Jump to content

Recommended Posts

 Clarkspeed said,"I run a little higher front RC (I hope you measured to the ball joint center!)."


That brings up a good point.  I have had to estimate the position of the ball joint center.  I know that it is offset rearward and inboard from the center of the strut axis.  The inboard offset has the effect of raising the roll center, and the rearward offset provides mechanical trail. I can do the math to establish the relationship between the strut axis and the steering axis if someone has GOOD measurement of the ball joint center position relative to the strut. 




If nobody has these dimensions, I can make the measurements myself.  I have a spare strut and a ball joint that I have cut apart (to extract the ball), but I do not have a spare steering arm to complete the assembly. If someone can lend me one, I will be happy to take the necessary measurements and create a cad model of the front strut and ball joint.  I would also publish the results for everyone to use.

Edited by 74_5.0L_Z
Link to post
Share on other sites
  • Replies 103
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Popular Posts

That would cause other asymmetries with the car's steering.  I'll just have to suffer at the autocross events and find someone between 5'4" and 5'6" and between 115 and 120 ponds to sit in the passeng

Wow, there can be a million opinions here. Making a Z car handle well is not that hard. Making a Z car handle great is hard. Generally speaking, the compression and rebound adjustment is a great tunin

Posted Images

Jon is sending me some steering arms so that I can make the measurements.  However, I think it would be a good idea for at least two people to make independent measurements to help catch mistakes.  I will put together a figure and post it tomorrow to show the exact dimensions that I need. 


I am trying to put together an accurate model of the complete suspension so that I can see the interaction of caster, camber, SAI, pin offset, etc.  There are changes that I want to make, but it is silly to make changes until you know exactly what you have so that you can determine what you want to change, and why.

Link to post
Share on other sites

Not trying to derail this thread but a number of us in the NW were running around 3 hz with the front 5 to 10% higher.  What was odd to me was that as we started to develop setups that were mostly spring and little to no bar we didn't need to change much with grip changes.  When we ran more bar and a lot softer in the springs we'd have to chase the track.  And when it was cold or wet the bars had to come off and often the car wasn't very much fun to drive.  


I got this chart from Eric Purcell a number of years back.  When I first heard about it I thought people were smoking something.  But having tried this it's worked very well for me.


Spring rate based on corner weight.

Sedans and radial DOT tires  -- .5 to .7 

Production and light GT cars -- .8 to 1

Medium weight, 200 to 300 HP cars GT cars -- 1 to 1.3  (FP)

Heavy high HP GT cars -- 1.3 to 2 (XP/EM)


Hope this helps,


Not sure I understand.  Wouldn't motion ratio factor into this? 


Interesting that the spring rates go up when the tire spring rate goes up.

Link to post
Share on other sites

I rotated a ball joint about 50 times.  The center sits about 0.5" above the control arm flat. It makes a difference if you are measuring RC.  I measured everything out last year and put into SusProg3d.  Not sure if my referance points would match what you are looking for.  What are you going to use for motion analysis?

Link to post
Share on other sites

Holy teeth chatter Batman!  There can't be many shocks on the market that can handle that. I may have to do some experiments with my tube frame car in the future to explore this.  It should be fairly rigid, light, and gobs of grip on 12" slicks.


Oddly the ride isn't that bad when the shocks are right.  For a unibody car I would think around 1:1 is about all you would want.  With a stiffer chassis then you could look at the higher numbers.  For shocks I now have Penskes but I keep hearing people claim in autox circles that Koni 8611s will take springs up to a 1000 lbs-in I have no experience to say one way or the other with the Konis.  The ADs I previously ran worked at 800 lbs-in.  The fastest setup I had was digressive front and linear rear.  Unfortunately ground Control never gave my a dyno sheet with the shocks on any of the rebuilds.  They claimed they were set from my measured numbers. 

Link to post
Share on other sites
  • 1 month later...

It's informative to look at a ten year old thread, particularly the spring rates talked about and more particularly using heavier springs at the back. Now in 2014 I know of no S30 in my part of the world that has heavier springs at the back, all are front biased to various degrees.

What have we learned in the last 10 years that caused the thinking to switch to stiffer springs in front, even when there's still a rearward weight bias?


And is the "new thinking" only for track cars with stiffer springs and smaller bars as opposed to the more traditional street setup with relatively softer springs and stiffer bars?

Link to post
Share on other sites
  • 2 weeks later...

My oppinion is over the last 10 years the fast race Z's have gotten much more hp and aero. Back then JohnC stated the high power V8 or otherwise Z couldnt keep up with ITS car. Im somewhere about 7 seconds faster than an ITS car on a 2 min track so if John was right we've made a lot of progress on the faster end of things. Tuning at least for me is centered heavily around getting power to the ground and aero balance.


