Spring Rates...Little bit of advice needed.

[TomZupra]

Ian,
Not sure what year 260z you have but the '74 FSM says the spring constant is the same front and rear (1.85 mm/kg or 104 lb/in) originally. Conventionally (from speaking to some mechanically minded people) you would run a higher spring rate at the front, but its very much chassis dependent.

I am looking at spring rates myself for a GAZ setup on my 260, most people seem to be running 250 front 200 rears or a balanced setup for track use, I'll let you know if I find out anything interesting

 

[Ian]

I was thinking about running the harder springs up front as the front end is going to be heavier than the rear and if you look at cars that are similar they are usually set up that way.


Need to work out the implications of using the longer springs on the front.

 

[johnymd]

I think I'm running 350 front, 275 rear and the rear could maybe do with going up a little. With the damping turned down for the road it's a pretty comfy ride and doesn't feel hard at all.

 

[TomZupra]

With your strut braces and cage you have a stiff chassis johny, I just wonder what strain running rates that high with small profile tyres might put on a stock frame.

 

[Ian]

I think I'm running 350 front, 275 rear and the rear could maybe do with going up a little. With the damping turned down for the road it's a pretty comfy ride and doesn't feel hard at all.

With my spring rates being softer than that I hope mines decent on the road too.

I guess you would just like to stiffen the rear but not touch the front?

With your strut braces and cage you have a stiff chassis johny, I just wonder what strain running rates that high with small profile tyres might put on a stock frame.

I'm guessing it puts a fair bit of stress on the frame, although my spring rates aren't that high. Not taking any chances though which is why the front end will have stictch welded seams and the rear will have a half cage.

 

[racer]

I can confirm that Johns car does ride very well on the road. Good dampers can control higher spring rates.

Tom I'm not sure what diameter springs you have? Remember spring rates for 2qtr coilovers will always be higher.

As much bracing as possible is always a good idea. I could feel the extra flex in the race car if I took off the front strut brace. The week point on a zed is the ARB mounts on the front chassis rails, very thin metal.

 

[Ian]

Good point about the anti roll bar mounts. I'll need to look at reinforcing that area, I guess if you were to just weld on some extra plate around that area that should do the job?

 

[racer]

Yes that will do the trick. Although some people do plate top and bottom of the rail and bolt all the way through for extra strength.
My car just has the bottom plated and did 8 seasons with no issues but, you will be running bigger rubber than I did and allot more Hp when he Rb comes.
Depends on how much you will be on the track?

 

[Ian]

Won't get much chance to do track work, probably only going to be 2 or so sessions a year, especially as my Civic is so well setup for track aswell, means I dont have to abuse the Z too much.

 

[johnymd]

I wish I had put some thought into the arb mounting as I've had to repair this area twice already.

I should look at a full Weldin cage on mine as it does get a lot of hard use. It's holding together pretty well considering but I do have to keep an eye on things. The shell tends to groan a lot when used hard. Poor old girl!

 

[andrew muir]

It all sounds a bit hard (stiff) to my mind will need an awful lot of damping to control a spring that stiff, it will also depend on how fast you drive, wheather the spring and damper rates are appropriate!
standard cars are around 150-160, mine are now 185 and 195, and they seem to be nice on the bumpy roads we have up here! If I had nice smooth roads I would put them up to 200 and 215, and on track a little bit more.
I think most people go too hard I have seen 240z on bumpy roads handle like s**t because the tyres barely touch the tarmac anymore.
By the way I drive pretty hard on occasion and when I had my fast roadbike not many ever beat me over the "beef-tub" 107mph average over 17miles. some tried but sadly not able to tell the tale, I always seemed to have my setup softer than everyone elses.

Go conservative your car and spine will thank you for it.