSCC Road legal race car used to run 400lb Front and 350lb Rear springs.
That's about the limit for a Bolt in caged car.
John I believe yours are 300lb front and 250 Rear, witch I think we decided was just a tad soft at Spa?
Dan
If your car is fully caged and for road and track use, I think your planned 330/280 set up sounds like a sensible starting point Imo. I'm sure Gaz will advise you but they may try and tempt you to go much harder on the front.
 
Alphabettispaghetti

Alphabettispaghetti

Club Member
Glad I'm not the only one going for a softer but updated spring with dampening ti suit and better arbs. if most of the use is on the road maybe a 'fast road' setup would be the way forward? Or get two sets of springs with a dampening range to suit both( well a compromise), springs are quite cheap.
 
MikeB

MikeB

Well-Known Forum User
I have put 225lbs/inch coil overs on my 240Z ,front & rear. It had been fitted with 140 fronts and 160 rear, but I suspected that these were not matched to the dampers and we producing ab bumpy ride due to the suspension not rebounding quick enough. I did a few calcs based on advice in Allan Stanifoth's Race & Rally Car Source Book, which is a bit of a bible for us hillclimbers. Upping to the 225s has produced a better ride quality, and the car does not roll excessively, even with the std roll bars, no understeer either.

Before you ask, I'm not sure which dampers are fitted to the coil over conversion, as I've yet to get the special spanner made to remove the 4 slot alloy nut on the top of each strut. I suspect it's an old Leda system, so something modern might improve the ride further, to be compliant with the bumpy Ulster roads and to be sure that they match the spring rate.

Cheers

Mike
 
Ian

Ian

Club Member
My coilovers are 4kg/mm and 5kg/mm, I was planning to fit the 4's on the rear and the 5's on the front but it seems they are designed to be fitted the otherway round as the spring on the 5's is longer.


I think I could still fit them either way as I think its only 2cm longer but I'd like to know which way other people think they would be best fitted:



Would you have:

5kg front/4kg rear

or

4kg front/ 5kg rear?
 
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