" . . . don't you guys pick your heaviest drivers for the skidpad?"

[Daves]

This was said by Vinh from the University of Toronto in the following topic:Topic: Delft Car (http://fsae.com/eve/forums?a=tpc&s=763607348&f=125607348&m=3846009273&r=6196079283#6196079283)

I must diagree with the theory that the heaviest drivers should be used for the skidpad event, and this is why:
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Weight transfer is one limiting factor in the amount of grip a car can generate with its tires. The friction force a tire can generate increases as the load on it decreases, but not as fast as the load increases. In other words, the coefficient of friction is non-linear. A lighter car on the same tires will be faster than a heavier car with identical suspension geometry and power-to-weight ratio. In a turn, the lateral acceleration transfers weight from the inside tire to the outside tire. The grip generated by the outside tire increases, but not as much as the inside tire's grip decreases. So weight transfer decreases overall grip. ~ "Balancing Act" by Dan Barnes, p.92 of March 1997 Sport Compact Car<HR></BLOCKQUOTE>

http://what3542.5u.com/dave/images/lateral_tire_grip.jpg

http://www.letu.edu/formula

Formula Photos & Links (http://what3542.5u.com/dave/fsae/formula_photos.html)

[Mi_Ko]

Dave thats theory! You have to consider some other factors:

- your heavy driver is a better than your lightweight one. http://fsae.com/groupee_common/emoticons/icon_cool.gif

- If tire are loaded with more weight, their temperature increases and so do the c.f.

- the heavy driver has a lower c.g. (a fat ass) http://fsae.com/groupee_common/emoticons/icon_smile.gif

- most of fsae tyres are build for much heavier cars. As you can see the c.f. is near linear in the area we are in.


The best way is to test drive a lot and pick up a responsible driver with good timing and one fast guy!

2002/03 University of MARIBOR - Team Member

[vinHonda]

I said that because of temperatures. And purely that only.

What the theory says is right, but its only a 2D representation of full out tyre data. Understanding temperatures is a whole other dimension.

Vinh

University of Toronto Formula SAE Racing Team
www.fsae.utoronto.ca (http://www.fsae.utoronto.ca)

[Charlie]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by vinHonda:
I said that because of temperatures. And purely that only.

What the theory says is right, but its only a 2D representation of full out tyre data. Understanding temperatures is a whole other dimension.

Vinh

University of Toronto Formula SAE Racing Team
http://www.fsae.utoronto.ca<HR></BLOCKQUOTE>

Wow, interesting to hear you say that- I was trying to get you to talk temps in the other thread to no avail. http://fsae.com/groupee_common/emoticons/icon_wink.gif

-Charlie Ping

I just need enough to tide me over until I need more.

[Joseph]

Why doesn't someone just try it and compare times. Get a good driver that's not too heavy and start adding lead weights to the car close to the mass centroid. If the time improves then your know for sure.

Joseph Kliewer
University of Oklahoma

[Sam Zimmerman]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Joseph Kliewer:
Get a good driver that's not too heavy and start adding lead weights to the car close to the mass centroid. If the time improves then your know for sure.<HR></BLOCKQUOTE>

If I remember right, SVSU did just that in the SAE paper #2002-01-3300 and found, in their case, that the extra weight hurt in the skid-pad.

Having said that, I have heard of teams trying to pick drivers by their weight and I think that is ridiculous. Having drivers get into shape is a good idea but the difference in skill between drivers will more than make up for a beer gut. Last year our fattest driver was also our fastest and I would like to think that it had more to do with skill than the extra ballast. http://fsae.com/groupee_common/emoticons/icon_wink.gif

Sam Zimmerman
Vandals Racing (http://www.uidaho.edu/~racing)

[vinHonda]

Charlie, my apologies! I dunno why I didn't make it more clear..... but it's so true that even with tyre data, we only know so much.....

I've noticed thru on-track testing, that temps make a huge difference.

I would also add to post about bigger drivers being faster: all our circuit drivers are big guys......and I dunno whY?? perhaps they can reef at the wheel better thru the slalom?

Vinh

University of Toronto Formula SAE Racing Team
www.fsae.utoronto.ca (http://www.fsae.utoronto.ca)

[gug]

could it be the extra weight making your snow chains dig in better?

[A Reinke]

more weight means less power at the engine to drive the oil pump for the muffler bearings. it could be catastrophic!