F1 Tips Part 1 - Weight Distribution

[dale]

F1 Tips

F1 cars on tarmac can be tricky things to get working; they never seem to have enough rear end grip. I remember when I first had one back in the 90s how annoying I found it. I'm finding it a bit easier now I have more experience, so I thought I'd share some hints and tips. This is intended to be the first of a few posts.

Most of this will be relevant to any rwd pancar, and some of it will be relevant to any car.

Weight Distribution Basics

In a straight line, moving the weight distribution (WD) onto the rear axle gives more rear traction. Period. Look at a dragster. They only have to go straight, and where is all the weight?

When you come to a corner, it gets a bit trickier. All that weight that was pressing downwards in a straight line will now want to push sideways through the corners. So you tend to find that when turning into the corners, a car with a lot of weight on the rear will hang the back end out. Watch some videos of Porsche 911 racing to see this in action.

You can minimise this by having a lower centre of gravity; with a lower CoG, less weight will transfer onto the outside tyre, and less grip will be lost.

Starting Point

So, where do you start? The general starting point should be to have a weight distribution that matches the tyre widths. So if the front and rear tyres are equal widths (like a touring car), you would start with a 50/50 balance. If the rear tyres were twice the width of the fronts, you would want a 67/33 split (with the rear being heavier). The reason for this is so that each square mm of tyre (both front and rear) has about the same amount of weight on it through the corners, making for a balanced car.

For the F103/F109 tyre widths, a 60/40 split seems to work pretty well, as the rear tyres account for about 60% of the total tyre width.

The HPI and F104 will probably work better with a 55/45 split.

Measuring it

To measure the weight distribution you need
- A flat surface
- Two cheap sets of digital scales
- A block of wood the same height as the scales

- Put the block and scales onto a flat surface
- Place the front wheels on the scales. Make sure they are in the centre of the scales, as cheap scales can give different readings in different areas of the scales!
- Place the rear wheels on the wooden block
- Write down the total weight of the front wheels
- Swap the car round so the rears are on the scales.
- Write down the total weight of the rear wheels.

Your rearward weight distribution is:

rear_weight / ( rear_weight + front_weight )

e.g.

Fronts = 450g
Rears = 650g

Distribution
= 650 / ( 650 + 450 )
= 0.59
= 59% rear (so 59/41 split)

How to adjust it

As a general rule, you never want to add lead to the car. You have to accelerate and brake this weight, and remember that all of the weight wants to push sideways round the corner. So you want the car to be as light as possible.

You should aim to get the desired weight distribution by moving firstly the batteries (since they are heaviest) and then the radio gear. You can even move the motor; if you fit a smaller spur and pinion you can get the same ratio, but the motor will have moved closer to the rear axle.

On the real F1 cars, we even change the wheelbase to get the WD we want, as sometimes it's just not possible to do it with ballast. This shouldn't be necessary with an RC car though as we can move a lot more stuff around.

Quick guide

If you find the car spins out too easily coming out of the corners, moving the WD rearwards should help (e.g change the batteries from being mounted along the centre of the car like the F109 is as standard, to being mounted across the rear of the chassis, like an F103).

If however you find the car is spinning out when turning into the corner, it's probably already too far rearwards and you should move the WD forwards (e.g. move the batteries forwards).

[dale]

Part 2 now posted - Tyres

[werner1619]

Hi, great post !

Nice of you to share your insight gained through experience.
Hopefully some of the pro's will learn from this and also share their experience.

If you could, elaborate on motor power and WD.