<---- running modifiled stock front bar, no rear, and am testing 500/425 springs up from 425/375 last year. Yet to see which is faster.

Link to post
Share on other sites

Jon, there is no right just what works. This is what worked for BSR S30 race cars. The fronts were solid rods run through the engine bay frame rail.


We don;t run a rear bar and it handles just fine. I had JR Mitchell who worked for Bob back in the day drive it and the only comment was to go from 1/8 toe in the rear to zero.

Link to post
Share on other sites
  • 2 years later...

Time for another update as I have made a few changes to the car.


I have replaced the front crossmember with a custom built unit and replaced the 260Z rack with a 240Z rack, I have completely rewired the car, I have removed the window regulators and door glass, I have replaced the rear drop legs with TTT units, I have installed a 3 quart Accusump, side view mirrors, and air ducts for the front brakes.


I am also now only running track day events. I think I am done with autocross.



Total Weight: 2617 with 6 gallons of fuel and me in the driver's seat (Front Weight: 1257 , Rear weight 1361), (Left Weight: 1353, Right Weight 1266)


LF = 649 Lb RF = 607 Lb

LR = 703 Lb RR = 659 Lb.

(LF + RR) = (662 + 661)= 1307

(RF + LR) = (708 +623) = 1310



These were my percentages with me in the car:

(LF + RF)/ Total = (649 + 607)/2617 X 100%= 48.0 percent on the front

52.0 % on the rear.

(LF + LR)/ Total = (649 + 703)/2617 X 100% = 51.7 % on left and 48.3% on right.


Here are the final numbers with fuel but no driver:

LF = 593 Lb RF = 605 Lb

LR = 617 Lb RR = 609 Lb.

Total = 2424 Lb


These were my percentages for the car without driver:

(LF + RF)/ Total = (593 + 605)/2424 X 100%= 49.4 percent on the front

50.6 % on the rear.

(LF + LR)/ Total = (593 + 617)/2424 X 100% = 49.9 % on left and 50.1% on right.


The car has gotten a little lighter and has gained a little more rear percentage.


Here are the rest of the current stats on the set-up.

Roll Centers: Front 1.9 inch, Rear 4 inch


Spring Rates: Front 500 lb/in, Rear 400 lb/in.


Sway Bars: Front 20mm with shortened arms, Rear none

Struts: Front, Koni 8610-RACE Rear, KONI 8610-1149




TOE: FRONT 1/8" toe out, REAR 1/8" TOE IN

CASTER: FRONT 6.5 Degrees


TIRES: Avon 240/600-15 radial slicks mounted on 15 x 10 wheels at all four corners


Power: 396 rwtq at 4000 rpm, 386 hp at 5950 rpm (greater than 350 ft-lbs of torque from 3000 rpms to 6000 rpm all measured in 4th gear.


Gear: 3.36 CLSD, G-Force T5 (2.95, 1.94, 1.33, 1.00, 0.8)


I have been very happy with this as a track setup (though I have only done four track days so far). I will be running at Daytona on the infield course April 9th, and I'll be back at Daytona to run the Rolex course may 5th.

Edited by 74_5.0L_Z
Link to post
Share on other sites

1972 240Z vintage track car:


  • L series engine w/triples
  • ZX 5-spd
  • R180 w/Quaife
  • FG fenders, hood and hatch w/lexan, one piece valance, headlight covers, BSR airdam & spoiler
  • qtr windows and door SS frame
  • doors gutted
  • 3-qt accusump
  • 10 lb fire bottle
  • 16 gal fuel cell w/dual Holley pumps, twin filters
  • no rear sway bar
  • BBS 15x7F 15x10R wheels with Hoosiers (225F/275R)
  • driveshaft hoop
  • dual exhaust with trumpets
  • TTT RCAs
  • Stock LCAs
  • Z31 calipers w/vented rotors and drum rears
  • No booster
  • AZ Z oil pan and oil cooler (11 qts total)
  • AL dash with multiple gauges

total weight w/ 8 gals and 175 lb driver = 2300


FL 563  FR  563

RL 584  RR  590


F 49%    R  51%


Cross   50/50


Edited by gnosez
Link to post
Share on other sites

I am slowly putting my car on a diet.  I would love to get down near 2300 lb.


I still have the stock windshield, stock rear hatch, and stock dash. 

I also can lose some more weight on my doors.  I have removed the glass and regulators, but otherwise the doors are intact with the factory inner door skins.

I am also still carrying a passenger seat and harnesses even though I cannot carry passenger on track.


