Car tyre & surfaces recording without engine sound. I want to record different surfaces in average speed (Gravel, tarmac, mud, water, sand, etc...). Any ideas ?
A few suggestions:
find a downhill slope, so you can get up to speed, kill the motor and record steady state onboard sounds
up & stops are ok, just get up to speed & turn off the motor
aways are trickier, again a steep downhill slope may be the best way, even if you have to back up, get started a bit, kill the motor then slowly roll past recorders as gather speed from the slope
One thing to be aware of: some vehicles, mine included, have power steering & power assisted brakes. So when you turn off the motor your ability to steer and to stop is diminished. You will want a confident careful driver who is aware of this & does some tests before pulling up close to a recordist. Safety first!
My immediate answer would be to try and get access to an electric car - no engine noise and you can run them at fair speeds these days.