GT3 shifting points

Robert Bryson has been working for last two years to collect and analyse all reving data from GT3 class. Here we have some tips to improve our engine performance (along with external tools) and choose a better shift timing. 

GT3 Optimum Shift Points
Updated: S2 2017

tl;dr (more info below) If you use a shift tone or dashboard app, give these values* a try:
* values are alert RPMs, not shift points—see below

Audi R8 LMS

For use with a shift tone with no accompanying shift lights:
— 1st: 7278
— 2nd: 7578
— 3rd: 7538
— 4th: 7515
— 5th: 7543
For use with per-ratio programmable shift lights with or without an accompanying tone:
— 1st: Illuminate from 5572 to 7475, tone at 7475
— 2nd: Illuminate from 6674 to 7699, tone at 7699
— 3rd: Illuminate from 7010 to 7611, tone at 7611
— 4th: Illuminate from 7214 to 7567, tone at 7567
— 5th: Illuminate from 7382 to 7568, tone at 7568

BMW Z4 GT3

For use with a shift tone with no accompanying shift lights:
— 1st: 8320
— 2nd: 8488
— 3rd: 8744
— 4th: 8786
— 5th: 8842
For use with per-ratio programmable shift lights with or without an accompanying tone:
— 1st: Illuminate from 6801 to 8505, tone at 8505
— 2nd: Illuminate from 7539 to 8673, tone at 8673
— 3rd: Illuminate from 8206 to 8813, tone at 8813
— 4th: Illuminate from 8485 to 8816, tone at 8816
— 5th: Illuminate from 8719 to 8872, tone at 8872

Ford GT GT3 – Short Final Drive

For use with a shift tone with no accompanying shift lights:
— 1st: 7037
— 2nd: 7266
— 3rd: 7290
— 4th: 7311
— 5th: 7326
For use with per-ratio programmable shift lights with or without an accompanying tone:
— 1st: Illuminate from 5837 to 7195, tone at 7195
— 2nd: Illuminate from 6575 to 7359, tone at 7359
— 3rd: Illuminate from 6827 to 7351, tone at 7351
— 4th: Illuminate from 7011 to 7353, tone at 7353
— 5th: Illuminate from 7143 to 7354, tone at 7354

Ford GT GT3 – Standard Final Drive

For use with a shift tone with no accompanying shift lights:
— 1st: 7150
— 2nd: 7337
— 3rd: 7329
— 4th: 7344
— 5th: 7361
For use with per-ratio programmable shift lights with or without an accompanying tone:
— 1st: Illuminate from 6177 to 7280, tone at 7280
— 2nd: Illuminate from 6785 to 7407, tone at 7407
— 3rd: Illuminate from 6985 to 7382, tone at 7382
— 4th: Illuminate from 7135 to 7374, tone at 7374
— 5th: Illuminate from 7251 to 7373, tone at 7373

Ford GT GT3 – Tall Final Drive

For use with a shift tone with no accompanying shift lights:
— 1st: 7211
— 2nd: 7372
— 3rd: 7355
— 4th: 7374
— 5th: 7375
For use with per-ratio programmable shift lights with or without an accompanying tone:
— 1st: Illuminate from 6369 to 7324, tone at 7324
— 2nd: Illuminate from 6906 to 7433, tone at 7433
— 3rd: Illuminate from 7083 to 7397, tone at 7397
— 4th: Illuminate from 7219 to 7397, tone at 7397
— 5th: Illuminate from 7312 to 7384, tone at 7384

McLaren MP4-12C GT3

For use with a shift tone with no accompanying shift lights:
— 1st: 6860
— 2nd: 6870
— 3rd: 6790
— 4th: 6780
— 5th: 6691
For use with per-ratio programmable shift lights with or without an accompanying tone:
— 1st: Illuminate from 5675 to 6998, tone at 6998
— 2nd: Illuminate from 6179 to 6947, tone at 6947
— 3rd: Illuminate from 6398 to 6844, tone at 6844
— 4th: Illuminate from 6550 to 6799, tone at 6799
— 5th: Illuminate from 6551 to 6691, tone at 6691

