I still have no idea what you're talking about here. In the OEM or Nismo setup, the height is NOT adjustable. On the Teins, you have the rear spring perch that is adjustable, but the shock body is adjustable as well. Therefore if you lowered the spring perch setting, and then lower the shock body, you effectively has the same "delta" effect, and therefore the same dampening.

In your setup, you're going to limit your wheel / tire options in the rear since your rear coilover is going to take up more room.

 

Agreed, although the dampers play just as vital a role as the spring rates.

From "Suspension 101"

Solutions

 

we'll see how it is after installed.

 

I know I'm being a jackass here, but I just have a problem with you advertising two different lines, one for the street, and one for "racing". For the street, most drivers won't notice a difference in how you stagger the spring rate bias, but how can you market it for "racing" if it hasn't thoroughly been tested and proven on the track? I can assure you right now after having driven the 350Z with equal spring rates fore and aft that the car turns in / rotates MUCH better with the higher spring rate in the rear.

Given, having a 50mm piston is impressive, but there are many other factors that go into the development of a damper system and it being tuned properly for a specific spring rate.

 

John - Are the JIC's a coilover in the rear? I'm assuming they are, but still just wanted to double check...

 

well, D2 racing motors is very well know in F1 and DTM races. I'm sure they know what they're doing. We are just their U.S distributor.

 

Please keep us up to date on these.

 

No, it's a design similar to what you see on BMWs, with the spring being adjunct from the damper.

For some reason, I thought you all were developing this suspension since I was not familiar with D2. I'm still pessimistic as to its performance, but as you said, I guess we'll see once you install them.

 

The reason I ask about the spring/damper relationship is that you are comparing two different setups....apples to oranges. In order to compare, you must know the wheel rates of each. The coilover design requires less spring rate in order to achieve the same wheel rate as the other design. This is why the spring rates may seem to be way off when you guys are comparing to rates used by other manufacturers. I have not calculated the wheel rates to compare, but I would guess this D2 setup will be much more neutral than some might expect....


BTW, I can explain this in detail if anybody needs a better understanding of what I'm referring to here.

 

Perhaps that's the case, but I would only imagine that would occur if the rear of the Z was that much lighter than the front. 45-48% of the Z's static weight sits over the rear wheels, and when in motion, there is more on the rear wheels.

But by all means, I'd really like to hear the explanation of the wheel rates.

 

John, I'll try to post something later, including actual numbers as an example. It will probably be later tonight though. What are your spring rates? That would be a good comparison since yours is well balanced. I'll have to get some rough measurements off my car's suspension too.

 

Total weight: 3130 (spare tire removed, 1/4 tank of fuel)

weight front / rear: 1690lb / 1440lb (54% / 46% respectively)

Spring rates front / rear: 560lb/in / 670lb/in

Car is corner-weighted and pretty much within 1% diagonal balance.

 

Ok, this is quick and dirty but here goes....

The first thing you need to have is relevant measurements off the suspension. I took the following very rough measurements off my car (not very accurate, but will serve the purpose here):

A. Distance from control arm inner pivot to spring centerline for non-coilover= 10.5"

B. Distance from control arm inner pivot to spring centerline for coilover= 14.5"

C. Distance from control arm inner pivot to outer pivot= 17.75"

D. Angle of coilover= did not measure
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Now, we need the motion ratio for each rear configuration. The formula for this is:

(Distance from control arm inner pivot to spring centerline/Distance from control arm inner pivot to outer pivot)^2

The motion ratio for non-coilover is (A/C)^2, which is 0.350. For the coilover motion ratio we take (B/C)^2, which is .667.

The motion ratio is used as a multiplier for calculating the wheel rate. Technically, the angle of the coilover should also be figured into this, but for the purpose of this discussion I'm ignoring it. So, the wheel rate is just the spring rate multiplied by the motion ratio.