How did you get your left to right balance so close.  I have done almost everything I can think of to move weight to the right and I am still left side heavy. I am carrying a passenger seat and harnesses, my battery is behind the passenger seat, the Accusump is offset to the right behind the passenger seat, my radiator catch can and alternator are on the right, my fuel cell is shifted 4 inches to the right. I have also shifted the driver's seat about 3/4" to the right, and I am still have 51.7% left side weight.  I am not terribly heavy (193 lbs with helmet on).

Link to post
Share on other sites

We made a mistake in positioning the fuel cell and moving the battery to the back. The fire bottle and Accusump got mounted in the passenger foot well which made a good off-set. We tossed the stock pedal assembly, booster and MC (20+ lbs there gone) and have a fuel filter, expansion tank, oil filter and oil cooler hoses mounted on the right side of the engine along with a 3 lb alternator.


I'm 5' 10" on a good day so the seat is up close to the steering wheel and the steering column and seat were moved closer to the tunnel then in a stock set-up.


The hard part then becomes the process of counter balancing with Step 1 the most difficult - getting everything level. Measure, turn the coil-over, roll the car, record the weights, repeat, repeat, repeat....





Link to post
Share on other sites

When corner balancing a car by adjusting the coil-over spring perches, you cannot change the left to right or front to rear weight distribution.  You can only change the diagonals.


During this round of corner balancing my car it took me three tries to get the car where I wanted it.


Here is the procedure and results:


1.  Disconnect sway bars.

2.  Set tire pressures.

3.  Verify steering is straight ahead.

4.  Measure ride height at four corners (I measure at LCA attach points)

5.  Settle car and roll onto scales.  Take measurements of car with no driver.

6.  Get in car and take measurements with driver in car.


Here are the results from my first weigh before adjustments:


No Driver:


LF  616     RF   581

LR  595     RR  632


With Driver:


LF  675     RF  581

LR  679     RR  682


The diagonals were a mess.


No Driver 

      (LF + RR)/Total  = (616+632)/2424 = 51.4%

      (LR+ RF)/Total = 48.6%


With Driver

      (LF + RR)/Total = (675 + 682) / 2617 = 51.9%

      (LR + RF)/Total = 48.1%


I needed to take weight off the (LF + RR) diagonal and give it to the (LR + RF) diagonal.  There are two way to do this.  First, I can raise spring collars on the light diagonal, or second I can lower spring collars on the heavy diagonal.  I opted for little of both.


For the first adjustment,  I lowered the RR spring collar 3/4 turn.


I then resettled the car and rolled it back onto the scales to measure the changes.


No Driver:

LF  601     RF  595

LR  608     RR  618


Diagonal Percentages: (LF + RR)/Total  = (601+618)/2424 = 50.3%

      (LR+ RF)/Total = 49.7%


With Driver:

LF  662     RF  593

LR  689     RR  672


Diagonal Percentages: (LF + RR)/Total  = (662+672)/2617 = 51.0%
      (LR+ RF)/Total = 49.0%


The diagonal got much better but still needed work.  I needed to take more weight off the (LF + RR) diagonal and give it to the (LR + RF) diagonal.  


For the second adjustment,  I raised the RF spring collar 1/2 turn. Again, I resettled the car and rolled it back onto the scales to measure the changes.


No Driver:
LF  593     RF  605
LR  617     RR  610


Diagonal Percentages: (LF + RR)/Total  = (593+610)/2424 = 49.6%
      (LR+ RF)/Total = 50.4%

With Driver:
LF  653     RF  604
LR  700     RR  662


Diagonal Percentages: (LF + RR)/Total  = (653+662)/2617 = 50.2%
      (LR+ RF)/Total = 49.8%


I was happy with the diagonals at this point.


One thing that should be noted is that the left to right and front to rear percentages did not change during this process.  When I started, the percentages were as follows:


Without Driver :

      Front percentage:  (LF + RF)/Total = (616+581)/2424 = 49.4 percent

      Left Side percentage:  (LF + LR)/ Total = (616 + 595)/2424 = 49.96 percent



With Driver :
      Front percentage:  (LF + RF)/Total = (675+581)/2617 = 48.1 percent
      Left Side percentage:  (LF + LR)/ Total = (679 + 682)/2617 = 51.7 percent


These percentages are the same as my final values as expected.


The only ways to change the left to right and front to rear percentage is to move things around the car or to remove/add weight.

Edited by 74_5.0L_Z
Link to post
Share on other sites



I highly recommend the NASA HPDE to TT program. You will eventually get bored just going fast without lap times IME. Funny too I've landed on a setup that is really close to yours with slightly less power and slightly heavier both of which I'm procrastinating spending the $$$$$ to fix. Also same here can't get enough rear or right side weight with the V8.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...