BRZ Shocks dynoplot!

[OrbitalEllipses]

Courtesy of your boys at RaceComp Engineering!

Facebook discussion link.

[WingsofWar]

hmm surprisingly softer than i initially thought based on reviews. Im liking that low speed section for average driving.

[Dimman]

I am weak as a kitten interpreting these...

All I (think I) know is low speed is for weight transfer/handling and high speed is for bumps/impacts but how to they interact with spring/wheel rates?

Ideally we want highish low speed and low high speed (basically opposite) but that's impossible so they try for digressive which is low speed increases quickly then slows the increase at higher speeds.

But why?

[WingsofWar]

Originally Posted by Dimman

I am weak as a kitten interpreting these...

All I (think I) know is low speed is for weight transfer/handling and high speed is for bumps/impacts but how to they interact with spring/wheel rates?

Ideally we want highish low speed and low high speed (basically opposite) but that's impossible so they try for digressive which is low speed increases quickly then slows the increase at higher speeds.

But why?

well for performance ..we want the rebound force high at low speeds (braking, accelerating, turning) which levels out at the transition from low to high speed (bumps, dips, road surface imperfections). To do that we have to shorten the stroke of the damper, so the compression of the stroke has to be closer to 0. Which makes the shocks hard.

What Toyota and Subaru have done by taking the load off the tires and suspension because of the low CoG. We can have a soft shock profile without having the vehicle feel like its floating. While still retaining a decent performance level stiffness.

So from the graph, we have a very small peak rebound rate (70ftlb Front & 140ftlb Rear. With a peak bump force between 300-350ftlb front and rear.

What im surprised at is that the rebound force is very tamed for being a sports car, while the compression is very long for that kind of profile. I was expecting to see a tighter compression profile even with that kind of softness from the reviews. But everything is just soft..Im having a hard time thinking what a stiffer suspension setup is going to feel like in this car.

[Bristecom]

Interesting... the BRZ has the same spring rates front and rear. Is that normal for a RWD car?

[WingsofWar]

Originally Posted by Bristecom

Interesting... the BRZ has the same spring rates front and rear. Is that normal for a RWD car?

hmmm? i don't recall ever having seen the factory spring rates. but springs are typically stiffer in the rear than the front in a FR vehicle.

Having equal spring rates all around means the the manufacturer thinks that the chassis is very balanced and front and rear weight distribution is small. Meaning the spring rates can be set mildly aggressive without worrying about sacrificing to much comfort.

[Bristecom]

Originally Posted by WingsofWar

hmmm? i don't recall ever having seen the factory spring rates. but springs are typically stiffer in the rear than the front in a FR vehicle.

Having equal spring rates all around means the the manufacturer thinks that the chassis is very balanced and front and rear weight distribution is small. Meaning the spring rates can be set mildly aggressive without worrying about sacrificing to much comfort.

Check the Facebook page. Racecomp Engineering says, "Stock spring rates are 185 lbs/in front and rear."

[OrbitalEllipses]

It was known that Subaru opted for matched spring rates vs soft fronts/stiffer rears of the Toyota counterpart. Stiffer fronts (thus matched front/rear) foster the tendency for "understeer" and mid-corner stability that Subaru was looking for. Increasing rear spring rate creates instability or oversteer. That's the extent of my knowledge on the topic.

[Draco-REX]

Interesting. It kind of puts some light on those aftermarket companies that have prings/coilovers already with MUCH stronger front rates than rear. Seems like they didn't do their homework and just went with what they usually do with big front-heavy cars.

It also reinforces my high opinion of RCE that they immediately saw that the rates were equal or close to it and took that into account for their product rather than just quickly bringing something "close enough" to market to make a quick buck.

[Dimman]

Originally Posted by Bristecom

Check the Facebook page. Racecomp Engineering says, "Stock spring rates are 185 lbs/in front and rear."

With suspension leverages the rears are going to be effectively softer.

[DarkSunrise]

Wow that was quick. Great job RCE! (as usual)

[Racecomp Engineering]

Thanks for posting! We'll be posting a few things over the next few days on our FB page and eventually doing one big data dump here on the board.

There are a few interesting things here and with the other data we'll be posting. Pretty good overall for an OEM in my opinion, though obviously not an advanced race shock. Stability is the name of the game here but it's not sloppy by any means and there's still some response in there. The softish rear rebound with decent compression is a good compromise for a street RWD car and makes it fun/easy to drive fast while keeping it safe and stable. How people work with this is going to be very important in getting the car to feel as fast, fun, AND controllable as it does stock. Working with the shocks as opposed to around them is going to be crucial here if you want to improve the car. That sounds silly but really there is some potential here if done right.

The forces aren't very high but remember we're dealing with a fairly light car here that doesn't need a lot of spring rate. We definitely had a lot of headroom with the valving to get the rates we wanted for our lowering springs without sacrificing durability. Details coming soon on those.

- andrew

[Ryephile]

Thanks Andrew and RCE for putting forth the time and effort to get good baseline data.

Damper dyno basics: The top [positive] numbers are the compression forces, the bottom [negative] numbers are the rebound forces. The low speed numbers on the left represent corner transitions and big heaves, and the high speed numbers on the right represent pot holes, concrete shelves, & cobblestones. Ideally you want a damper that has high force at low speed, and low force at high speed [a digressive damper]. This gives excellent body control and quick transitions while soaking up bumps. An undesirable damper would have the lines close to each other around the 0 force mark on the left side of the graph and then quickly diverge. [i.e. a progressive damper]

[Dimman]

Originally Posted by Racecomp Engineering

Thanks for posting! We'll be posting a few things over the next few days on our FB page and eventually doing one big data dump here on the board.

There are a few interesting things here and with the other data we'll be posting. Pretty good overall for an OEM in my opinion, though obviously not an advanced race shock. Stability is the name of the game here but it's not sloppy by any means and there's still some response in there. The softish rear rebound with decent compression is a good compromise for a street RWD car and makes it fun/easy to drive fast while keeping it safe and stable. How people work with this is going to be very important in getting the car to feel as fast, fun, AND controllable as it does stock. Working with the shocks as opposed to around them is going to be crucial here if you want to improve the car. That sounds silly but really there is some potential here if done right.

The forces aren't very high but remember we're dealing with a fairly light car here that doesn't need a lot of spring rate. We definitely had a lot of headroom with the valving to get the rates we wanted for our lowering springs without sacrificing durability. Details coming soon on those.

- andrew

Andrew,

1.5 Hz front?
1.35 Hz rear?

How close on my guesstimates?

Also, on calculating the motion ratio on the fronts, I remember MotoIQ mentioning that the strut is mounted a bit more inboard than a typical MacStrut. Does this affect the ratio? Would you draw an imaginary line down the strut and use where it intersects with the lower arm as a point like you would on the back? Or is it still the typical MacStrut 1:1?