Hopefully this diagram will explain it.
Having trolley wheels at the front like most cars only eliminates half the problem.
Cars with all trolley wheels experience no corner drag.


Click on picture for a larger view. Also, the red line is the track around a bend.

Fixed wheel cars with a shorter wheel base, ie, shorter car length, experience less drag (compared to longer wheel base fixed wheel cars) because the angle between the wheels motion and the track will decrease.

Thats why, if your going to have a fixed wheel design, your wheel base needs to be as short as possible.

But overall, a castoring trolley wheel design on ALL wheel is the most efficient design.

Ian Gardner's simulations show that having fixed wheels is like carrying an extra 750grams.

I have noticed in the past that most cars have their front guides very close together, so that they are rolling along the track. Is this the only way to go? Will having a bigger gap between your front guides cause problems?

TonyB wrote:Ian Gardner's simulations show that having fixed wheels is like carrying an extra 750grams.

750 grams?! That's a bit rich. Look at NFG (last year's nationals winner). No steering in sight. It should have been a tassie blitz if it was 750 grams as you say.

PWK wrote:

TonyB wrote:Ian Gardner's simulations show that having fixed wheels is like carrying an extra 750grams.

750 grams?! That's a bit rich. Look at NFG (last year's nationals winner). No steering in sight. It should have been a tassie blitz if it was 750 grams as you say.

My mistake, its actually 350 grams. However, if your running the nylon wheels its less because there is less friction, and drags easier.

Using alloy fixed wheels is like carrying 350grams more weight.

Run this in the simulator and you will see the difference.

Redland, having a slightly bigger gap than is necessary at the front will mean your car will be constantly changing direction. However this shouldn't cause a problem if your car can run true and you have casting front wheels. It's vital for fixed wheels to have their guides close. This is because if each wheel isn't 100% lined up, your car will be constantly dragging. You don't want that! Redland (A.C.) wasn't your design casting. Thats the way to go!
Girrawheen SHS follows a similar size gap to Belridge. Belridge usually has around 1-2mm for each side. Making around 19mm apart. Also you need to consider whether or not to use wheels on your bearings! If you use a wheel on you bearing, there will be less drag due to less friction and force on the support is much less! Centripetal Force=mv^2/r
It is worth putting some time into this because you can lower the guides further down. Also if your bearings are not as good as others then, they don't require to spin as fast.

Girrawheen cars all have a low center of gravity and therefore really stable! Our guide are 2-3mm above from the track although they are plain bearing on a screws. This is similar to the height you need to have them for wheels. Belridge has theirs around 4mm. In the Western Australian competition there were a few car which had theirs around 7-9mm They had serious problems