Susupension Thread

[Dimman]

Originally Posted by Ryephile

Cool, I'll bite.

1st off, I'd appreciate a baseline measurement disclosure [i.e. stock spring rates, damping curves, stroke numbers, swaybar data, and hopefully some built-in alignment range. Yes, this gives competitors the results of your rather simple measurements, but it more importantly gives the customers a base in which to make reasonably informed decisions [i.e. if the dreaded lowering springs are still a bad decision for those that still want some compression travel].

From there, actually publish some data on your new offerings. Offering "custom" coilovers without being willing to disclose damping curves isn't going to impress me. Offering anti-roll bar drop links with non-teflon lined spherical bearings and not weather sealed at all isn't going to fly, no matter what trendy color they're anodized. Next, hard anodizing and powder coating is your friend. Offer parts that will actually survive and look good doing it.

I see from your webstore that you're in collaboration with KW and AST, that's good. Most people that want a simple drop will appreciate the ST or KW V1 coilovers, however if I were involved I'd lobby to have those dampers built as digressive as the budget allows; KW V1's are typically tuned quite linear, which isn't exactly world class. There will be a couple customers that want more though. Consider talking to Nitron, Ohlins, JRZ, et al to put together a legitimately competent race coilover set with Hoosier's in mind.

Cheers,
Ryan

Can you explain the relationship of the damping curves to spring rates?

I was looking at adapting some QA1 dampers to my Supra, and they provide damping curves and re-valve kits for all their shocks. But the less-expensive non-adjustable ones you would have to rebuild and change shim-stacks instead of nifty clickers. But didn't know what starting point would be suitable. I get that high speed is more impact related and low speed is more weight-transfer, but what do the numbers mean and how do they relate to the spring rate/unsprung weight?

(check that, they used to have the curves on their site, can't seem to find it now...)

Edit: Saved earlier.

[Racecomp Engineering]

Yup there is a balancing act on our end for sure on releasing data to help people make informed decisions and doing other companies R&D for them. But generally we lean towards releasing the info when people ask because the companies that have the knowledge to actually use the information usually could just do it themselves at that point.

We are very close with Ohlins and JRZ....we used to be located in the same building as east coast JRZ USA and learned a lot about shocks from Bryan. Ohlins we've worked with for years. Those two alongside AST generally make up what we do for higher end race applications. We also work with Bilstein and hope to have some good monotube offerings from them on the more affordable side of things that function better than other entry level stuff from Europe, Japan, or China.

We also have a few things up our sleeves for our custom KW options that should be very nice (in the mid-level and higher end of things).

- Andrew

[Ryephile]

I'm sure there are fomulae to predict the correct damping force per spring rate based on motion ratios and sprung/unsprung weights, however I don't have that information, nor am I a damper dyno expert.

Since every car, and even every trim level within the model lineup are slightly different, I'd approach "ideal damping" a bit differently. I'd put suspension stroke linear sensors and accelerometers at the hubs and chassis to measure the "Q" of the bump response. I'd then back it up with seat time at the track and referenced street sections to ascertain low, medium, and high speed bump and rebound response. Of course, you could do it like so many race teams do; get out on the track with timers and see what goes quick and what doesn't. With enough testing time, you can narrow down what settings work best for your car and your driving style.

-->Dimman: With your Supra, you may want to have QA1 dyno your existing dampers, and use a deduction based on new spring rates and personal preference as to what new damper curve they should shoot for.

[BeRZercar]

Originally Posted by Racecomp Engineering

Agreed!

All this is one reason why I can't stand companies that won't release any data, not even spring rates. Then they claim it's some top secret magic special sauce.

*Cough* Epic *Cough*

Originally Posted by Racecomp Engineering

I'm REALLY glad so many of you are on the same page. It honestly gives us a boost that you guys care about function and are intelligent. It's one way we gauge a market and this is all very very encouraging.

- andrew

It's nice to see a dedicated aftermarket company interested in the why and not just the $$$. One of the reasons I have a set of your wagon springs.

If I end up getting one of these, like I"m planning to, I'll be very interested in what RCE brings to the table for this model.


Edit: can a mod change the spelling of suspension in the title of this thread?

[maximumunicorn]

Originally Posted by nrclptcnsmniak

can somebody confirm... I am sure that I read that the suspension is going to be different from the FRS to the BRZ. And if it is how different is it?

Are you referring to this: "BRZ car line manager Todd Hill pointed out that 'the suspension tuning will be different than the Toyota version of the car. I can't say how, but it will be a little bit different.'"

Read more: http://www.motortrend.com/roadtests/...#ixzz1fFxzXLlj

I'm also trying to follow this as closely as possible. It's fine if the Scion drops some amenities to lower the cost, but I'd be wary if they go too cheap on the suspension front.

On the other hand, we've got RCE here to (hopefully) provide us with great aftermarket upgrades for the suspension! Glad to know that there's still some people interested in the performance of the car!

[ap5512]

Originally Posted by Racecomp Engineering

Hello,

We are already thinking about shocks, coilovers, springs, swaybars, bushings, brake ducts, etc. for this car. We've got lots of experience with the Subaru Impreza platform, though this is a different ballgame. Also plenty of experience with Mitsubishi EVO, Porsche, and BMW.

We've got good relationships with Ohlins, Bilstein, AST, KW, Whiteline, JRZ, and also design a few of our own parts. Can't wait to bring high quality parts to this car.

If the standard shocks are made by Showa, that's a pretty good thing. The 2008+ STI switched to Showa from KYB and there was a nice improvement in valving quality to go with it. From the sound of it they've paid more attention to valving than usual. Not as good as Bilsteins but a big step up from the usual OEM japanese stuff. Plenty left on the table for a good well designed spring to upgrade to (if done correctly). We'll have them dyno tested as soon as it's possible. This spring is going to be great! At least 2 of us in the office really want this car.

