Deep Forest Tunery Test Data
How to select and optimize drivetrain components, and the not so obvious effects.
by budious
Do you think your drivetrain is already optimized? If I had one guess at your car, I'd say it's equipped with a twin-plate clutch and semi-race flywheel, but if this is the the case, then you should think again. So now you're probably thinking, "so why would the best 'not be the best'?"
This is the current
issue plaguing many tuners between their
offline and
online tunes, so let's clear up that misconception first. There is
nothing different with the physics between the two modes, there is only one difference, circumference of your tires is no longer constant; therefore, problems that currently exist in your "
offline" tune are simply obscured by residing on the threshold between being noticable and being a non-factor. Once tire wear is factored into the equation, the physics engine starts showing you where your tune is wrong. It's not in the suspension, it's not in the aerodynamics, it's not in the tire grade, it's not in the power plant, nor the weight of the car - it's simply the drivetrain.
Let's theorize as to why this is, first and foremost, clutching. How is that relevant to playing with a dualshock 3 with automatic shifting? The game is handling the emulation of the driver shift for you within the physics engine, the snap of the clutch engagement can be measured under the right test conditions. The purpose of this guide is to provide a walk through and demonstration of the testing process, how to identify common symptoms, and optimization of your drivetrain.
Let's begin by identifying the primary drivetrain components and their function, and how that function is implemented (
theoretically) within the Gran Turismo 5 racing engine. The following details and exploration will give you a new appreciation for the attention to details polyphony digital went to in designing the new engine. No wonder my PS3 fan keeps kicking on, the cell processor is working overtime.
Clutches couple the engines power to the drive shaft or differential. In all clutches, friction exists to one degree or another, providing a transitional state between engagement and disengagement. A measure of a clutch's worth is the amount of friction that can be transferred. Performance designed single plate clutches offer a step up in friction offering from stock models, more elaborate models such as the double plate transfer even more.
Unfortunately, if the friction exceeds the capacity of the engine to deliver additional torque any performance gains are negligible, but detrimental effects on handling become apparent also immediately.
Why would too much friction inhibit the car's handling ability? If the driver disengages the clutch entering a corner to downshift, the following re-engagement of an engine idling at high rpms will send torque straight to the wheels, even if no throttle is being applied. The effect once transfered to the drivetrain can be mitigated by a high acceleration value on the LSD. (see symptoms -
snapping)
Why a higher acceleration value? Locking the rear wheels together means both wheels are moved by the idle engagement torque; a lower value will cause the torque to be transfered to the side of least resistance, ala the dreaded
snap.
Since the idling speed of an engine is influenced by the flywheel equipped, choosing the correct flywheel becomes part of the overall equation, higher idle is not necessarily better.
Symptoms of clutch engagement being counter productive can also include
lurching in which a sudden change in acceleration or deceleration becomes apparent. Lurches are most noticeable in transitions between extreme acceleration or deceleration. A lurch on acceleration will be apparent when driver goes full throttle on corner exit from a previous state of coasting or deceleration; the car will suddenly lunge forward.
The opposite occurs following a release from full throttle to no throttle; the sudden transition will result in rapid deceleration caused by the engagement of the drivetrain to the now idling or dropping off of engine rpm's before the clutch finishes fully disengaging, a result of too much friction. This will be more pronounced on engines equipped with lightweight flywheels.
Each of these symptoms can be detrimental to the driving experience of your tune. Compounded, they present even more significant driving anomalies.
In the supplemental test case and test car specifications, a combination of a semi-race flywheel coupled to a LSD with an acceleration value of 30 displayed tendencies towards extreme and sudden direction changes,
veering for the purposes of my terminology to differentiate it from
snapping. Raising the acceleration value to 50 mitigated many of these behaviors, but introduced complexities of it's own.
Veering often occurs under prolonged acceleration at full throttle during which a small surface irregularity can disrupt traction.
