Friction coefficient!!

[Necrobata]

Hey guys, i wanted to calculate the friction coefficient of our tires.

Now i have a couple of ideas for this.

1- Attacth the tire to a Pulley-rope system, in wich the tire wont roll but slide, adding weights to the system until the tire slides. Knowing how much weight we added, gives us the strength needed to move them, therefore the friction force and then we can get the Friction coefficient from there.

2- I have another theory, i possess the performance curve of the tire set (Traction vs vertical force), if the static Traction is given, that is in fact force, can i take it as the Force of friction?

Im pretty much sure about the second idea, but i wanted to hear opinions. Maybe i should take an average of both methods? Im listening,

Thanks for reading,
Att: Angelo S.
Chief of suspension division
Team FSAE UCV

[Necrobata]

Hey guys, i wanted to calculate the friction coefficient of our tires.

Now i have a couple of ideas for this.

1- Attacth the tire to a Pulley-rope system, in wich the tire wont roll but slide, adding weights to the system until the tire slides. Knowing how much weight we added, gives us the strength needed to move them, therefore the friction force and then we can get the Friction coefficient from there.

2- I have another theory, i possess the performance curve of the tire set (Traction vs vertical force), if the static Traction is given, that is in fact force, can i take it as the Force of friction?

Im pretty much sure about the second idea, but i wanted to hear opinions. Maybe i should take an average of both methods? Im listening,

Thanks for reading,
Att: Angelo S.
Chief of suspension division
Team FSAE UCV

[whiltebeitel]

Consider with the 1st method that the Coefficient of friction varies with load in tires, which is why a lighter car can turn faster than a heavy car. If you have good emprical data, I would use that, but that is also dependent on the surface it was tested on. Rough aggregate concrete would give you a larger CoF than smooth asphalt or a steel belt.

Is the 2nd method a tire model, like the Pacejka? that would be the best thing to use if you can't test the tires on a car if you're trying to find a design load case.

[Edward M. Kasprzak]

Your school is a member of the TTC, so if we've tested your particular tires you can look at the data.

Note that your method #1 will give you a sliding coefficient value, but this will not be the peak value. You also want to do your tests with the tires at operating temperature--they're very load and temperature sensitive.

[Necrobata]

So we have the data on our TTC database? well, guess im gonna have to look for it, the database u guys provide is wide and im a rookie XD ill keep searching, thanks!!

[Necrobata]

Victory!! Well, i used the second method, it gave me around 2.6 and the one TTC provided was 2.47, i think i might go for an average! Thanks!!

[woodsy96]

I would be sceptical of assuming a friction coefficient of anything that high.

Remember that the Coefficient of Friction depends on both surfaces - and the TTC data from TIRF @ Calspan is run on a coarse sandpaper belt. When you use the MRA model it uses a friction coefficient input to acount for the difference between running in a perfectly clean laboratory and driving on a dusty asphalt/concrete pad.

Read http://fsae.com/eve/forums/a/t...426032855#9426032855 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/8076081755?r=9426032855#9426032855) for a start, there is another thread where teams discuss the varying max braking forces. From memory most teams only peak about 1.1-1.2G braking but are much higher for cornering (1.5G+, possibly even as high as 2G in transient situations). Look at the skidpad times from various competitions to give you a better idea.

[Simon Dingle]

Peak braking accel. should be much higher than 1.2g. There's data from one of FS Austria's special events with recorded *average* braking accel at 1.7g, I would expect peak to be slightly higher.

[Simon Dingle]

And here's the link:

http://fsae.com/eve/forums/a/t...=546101683#546101683