A very common spring rate is 12KF/15K rear.

 

850lb spring is fine.....about 15kg
http://www.dfaulknersprings.com/convert.htm
8kg springs is 448lbs.
hokiruu, thanks for the correction

 

Heck why not run 18K/20K. Be the go kart.

 

AFAIK this is incorrect.
This is what I am using: http://www.onlineconversion.com/foru...1110951659.htm and according to that 660 lb. comes out to almost 12kg/mm.
I said I have 850lb. springs, so that comes out to 15.215kg/mm.
That would be on the upper end of what is desireable for BSP right?

 

you are right, i was incorrect
for some reason i thought i had 660 rear, its 448 for 8kg
http://www.dfaulknersprings.com/convert.htm
850lb spring wouldn't be bad at all

 

One thing to keep in mind is the spring rate added by sway bars in cornering. You could run softer springs and stiffer bars and get the same amount of roll control as someone running stiffer springs and soft bars. . .

My thought is, and I'm FAR from an expert on these issues, is that you want to run as much spring as you need to limit front end dive on braking and rear squat on accel to acceptable levels. Then add bar to take car of any excess body roll in cornering . . .

That *should* make the car more compliant than, say, running 1200# springs all around and no sway bars . . .

Probaby not much of an issue on the smooth Topeka surface, but when you find yourself on surface with a lot more bumps I would think the softer spring/stiffer bar combo would be the way to go? Any thoughts on this??

 

So you ditched the 40/60 center diff after the rear diff upgrade huh?

 

Marshall,

I knew someone would pick up on that, should have known it would be you. I didn't exactly ditch it in favor of the 50/50. The 50/50 w/TRE rear works very well. I still think the 40/60 works better since the car really feels more like RWD and corner exits are amazing. Hopefully it'll make it's way back in for next year. You know after nationals I was thinking how much fun it would be to local to you and Tom. I think it would be a blast competing with you guys on a regular basis.

Anyone else notice that the sole BSP 350Z that was at Nationals has been sold? Some more of you evo guys need to make the trip to nationals next year, we need some participation, seriously.

hokiruu,

Thanks for the compliment on the blog. Nice to know people enjoy reading our stuff and watching the videos. As for your spring rates, I don't know if you are referring to the 850s for front or rear, in combo with what bars, etc. I'd need more details. Honestly though we don't talk too much about that stuff since that is the major component that differentiates most of the BSP evos (spring & bar setups and ride heights). Power is easy, brakes are brakes, tires are all similar, etc. Ask Marshall, I started prying at the nationals awards ceremony and he clammed up on me.

As for spring rate conversions...here's a quick and easy approximation..55 lbs/in is roughly 1kg/mm. So 12kg/mm = 660 lbs/in. The actual is more like 670 lb/in, but it's close enough when trying to compare in a conversation.

 

[QUOTE=kekek;6203481]Marshall,


Anyone else notice that the sole BSP 350Z that was at Nationals has been sold?

QUOTE]

How did it do?

 

In a perfect world you would want different setup (spring/bar) to achieve the desired wheel rate depending on the surface.

On smooth surfaces, higher spring rates with less sway bar would be more apropriate and faster than less spring and more bar.

Bumpier surfaces requires more compliance to keep tires from bouncing over bumps and lower spring rates are needed. Going this route is also a compromise because the more bar you have to run, the less independant your suspension becomes .

In the local ****ty lots in my region 12k front springs, for example, feels great and apropriate but are too soft(unless you run a stiffer bar) for smoother surfaces like Fingerlakes and Devens that would allow 14k and less bar. The right choice IMO, would be to pick the spring rate that is optimal for your most important event surface and compromise on other surfaces by adjusting tire pressure, shock dampening etc.

 

You do know google convert will do this too, right?

try: 12,000 kg/mm to pound/inch

d

 

You guys here are a wealth of knowledge, this thread was very interesting to read, although I did skip a few pages here and there. I was worried my 14K rear springs as suggested by madmax would be too much, but with the whiteline 24mm adjustable rear bar and all of the whiteline bushings in rear, I should be OK for most rough surfaces and almost soft for super smooth ones perhaps!

 

before i'd agree with that statement i'd want to know what your damping ratios were for the different suspension modes. Many cars require swaybars to prevent the car from being overdamped in roll when properly damped in heave. I'd say that for a given roll gradient there is an optimum spring/bar ratio regardless of the surface roughness.

Now depending on what you can get away with on your alignment you may or may not be able to soften your roll gradient for rougher surfaces.

 

hmm...and here i was all ready to cross 40/60 center diff off the list. damn BTW, we have an event this weekend. come on over...it's only 3000 miles.


Hey it's not fair to take advantage of drunk people. A couple more beers and I might have kept on talking. hahaha

 

I can totally see where you are comming from, and if one were to rely on spring rates alone, to reach the desired roll angle you would end up with ridiculously high natural frequencies(much higher than 2.5 HZ).
So, sway bars are needed, in conjunction with the springs to keep roll in check and fine tune the overall balance at an optimal ratio like you proposed.

I made my statement(with the limited knowledge I have from reading on the subject) primarely because, using the stock sway bars rates, the acceptable spring rates seems higher than what most use (in the 16k range in the front if I remember correctly). So theoretically, more springs (up to a point) and less bar is optimal, and would be the way to go.

However, rougher surfaces and the lack of apropriate damping(60 to 65% of of critical damping) on most available shocks for the evo seems to make running the higher optimal spring rate, not the best proposition unless running on silky smooth surfaces.

I'd like your input and others who are konwledgeable on the subject since it's important in order to set the car properly and not very dicussed on the forum, let me hear what you guys think .