Running a high LSD acceleration value will cause the car to run wide as it accelerates through corners; however, somewhat contrary to the implication of running a lightweight flywheel, utilizing the combination of a semi-race flywheel with an LSD acceleration value of 50, a car can power oversteer its way through corners; whereas, when paired with a stock flywheel it would just run wide into the barrier or grass. For purposes of this guide, I refer to this behavior or running wide as
snagging, hence, you'll be all over a wall.
In regards to the other extreme of LSD acceleration, a value too low will often result in
spinning as the car looses traction in the corner, the torque is transferred down the path of least resistance and thus begins to spin.
Spinning can be counteracted by raising LSD acceleration and/or downgrading the flywheel.
The test car displayed a pertinacity for popping
wheelies at the crest of the hill exiting the first hairpin on Deep Forest Raceway when equipped with single-plate or twin-plate clutches. The effect is intensified through pairing with an upgraded flywheel.
Surging is evident on the test car when equipped with a twin-plate clutch and upgraded flywheel.
Surging would best be described as tapping the brake or short braking; except, upon release the clutch is re-engaged before the engine has had time to idle down and a sudden burst of speed is experienced mid-corner or on corner exit without deliberate throttle application.
Barreling is evident on the test car when equipped with a single-plate or twin-plate clutch, an upgraded flywheel, and an LSD acceleration value of 50.
Barreling is an extreme form of
snapping that could be characterized as having the feel of Skid Recovery Force with an exception that there is only a 50/50 chance that it will be in the direction that you wanted to go.
Carbon drive shafts, while the demonstrated test scenarios and test car do not utilize it (mid-engine), I did test it on my Chevrolet Corvette Convertible (C3) '69
Seasonal Event 6 Spec in comparison to the stock drivetrain, it shaved almost two full seconds off of lap time alone in place of the standard drive shaft while using stock clutch and stock flywheel; there was considerable improvement in both acceleration and deceleration.
Symptoms and Remedies Recap
- Snapping is caused by having a low LSD acceleration value set in combination with a lightweight flywheel upgrade, the sudden engagement of the clutch can trigger a direction shift. When combined with an upgraded clutch a more extreme form emerges, see Barreling.
- Lurching becomes most apparent during extreme transitions of acceleration to deceleration, or from deceleration to acceleration. Acceleration lurches result from sudden torque application through an upgraded clutch that provides more friction than the stock component. This will be more pronounced on engines equipped with lightweight flywheels. Deceleration lurches are the sudden transitions to rapid deceleration from the engagement of the drivetrain to the now idling or dropping off of engine rpm's before the clutch finishes fully disengaging, a result of too much friction. This will be more pronounced on engines equipped with lightweight flywheels.
- Jerking is a prerequisite behavior to veering but without the complete loss of control. Jerking (and likewise, veering) often occurs under prolonged acceleration at full throttle during which a small surface irregularity can disrupt traction.
- Veering results from a combination of a semi-race flywheel coupled to a LSD with an acceleration value set too low. Raising the acceleration value to 50 mitigated many of these behaviors, but introduced complexities of it's own. Veering often occurs under prolonged acceleration at full throttle during which a small surface irregularity can disrupt traction.
- Snagging is a unique situation resulting from too high an LSD acceleration value combined with an stock flywheel. Running a high LSD acceleration value will cause the car to run wide as it accelerates through corners; however, somewhat contrary to the implication of running a lightweight flywheel, utilizing the combination of a semi-race flywheel with an LSD acceleration value of 50, a car can power oversteer its way through corners; whereas, when paired with a stock flywheel it would just run wide into the barrier or grass.
- Spinning is the counter action of snagging. An LSD acceleration value set too low will often result in spinning as the car looses traction in the corner, the torque is transferred down the path of least resistance and thus begins to spin. Spinning can be counteracted by raising LSD acceleration and/or downgrading the flywheel.
- Wheelies is a behavior which may be displayed on the crest of hills when cars are equipped with upgrade clutches. An upgraded flywheel will intensify this effect.
- Surging would best be described as tapping the brake or short braking; except, upon release the clutch is re-engaged before the engine has had time to idle down and a sudden burst of speed is experience mid-corner or on corner exit without deliberate throttle application. Surging is most evident on cars equipped with upgraded clutches and flywheels.
