Yeah some of us are not using the engine beat, its distracting for some folks...
I think it would make more sense if Andre had it come in like how Simvibe uses "engine load" based on the pedal depression but letting us adjust the start point %. Like eg 60% depression. An alternative would be for it to look at the cars max RPM being used and become active in the last 70% of this which would activate for each gear. So with say an 8000 RPM car it would come in and increase in strength from 5600 rpm to max volume at the 8000 RPM. This then makes gear changes more fun also as this is active at the high rev values only.
I created good effects layers like this in Simvibe in the past that people seemed to enjoy.
SSW Mono Front Pedals & Seat Rear
In audacity, you would select effects to operate on your L or R channels to represent front/rear.
So this means you have to adapt any typical stereo files that they are not on both L/R.
As an example, if L channel was your pedals and R your seat.
Then you could try wheel slip effect set to L only (blank on the R channel)
But as this uses (8) & (9) typically for "left" and "right" wheels then both these files would need to be the same.
So I assume you would want to ensure the file for them is at a lower dB as both will be active at the same time on your mono channel for say pedals. If you wanted it for seat youd do it that (8) (9) operated only for the R channel and (blank on the L channel)
You have to adapt stereo effects as it would be a bit weird to feel the left wheel in pedals and right wheel in seat. Or left bumps in pedals and right bumps in seat.
I think you should try Acc for Seat only and Dec for Pedals only.
For Lateral G (14) (15) do the same as with wheel slip but set those to the R channel to operate only on your seat.
This way you could have:
Acceleration in seat
Braking in pedals
Wheel slip in pedals
Lateral G in seat
Bumps in both (As Dual Mono)
Damage in both
Gear in both
Engine in both
Hard to explain but actually simple to do....
As using 2 Channel mode you must ensure ALL files use (L/R) 2 channels.
Just make sure the non-needed side is blank but not deleted.