Mercedes-Benz AMG GT3 – Short Gear Stack

For use with a shift tone with no accompanying shift lights:
— 1st: 6903
— 2nd: 6878
— 3rd: 6509
— 4th: 6465
— 5th: 6464
For use with per-ratio programmable shift lights with or without an accompanying tone:
— 1st: Illuminate from 5577 to 7073, tone at 7073
— 2nd: Illuminate from 6143 to 6974, tone at 6974
— 3rd: Illuminate from 6093 to 6565, tone at 6565
— 4th: Illuminate from 6203 to 6500, tone at 6500
— 5th: Illuminate from 6313 to 6483, tone at 6483

Mercedes-Benz AMG GT3 – Standard Gear Stack

For use with a shift tone with no accompanying shift lights:
— 1st: 6903
— 2nd: 6878
— 3rd: 6650
— 4th: 6486
— 5th: 6479
For use with per-ratio programmable shift lights with or without an accompanying tone:
— 1st: Illuminate from 5577 to 7073, tone at 7073
— 2nd: Illuminate from 6143 to 6974, tone at 6974
— 3rd: Illuminate from 6239 to 6678, tone at 6678
— 4th: Illuminate from 6259 to 6525, tone at 6525
— 5th: Illuminate from 6372 to 6507, tone at 6507

Ruf RT 12R Track

For use with a shift tone with no accompanying shift lights:
— 1st: 8216
— 2nd: 8251
— 3rd: 8653
— 4th: 8761
— 5th: 8802
For use with per-ratio programmable shift lights with or without an accompanying tone:
— 1st: Illuminate from 6000 to 8458, tone at 8458
— 2nd: Illuminate from 7029 to 8409, tone at 8409
— 3rd: Illuminate from 7984 to 8735, tone at 8735
— 4th: Illuminate from 8415 to 8798, tone at 8798
— 5th: Illuminate from 8653 to 8820, tone at 8820

Testing Methodology and Data Collection

To determine the optimal shift points in an intuitive manner and without access to the engine torque LUTs for each car, I did telemetry runs on the back straight at Talladega to form a graph for each car of longitudinal acceleration as a function of speed and gear. The optimal shift points are those intersections resulting in a frontier of greatest area covered, or put another way, those granting the least area lost relative to a constant power contour.

Planning and Execution

Inadequate instrumentation has long been a pet peeve of mine in sim racing. One of the most frustrating things for me to watch is an extremely talented driver shifting at all the wrong times due to a lack of information and/or a poor execution strategy. It is nice to know and understand what the optimal shift points are for each gear, but it takes a little bit more to make it happen on track and make real gains.

With the raw numbers out in the open from the telemetry runs, our goal is to nail as many full-throttle shifts as close as possible to those points over the course of a lap or race distance using as little concentration as possible. This calls for effective cockpit aids to give the driver precisely the information he or she needs as clearly as possible so they can focus on all the other parts of driving. For a long time now this has been done with shift lights and/or tones.

It is in my opinion that shift lights and tones are tools of timing—that they exist to tell the driver when to shift, and not anything else. The important distinction here is that I don’t see shift lights and tones as ancillary tachometers, that the RPM itself is only secondary to the issue of timing. As such, a slick and streamlined light/tone system is programmed off of time domain offsets, not frequency (RPM).

Long story short, we want to set the tone RPMs at a specific time interval before each shift point arises in a full throttle acceleration trace, and likewise with the shift light illumination intervals. Careful analysis of top level motorsport shows that this is and has been done for a long time. It’s very easy to spot from F1 onboards, particularly when compared to rudimentary implementations in the sims and sim hardware we’re used to seeing.

I believe that when done correctly, the result is that a driver will put more shifts closer to the optimum with less thought needed, granting him or her more focus for the driving itself.

