Megan is using a longer spring in the rear now.

 

Slight pushing. I would do two things.

Easiest swap/trial:
Go up to a 8k rear spring. Leaving FSB/RSB as-is. And leave it square (8k/8k). Front tire pressure at 34 and rear at 36. Based on the driver feel you've mentioned - you might find that neutral for you.

More involved:
Or drop the front down 1-2k and up the rear to 8k (7k/8k). Drop FSB to medium or soft and RSB to medium. That should feel slight oversteer. Front tire pressure at 34 and rear at 36.

 

^ I agree with that 100%. Start with 8k/8k, especially with the rear bar you already have and go from there.

- Andrew

 

Definitely flip those rates around. Your NF's are about 2.2 front and only 1.5 rear (Roughly, depends exactly on your current Ft/Rr weight).

Switching them around will bring them in the range of 1.9ft/1.75rr. Thats still a bit soft in the rear, but better than no change and its free .

 

So Ive been looking at that dyno plot all day, and while I'm still a rookie at reading these things, some things stand out to me.

Rebound vs Compression ratio... Its almost 3:1 at the lowest setting and 7:1 at the highest. I thought 2:1 was a good starting point. Are they trying to make it feel softer cruising around? Looking at the "Track" dyno plots, they're almost exactly the same ratio. Going by Works white page the highspeed rebound can handle 1.8-3hz, but compression only 1.2hz.

Knee, or lack there of. So these are going to have pretty much no extra help on turn in or braking to slow weight transfer? I'm guessing drivers will crank the knobs to get better turn in and end up packing down the suspension.

Unknowns- variance between shocks, hysteresis, gain per knob turn, longevity (Im guessing this might be decent with the low compression forces, though if running 2.5-3hz it is relevant).

Am I on track in reading these? Anything Im not seeing, (GTworx - Unlike others, I want your opinion ).

 

Pretty good actually.

Instead of focusing on the "knee", I would say that what I first noticed is that they are not very digressive. This will result in poor ride quality _and_ unpredictability at the limit.

The chart has poorly chosen y-axis limits, so you can't see a lot of detail. It's silly to run the plot of to 1250 lbs when the shock doesn't generate nearly that much force in the available range. It's clear that whoever generated that plot was not intending on re-reading it later. Track cars don't care very much about the high piston speed areas, and many experienced dyno operators will use the available space to illustrate the details in the 0-5 in/sec range.

I would sum it up as: You can't see what you need to and what you see is bad.

I don't sell shocks.

d

 

It seems like not having a digressive curve would hurt mid corner when you hit a bump or heaven forbid, the curb.. Makes sense to me.

I def agree on showing completely the wrong scale. In autocross we spend 98% of the time below 3hz...Give me more info there pls! I cant imagine the guys who designed these know less than I do so that only leads me to believe their is stuff to hide in that range.

 

The shape of the curve doesn't tell you that. You can still have reasonably high forces at low velocity to control body motion or low forces at high velocity to soak up the bumps. The reason people like a digressive curve is that it gives you _both_. You can take the ugliest curve in the world and scale it to work at a single speed.

I should point out that I was talking about inches/sec of the shock piston, not the frequency of the spring. 0 - 5 in/sec is generally the range of body motion, induced by handling inputs (steering, throttle, brake). Anything faster than that is high-frequency, often violent, surface input. This is data I've gotten from several engineering texts as I'm not a vibration expert.

Accepting those values, there's a few things you want

1) linear response in the 0-5 (or 0-3) range. You don't want a "knee" down around 1 in/sec . It's pretty obvious when you think about it. You don't want the shock behavior to suddenly change at turn in. You want it linear.

2) You want to SEE what the shock is doing in this speed range. Many, many dyno plots are bad at this. This is not unique to shocks, automotive engineering, or even engineering in general. Effective presentation of data is hard. What isn't hard is to use all of the ****ing page. A graph where 90% is whitespace is wasted.

3) If anything is custom on your setup, you want to see plots for each and every shock. Consider engines. An assembly line engine can probably get away withou being dyno'd. Would you build a custom engine then skip the dyno test?

I wouldn't make any assumptions about the guys who designed it. Meghan/helix/whoever probably sourced the damper technology from somebody else. There's no reason to think that they do (or even want) to understand how to properly damp a car. They are probably just dealing with the package they have. If you strip away all the associated hardware (spring, mounts, strut bodies, etc.), the actual damper probably only costs $25. If you're only getting $25 per unit, how much effort would YOU put in?

is the original topic still around?

d

 

Oops, I meant In/sec..wrong units, Bad engineer .

Youre probably right about the guys who design it.. Guess you get what you pay for. I just dont understand how people can spend 10k+ on built motors and turbos, but an extra 1000 on "good" coilovers is outrageous .

So, Megan springs...

 

I just finished swapping out the springs for the rear. Now I have 8k/8k. If you have the Street Series, you dont want to go higher than 8k. It can kill the shock so quick and the ride will be rough.

 

What spring and spring length did you go with in the rear?

 

Megan springs. 62 220 008

 

Were your original 6kg springs 200 or 220mm in length?

 

Yes 6kg 200

 

2 more questions:
Are your front springs 180mm in length?
Did the longer rear spring fit ok?