BLkAP1

Hi there,

This may come across as a silly question but I'll attempt to pose in the least stupid way...

In short, what effect on handling does an increase in spring rates have? (Assuming you have increase the rates by the same % at all corners) For instance, it's generally accepted that for serious track use, the stock spring rates are far from ideal and upping them by 3 or 4 times (with appropriate damping) is effective.

I know it seems like a silly question, but it seems common knowledge that adding a front sway bar or disconnecting the rear bar, will introduce more understeer or tame oversteer. What overall handling trait are we trying to introduce by increasing spring rates? It never seems to come up as an answer to a "handling issue" query...but every serious car has very stiff suspension.

TTMartin

Momentum (movement of the suspension) is equal to mass (weight) times velocity (speed).
As speeds increase the more force that a given road imperfection (bump) imparts into the vehicles suspension.
The greater the force the more spring compression for a given spring rate.
The higher spring rates cause less suspension travel better keeping the tire in contact with the road.
However at lower speeds not enough force is imparted into the higher rate spring to compress it, making the ride uncomfortable.

edit: As to why spring rates aren't used more often to tune a suspension. Changing springs is a lot more work than turning a dial on a shock. This is why over dampening is often used instead of proper spring rates. Also, most people don't know what a specific spring rates are need or do. They often rely on a company like Swift to send them the best spring rates. The company then chooses a spring rate that is some where between stiff enough for the track, and soft enough for comfort, people then make up the difference with over dampening. I wouldn't want to change out my springs before every track day, and I wouldn't want 12K springs on my car driving on the roads. Also a car used at Autocross has even different needs. Keeping body roll to a minimum can be done with either higher spring rates or stiffer sway bars or a combination of both. I believe a slight increase in spring rates, and a much greater increase in both front and rear sway bars is a better way to accomplish that goal.

Billj747

Higher spring rates = quicker weight transfer, loads the tire more (which can lose overall grip), and reduce body roll or squat/dive.

Softer springs don't load the tire as much and generally speaking, make more grip than stiffer springs. Many people are leaving the stock springs in the S2K Challenge and are turning very quick laps.

Stiffer springs do reduce travel and movement of the suspension, which can make the car 'skip' over bumps and lose contact with the ground. Softer springs are more compliant in both low and highspeed corners and will keep the tire in contact with the ground, making grip, much better.

How do you fix a poor handling suspension (whether geometry or a cheap, poor quality shock)? -You spring the heck out of it and prevent it from moving. Many poor quality dampers do this, and its an easy fix for any bumpsteer issues.

Once you start introducing aero into the picture, it becomes more important to maintain an aero platform, keeping the body of the car fairly consistent and improving the function of a splitter and wing.

To view things simply and relevant for most S2K owners who track their cars: Going slightly stiffer will make the car slightly more stable by reducing body roll (which isn't necessarily faster but can be subjectively faster by improving the drivers confidence in a car that dosn't roll all over the place), From there - stiffening either the front or rear bar or spring rates will reduce roll (AND GRIP) even further -to balance out the car from either under or oversteer.

Higher rates will work the tires harder, which will to a point eventually overheat the tires. They also will affect dynamic camber gain from travel as well as affect ideal static camber. Everything is an involved and integrated system. It's not always simple. But to view things from a fundamental and simple system: Stiffer springs increase response, reduce roll, and reduce grip.


0.02

robrob

I ran PSS9 coilovers with r-compound tires for the first couple of years I tracked my car. I then swapped the shocks out for KWV3s and I made a quantum leap in my car control skills and lap times. The PSS9s were too softly sprung and damped and even with a Comptech Adjustable front bar on full stiff and the 2001 rear anti-roll bar the car was difficult to control. It may have had more ultimate grip but the transition to and from slide was abrupt and did not inspire confidence.

I had obviously outgrown the PSS9s because I was shocked how much easier it was to slide the car around the track with the V3s. My lap times around Summit Point's Shenandoah (tight & technical) circuit dropped by almost 3 seconds. In one day I went from middle-of-the-pack track guy to "that guy in the yellow S2000." I'll never forget how much I enjoyed that first day on the much stiffer KWV3s--they seemed to suit my driving style perfectly.

You can definitely go too stiff with springs but for most people a stiffer than stock shock/spring package will make you and your S2000 faster around the track.

psychoazn

Rob, do you have any seat time in the "stiff" coilover setups? I'm thinking SRC or something similar, which run 16k or higher springs.

I've driven s2ks back to back with different setups, and I totally agree with what Billy had to say about high spring rates; they do work, but its a hack, rather than a pure improvement. There was a certain turn at the track where I was driving these cars where the 16k spring cars were hopping/skipping over the pavement, which ultimately yielded a slower exit out of that particular corner. However, because of the nature of this track (tight, twisty, lots of consecutive lateral transitions), the higher spring rate ultimately proved faster. I suppose if you wanted to get down to that level, a different spring would be better for different tracks, although most of us socal drivers just get one setup and drive it on all of the local tracks.

Bullwings

To add to what everyone else is saying... under ideal conditions, the best suspension is no suspension at all - completely solid, fixed, and zero flex or give. However, this would only work on the smoothest of smooth perfect surfaces.

The whole point of suspension is to allow the vehicle to adapt to imperfect road conditions - off road vehicles being the complete opposite of track cars (because they have no road). So, generally, a stiffer setup will work better on the track since from the factory cars are designed to be able to handle a "broader" range of road conditions that might be encountered in everyday driving.

BLkAP1

Thanks for all the replies, this was the conversation I was hoping to generate. It seems like the common theme is

- expect a general increase in chassis response due to less wasted motion
- more load is transmitted to the tires. Possibly a loss of grip.
- greater confidence at high speed

I am planning on replacing my Tien S-tech with Ground Control sleeves (currenty running Koni Yellows). My car is also a DD so probably go up to around 500 lbs. I feel I have reached the limit of my current suspension when transitioning between corners, chicanes etc. Just curious on what to expect.

More advice is welcome!

Billj747

Reducing body roll can improve confidence, but having the suspension too stiff, skipping over the ground, losing grip, and sliding won't be confidence inspiring.

500lbs front and rear wouldn't be too bad, but I might suggest slightly stiffer front rates than rear. 550F 450R, 600F 500R, 650F, 550R

JJ7

This is a good thread. What about the relation between tire grip and spring rate. To be extreme, if you have 275 r-comps what would have the potential for more over all grip, OEM springs or 12k springs?

JJ

BLkAP1

Yep, I was planning to go 550F 450R. I run stock AP1 wheels with Direzza Z1.

Good question, is there a point where tire width/compound will override the loss of grip from higher spring rates?