In deciding what car to get I was questioning if the F10 M5 had too much torque. That is, is there any point during regular city/highway driving where the car is NOT traction limited. I would be very interested in everybody's opinion.
I am taking delivery of my M5 next week and can report some first hand info then. I ordered the car based on test driving it and its competitors, loved it, and loved the torque, but got to wondering if it was all needed other than at the track.
So, being a computer type, I wrote a little acceleration simulator in Perl. It models all the following
- Engine torque curve
- Drivetrain losses
- Gear ratio
- Drag
- Downforce
- Rolling resistance
- Estimate of inertial mass of rotating parts
- Weight transfer to back during acceleration
- Traction
My understanding of the way that traction works is that for a decent road tire and with good use of the accelerator, the tire can push forward with about the same force as the downwards weight on the driving tires. An F1 car can do way better than this, and bad tires on a bad surface way less.
When the car is accelerating full out, weight transfers to the back. My modelling tells me about 66% heads towards the back. Given the car and passenger is about 4400 pounds, and downforce adds relatively little until high speed, that means the car is limited to pushing forwards with only about 4400*66% = 3000 pounds of force. Given the gear ratios and such, my little simulator says that almost right around 100 km/h (2nd gear @ 6000 RPM) all the engine torque can be put down on the pavement.
Once you shift to 3rd, the driving force on the tires at the highest part of the torque curve is about half the weight of the car, so you are golden in 3rd.
So that means when cruising down the highway at about 100 km/h in 3rd gear (a very regular happening), we are no longer traction limited and so, no, the M5 does not have too much torque! Phew!
Does your practical experience jibe with this?