- Barreling is an extreme form of snapping that could be characterized as having the feel of Skid Recovery Force with an exception that there is only a 50/50 chance that it will be in the direction that you wanted to go. Barreling is most evident on cars with upgraded clutches and flywheels and an LSD acceleration value set too high. (50 in these test cases)
Test Briefing and the Deep Forest Driving Experience
The following scenarios were tested using the Lotus Elise 111R
Test Spec which you can find below. I strongly urge you to invest the 300k credits to build it; reading this guide is not enough, you must experience it first hand to recognize these behaviors on your tunes. Test Spec utilizes the Chassis Reinforcement, the extra rigidity makes these imperfections all the more obvious. If you like the car, I suggest you build another without Chassis Reinforcement for an every day racer.
I strongly advise that your first drive with the car be on stock transmission; stock clutch; stock flywheel; LSD @ 12/30/16; until such time as you are comfortable with it and ready to begin test scenarios.
The testing scenarios were from an initial batch and thus limited in complexity. I opted for Race Soft since only the most violent of imperfections would be noticeable due to their enhanced grip; also, I wanted it to be a friendly test car scenario for a wide range of readers who may want to give this a try for themselves. I plan to do further testing scenarios utilizing Sport Softs and the Sports flywheel as a follow up to this piece.
Each of the test scenarios was run twice; two sets of five laps for each scenario on Deep Forest Raceway while either in offline practice mode or grinding A-spec. Notes were taken, some lap times were recorded just for comparison, I approximated a generalization of lap performance in parenthesis after each test data remark. The times are not indicative of best performer, just as a simple metric for those who want to quickly browse over the data.
Notice: February 5, 2011 - Tests and observations performed by me were using DualShock3 and AT shifting. I am requesting feedback from sequential shifting wheel users, as well as from those with H-pattern and clutch pedal setups, to run through these scenarios as well and to report back with your findings.
TCS off
ASM off
SRF off
ABS 1
Test Scenarios and Recorded Observations
- Stock Clutch; Stock Flywheel; LSD @ 12/30/16; Race Soft
- Smooth and consistent feel; but measurably lower average lap times. (1:15")
- Stock Clutch; Semi-Race Flywheel; LSD @ 12/30/16; Race Soft
- Snappy, prone to sudden veering, jerking, corner spin on cold Race Softs but good after first lap. (1:13.5")
- Stock Clutch; Stock Flywheel; LSD @ 12/50/16; Race Soft
- Runs wide in corners, snagging a real danger. Lurching present upon full throttle or release from full throttle. (1:14")
- Stock Clutch; Semi-Race Flywheel; LSD @ 12/50/16; Race Soft
- Capable of power oversteer to counteract snagging; better performing than scenario 3. (1:13.5")
- Single Plate; Stock Flywheel; LSD @ 12/30/16; Race Soft
- Smooth and consistent feel; slight wheelie on crest. (1:13.5")
- Single Plate; Semi-Race Flywheel; LSD @ 12/30/16; Race Soft
- Pops wheelies at crest; clutch engagement snap evident. (1:14")
- Single Plate; Stock Flywheel; LSD @ 12/50/16; Race Soft
- Pops wheelies at crest; smoother cornering than scenario 6; runs wider in turns; milder clutch engagement. (1:13.5")
- Single Plate; Semi-Race Flywheel; LSD @ 12/50/16; Race Soft
- Smooth and consistent; a touch of barreling present; great off the line grid start first lap time, three consecutive 1:13" laps ran. (1:13")
- Twin Plate; Stock Flywheel; LSD @ 12/30/16; Race Soft
- Smooth; but clutch engagement more noticeable over single plate. (1:13.5")
- Twin Plate; Semi-Race Flywheel; LSD @ 12/30/16; Race Soft
- Smooth acceleration; strong desire to wheelie crest; prone to sudden snaps; erratic in corner radius diameters - snagging; jerking over irregularities on track surface; lurching evident. (1:14")
- Twin Plate; Stock Flywheel; LSD @ 12/50/16; Race Soft
- Smooth and consistent feel; but measurably lower lap time. (1:14.5")
- Twin Plate; Semi-Race Flywheel; LSD @ 12/50/16; Race Soft
