On Feb 10, 2:03 pm, (Doug Miller) wrote:
In article , Tom Watson wrote:
On Sat, 10 Feb 2007 13:39:23 GMT, (Doug Miller)
wrote:

In article .com,
"onoahimahi" wrote:
On Feb 9, 2:39 pm, (Doug Miller) wrote:
In article . com, "Geo"
wrote:

Just a couple other things that might make a difference. I've heard
that having 3 wheelers makes a difference. Check your rules on that
one. That is, one of your wheels simply doesn't touch the track. The
friction of three wheels is less than four.

Incorrect -- the total friction is unchanged, because the weight supported
remains the same. With only three wheels touching the track, the wieght on
each wheel, and consequently the friction force on each wheel, goes up by
33%.

A three wheel car is faster because it takes less energy to spin three
wheels than four.

Again, incorrect. The total energy is the same, because the total friction is
the same.

If anything, a car riding on only three wheels is likely to be somewhat
slower: since the friction force will be imbalanced left-to-right, the car
will travel a slightly curved path, with the two wheels on the concave side.

Also, on the wheels
themselves some people make the part of the wheel where the nail goes
through convex. Again, less friction.

Again, incorrect. Changing the size or shape of the contact area does not
change the amount of friction.

Moving the friction point closer to the axle reduces the torque on the
wheel.

And that makes a difference how?

http://www.pinewoodderbyphysics.com/...cture%2011.pdf

Thanks, Tom, that says pretty much exactly what I've been saying all along.

Again incorrect - you said above "If anything, a car riding on only
three wheels is likely to be somewhat slower" but this reference, as
well as the comments of other posters who actually know how to help
their sons build fast cars, says "raising one front wheel does
increase speed considerably"

I can speak with authority on this subject because my son's last two
cars have been superfast not only winning first place pack but going
on to win first place district. Last year at the District race, he had
three of the 5 fastest times of the day for all age groups. Further,
we got to "Support our Troops" in a small way by helping a boy whose
dad is deployed in Iraq. He came down to my shop and we helped him
build his car and he won first place in his pack. Both cars had a
lifted front wheel.

-Scott

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.