At it's most basic level setting up an RC car involves making changes to the way the car reacts to weight transfer. Diving too much under braking ? Stop the weight going forwards.. Not able to make a turn coming out when you're on the throttle ? too much weight moving backwards.
Below are some of the changes that can be made to help you get a setup that not only works, but more importantly, works for YOUR DRIVING style.
- Camber:
This is the angle that the wheels lean left or right when looking at the car from in front or behind the car.
Camber can be POSITIVE (top of the wheel further away from the chassis than the bottom) or NEGATIVE (top of the wheel closer to the chassis than the bottom.
Note: Generally, you will NEVER need to use POSITIVE camber.
- Caster
This describes the forward/backward angle of the steering block in relation to a line perpendicular to the ground.
A higher caster angle has the effect of leaning the tyres into the direction of the corner.
More caster will result in:
- better straight line stability
- less steering on corner entry
- more steering mid corner and corner exit
Less caster will result in:
- decrease in straight line stability
- more steering on corner entry
- less steering mid corner and corner exit
To adjust caster, you would normally have the change the steering blocks out for ones with a different amount of caster on them.
- Toe Angle:
This is the angle that the wheels point left or right at when looking from above the chassis.
Toe can be IN (front of the wheels pointing towards the chassis) or OUT (front of the wheels pointing away from the chassis).
Front:
More Toe In:
- Increases understeer
- Less steering at corner entry
- Decreases straight line stability
More Toe Out:
- Increases oversteer
- More steering at corner entry
- Increases straight line stability
Rear:
More Toe In:
- Increases understeer
- Increases stability on power
Less Toe In:
- Decreases stability on power
Generally the Rear wheels should never have toe-out, but the Front wheels can have either toe-out or toe-in
- Shock Damping/Springing
Shock absorbers and the springs you use are one of the most critical elements of any setup.
Shock springs:
A Stiffer spring (higher rating):
- Make the car more responsive
- React quicker to steering
- Better suited to tracks where bumps are quite low
A Softer spring (lower rating):
- Allow the chassis to roll around a little more
- Tend to perform better on bumpy tracks
- Make the car less responsive
Damping:
Damping mainly helps with a change to the cars suspension, such as a bump or braking for a corner. It is managed through the use of a shock oil and a shock piston.
Shock oil is rated on how viscous it is with a higher rating meaning the oil is thicker and more viscous.
Shock pistons have a number of holes in them to control the flow of oil through them.
Front:
Softer Damping (either through thinner oil or a piston with more holes):
- Slower steering response
- Decrease initial steering
- Increase steering at corner exit
Hard damping: (either through thicker oil or a piston with less holes):
- Faster steering response
- Increase initial steering
- Decrease steering at corner exit
Rear:
Softer Damping:
- Faster steering
- Increase rear grip at corner exit
- Decrease rear grip under braking
Harder Damping:
- Slower steering
- Decrease rear grip at corner exit
- Increase rear grip under braking
Getting shock damping and springing right for the track conditions is something that can transform the way your car handles.
- Droop/Downstops
Droop is a much discussed topic (how to measure it, what it is etc) Put simply, droop is the amount of difference between the ride height and the limit for the suspension arms.
Downstops are found on most modern touring car chassis and are used to limit the amount of downtravel that the suspension arms have. When someone running a touring car says they are running "5 droop on the rear and 4 on the front" they actually mean that the suspension arms are measured at 5mm below the chassis level and NOT the actual droop measurement.
To measure droop, use a ride height gauge and take a measurement of ride height at one end of the vehicle. Now lift that end of the vehicle slowly until you get to the point where the tyres leave the ground. Measure the ride height again at this point. The difference between the first and second measurement is Droop.
To measure downstop travel, remove the shocks and any anti roll bars you may have installed on the vehicle. PLace the chassis on some droop blocks and make sure the suspension arms drop under their own weight. Now take your droop guage and take a measurement from the bottom of the suspension arm. This can be changed by turning the downstop screw in that suspension arm (higher number on the guage = less downtravel).
Note: Generally, the terms droop and downstops are used interchangeably when referring to a Touring Car setup change.
- Ride height
This is how far from the ground the chassis is when stationary. It is normally measured in mm. You can raise or lower the ride height depending on track conditions.
- Gearing:
You can change the gearing of the vehicle to tune the speed of it to the track you are running on. A good start point is to set the FDR so that the top speed is reached at about 3/4 of the way down the main straight. From there you can tune it to your liking.
FDR (Final Drive Ratio):
This term relates to the final drive ratio on an rc vehicle.
A lower FDR will generally increase the top speed of the vehicle, but make the acceleration slower.
A higher FDR will generally do the opposite.
Internal Ratio:
This varies between manufacturers and is a ratio between the pulleys in the transmission car. For example and Xray T2 '007 has 34 tooth pulleys for the front and rear differential locations, and a 20 tooth fixed pulley in the centre, giving an internal ratio of 1.7 (34/20). The internal ratio is used to help calculate your FDR.
Rollout:
This is another way to measure gearing based on how far the vehicle will roll in a single revolution of the motor.
Formulas:
FDR = Spur size / Pinion size * Internal Ratio
Rollout = Pinion * Tyre diameter * Pi / Spur
- Ackerman
- Roll Centre
