Removing Differential Grants Superspeed

I did a search and looked through the bugs list and found nothing on it, so thought I'd make a thread for it.

If you remove just the differentials for vehicles, it has a weird effect on the transmission and torque. It lowers most vehicles' acceleration dramatically, but if you're patient and clutch kick them into the powerband until they get up to speed, it allows the majority of them to reach much greater top speeds than would usually be possible stock, often only using 1 gear (or Reverse gear, if you can keep it stable). I wrote down all of the results of the top speeds for all of the cars currently in the game below. Any custom alterations or specifications to vehicle presets will be noted in parentheses. All results are with differential removed, in first gear, from the Pure Grid default spawn unless otherwise noted.

Example top speeds (airspeed) from Debug 1:
Gavril D15 I6 RWD: 133 MPH
Gavril D15 V8 4WD Off-Road: 75 MPH
Gavril D15 V8 RWD Sport: 146 MPH
Gavril D15 V8 4WD Stripped: 123 MPH
Gavril D15 V8 4WD Stripped (No transfer case): 173 MPH
Gavril D15 V8 4WD Stripped (No cab, no transfer case): 263 MPH, 2nd gear
Gavril D15 V8 4WD: 105 MPH

Gavril Grand Marshal V8 RWD Police Package: 173 MPH, 2nd gear
Gavril Grand Marshal V8 RWD Sport: 180 MPH, 2nd gear
Gavril Grand Marshal V8 RWD: 179 MPH, 2nd gear
Gavril Grand Marshal V8 RWD (Custom Stripped): 207 MPH, 2nd gear

Ibishu Covet 1.5 DXi Turbo FWD Rally: 159 MPH
Ibishu Covet 1.5 DXi Turbo FWD Sport: 159 MPH
Ibishu Covet 1.5 DXi Turbo FWD: 111 MPH
Ibishu Covet 1.5 DXi Turbo FWD Rally (Custom Stripped): 179 MPH

Gavril H45 Cabster V8 RWD Cargo Box Uplift: Unexpected bug, can't remove differential without game crashing. My guess is something to do with the dualies.
Gavril H15 Vanster V8 RWD: 131 MPH
Gavril H15 4WD Stripped: 125 MPH
Gavril H15 4WD Stripped (No transfer case): 187 MPH

Civetta Bolide (Unmodified, control test): 146 MPH, 4th gear
Civetta Bolide (Stripped of body, control test): 213 MPH, 5th gear

Note, the Civetta Bolide has no differential option to remove, which is why it's my control test. Also of note, the Civetta Bolide seemed more unstable than just about any of the other vehicles tested, both unmodified and stripped. It typically needed constant steering corrections to keep it straight accelerating full throttle at any speed unless you found a perfect sweet spot of balance. (Getting the green dot to stay in the horizontal center on the G circle in debug mode 1 is a good way to try and find this if you're having trouble visually gauging this.) Even then, it tended to fall back out of it within a few seconds and start veering again with little recognizable consistency.

 

This is because you're removing the differentials gear-ratio from the wheel-torque calculation, which means it'll become from 3-4 to 1.0(meaning it's a direct drive from the gearbox to the wheels). This is why the acceleration goes down yet top speed goes up.. So no, not a bug. Though technically it should be impossible to drive around with no differential, since you'd have nothing connecting the gearbox to the wheels in real life.

 

I wasn't sure if I should post it in the bug forum or general discussion, but there was a lot of buggy and strange behavior associated with removing the differentials overall, so it seemed like it would be a good thing to bring up in general in the bug report forums.

 

I'm trying to see what makes this happen so i started changing numbers in the rear diff.

I tried this with the Grand Marshal default.

done with stock 3.27 gears:
axleFriction at 12 (default): 116mph
axleFriction at 0: 117 mph
axleFriction at 50: 115mph
No real difference.

done with 1.0 gears:
axleFriction at 12 (default): 125mph. ran into edge of pure grid
axleFriction at 0: 125mph. ran into edge of pure grid again

So then i thought that maybe the game defauts the diff gears to 0 but the car doesn't move then.

After that I just deleted the rear diff code for the default Grand Marshal and got 179mph after a long time.


I can't really tell why it goes faster

 

Commenting out just the "differentials" section does give an unrealistic amount of power and top speed. Acceleration is also much faster if the gear ratios are the same.

Power should be realistic when differentials are defined. I think the default calculation for no diffs broke when the new diffs were added. It's like the opposite of RoR, where adding diffs doubled power.

 

Not sure if it's a clue to anything or not, but it has a very different effect on 4WD vehicles. Take the D15. On the standard V8 4WD model, removing the differential only increases the top speed of it by about 6 MPH. With the V8 4WD Off-Road model, taking out the differential severely reduces the performance of the vehicle, making its acceleration dreadful and lowering its top speed by 36 MPH.