I have heard and it makes sense to raise one wheel up a little bit to reduce
friction, but which wheel one of the rear wheels where the weight is or one
of the front wheel and hope it goes straight with one front wheel?
It will steer towards the side rail with an unbalanced situation like you
describe. If any thing you will be increasing friction. The only real
friction is between the axel and the wheel. If you eliminate 1 wheel the
other 3 wheels will have more friction. Use tons of graphite on the wheels
A trick I used was to put the nail/axel in my drill with the wheel mounted
and added lots of graphite. With the axel spinning quickly in the drill and
holding the wheel all surfaces became polished/burnished and loaded with
graphite. My son won 2 trophies that year with that car.
Joe, you can't raise a rear wheel, or the car will sit cocked.
You can raise a front wheel and adjust the steering by tweaking the other
front wheel so that the car runs true.
It doesn't increase or decrease friction (all else being equal) to ride
on only three wheels. The total drag from friction is the same in both
cases. However, potential energy can be saved if the car runs true down
the track, because the lifted wheel will not be rotating full speed when
the car crosses the finish line. The lower momentum of that wheel must be
conserved, and the only place for it to go is into the forward momentum
of the car. So, there is some potential benefit from raising a wheel.
I don't mean to downplay the importance of lubricant and polished bearing
surfaces. That's paramount.
You are kidding, I hope. The angular momentum of the wheel would be tiny;
and any force you would save by not generating it would be a drop compared
to the rest of the forces.
I have heard that raising a wheel reduces friction, but the odds of having
it track as well as 4 wheels is not good.
Not kidding. It can produce a measurable result. That's not to say it's
particularly important in the grand scheme of things, and I did try to
make that clear.
Well, it doesn't reduce friction, and it is true that it's harder to get
the car to track as well with only three wheels. But not impossible.
Since I haven't seen it mentioned here, I should point out a
very important performance factor that is usually neglected, and that is
the track itself. A car which could perform extremely well on a top-
quality track often fares poorly on a bad track. For example, on a bumpy
track, you can't push the weight back as far as you'd like (and could get
away with on a smooth track).
True. The axle load on a car with four wheels would be 1/4 the car's
total weight. It would be 1/3 on a car with a lifted wheel. But the axle-
wheel friction is directly proportional to the axle load. That is, for
any given wheel:
f = c * (1/4)m = cm/4
where f is the friction, c is a constant, and m is the car's weight.
So t_4 = 4f = 4cm/4 = cm
where t_4 is the total friction from wheel drag in the 4-wheel case.
Similarly, with three wheels, as you noted, we have, f = cm/3, but
now there are only three wheels, so the total friction is
t_3 = 3f = 3cm/3 = cm
Since c is the same in both scenarios, t_4 = t_3. That is, the total
friction is the same in both cases.
Yeap, the graphite is key, as well as, making
sure the wheels are aligned straight. Make sure
to roll along a flat surface and it maintains a
true straight line. Trophies two of three
years. The one year an axle came lose. Ha!
On Thu, 05 Jan 2006 20:24:19 GMT, "Leon"
" making sure the wheels are aligned straight."
When our sons did this, I sawed two kerfs in a 2x4 block and set the wheels
in them for alignment. They did well, years later I did the same for a
grandson, his didn't do worth a darn.
As a grandfather I have made many Pinewood Derby cars for scouts in our
family. The kids designed them, I did the body work, they painted and
finished wheels and hop-up. We had many winners.
My daughter was Den Mother for her son's Cub pack and helped run the
derby. In her final year she entered the race against the dads, and she
The track always had a 3/8" center strip to keep cars on track so our
main concern was clearance underneath the body.
If you search the Internet, you should find a site with all kinds of tips
for faster cars, our son did but I don't know where.
"He must have been proud of all the hard work you did!
This is supposed to be a father/son project, unfortunately some sons don't
get to touch them.
I think that this depends on the judgment of the parent and the age of
Last year, the first year that my boy was in a PineyWood Darby, he was
seven, and I let him draw the car and then I roughed out the blank on
the bandsaw, according to his drawings.
He then used the rasp and various grades of abrasives to bring the car
to its final shape.
He did the finishing.
I knew, nothing about the preparation of the wheels and axles.
He came in Third in his pack and was well satisfied.
This year he will be Eight. I will explain the physics of weight
placement, friction, etc.
He will true the wheels and polish them.
He will true the axles and polish them.
We will not cut out on the bandsaw, because I am too afraid of my
eight year old running it.
We will use a coping saw.
What I learn wd from last year is that we should build two cars. I
will build one and show him the steps. He will build the other, step
by step with me.
He should learn a lot from this.
Above all, I want the boy to have fun. I don't want it to become a
We will use our best efforts to produce a car that does as well as it
Tom Watson - WoodDorker
tjwatson1ATcomcastDOTnet (real email)
Many smart people disagree about whether it is better to have one wheel
raised or not. Truth is, you're not very likely to get your axles
positioned accurately enough for all 4 wheels to carry weight anyway.
Three will be carrying the weight and one will be loafing along. Oh,
it will be turning alright, but it won't be carrying much weight. If
it touches the track at all, it be a result of the slack between the
hub and axle that allows the "high" wheel to drop down to contact the
track. The light wheel will also rub along the center rail, so it
needs to be treated the same as all the others.
That said, most of the faster cars I ever saw had one wheel raised just
a little. You can only raise a wheel on the light end of the car. If
you try to raise a wheel on the heavy end, that wheel will just go down
anyway and raise the one on the opposite corner.
Find a hard, smooth surface and roll the car to see if it rolls
straight or not. If it doesn't, tweak the front axle by bending it
slightly fore or aft until the car rolls straight.
"Give a hungry man a fish and he will eat for a day. Teach him to fish
. . . and he will sit in a boat and drink beer all day."
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