You are comparing apples to oranges. Your friend's bimmer has a strut-style front suspension that has no camber gain through compression travel thus actually generating more grip by reducing the body roll (higher spring rate due to spring and bar) and due to the softer rear spring-bar combination, will 'tri-cycle' on throttle in some situations.

I'm not familiar with the suspension layout of the SVT, but their are tons of exceptions and compromises that must be made. What works on a FWD Acura TSX in terms of spring rates due to weight distribution and suspension layout won't work on the 350Z (same concept applies when you bring up the Bimmer and SVT).

Every aspect of the suspension affects everything else and you have to look at the system as a whole.

Springs (whether spring or swaybar) dictate the peak amount of roll while the dampers control the rate of the roll (not the amount of roll).


0.02


EDIT - I was referring to sports car endurance racing, not Time Trials.

 

Suspension setup has been one of those things that seems to vary widely with this car. On one end, there's the 600lb(f)/690lb(r) T2 springs and on the other end are the Truechoice shocks/spring package that Unitech Racing helped to develop: 550lb(f)/400lb(r). Both units use the OEM spring locations, but the disparity of these two setups is surprising as steady state balance should differ wildly if sway bar settings are the same. And, if IIRC, both series required the Z to use staggered tire widths. Perhaps both you gents are correct, and that the apple tastes just as good as the orange.

That's one reason why I use 500lb/500lb springs because it sort of falls in between these two setups. However, my OTS Koni Yellows are not equal to the Truechoice or TCKline shocks.

All I know is that I'll be trying out daveh's spare 550# springs to see if it adds any more grip up front.

 

Figuring out the motion ratios and corresponding wheel rates would mean a lot more...


In Grand Am Koni Challenge ST class (sports car endurance racing) their was 2 major teams running Acura TSXs.

One team ran ~600/2,000lb spring rates F/R
the other ran ~1,200/600lb spring rates F/R

With almost completely opposite setups (also taking into consideration swaybar differences which is limited due to the "street stock" nature of the class), both won numerous races.

Was one setup worse than the other? Drivers and crew chiefs have different beliefs and both worked for prolonged periods of time, and both won multiple times on this A-arm front/multi-link rear platform.

Both cars drove differently and went around the corner differently. Was one better than the other? - no. I personally would be biased towards one over the other for the small differences/benefits it provided.



0.02

 

A broad generalization: Momentum suspension setups tend to run stiffer, more balanced spring setups all around. Power setups tend to run softer rear springs.

The 350Z in T2 is down on power compared to most any other car in the class and relies more on corner speed to make fast laps. I'm not up on the engine mods allowed in GA ST but I'm thinking those cars can make 15 to 20% more power then a T2 350Z, but that's just a guess on my part.

I tend to argue that all suspensions should be setup for momentum but my background is racing ITS 240Zs and Spec Racer Fords. I'm biased too

 

well my nismo is very loud.

 

T2 runs same sized tires on 9" (or 9.5"?) wide front and 10" wide rear wheels.

 

Most the N/A "ST" cars are running ballpark-less BHP tuned than a stock 350Z...

I would disagree with a generalization that "momentum cars running stiffer suspension". You have to look at weight of the car, polar moments, rule restrictions, etc... Stiffer springs transfer weight faster while reducing grip slightly.

But I digress, I don't care to bench race

 

Based on the wildly varying spring rates between the two Acura TSX teams, it seems pointless to figure out motion ratios and wheel rates as there is evidently no baseline to work with. These are cars that have the same suspension geometry and similar power, so it makes absolutely no sense that both can be equally quick unless they are both so poorly setup that they are equally slow.

 

Yea, race-winning grand-am ST teams don't know what they are doing...


Better understanding of the platforms and vehicle dynamics would help turn some light bulbs on... Their is more than one way to make an understeering FWD car turn.

 

I have no doubt they know what they are doing. I understand enough to believe that even the smallest changes to suspension adjustments make significant differences. Disparagingly huge differences make no sense unless there are disparagingly huge differences in other aspects of the design (ie, rear 350z oem spring location vs coil-over).

"Better understanding of the platforms and vehicle dynamics would help turn some light bulbs on..."

This is why we have threads like these. What is missing from your post re: spring rates is why the two TSX teams are both doing equally well with those spring rates. Is one team running 2000lbs rear springs w/o a rear sway bar? Or is the rear ride height 1" taller than the other team. You can't expect bulbs to light up without discussing the reasons behind choices. What are YOUR experiences with the Z? What are the things you've tried that worked and didn't work. You recommended calculating motion ratios and wheel rate. Now, what do you recommend I do with them? Light my bulb...

 

Front motion rate is .688
Rear motion rate is .649 (at oem location)

^On my Bilstein revalve, we didn't rely the numbers alone, we preformed a bounce test to add in the oem bushings influence on wheel rate.

What spring rates to run ultimately comes down the math being right AND proving the math with actualy testing. The following give's some insight to a winning Grand-Am teams testing on the 350Z in terms of spring rates.

