Longitude Tire Force: low-mu to high-mu road

Hi Joe, did you run at constant speed, braking or accelerating at the point you hit the high-mu border? 
What is "shortly after"? A second, a tenth of a second, a hundredth of a second? Does your tires have lag?

Hi Jesper, 

No braking at any point. Throttle demand is 100% while on low-mu. once the front wheels hit the high-mu road, throttle demand goes to zero.

LC#2 has a higher wheel speed and wheel slip at the start of the high-mu road. The resulting long tire force magnitude is essentially the same in the high-mu road as LC#1 (which has a lower wheel speed and wheel slip at the start of the high-mu road). 

Apologies, by "shortly after" I mean from when the front wheels enter high-mu to the when their wheel slip goes to zero slip.

Could this be because for the tires long force vs slip relationship, the wheels are slipping so much that they are in the flat portion of the curve...and so a difference in wheel slip at that point won't generate a different long tire force? (see below)

What is the slip? You should be able to plot that and understand what is happening.

The slip should drop quickly when you drop the throttle. How fast depends on the inertia of the driveline, seen from the wheel end. The engine (flywheel) is very "heavy" seen from the wheels, with I_eff = I_eng*r^2 where r is the gear ratio. So it might take some time for the wheels to slow down. All should be visible from plots of wheel speed, tire slip and vehicle speed.

Thanks for the help Jesper. After looking into it some more, the wheels have a very large slip from the full throttle on ice. When plotting long tire force vs slip it confirms the long force has saturated at this high slip. Was just counter-intuitive initially when initially seeing the results...but makes more sense to me now.

Thanks again,

joe.

Thanks for the help Jesper. After looking into it some more, the wheels have a very large slip from the full throttle on ice. When plotting long tire force vs slip it confirms the long force has saturated at this high slip. Was just counter-intuitive initially when initially seeing the results...but makes more sense to me now.

Thanks again,

joe.

Reminds me of an old friend who, during a winter test session in Northern Sweden, pointed out to a famous European sportscar manufacturer that when they thought they were testing driveline performance on ice by giving full throttle from stand-still, in reality they only tested the tires. 25 Nm would have been enough to break free the tire grip on that surface.