Spring and damper rates: front vs rear, explanation needed

[Ashikabi]

So I'm curious how using a stiffer spring on either the front or rear would affect handling on the street and in auto X. Additionally, how would stiffening dampers on one end or the other affect handling? I have an FRS which I seem to recall seeing had even spring rates and the BRZ had 6k up front and 7k in the rear. I switched to Stance coilovers for their dropability but with autoX season approaching I'd like to know more about how I can manage my handling for the best times possible

[Calum]

The FRS has softer front springs in the front than the brz and stiffer rear springs than the brz. I forget the exact numbers but they aren't anywhere near as stiff as 6k and 7k. There's a lot of debate and differing opinions on the subject of suspension tuning. Ultimately it comes down to personal preference. If I were you, I'd put the stock suspension back on, run a few auto crosses and see if you can find fault in the stock setup. If you can and you can afford the points to change the parts then I'd recommend you go to the Q&A thread in the stickies above. RCE and CSG both have sufficient experience to help you, as do a host of other guys that post in that thread. You'll find some differing opinions on tuning philosophy, but I don't think any one is more correct than the others. Just different approaches to suit different styles of road and driving technique.

There's also the camp of people that say the stock setup is excellent and any fault can be driven around with sufficient skills.

[dp1]

Remember that changes in your input into throttle, brakes and steering have significant impact on how the car behaves during weight transitions, in addition to shock travel and damping and tires and camber and toe, etc...first practice makes perfect (smoother usually equals faster) then setup makes better.

[Ashikabi]

Thanks for the replies guys. I ran stock last year and it handled well except for the Prius tires. However conflicting interests of how it looks and how it races demanded Coilovers.

[Shankenstein]

Compromises.

The primary compromise is ride vs handling. Soft springs generally ride more comfortably over rougher surfaces. Stiff springs generally create less weight transfer during handling maneuvers and allow for a lower center of gravity.

That's the reason I put some emphasis on natural frequency in my modeling thread. It gives you a ballpark set of characteristics for the vehicle.

You can stiffen things up, but at some point, the spring rate isn't compliant enough to follow the road's undulations:

[ame="https://www.youtube.com/watch?v=Av44B8bWimE"]Cam and Follower Jump Phenomenon - YouTube[/ame]


This is where you start analyzing the variance in road surfaces and natural frequency comes in.

Dampers are there to absorb energy, but they can also create extra control in certain situations. You can run more spring rate with dampers that control disruptive situations. Dampers for the street and rough-surface track with some digressive characteristics. You get strong control during steering, braking, and acceleration (low frequency)... but it doesn't disrupt your grip (read: pogo) if you hop a curb at the track or hit a pothole (high frequency).

[Ashikabi]

But this isn't answering the question off front vs rear. I understand the basics of how things work but how changing the front or rear(but not both or making the same change to both) is still a mystery to me

[Shankenstein]

Generally, front suspension stiffening will give you a more planted feel during slaloms, braking, and steering during weight transfer. Alot of people associate the additional feel with performance, but many coilovers that bias to the front will reduce the ultimate grip of the car.

Rear suspension is really a "do whatever works" situation. You want it compliant enough to put power down smoothly, but it also needs to have a comparable ride frequency to the front (not necessarily flat ride). If there's a massive difference, it can hurt ride quality during weight transfer.

Check out the video from Shaikh at Fat Cat Motorsports
[ame="https://www.youtube.com/watch?v=ZR0W0XyxN_Q"]Fat Cat Motorsports - What is Flat Ride and why should you care? Suspension design concepts - YouTube[/ame]

[Gunman]

Originally Posted by Ashikabi

But this isn't answering the question off front vs rear. I understand the basics of how things work but how changing the front or rear(but not both or making the same change to both) is still a mystery to me

It's a matter of adding or reducing the mechanical grip on one end of the car. More grip on one end, will affect the balance, ie more grip on the front will cause oversteer, aka loose. More grip on the rear will make the car understeer, aka push.

In very general terms, going softer on the spring will add mechanical grip, going stiffer will reduce it. This is disregarding the pitch change, weight transfer change, etc.

[cjd]

Originally Posted by Gunman

It's a matter of adding or reducing the mechanical grip on one end of the car. More grip on one end, will affect the balance, ie more grip on the front will cause oversteer, aka loose. More grip on the rear will make the car understeer, aka push.

In very general terms, going softer on the spring will add mechanical grip, going stiffer will reduce it. This is disregarding the pitch change, weight transfer change, etc.

It's worth noting that none of this lives in isolation - every change is in relation to everything else in the system. Change spring rates significantly and you probably need new dampers.

It's possible to reduce rear traction simply by going insanely stiff on the rear damper compression setting, but it rides horribly (over 13 years I lived with that!) Increasing spring rate has a similar result to rear traction, but does very different things to ride (and eventually overpowers the damper.) Then there are setups like CSG has reported with the Tein SRC and 10/12k (F/R) spring rates and reports of a ride more comfortable than stock being achievable...

IIRC up through '14, stock BRZ front is ~2700k, rear ~3500; FRS front ~2300k, rear ~3800k.

C

[Ashikabi]

So this is a stupid question butyou say the FRS is 2300k and 3800k... I just quoted the spring rates I saw when purchasing(6 and 7k). Would that mean they are actually 6000k and 7000k?

[Shankenstein]

Originally Posted by Ashikabi

So this is a stupid question butyou say the FRS is 2300k and 3800k... I just quoted the spring rates I saw when purchasing(6 and 7k). Would that mean they are actually 6000k and 7000k?

kg/m?

His values are correct for an FR-S. BRZ is roughly 2.8 front & 3.6 rear (in kg/mm)

[cjd]

Originally Posted by Shankenstein

kg/m?

His values are correct for an FR-S. BRZ is roughly 2.8 front & 3.6 rear (in kg/mm)

I rounded down vs up I think from lb/in (couldn't find kg/mm, didn't look too hard...) but that still ends up a couple lb/in difference either way - we may be chasing rounding errors all around if the lb/in numbers I used were rounded kg/mm. hah.

fwiw 6kg = 6000g, you usually see either 6k or 6000. 6000kg/mm springs would be a bit much.

C

[Ashikabi]

That's why I was asking. I want questioning if your numbers were accurate but if we were using the same numbering system