GM: common torque control feedforward

[sshane]

[twilsonco]

I wonder how many other makes would benefit from this, which is essentially increasing the FF slope at lower speeds. Here's Sonata, for example

[morrislee]

this will be very nice addition, feedforward from tim before mitigated a lot of the inconsistencies between speeds in curves! i am willing to assist in any driving data needed for this on the sierra

[sshane]

new PR: https://github.com/commaai/openpilot/pull/26371