Results

Definitions and constants:

Rev Limit (RPM): maximum rpm allowed by the engine
Estimated Max Power (RPM): estimate from telemetry for the rpm at which the engine produces maximum power
Ideal Shift Point (RPM): optimal rpm at which a shift should be performed in perfect conditions
Adjusted Target Shift Point (RPM): a shift point lower than the ideal allowing for varying reaction time and small engine rpm fluctuations to avoid hitting the rev limit
Rev Limit Offset Time (s): minimum time buffer between an adjusted target shift point and a rev limit as a reaction time allowance before hitting the limiter
Tone Reaction Time (s): desired time between the tone sounding and the target shift point occurring under full throttle
Shift Light Illumination Interval (s): desired time between the first and last states of the shift light illumination pattern

I use the rev limit offset time to set adjusted target shift points when they are close or coincident with the rev limit RPM.

For the following tables, these values were used:

Reaction Time (tone, no shift lights): 280 ms
Reaction Time (with shift lights): 180 ms
Shift Light Illumination Interval: 800 ms
Rev Limit Offset Time: 80 ms

Audi R8 LMS

Audi R8 LMS
 Parameters:
 - 280 ms reaction on auto lift with tone only
 - 180 ms reaction on auto lift with lights
 - 800 ms illumination time
 - 80 ms rev limit proximity allowance
 Rev Limit RPM: 8000
 Estimated Max Power RPM: 7000
 Setup: baseline (s2-2017-p1) + 60.0 L fuel, wing setting D, standard
 final drive
 Notes: Final drive options are very close to each other (~4%)

Default cockpit shift light table:
 G G G G Y Y R R R R
 6450 6600 6750 6900 7050 7200 7350 7500 7650 7800

Ratio Ideal Adj_Target Tone_No-L Tone_L Light_Interval
 1 8000 7822 7278 7475 [5572,7475]
 2 7890 7890 7578 7699 [6674,7699]
 3 7730 7730 7538 7611 [7010,7611]
 4 7630 7630 7515 7567 [7214,7567]
 5 7600 7600 7543 7568 [7382,7568]
 6 -- -- off off off

BMW Z4 GT3

BMW Z4 GT3
 Parameters:
 - 280 ms reaction on auto lift with tone only
 - 180 ms reaction on auto lift with lights
 - 800 ms illumination time
 - 80 ms rev limit proximity allowance
 - 99.6% respected rev limit
 Rev Limit RPM: 9000
 Estimated Max Power RPM: 8300
 Setup: baseline (s2-2017-p1) + 58.0 L fuel, wing setting 4 deg,
 standard final drive
 Notes:

Default cockpit shift light table:
 G G Y Y R R R R
 7700 7850 8000 8150 8300 8450 8550 8650

Ratio Ideal Adj_Target Tone_No-L Tone_L Light_Interval
 1 9000 8852 8320 8505 [6801,8505]
 2 9000 8894 8488 8673 [7539,8673]
 3 9000 8964 8744 8813 [8206,8813]
 4 8900 8900 8786 8816 [8485,8816]
 5 8900 8900 8842 8872 [8719,8872]
 6 -- -- off off off

Ford GT GT3 – Short Final Drive

Ford GT GT3 - Short Final Drive
 Parameters:
 - 280 ms reaction on auto lift with tone only
 - 180 ms reaction on auto lift with lights
 - 800 ms illumination time
 - 80 ms rev limit proximity allowance
 - 99.6% respected rev limit
 Rev Limit RPM: 7600
 Estimated Max Power RPM: 6800
 Setup: baseline (s2-2017-p1) + 58.0 L fuel, wing setting 7, short
 final drive
 Notes: Don't use the shift lights in the cockpit, they're leftover from
 the Doran Ford GT and have no relevance to the GT3's engine--not
 that they were well-suited to that car, either! Large differences
 in final drive selection call for adjusted timing in the RPM
 tables, though the shift points themselves are the same between
 the three.

