Tokico HP - Z is two inches taller

[Carl Beck]

Hi Guys:

During our discussion, we may be introducing some misunderstanding or errors in terms... So this is how I understand it...

Stock Ride Height:

Measured from the garage floor - to the bottom of the rocker panel, at the front and rear jacking points - a stock 240-Z sits about 7 3/4 to 8 inches high (the 73's actually sit a bit higher than the earlier cars do to the headlight height standards and bumper height standards for that year). Bottom of the rocker panel - means just that - NOT to the pinch weld that sticks down farther... (this is from the Factory Service Manuals, not from older springs..).

Installed Height:

"Installed Height" = the height as installed on the car. This is not the compressed or non-compressed length of the spring on the strut before it's installed on the car. So shock travel doesn't effect installed height. Free Length, Spring Rate and the Load placed on the spring does. (that way the shock can travel higher than the installed height - as well as lower).

Coil Springs compress at a "more or less" constant rate - once they are pre-loaded to about 80% of their length. The rate will vary greatly during that first 20% because the distance between the coils and shape of the spring wire at the top or bottom are made to sit in the different types of spring perches. So Free Length and Load are managed to provide the desired Installed Height at any desired spring rates.

Once the spring is installed on the strut, and the car is sitting on the strut - from that point forward the spring rate will be more or less constant.

So only three factors determine "ride height" as far as the springs are concerned(ruling out wheel/tires) ... once the spring is installed on the car. The Installed height of the spring is determined by its Free Length, Spring Rate and Typical Load.

If the Free Length of the Stock and Euro.Spec. Springs were the same to begin with..and the only difference between them was their spring rate - then yes - the stronger spring would result in an increased ride height.

But that isn't the case.. the Stock Front Springs have a Free Length of 14.7 LF and 15.2 RF with a spring rate of 83 in/lb. and an Installed Height of 7.9 inches. Typical load is 604lbs on the Right and 562 lbs on the Left.

The Euro Spec. Stage I Springs have a Free Length of 13 inch, a spring rate of 102 lb/in and an installed height of 7 inch.

So if everything is to spec. - The Euro Spec. Springs "should" lower the front of the car 0.7 inch.

The Stock Rear Springs are 15 inch in Free Length, are rated at 103.6 lb/in and carry a typical load of 635lbs. So their installed height comes out to 8.86 inch.

The Euro Spec. Stage I springs have a Free Length of 14.2 inch and are rated at 112 lb/in.. with a typical load of 635lbs. - - - so their Installed Height is supposed to be 8.86 inch as well.

For a rough aproximation of the installed height - you can take the Free Length and apply the Load to a given Spring Rate... The spring rate isn't as constant at it's free length - but you'll be close to the real world..

Stock Rear:

15 inch free length minus (635lbs divided by a 103.6 lb/in rate) =6.13 inch of compression) = 8.87 inch installed height

Euro Spec Rear:

14.2 inch free length minus (635lbs divided by 112 lb/in rate)= 5.67 inch of compression) = 8.53 inch installed height.

Of couse all this is based somewhat on the Factor Spec.'s being correctly rounded, converted and reported...

FWIW,

Carl B.

[Carl Beck]

..... The Stage 1 springs alone raised the front ride height about 1/2" when compared to the stock springs on the exact same shocks. My car still has non-gas shocks in it, but that is immaterial here, because I am comparing changes from the springs only.

Hi Arne:

Measure the distance at the front end of the rocker panel, from the ground to the bottom of the rocker, and let us know what you find. Then do it again after you install the rear springs..

thanks,

Carl

[Arne]

First, remember that my car currently has under-sized tires on it - 205/60-14.

The rears aren't done yet, probably this weekend. But the front ride height at the rocker are - Before = 7.25", After = 7.75".

I'd never heard that definition of "installed length" before, I've always called that spec "loaded length". And it's hard to measure that, and trying to allow for the step in the spring seats, and such. But the installed length of the Euro spring in front appears to be about 7.5".

All of this could change once the rears are done, the weight distribution might be messed up right now with the mis-match. I'll post the final results when I finish the rears.

[mlc240z]

Carl,

Are those front weight specs for LHD models? No driver/passengers?

40 lb difference......battery weight?

[Carl Beck]

The front and rear weights are from the US Factory Service Manuals... so yes, they are for LHD models. So far, I have not found an explanation for why the 40lb difference, but I would think you are right - the battery.

If you add all the corner weights up they come to 2436lbs.. and that's about what the "curb weight" is. So no driver nor passenger, with oil and 1/2 tank of gas.

Carl B.

[mlc240z]

which by a quick figure on the calculator equals about a 48%-52% f/r weight distribution.

not too shabby at all. i was never sure of the figure.

sorry for hijacking and thanks for the info, Carl

[Arne]

OK, final measurements. All four Euro Stage 1 springs are installed, the shocks are NOT gas-charged, tires are 205/60-14 and the car has been driven 8-10 miles since the installation, so they should be as settled as they will get.