We also need to convert the D2 rates from kg/mm to lbs/in (x 56)...
street: 7 x 56 = 393 lbs/in
race: 11 x 56 = 616 lbs/in
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Rear wheel rate examples:

D2 street(coilover) = 392 x 0.667 = 261.5 lbs/in
D2 race(coilover) = 616 x 0.667 = 410.9 lbs/in
John's JIC(non coilover) = 670 x .350 = 234.5 lbs/in

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So, looking at the few examples above, the results may be surprising. The coilover wheel rates will actually end up a little bit lower due to the angle of the coilover, but I didn't want to get too complicated with this. Keeping that in mind, you can directly compare the D2 street setup to say....John's JIC setup. Both run the same spring rate in front, but the configuration is the same up there. In the rear, compare the wheel rates... 261.5 for the D2 versus 234.5 for John's. It looks like the D2 will be a little more tail happy if anything (not picking on you John, just using your's as an example).

That was quick and dirty, and not very accurate as far as the measurements are concerned. I was going to draw a picture and post it, but I searched and found a nice page that shows all this and explains it :
linky

 

Interesting.

From where on the coilover spring centerline did you measure the distance to the control arm inner pivot point? Or were you simply measuring to shock body centerline?

 

Great link, thanks for posting it! Does anyone have a pic of the JIC rear setup so I can compare them?

Looks like the D2 Coiler Street setup is about as stiff as the JICs. Wonder why they are so much cheaper?

X

 

D2 racing sports does not come with Pillow Ball Upper Mount. I don't know if this applys for 350Z. Cuz some people use it to adjust the camber setting. In this case cannot do that on 350Z. One good thing about D2's coilover is that you can add the extended damper oil tank as an option. This is just like Apexi N1 coilover. D2 is a great deal compare with all other brand. This coilover has been tested on race tracks. No oil leak or any problems with it. But we want to make sure it is good. So we'll out them on our redline track and see how it is. For those poeple in the TRI state area. Welcome to test the coilover on our Z.

 

I measured from the lower pivot point (mount) for the shock. Its really the centerline of the shock body and the coilover spring. You have to take into account the mounting angle to accurately do the calculation though.

Actually, another thing I didn't really take into account is the fact that the stock coil spring cup is on the lower control arm, but the shock/coilover mount to the upper control arm. This changes things as well, so the numbers I previously posted really aren't true at all. I'll try to get better measurements and do the real calculations later.

 

The plot thickens... LOL

 

Very interesting discussion!

Somewhat off topic......does anyone have a clue as to what our front split lower a-arm(or does "two piece lower upright control arms" more correctly describe it?) with 2 pivots does? I'm guessing maybe to alter the camber gain curve?

 

Ok, I got off work early so I went to the shop and pulled a rear wheel off. First thing...I didn't even realize how the shock was mounted before. I had never really looked, but mistakenly assumed it was on the upper control arm. Turns out it's mounted to the hub carrier directly, so the shock/coilover actually has a motion ratio of 1. Next, I was able to get better measurements of the lower control arm. These are the best I could get without taking the control arm off. Finally, I measured the angle of the shock. So here we go:

Distance from control arm inner pivot to spring centerline for non-coilover= 10.5"

Distance from control arm inner pivot to outer pivot= 17.5"

Angle of coilover= 6 degrees

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So the motion ratio for the non-coilover setup is:

(10.5/17.5)^2 = 0.360

And, the motion ratio for the coilver setup is:

1

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We also need to account for the angle. Angle correction factor is the cosine of the angle.

For non-coilover, the angle is 0. Angle correction is 1.

For coilover, the angle is 6. So the angle correction factor is cos(6) = 0.9945

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To get the wheel rate, use (motion ratio)x(spring rate)x(angle correction).

Examples:

D2 street(coilover) = 1 x 392 x 0.9945= 389.8 lbs/in
D2 race(coilover) = 1 x 616 x 0.9945 = 612.6 lbs/in
John's JIC(non coilover) = 0.360 x 670 x 1 = 241.2 lbs/in

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So there are the numbers. It looks like the D2 is really quite stiff in the rear. I know the numbers are surprising, but this is how the math works out. I say the D2 setups will allow the car to rotate very well, maybe too well for some drivers.