Unsprung weights, motion ratios, and natural frequencies?
 

I tried posting this in the suspension section, but nobody seems to have any answers. I've seen some pretty technical discussions going on over here, so hopefully y'all can help me out.

I apologize if this information is available elsewhere, I honestly couldn't find it.

I was wondering if anybody had estimates for any of these numbers for a g35 coupe (or 350z) in stock form.

1) unsprung weights
2) motion ratios (I've heard 0.76 F and 0.39 R, but nobody was sure)
3) natural frequencies
4) Corner weights (don't have access to a set of scales, sorry)

I'm picking out suspension components and trying to get a really good handle on the natural frequencies of the vehicle. Thanks in advance guys, have a good one.

Corner Weights

2006 350Z Base with 1/2 tank of fuel, not spare, tools, no driver.

LF 889 RF 903
LR 694 RR 730

Left Side 1583 49.2%
Right Side 1634 50.8%
Front 1792 55.7%
Rear 44.3%
Cross (RF/LR) 1598 49.7%

Unsprung Weight

Stock spring, Koni Sport, Enkei RPF1 18 x 10 w/Hankook R214 285/30-10, stock calipers, Hawk DTC70 pads.

Front 135 lbs. (estimated)
Rear 130 lbs. (estimated)

Motion ratios and bump steer curve are already posted in this forum. Just do a search.

I really have searched, and I've come up with conflicting information. Here's what I've found so far for motion ratios.

1) 0.79 F 0.36 R
2) 0.53 F (with 10 degree AC) 0.36 R
3) 0.688 F 0.649 R

The third option sounds more correct considering the stock spring rates, but I've seen the other two options quoted much more frequently. Which is correct?

Thank you for the information on corner weights and unsprung weights. I'll tack on the difference in wheel weights (I'm rolling on the Infiniti OEM 19's) and call it a day.

Be careful with my unsprung weight numbers. They are estimates based on weighing the main components separately over a period of time. I've used the third motion ratio numbers for my calcs and things worked out fine.

How would you use the motion ratios? I can't see an application unless your planning on mod'ing a pickup point.

Perfect, thanks a lot. I was hoping those were the correct ones, the other didn't make much sense when you started doing the math.

To figure out wheel rates with the stock pickup points.

Good to know, but I'm referring to what your end result is. Are you corner balancing the car, trying to get a idea for a new spring package, etc. Just wondering what I'm missing, and could be looking at. :thumbup:

Yeah, I'm just running the numbers for different aftermarket suspension kits. Seeing how the roll stiffness and natural frequencies are affected. There's not a whole lot I could do until I get the springs on my car, but I'm a mechanical engineer and I like running the numbers :). Makes me feel better and I like to make sure everything makes sense before I buy the stuff.

That's a great way double check the company has done their research and not just spec'ed a part because it just looked like a good idea.

+1 as an ME myself too i am forever doomed to run numbers like that. ive been surprised at some of the numbers & conclusions I've come up with from so called performance parts though.

Common sense tells us there is no way the rear motion ratio can be 0.36 guys!

Good find Sash,

Found a calculation chart from third party's site. On SPL's website under the 350z's suspension area (springs to be precise). It has a Excel Calc that shows the ratio around 1.66 (Note SPL listed this as an inverse relationship than what is generally measured, spring to wheel Vs wheel to spring motion).

http://www.splparts.com/main4/parts/...Calculator.xls

Nechro bump!

From my understanding there are two points to calculate from at the rear.

Rear OEM coil ratio is 0.36. The rear shock loaction ratio is 0.59. Is that used when your calculating for a proper rear mounted coilover?

How is the front calculated?

.97 is commonly used in the rear when the spring is mounted on the shock. Front I would have to look, but I thought I'd was like .73 or .68