Why a balanced setup is better than a "understeery" setup.
 

This is a snapshot of data being taken from two different cars at the "Sweeper" at Buttonwillow Raceway Park, which is a flat, 180 degree turn. The lines are as follows:

- GPS Speed (Speed as determined by GPS, not by the car's ECU)
- Steering angle in degrees
- Gas pedal input (in percent from none to WOT)
- Lateral acceleration as determined by GPS (Lateral G's)
- Rate of yaw, as determined by GPS (yaw rate in degrees per second)
- Lap time differential between the green and blue traces

https://fbcdn-sphotos-e-a.akamaihd.n...31176518_o.jpg

The first thing to note, is that the green car is slower through the entire corner (graph 1); the corner is identified by the red line at the top of the graph labeled "16".

The second thing to note, is that the green car reaches peak cornering grip (graphs 4 and 5) at about 80 degrees of steering input (graph 3), whereas the blue car only requires about 60 degrees of steering input. Even with less steering input, the blue car actually maintains higher cornering grip (compare the green and blue lines on graphs 4 and 5)!! The time gained by the blue car is shown by the differential dropping in graph 6. Even though the Green car is on the throttle more through the second half of the corner, it actually makes the understeer worse, and the blue car is able to go faster!


The Green car is representative of coilovers that utilize the same spring rates front and rear, or have a small stagger with the rear being larger.

The Blue car is representative of cars that utilize coilovers that have a 20-25% higher spring rate in the rear.

This is awesome!

Nothing like braking with front tires while getting on the gas ;)

Mike why are you so cool?! Lol

Great info man!

I'm becoming a firm believer of this.

Now, what are the best options that take advantage of this?

There are a TON of ways to achieve proper balance. However, fine tuning it will require you to have a highly experienced local driver that can guide you, or you need to be willing to spend a lot of time learning to do it yourself.

For example, you can take ANY suspension, and literally "hack" the balance together by changing the spring rates. But, then the dampers wont match the springs. Or, you can change the sways to change the effective spring at the wheel, but again, dampers.

The real problem, is that unless a 1 way system is very carefully designed to be balanced (and there's none that I'm aware of on the market for this car, or most cars for that matter), you need at least a two way damper, so that you can change springs to taste, and still be able to critically damp the springs.

Also, most cars understeer from the factory. This is done intentionally by design, because the natural tendencies of the average driver suits understeer better than balance or oversteer.

This is also why rates of 10k/12k were selected as our default for the CSG-Spec SRCs. Not only does it balance the car, it lets you use your tires and fuel more efficiently. However, we do also acknowledge that "balance" means that without a lot of experience, it's very easy to unintentionally make the car rotate (spin), so rates of 9k/10k are recommended with the CSG-SRCs, for the less hardcore drivers. Furthermore, some setups actually require MORE static rotation. @ImperiousRex's BRZ with JRZs for example, was set up by CSG to utilize 9k/11k spring rates, which would normally result in a car that wants to oversteer everywhere. However, the car's geometry, sway bar rates, and aero were all simultaneously tuned to work in conjunction, resulting in a beautifully balanced car that is still the fastest privately owned track FRS/BRZ in North America.

This type of balance can be achieved with most mid-grade and higher 2 way dampers.

Are these cars using the exact same tires?

I don't disagree with anything you have said. Are they the same driver? Same tires? Also assuming that these aren't stock cars?

There are a lot of factors as you know that could make these results.

Nice data, thank you. What is the rest of the setup like for the cars? Tires, bars, dampers, alignment/camber, absolute spring rates/stiffness, aero, ride height?

And yet @ImperiousRex chose to take a S2K to COTA.

Tsk tsk.

-alex

Great questions.

- Tires don't change the static balance of the cars. However, having more grip than what the car itself can readily overcome can hide handling imbalances. In this case, both cars used comparable (but not identical) tires.

- Both cars are on stock sway bars.

- The balance is determined by spring rate at the wheels, not the dampers. You can FORCE a change in balance by *reducing* grip at an axle, by using incorrect dampers. While the damper models are different, both cars were critically damped.

- Both cars had alignments to maximize on-track performance. Alignments were slightly different to accommodate spring rates, but are within a few tenths. Both cars have zero toe front and rear.

- I unfortunately cannot disclose the absolute spring rates without potentially revealing the coilover models. This post is purely to demonstrate the difference between a balanced spring rate f/r versus a common "front spring heavy" car.

- Both cars have zero aero.

- Ride heights were set to manufacturer recommended heights.

Comparable, but not identical tires.

I am the driver in both cars.

Both cars are mildly modified, but none of those modifications, IMO, have any significant impact on the car's behavior in static corners. For example, one car could be turbo, but that extra power wouldn't change how the car takes a 180 degree, flat surface turn, unless you were drifting. Both cars are NA, and lack sufficient power to hold a drift at that speed.

:bellyroll: :bellyroll:

I was supposed to take the BRZ as a support car... but budget issues...

You're the driver?!?!?? Lord help us. :bellyroll:

Right on! Sounds like a great comparison. :)

Being that the cars aren't on the same tires, the comparison is pretty much void anyhow. Nice try, but the scientific method does apply to most comparisons like this, and you have drawn conclusions where they can't reliably be drawn.

then take your foot off the throttle and let the front tires work? You romp on the gas mid turn and expect the front end to grip. Weight transfer to the rear takes load off the front and makes the front end work worse, not better.

Steering angles were similar entering the turn, though it looks like you turn in later with the blue trace. The blue trace shows some notable rotation (big spike in the yaw rate). Rotation = lose, not neutral. After that, I'd expect less steering was needed, as all the turning was done on corner entry (admittedly good place to do it). Similarly, I notice the steering angles are identical until you jam on the throttle in the green trace (10,550 mark) after that the understeer is in full effect. Maybe that's an ill timed heel-toe downshift (we don't have that info on the graph) - but who does that mid turn, that should be the blip at 10,300.