Default cockpit shift light table:
 G G G R R G G G
 6700 6800 6900 7000 7000 6900 6800 6700

Ratio Ideal Adj_Target Tone_No-L Tone_L Light_Interval
 1 7600 7461 7037 7195 [5837,7195]
 2 7570 7518 7266 7359 [6575,7359]
 3 7460 7460 7290 7351 [6827,7351]
 4 7430 7430 7311 7353 [7011,7353]
 5 7400 7400 7326 7354 [7143,7354]
 6 -- -- off off off

Ford GT GT3 – Standard Final Drive

Ford GT GT3 - Standard Final Drive
 Parameters:
 - 280 ms reaction on auto lift with tone only
 - 180 ms reaction on auto lift with lights
 - 800 ms illumination time
 - 80 ms rev limit proximity allowance
 - 99.6% respected rev limit
 Rev Limit RPM: 7600
 Estimated Max Power RPM: 6800
 Setup: baseline (s2-2017-p1) + 58.0 L fuel, wing setting 7, standard
 final drive
 Notes: Don't use the shift lights in the cockpit, they're leftover from
 the Doran Ford GT and have no relevance to the GT3's engine--not
 that they were well-suited to that car, either! Large differences
 in final drive selection call for adjusted timing in the RPM
 tables, though the shift points themselves are the same between
 the three.

Default cockpit shift light table:
 G G G R R G G G
 6700 6800 6900 7000 7000 6900 6800 6700

Ratio Ideal Adj_Target Tone_No-L Tone_L Light_Interval
 1 7600 7495 7150 7280 [6177,7280]
 2 7570 7540 7337 7407 [6785,7407]
 3 7460 7460 7329 7382 [6985,7382]
 4 7430 7430 7344 7374 [7135,7374]
 5 7400 7400 7361 7373 [7251,7373]
 6 -- -- off off off

Ford GT GT3 – Tall Final Drive

Ford GT GT3 - Tall Final Drive
 Parameters:
 - 280 ms reaction on auto lift with tone only
 - 180 ms reaction on auto lift with lights
 - 800 ms illumination time
 - 80 ms rev limit proximity allowance
 - 99.6% respected rev limit
 Rev Limit RPM: 7600
 Estimated Max Power RPM: 6800
 Setup: baseline (s2-2017-p1) + 58.0 L fuel, wing setting 7, tall final
 drive
 Notes: Don't use the shift lights in the cockpit, they're leftover from
 the Doran Ford GT and have no relevance to the GT3's engine--not
 that they were well-suited to that car, either! Large differences
 in final drive selection call for adjusted timing in the RPM
 tables, though the shift points themselves are the same between
 the three.

Default cockpit shift light table:
 G G G R R G G G
 6700 6800 6900 7000 7000 6900 6800 6700

Ratio Ideal Adj_Target Tone_No-L Tone_L Light_Interval
 1 7600 7506 7211 7324 [6369,7324]
 2 7570 7532 7372 7433 [6906,7433]
 3 7460 7460 7355 7397 [7083,7397]
 4 7430 7430 7374 7397 [7219,7397]
 5 7400 7400 7375 7384 [7312,7384]
 6 -- -- off off off

McLaren MP4-12C GT3

McLaren MP4-12C GT3
 Parameters:
 - 280 ms reaction on auto lift with tone only
 - 180 ms reaction on auto lift with lights
 - 800 ms illumination time
 - 80 ms rev limit proximity allowance
 Rev Limit RPM: 7820
 Estimated Max Power RPM: 6600
 Setup: baseline (s2-2017-p1) + 65.0 L fuel, wing setting 5, tall final
 drive
 Notes: Recommend using the tall final drive ratio on most tracks.