EDIT: Sachs isn't bad either....they make a wide range of stuff though. Some very very high end stuff and some simple OEM type replacements. I feel pretty confident the standard shocks will be impressive for an OEM (though maybe not Koni Yellow or Bilstein Sport good).

- Andrew

You don't work at that Porsche tuning garage off Route 1 near 175 do you?

[old greg]

Originally Posted by Dimman

Can you explain the relationship of the damping curves to spring rates?

I was looking at adapting some QA1 dampers to my Supra, and they provide damping curves and re-valve kits for all their shocks. But the less-expensive non-adjustable ones you would have to rebuild and change shim-stacks instead of nifty clickers. But didn't know what starting point would be suitable. I get that high speed is more impact related and low speed is more weight-transfer, but what do the numbers mean and how do they relate to the spring rate/unsprung weight?

Ok, so damper curves are kind of like spring rates, in that they aren't very useful all by themselves (eg, is a 200 lb/in spring stiff or soft? depends on what it's holding up). A spring/mass/damper system (your suspension) is governed by a second order ordinary differential equation:

m*(d^2 x)/(dt^2) = C*(dx)/(dt) + kx

Or, in more mundane terms:

m*a = C*v + k*x

It's the three forces in the system, force from the damper + force from the spring = the force acting on the sprung mass. The "ma" comes from Newton's Second Law, and the "kx" comes from Hooke's Law. C is the damping coefficient. It's the slope of the lines in your chart. An important concept to know before I go any further is Critical Damping (represented by Cc). Critical damping is a value of the damping coefficient that will bring the sprung mass back to equilibrium as quickly as possible after a disturbance without over shooting. Values of C that are less than Cc are considered underdamped, and values of C that are greater than Cc are overdamped

Cc = 2*sqrt(k*m)

Damping Ratio (similar in concept to ride frequency),represented by zeta = C/Cc with zeta<1 is underdamped and zeta>1 is overdamped. Zeta=1 is critically damped.

Being critically damped isn't actually a good thing, it means that the damper is actually causing the suspension to bind up a bit. At the very least it will reduce mechanical grip on less than perfect tarmac, and at worst could cause your suspension to pack down on rough roads. The flip side to that coin is the stereotypical beat up old Cadillac Deville with blown out shocks that never stops bouncing. Zeta = 0.7 is a good compromise and a good place to start. Getting a little more indepth, the forces acting against the damper are usually about two times higher in rebound than in bump. So you'll want more like zeta = (2/3*0.7) = 0.47 in bump and (4/3*0.7) = 0.93 in rebound. But then, you need the damping coefficient to be digressive to soak up big bumps. A good place to start is to halve the damping coefficients for high speed bump/rebound starting at ~4-5 inches/second.

So you end up with the ballpark figures of:
High speed bump: C = (1/3*0.7)*Cc = 0.233*Cc
Low speed Bump: C = (2/3*0.7)*Cc = 0.47*Cc
High speed rebound: C = (2/3*0.7)*Cc = 0.47*Cc
Low speed rebound: C = (4/3*0.7)*Cc = 0.93*Cc

Example:
Let's say your car's sprung mass weighs 1800 kgs, and you're a total badass w/ coilovers and kidneys of steel, so your super stiff springs are giving you a ride frequency of 4 Hz.

so: 2*pi*4 (s^-1) = sqrt (k/1800kg) .... k = 181,000 N/m for a wheel rate of 45,000 N/m. Let's assume you've got a 1.1:1 motion ratio, so your imaginary spring rate is 50,000 N/m.

That means that Cc= 2*sqrt(50,000 (N/m)*1800(kg)/4*1.1) = ~10000 (N*s/m)
--You need to include the motion ratio in here.

So you'd want start with roughly:
High speed bump: C = 2300 N*s/m
Low speed Bump: C = 4600 N*s/m
High speed rebound: C = 4600 N*s/m
Low speed rebound: C = 9200 N*s/m

[Ryephile]

Thanks old greg I figured it was too juicy a topic for you to ignore.

[JFC]

Personally from all the footage Ive seen thanks to this site, the 86 wont need alot of attention suspension wise.

The Japanese news/tv showing the factory has an orange 86 driven off the production line and it seems very stiff already.

Also alot of the driving/track footage has the car showing not bad body roll but if you compare the amount of body roll V's the size of the sway bars (tiny) id say there isn't a whole lot you can do with out going all out unstreetable spastic.

[Dimman]

You rock, Old Greg. First spraining my brain with Mr Young's Modulus and now this.

If this was what they used in high-school physics, I might have hung with it longer.

More questions will follow, naturally. (I'm also reading up on frequency as well. 4 Hz is a deliberate hyperbole, right? That would be a high-downforce car, no?)

[old greg]

Originally Posted by Dimman

I'm also reading up on frequency as well. 4 Hz is a deliberate hyperbole, right? That would be a high-downforce car, no?

Yep, hence the kidneys of steel remark.
A car like that would eventually cause organ damage if you used it on the street for any length of time.

[NESW20]

i love learning things. thanks old greg.

[Racecomp Engineering]

Originally Posted by ap5512

You don't work at that Porsche tuning garage off Route 1 near 175 do you?

I think you're referring to TPC. They're not far from us. We used to work out of At Speed Motorsports but have since moved to our own new place in Severn.

Here are two pics of our garage...can't seem to find any more and it's late and I just got back from PRI. We'll do an MTV style cribs video soon.





- Andrew

[Dimman]

Le bump...

Is there a formula for determining a spring's 'fitted' rate? (The one based on the mounting angle, not wheel rate which is the leverage thing.)