You appear to totally short shift the blue car, why? Different tires can have a huge impact on handling balance (I've done that experiment), setups can vary dramatically with compound changes/sidewall stiffness, etc. It's fancy data, but with 0.09 seconds delta between the cars (which evaporates shortly after corner exit) I think we might need to put away the jump to conclusions mat.

wheres the line for the car that was sideways the whole time?!

But awesome info+time spent putting this together and explaining

I seriously LOL at all the "racers" who contradict what @CSG Mike says because the conditions were not perfect/exactly the same. I'm pretty confident he's done enough testing to know what the hell he's talking about. However, with that said, the alignment of the moon was different between laps, therefore the information he presented is completely useless/not applicable to anything.

There are VERY FEW people who put forth the effort, time and knowledge to help the racing community that @CSG Mike does.

Great study! This pretty much justifies why the oem springs have a higher rate in the rear. I was checking for sometime the springs of different manufacturers and it looked to me that same rates front and rear would not give an optimal result.

At some point, a line has to be drawn for a reasonable comparison.

I'd approximate the grip difference between the tires on the two cars is about 20% of the grip difference between a fresh street tire and a heat cycled street tire of the same model.

Are you going to point out that the cars had different wheels too? Or different levels of fuel in the tank? Or that ambient temperatures aren't identical and a 2mph cross wind was present for one, and the angle of the sun affected tire grip?

This isn't the "best" laps between the setups being compared, but rather hand picked laps for the purpose of comparison.

Take the data for what you will. It's not perfect, and never will be perfect.

*edit*

Re: stomping on the throttle: has it occured to you that the car is still accelerating, in spite of the understeer? That's why that green lap is faster exiting ;)

@celica73

For you:

https://scontent-lax.xx.fbcdn.net/hp...92418894_o.jpg

Actually, I was going to ask about fuel in the tank, and a passenger in the left seat (a passenger will make a noticeable difference in these cars).

I don't disagree that you have made a comparison between two laps. I'd stop there though, because you might as well be comparing a granny smith to a golden delicious. They are both apples, neither are red.

I'll take your word that the "blue" car was more pleasant to drive, but you don't need data to tell you that.

I'd love to do that... but I generally don't get intentionally sideways unless asked to by the car's owner, and neither of the cars are mine...

The rate of yaw is more stable drifting, but the actual lateral G is "off" due to the slip angle; you actually have to interpolate it from lateral and longitudinal forces, using the actual yaw angle of the car relative to the corner.

That being said, if we actually DID interpolate the data in that fashion, the blue car in the example would actually have a little bit more lateral G, albeit a few percent which would barely show on the graph.

New data shows the downshift nicely. Thanks.

You can actually see me intentionally using the downshift to try to upset the rear, but the car is so front biased that it didn't actually step out. It did result, however, in achieving the highest peak lateral G momentarily when the rear was loaded more from the pseudo clutch kick.

If you want to see any other data in that corner, let me know and I'll be more than happy to post it.

I would love to see driver seat videos of this.

They'd actually be really boring; the only thing you'd really be able to compare is how much the steering wheel is turned to go through the same corner.

I'll see if I can borrow a gopro or two the next time I do something like this.

interesting, @CSG Mike, have you had any seat time with the higher end 1 ways? like MCS, JRZ, or Ohlins? or are they more glorified really nice street dampers? I have a feeling that to get competant track times, the adjustability needs to be for compression too, atleast.

Only a limited amount, and you're correct, the 1-ways are all geared toward inexperienced drivers, since the experienced drivers who know what they want won't be getting a one way.

interesting. Ill keep that in mind when looking at future upgrades, mainly keep it to springs. Once Ive completed some HPDE instruction and gotten more...legal seat time, then I will take a look at some double adjustables.

So if I already have a coil setup with spring rates favouring the rear by only 18% would a slightly larger rear sway bar compensate for the mild spring rate difference? I currently have an OEM WRX STI rear sway bar on the car for winter mode and DD but if it helps the balance of the car and overall grip as you've shown through fast corners should I dust off the 21mm?

you're probably already okay as-is :)

Not sure if I missed it, but I am curious if either car had a staggered wheel/tire setup.

Both cars have square wheels/tires.

how about gps trace, it might just be that the green car overshot the corner so needed more steering input? How come is the blue car losing all that time on the acceleration?

If that were the case, more steering input certainly didn't increase the lateral G, which demonstrates understeer.

The particular lap in the blue car wasn't meant to be a hot lap. This is strictly to demonstrate the effect of static understeer setup versus balanced setup.

Do you think the stock set up is neutral at 2.0 front camber and 1.5 neg camber with RS3s 225, 17s, on rpf1s at 7.5 in width at 250whp? (Vortech stock 9psi tune)

Does this confirm the reason behind the Fortune Auto 500 v5 being 6k/7k being a decent starting setup? Although the rates are not as high it should still provide a nice balance for the non-frequent trackster?

I'm interested in the above post as well. I have rce tarmac2s en route to me with both 400 and 500 lb spring sets. This makes me want to put a set of 500's on the rear and leave 400's on the front. I'm on stock sways and 450whp.

T2's with 400F/500R is similar balance to the CSG Tein SRC's in terms of front to rear spring rates, I've actually been looking at buying that setup myself.

Hmmmm. I have Tein MonoSports, which are 8k front and 9k rear. That's less than a 20% difference. Would that put them in the green car camp?

Why is it that at the exit the green car is carrying a little more speed out starting from the 12500 mark? Everywhere else on that chart the green was slower or at most same speed as the blue line.