Default cockpit shift light table:
 G G G G R R R R B B B B
 6300 6375 6450 6525 6600 6700 6800 6900 7000 7000 7000 7000

Ratio Ideal Adj_Target Tone_No-L Tone_L Light_Interval
 1 7260 7260 6860 6998 [5675,6998]
 2 7110 7110 6870 6947 [6179,6947]
 3 6930 6930 6790 6844 [6398,6844]
 4 6850 6850 6780 6799 [6550,6799]
 5 6720 6720 6691 6691 [6551,6691]
 6 -- -- off off off

Mercedes-Benz AMG GT3 – Short Gear Stack

Mercedes AMG GT3 - Short Gear Stack
 Parameters:
 - 280 ms reaction on auto lift with tone only
 - 180 ms reaction on auto lift with lights
 - 800 ms illumination time
 - 80 ms rev limit proximity allowance
 Rev Limit RPM: 7500
 Estimated Max Power RPM: 6200
 Setup: baseline (s2-2017-p1) + 60.0 L fuel, 4 deg wing angle, short
 gear stack
 Notes: Short and standard gear stacks have different individual ratios
 and thus different ideal shift points, as opposed to a swap in
 final drive. Recommend using the standard gear stack at most
 tracks. This car could really make use of a taller gear stack!

Default cockpit shift light table:
 G G G G R R G G G G
 6200 6300 6400 6500 6600 6600 6500 6400 6300 6200
 [ tachometer background R 6800 R tachometer background ]

Ratio Ideal Adj_Target Tone_No-L Tone_L Light_Interval
 1 7400 7354 6903 7073 [5577,7073]
 2 7130 7130 6878 6974 [6143,6974]
 3 6660 6660 6509 6565 [6093,6565]
 4 6560 6560 6465 6500 [6203,6500]
 5 6520 6520 6464 6483 [6313,6483]
 6 -- -- off off off

Mercedes-Benz AMG GT3 – Standard Gear Stack

Mercedes AMG GT3 - Standard Gear Stack
 Parameters:
 - 280 ms reaction on auto lift with tone only
 - 180 ms reaction on auto lift with lights
 - 800 ms illumination time
 - 80 ms rev limit proximity allowance
 Rev Limit RPM: 7500
 Estimated Max Power RPM: 6200
 Setup: baseline (s2-2017-p1) + 60.0 L fuel, 4 deg wing angle, standard
 gear stack
 Notes: Short and standard gear stacks have different individual ratios
 and thus different ideal shift points, as opposed to a swap in
 final drive. Recommend using the standard gear stack at most
 tracks. This car could really make use of a taller gear stack!

Default cockpit shift light table:
 G G G G R R G G G G
 6200 6300 6400 6500 6600 6600 6500 6400 6300 6200
 [ tachometer background R 6800 R tachometer background ]

Ratio Ideal Adj_Target Tone_No-L Tone_L Light_Interval
 1 7400 7354 6903 7073 [5577,7073]
 2 7130 7130 6878 6974 [6143,6974]
 3 6780 6780 6650 6678 [6239,6678]
 4 6570 6570 6486 6525 [6259,6525]
 5 6530 6530 6479 6507 [6372,6507]
 6 -- -- off off off

Ruf RT 12R Track

Ruf RT 12R Track
 Parameters:
 - 280 ms reaction on auto lift with tone only
 - 180 ms reaction on auto lift with lights
 - 800 ms illumination time
 - 80 ms rev limit proximity allowance
 Rev Limit RPM: 9400
 Estimated Max Power RPM: 8200
 Setup: baseline (s2-2017-p1) + 50.0 L fuel, wing setting 10
 Notes:

Ratio Ideal Adj_Target Tone_No-L Tone_L Light_Interval
 1 8900 8900 8216 8458 [6000,8458]
 2 8680 8680 8251 8409 [7029,8409]
 3 8890 8890 8653 8735 [7984,8735]
 4 8880 8880 8761 8798 [8415,8798]
 5 8860 8860 8802 8820 [8653,8820]
 6 -- -- off off off

Concluding Remarks

I hope you found this helpful and I hope it brings some more light on this subject. I’ve always nerded out over this stuff, so it’s nice to have a way to play around with it with it in a meaningful way.

