bPChaos

I'm actually curious to see what you find. I have the Godspeed Monomax - they are a 14k linear front / 8k progressive rears, and they do see the track fairly occasionally.

From what I can tell, having run with a lot of 370Z guys, the ideal setup to maximise grip is to run pretty significant front rates (all pending tire, other suspension mods, etc), squared wheels/tires, a stiff front bar (such as the hotchkis), and little to no rear bar.

It seems a little counter intuitive since most of these lead towards understeer, but it works.

That being said, our cars are mildly heavier and have a longer wheelbase, making them inherently less likely to snap oversteer.

slartibartfast

iTrader: (7)

For the track, it's about grip. Softer suspension is usually better in that regard.

The transfer case and front diff definitely add weight but not enough to justify 16k front rates. BC is not the only company to use that rate, though.

And let me tell you, the G will most certainly snap oversteer.

KidJai06

I agree transfer case will add some weight up front and overall weight distribution is slightly different with the X as compared to say the 6MT, RWD, S. We are only talking about adding ≈130lbs overall and ≈56/44 weight distribution vs ≈54/46. That is what leads me to speculate the spring rates are a little high.

Interestingly the 370z weighs in ≈400-500lbs lighter with a similar ≈54/46 weight distribution but the G often shares their spring rates which doesn't seem quite right either.

slartibartfast

iTrader: (7)

Boy howdy, you got that right. I'm going to have to increase the rates of my MeisterR. They're spec'ed for the Z (10/8) and I've smacked the road with the front subframe five times in less than two months. The stock suspension never did that though I could hit the bump stops at a certain intersection. I wanted 12k/10k but the rep thought the weight difference wouldn't be too much for the Z-spec front spring, that grip would be better for track days and I'd appreciate the ride.

I agree with the last two but I refuse to change my driving habits. I'm hitting the road but not the bump stops and that's with the car dropped only an inch.

You AWD guys need to pay extra attention since you're heavier in the front than me. Do not accept anything less than 12k (670 lb/in) up front.

KidJai06

I appreciate that info, it's really helpful to know. My hope is to tune my suspension to my driving habits (at this point mainly spirited weekend driving). My preliminary thoughts for the front was the 12-13k range.

What are your impressions of having 8k in the rear?

slartibartfast

iTrader: (7)

10/8 is comfy, not much stiffer than stock. Damper setting has a whole more impact on ride than the spring rates. If I could set the car to stock height, I don't think the front would hit anything.

bPChaos

Throwing this in here as well, since it applies to spring rates.

https://www.myg37.com/forums/brakes-...on-ratios.html (Thanks slarti)

Has anyone measured the motion ratios of the front? I can't seem to find 370Z motion ratios for the front, only 350Zs.

I think you'll be able to better determine flat-ride characteristics if you can normalize the front spring rates to the rear. I personally feel that 8k rears are a bit soft. The 14ks can be a bit harsh on sudden impacts, but as mine are cheaper dampers, that might be why. Higher spring rates in the front and rear should be fine if they're appropriately valved and suited to the spring.

Not an AWD, but I think the next set of suspension I buy (mine are due for a refresh) will likely be a 14k/15k front and a 10k rear. All anecdotal evidence, however.

slartibartfast

iTrader: (7)

There's more to spec'ing spring rates than motion ratio. Ideally, you decide what wheel frequency you want, then measure the suspension part lengths for motion ratios, sway bar rates, vehicle weight, wheel weights, frequency difference between front and rear, etc., etc. Throw some math at it, et voilà, spring rates.

FatCat sez the stock G RWD sedan has a wheel frequency of 1.1 Hz, assuming 8k rate front That's a rather comfy ride, not much stiffer than a floaty Cadillac. I'm aiming for about 1.5 Hz. Supercars are 2 Hz and stiffer. 800/600 lb/in or 14/10 kg/mm should do the trick, giving 1.5 Hz front and 1.6 Hz in the rear.

KidJai06

That is what I'm shooting for too. I got an email back today from Broadway Static and they are able to put together their Version II coilovers for the X. They're currently running a free Swift upgrade promotion with their Version II's which make things even more enticing. I think for the Z34 platform they actually have 14/10k as their standard. I may ask their thoughts on spring rates for the X and let them know what I'm looking for overall to see what they may recommend.

slartibartfast

iTrader: (7)

I think with 14/10 that the weight difference between the Z and G chassis won't be so much an issue as it is with the softer rates.

I think it's pretty awesome Broadway Static will fool with the x dampers.

Baadnewsburr

iTrader: (3)

Thats great info, any idea what the cost will be when all is said and done?

KidJai06

I replied back to see what their thoughts are for spring rates given weight and weight distribution differences. I also gave them an idea as to what I am trying to achieve with respect to wheel frequencies and overall quality of ride. Im interested in their response.

I'm not 100% but it seems their base price for their Version II is about $2k. They also have a 500S model that has a base price that looks to run about $1399. I actually just came across an application list for the 500S which lists the g37x, so when I have a few more minutes I'll add to the list.

KidJai06

Just as a quick update as I continue to correspond with Broadway Static. They are recommending between 14k/10k or 15k/11k. Im leaning toward the 14k/10k but haven't had a chance to take measurements or run numbers on my own yet to see if thats where I should/want to be. Anecdotally it seems reasonable. I did give them some numbers as far as weight, weight distribution, wheel/tire specs etc. so their recommendation wasn't blind.

The other upside is that with the Version II they are currently running a promotion for free Swift Spring upgrade. I have a few more questions to be answered but I am leaning heavily toward going with their product, plus comes with a 5 yr warranty.

blnewt

iTrader: (13)

All the groundwork that you're doing should end up w/ a great product for your AWD. Should also be a great resource for the platform in general. Look forward to your end result, and reviews. Kudos for doing the homework!

KidJai06

Thanks Brad, I appreciate the kudos. I didnt realize at the outset of this search that it would be so involved but I have learned so much about suspension tuning as a whole. I wish I had taken some physics in high school and college as it probably would have made things a little easier!

I am hopeful (steadily moving toward confident) that the end result will be a nicely tuned suspension for my X. I will certainly be sure to detail and review the outcome.