Before - height at the jack points was LF 7.25", RF 7.25", LR 7.25" and RR 7.0" I did not take any installed height measurements before I started, sorry.

After - also at jack points, All four at 8.25". Installed height in the rear is very close to what you noted above, Carl, at about 9". But it's about 8" up front, which seems a bit much compared to your specs listed above - actually close to what the stock US springs should be.

I forgot to measure the free length of the old springs until it was too late for the first three. (The old springs got moved straight to my parts car, whose Eibachs are about to close on eBay.) But I did remember in time to measure the old RR spring - it was 14.25" or .75" shorter than it should have been. I'm willing to bet (based on the before measurements) that the other three were probably all about .5" shorter than spec.

So the end result is that the car sits considerably taller than it did before on it's well-worn original springs. The ride is moderately firm, but not harsh. When I change shocks later, I may cut them a bit (especially the front) to tune it some, but all in all, I'm happy with them.

[Carl Beck]

Hi Arne:

Thank you so much.... that is very good feedback. I'll forward your results to all the members in the original group purchase, as well as to the guys at Courtesy.

Your observations related to the front strut's installed height is most interesting - and it rings a far away and somewhat faint bell.... Somewhere, at some time, I believe I read that the Euro Spec. 240-Z's had front struts with their bottom spring perch set at a different height than the US Spec. cars...

The bottom line then is - your car is sitting about 1/4 inch higher than the US Spec.'s show... and it's actually about 1/2 to 3/4 inch higher in front than expected.... Sounds like you could take about 2 coils off the top in front.. and maybe 1 to 1 1/2 coils in the rear?????

regards.

Carl B.

[Arne]

The bottom line then is - your car is sitting about 1/4 inch higher than the US Spec.'s show... and it's actually about 1/2 to 3/4 inch higher in front than expected.... Sounds like you could take about 2 coils off the top in front.. and maybe 1 to 1 1/2 coils in the rear?????

Probably a bit more than 1/4", Carl, when you consider that the 205/60-14s on my car now are a full inch smaller in overall diameter than the stock sizes. So in reality, my car is probably sitting closer to 3/4" higher than the stock US specs.

All in all, I'm not certain just why this should be the case, considering that everything all checks out the way it should, and I don't have gas pressure struts polluting the data. I do suspect that when I have them out of the car next time (when I replace the struts) that I'll cut them down some. Just how much depends on whether I use gas KYBs or hydraulic Konis. I'll keep you posted.

[beandip]

Arne , so when you do cut the coils , what are you meaning ? The flat top circle of the spring plus how much of the helical beyond that. On my present old springs I have removed the flat circle + 1/4 of the helical . I figure it dropped the front about 1'' . I am setting at 7 1/4 at all four jack points with 195/70 /14s Gary

[Arne]

Gary, I haven't yet calculated how much to cut, partly because I don't yet know what my end goal is. Something like what Carl suggested, I suspect, though. I've cut springs in the past, and have always been able to figure out how much to cut, I've yet to ruin a set of springs. (Insert sound of Arne knocking on wood.) I'll keep you in the loop, you and I will want to discuss this later, before you do your springs (if you decide to use them).

[Arne]

Thought it was time to revisit this topic, as lots has gone on since we last posted. Summary - I have moved the euro springs out of the yellow car, cut them down and installed them in the red car, and later removed them. In the mean time, Gary (beandip) has finalized his installation as well, but I'll let him chime in on his details.

I had installed the euros in the yellow car before I bought the red car. Since the springs made the car's ride height 3/4" too high, and also since I plan on keeping the red car, it seemed to make sense to take them out of the yellow car, cut them down and install them in the red car instead. Which is exactly what I did. At the same time as the springs, I installed NOS Mulholland strut inserts (non-gas).

Ride height results - I cut 1.5 coils from the front, and 1.25 coils from the rear. The ride height was 8 1/8" front, and 8 1/4" rear, or just a touch taller than stock. (Reference - the red car with 60k miles on stock springs sat at 8" front, 7 7/8" rear.) Ideally to give close to stock ride height for non-gas struts I'd probably cut another 1/4 coil off both ends. For KYBs probably 1/2 coil more each end.

As a side note, the euro springs are actually a very poor match to the Mulholland struts. The ride was incredibly firm and bouncy, as if I was riding on the bump-stops. (Which are new, BTW.) My theory is that the euro springs were designed to improve handling by increasing the spring rate as much as possible and still remain compatible with stock strut valving. Similarly, the Mulhollands were designed to improve handling by tightening the shock valving as much as possible and still be useable with stock springs. Put the two together and the ride was WAY TOO firm. So I went back to the stock springs for now, which was an improvement, although still VERY firm. Very good for track or autocross use, maybe a bit too firm for weekend touring. I may yet change them out to KYB in the future.

I have driven in Gary's car with the KYB/euro combination and the ride is pretty good. Firm, but not harsh. I figure the KYBs are about ideal for the cut-down euro springs.