While I realize iRacing has more ambitious projects, development, and fixes planned than they have time, I hope instrumentation gets a revisit at some point. The McLaren* in particular strikes me as an all too typical example of what I’ve come to expect from driving games: shift lights which either offer no help to the driver or actively hurt his or her lap time. iRacing has the advantage, however, in that it already has the infrastructure in place for ratio-specific tables, and so making changes would only be a matter of repopulating tables with different values.
* [S2-2017] Ford GT3 is a much better example

A Proposition to iRacing: I offer the following sample table to iRacing to test in the McLaren—I challenge that testers will notice the improvement immediately:

G G G G R R R R B B B B
1 5675 5675 6005 6005 6336 6336 6667 6667 6998 6998 6998 6998
2 6179 6179 6371 6371 6563 6563 6755 6755 6947 6947 6947 6947
3 6398 6398 6509 6509 6621 6621 6732 6732 6844 6844 6844 6844
4 6550 6550 6612 6612 6674 6674 6736 6736 6799 6799 6799 6799
5 6551 6551 6586 6586 6621 6621 6656 6656 6691 6691 6691 6691
6 9999 9999 9999 9999 9999 9999 9999 9999 9999 9999 9999 9999

This should fit into Z1’s Car 3 tab nicely for trial there, too.

A Further Remark to iRacing: I seem to recall an official video going over GT3 BoP and the use of acceleration traces when comparing cars in the class. I would hope that optimal shift strategies are employed or assumed in this process.

FAQ

When does shifting at the optimum RPM matter?
Put simply, it matters for any shift performed at full throttle. In traction limited scenarios, not only do mitigation techniques like short shifting or holding a gear take precedence, but the validity of the optimum strategy itself is often invalidated under partial throttle in cars with complex torque request maps, such as the linear mappings used in GT3.

What about changes to the final drive?
The final drive ratio acts only as a torque multiplier for the entire drivetrain, and so it doesn’t affect the spacing of individual ratios. Because the spacing doesn’t change, the shift points remain the same. The timing, however, changes subtly, but not enough to matter much given the limitations within GT3.

So.. wouldn’t mass, fuel load, and total drag level also affect timing since they affect the acceleration curve?
Yes, in theory these values are only correct for one particular vehicle condition, but the differences are fairly small.

Why is there a difference in specified reaction time between using only a tone and using a shift light pattern?
With only a tone, we react to a single audio cue whereas with shift lights, we have earlier warning and can act sooner after the final state is reached. It’s important to note that the values used are based on average reactions, not those achievable with full concentration.

What if my dashboard software doesn’t support ratio-specific shift light RPM intervals?
If your software lacks this feature, request it from the developer! While I don’t own a license to it nor endorse it, Z1 is the only program I’m aware of that has the ability to do this.

What makes for a good shift light pattern?
There is some subjectivity to this, but in my opinion a good pattern is one which is easily legible from your peripheral vision. You want to not only see the pattern, but recognize its shape as it unfolds.

The best-known pattern is probably McLaren’s PCU-6 style green-red-blue horizontal LED array. Originally consisting of three large, discrete states in easily-distinguishable primary colors, this pattern is easily followed out of the corner of your eye.

An example pattern that could be easily programmed for a MoTeC SLM:

1 G G
2 G G B B
3 G G B B R R
4 Y Y Y Y Y Y Y Y

Can something be done about narrow-interval light patterns flickering on and off from noisy RPM data so that they are easier to read?
What you’re after is a definable RPM hysteresis value: put simply, the RPM value governing the light pattern doesn’t update unless there is a change in engine RPM greater than the hysteresis amount—a means of filtering in this case. Most real multifunction displays have this functionality and it would be nice to see in iRacing or other 3rd party software.

Is this stuff backed up by any data—will I really make [big] gains on the racetrack?
These strategies do give laptime, but only a very small amount. How much time depends on how sharply the engine’s power falls off relative to its peak, and within GT3, only the McLaren and Mercedes are notable here. More notable are the potential fuel savings from extracting the same performance from lower revs.

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