- Smooth; some wheelies at crest; erratic snapping. (1:14")
- Stock Clutch; Sport Flywheel; LSD @ 12/30/16; Race Soft
- Smooth and consistent, clean laps; respectable lap times. (1:12.8")
- Stock Clutch; Sport Flywheel; LSD @ 12/50/16; Race Soft
- Smooth and consistent, clean laps; runs a tad bit wider in corners, but power oversteer to counter. Corner entry deceleration is smooth, full throttle exit smooth. (1:12.9")
- Single Plate; Sport Flywheel; LSD @ 12/30/16; Race Soft
- Smooth for the most part; a bit of wheelie; a small bit of snapping. (1:12.8")
- Single Plate; Sport Flywheel; LSD @ 12/50/16; Race Soft
- Smooth and consistent, clean laps; good torque to friction balance; perfect power oversteer; excellent corner entry deceleration and full throttle exits are smooth. (1:12.5")
- Twin Plate; Sport Flywheel; LSD @ 12/30/16; Race Soft
- Smooth and consistent, clean laps; clutch engagement is more noticeable at disengage/engage at high speeds; some gentle veering is present. (1:12.8")
- Twin Plate; Sport Flywheel; LSD @ 12/50/16; Race Soft
- Smooth and consistent, clean laps; has the quickest first lap time from grid start of the tested combinations; runs consistently in the low 1:13's"; full throttle works most of track but occasionally need to back off, recovery is quick. (1:13.1")
Conclusions and Summary
February 2, 2011 - I have completed the additional testing scenarios for Sports flywheel and added them above (13-18). The results from those were quite interesting, the test spec car handled exceptionally well on all configurations will the Sports flywheel and put up respectable lap times during each scenario, several new lap records were made.
The main culprit of the initial wild handling of this car can be solely attributed to the Semi-Race flywheel. The high-idle spin of the flywheel appears to the source of the sudden and violent reactions this car has to clutch engagements. While some of this behavior can be mitigated by clutch selection and use of an high acceleration value on the LSD, results consistently showed that the Sports flywheel produced better lap times and far better handling.
The clutch is almost a non-factor on this car, there were a few distinct differences but the driving was consistent among scenarios 14, 16, and 18 that I repeated each for three sets of five laps just to be sure the differences were reproducible and yet minimal. The stock clutch allowed the driver to freely use full throttle for almost the entirety of the race course; it put up a respectable 1:12.8" lap time with LSD acceleration at 30, but also another at 1:12.9" with LSD acceleration at 50.
The single plate clutch displayed a slightly more apparent disengagement and re-engagement at high rpm's, but impact on handling was minimal. A small tendency towards occasional snapping was present when used with an LSD acceleration of 30, but mitigated by setting the value to 50. The single plate when paired with the Sports flywheel and an LSD acceleration of 50 proved itself to be a consistent performer, repeatedly dishing out laps in the low 1:13's and setting an highly impressive 1:12.479" best lap time (best of all tested scenarios so far). Single plate clutch proved itself as the best clutch option for this particular car.
That is not to say that the twin plate clutch did not earn an honorable mention, it displayed it's own unique characteristics. The clutch disengagement to re-engagement was a bit stronger than on the single plate, but did not prove overly detrimental to handling when paired with a Sports flywheel as it did when paired with the Semi-Race flywheel. The slight bit of veering that was produced was mitigated by raising LSD acceleration to 50. Wheelies were only slightly noticeable at crests when paired with the Sports flywheel. Lap times were consistent, typically running in the low 1:13's" and a best lap of 1:21.8" was set with LSD acceleration at 30. The best lap time from stationary grid start was set at 1:19.618" when using an LSD acceleration of 50, making this the best first lap option, this scenario repeatedly demonstrated consecutive laps in the low 1:13's but could not make it under the 1:12.999" benchmark (15 laps were ran), but for lap consistency this combination proved itself truly unique.