The following quotes comes from a interview of the owner of Unitech Racing Jackson Stewart, the crew chief for the 350Z Grand-Am team Jeff Wisener and the owner of Perfomance Nissan, Michael Cronin.

SZM: "I noticed a trend that many Z owners are putting coil-over suspension systems on their cars, but you mentioned today on the track that many people are putting too stiff a suspensin and actually making the car handle less effectively. Is that true and can you comment on that again, please?"

Stewart: "Yes, it is absolutely true. Most of the aftermarket suspensions sold for the car are way too stiff. More often then not, for actual track performance, a lot of upgrades are hurting the performance of the car."

Cronin: "The common perception is you don't want a car to sway in turns, squat during acceleration, or dive during bracking, but those are things you need to have the car do to handle correctly."

SMZ: When setting up your race cars, did you use or try any of the common aftermarket suspension kits that are avaliable?"

Stewart: We looked at then in a sense that we wanted to know what was out there, but we also had gone through a range of springs on the car and if we went siffer, we lost performace. We have a range of a few poinds we use in the rear to make it oversteer or understeer. So if we see a spring someone is running on the street that is 50 percent stiffer, they are losing overall performance." {His use of the 50% number is a somewhat ironic number to toss out given that 314lbs upped 50% is 471lbs and yet they went with 525lbs or +67% in the front. Unitech did the R&D for the Truechoice 350Z coilover system and that setup uses 525/425 spring rates}.

Same interview makes mention of the following,....
Future parts for sale:
Moton Club Sport suspension package

To comment on the above, they switched to a Koni 2822 4-way monotube setup

 

IMO, having tested OTS yellows on 448 and 560lbs in the front, your already in need of a revalve. Though if I'm really being honest, your really in need of a better shock choice, I wouldn't pay to revavle them nor would I consider TcKline DA's. Though I get it that you might not be able to make a sigficant investment and maybe that might mean sticking with what you have and attempting to make the most of it.

 

I have an '04 base that I've autocrossed in BSP on and off for a few years. The car is pretty well prepped for BSP (wheels, tires, springs, shocks, sway bars, brake pads, intake, exhaust) and about the only thing I have left to do is install a limited slip diff. I really have to be careful with the go pedal in order to not spin a wheel through the entire course. If I actually use all the power I have on tap coming out of corners I could improve my times considerably. I'm curious which differentials people are using? I've had my eye on the quaife for quite some time, but it seems like the most expensive option. I also drive the car on the street (although not my daily driver) so I'd like to avoid the clutch-type tire chirping while still being able to put the power down. I've also been reading about the 4.08 FD and I'd like to do both mods at once, so I need a diff that will be able to keep both wheels hooked up with all the torque from the 4.08. Ideas/experiences?

 

The diff's that most of the guys use are clutch type. The top choice I would say is the Cusco or Nismo. Alot of people have the Cusco and love it. Oh yeah, I am pretty sure you are not allowed to change the factory gear ratio out in SCCA. You are allowed to change the LSD, just not the gearing.

 

I re-read the 2009 Solo rulebook and you're absolutely right, they never even mention final drive ratios until you get into the prepared classes. So it looks like no 4.08 gears for me! I'm still curious about the differentials though. I checked out that cusco and it's actually $400 MORE than the quaife. In fact, you can order the differential directly from Quaife for $876 (645 GBP)

 

I highly recommend the Quaife LSD. It's quiet, smooth, and ohhh so effective. (also ohh sooo expensive)

I have done many auto-cross events with my quaife and have noticed that having the outside tire get most of the power in a turn helps the car rotate through turns. (kind of like mild 4-wheel steering?)

I have never driven a clutch-type LSD but I can't imagine another LSD being any smoother.

 

You can't actually, they will just direct you to a US dealer

The Quaife is a nice unit - not the ideal choice for road racing due to the nature of helical diffs (both wheels must be on the ground for it to work), but it is a nice unit.

The nicest clutch type diff out there, bar none, is the OS Giken - it is buttery smooth, and the quality of construction is on another level. Check out this months Grassroots Motorsports for a nice write up of a few units compared to one another. It's also among the more expensive units (in the $1500 range). The Cusco RS is a popular choice as it's less expensive than Quaife, though a bit more sensitive to fluid selection (we use Motul in ours, works great and you can't tell it's there unless you are doing 3 point turns. It's significantly smoother than the NISMO/Kaaz type units as it uses springs in the center hub section. Adam uses the Cusco in his car now, and it's worked flawlessly. For the new rear he's building (trying different gears) he's going to use the Quiafe, just to try something different. Both are excellent units.

 

I've run a Quaife, Nismo, and OS Giken. I prefer the OS Giken which is in my car now. Add two bottles of friction modifier.

 

Z1, have you ever had any problems breaking a tire loose on a really tight corner? It seems like the quaife does a great job of keeping the tires hooked up UNLESS you still manage to break one loose, and then it just stops working until you get grip on both wheels again. Is that right?

 

correct, that is the inherent limitation of a gear driven unit - both wheels must be on the ground and have grip. For this reason I (personally) think it makes a better street unit than track unit, though it is a tremendous step forward from a lowly stock viscous