The last variable of the drivetrain optimization testing scenarios also seems to be a critical element. LSD acceleration repeatedly proved itself to be a valuable tool in mitigating unwanted snapping and veering associated with use of upgraded clutches and flywheels. While only two values were used for our testing purposes, testing clearly indicated that higher LSD acceleration settings tend to fair better in overall stability of the drivetrain, as well as produce higher lap times. There were some cases where the value being set too high could cause the car to run wide in corners, and this was most noticeable when paired with the stock flywheel, when paired with the Sports flywheel a well balanced and natural amount of power oversteer made sharp cornering possible. Under several of these scenarios using LSD acceleration of 50, I was not dropping below 127MPH at the apex of the last downhill bend to the straight away finish on Deep Forest Raceway without touching grass. Another unusual aspect of having LSD acceleration set to 50 was that straight line deceleration appeared to be much greater than with the value set to 30, this could just be a placebo effect, but I will do more testing to try and verify this aspect of it; upon passing the apex, it also made full throttle acceleration out of the hairpins very smooth and linear.
Based on the results I have seen already, I would not hesitate to crown test scenario 16 as the ultimate setup. The match of single clutch, sport flywheel, a LSD acceleration at 50 proved itself repeatedly with lap times and offered unrivaled handling during cornering, braking, and acceleration.
I will continue to test these setups further now that I have identified the top contenders using Race Softs; the next phase will be to test the finalists on Sport Softs.
Revisiting my theory on clutching being present in the simulation of drivetrain performance, my initial suspicion appears to be reaffirmed. My theory would be that the clutch shift interval (CSi) is present, and that each clutch upgrade fills this duration with a wider range of friction values.
Forgive the crudity of the following diagram;
---------------CSi-------------------------
|rrooyy----------stock------------yyoorr|
|rrroooyy-----single-plate------yyooorrr|
|rrrrooooyy---twin-plate-----yyoooorrrr|
--------------------------------------------
I'm trying to illustrate by
r for red and
o for orange and
y for yellow is the friction exercised by the clutch and that for each upgrade the friction spectrum is wider and longer; and thus amplification of torque transference during periods of slip occurs.
If anyone proficient in visual diagram creation would like to assist with graphics, you can offer to make me illustrations of a
red to yellow to white to yellow to red gradient color spectrum in three rectangular length boxes, varying the gradient according the example above to represent each clutch model's
theoretical impact on handling.
Lotus Elise 111R (non-RM) Test Spec
--------------
319HP
759KG
--------------
GT Auto
------
+ Front Aero
+ Extension Aero
+ Rear Aero
* Aero @ 0 F / 20 R
------
Tune Shop
--------------
+ Weight Reduction 3
+ Window Modification
+ Carbon Hood
+ Chassis Reinforcement (!Amplifies erratic handling;
Test Spec)
------
+ ECU
+ Engine Tune 3
+ Sport Intake Manifold
+ Race Air Filter
+ Sport Exhaust Manifold
+ Sport Catalytic Converter
+ Titanium Racing Exhaust
+ High-RPM Turbo
------
* Stock Transmission (!All test scenarios)
------
* Stock Clutch
+ Single-Plate Clutch
+ Twin-Plate Clutch
* Stock Flywheel
+ Sports Flywheel (!Coming Soon)
+ Semi-Race Flywheel
+ Limited Slip Differential
@ Initial: 12
@ Acceleration: 30 or 50 (!See test scenarios)
@ Deceleration: 16
------
+ Fully Customized Suspension
@ Ride Height: 0 F / 0 R
@ Spring Rate: 4.9 F / 7.2 R
@ Damper Ext: 7 F / 7 R
@ Damper Cm: 7 F/ 7 R
@ Anti-Roll Bar: 4 F / 4 R
@ Camber: 0.0 F / 0.0 R
@ Toe Angle: 0.00 F / 0.00 R
------
* Brake Controller @ 5 F / 5 R
------
+ Race Softs
--------------