In the last article, I talked about the uses of toe and how it affects both drivability and front-end dynamics. However, that is only one of the three basic geometric ways to move a tire on a race vehicle. Of the other two, camber is well-recognized, but for all intents and purposes, the least-understood of the three, caster, is sometimes the most overlooked about setups.
It’s so ubiquitious around the country that iRacing based its street stock on this car model! So wouldn’t it serve best to pull both wheels back to maximum caster and shorten the wheelbase? Well, yes and no. Caster feels different to a driver than what a setup may show, and most of it has to do with the camber and toe settings. Apr 24, 2020 Heck, even some of the iRacing baseline setups are difficult to drive. A few years ago, the Spec Racer Ford was easy to drive but in 2020, the back end is too lively for most drivers. Learning how to tame that behavior is important or you won’t have any fun in what is otherwise a really great car. Once you've done a pressure sweep, make a decently large camber change such as.5 degrees and then do a smaller sweep around the point where you achieved the highest grip prior. You can then do smaller camber changes once you've found the trend and are honing in on the optimal setting at the top of the curve. The proper way to calibrate the steering wheel in iRacing. The calibration software wants you to go left to lock, right to lock then centering the wheel to 50% dead on the screen, hitting next, then turning left until it says the correct rotation your wheel software was set to. Example 900 degrees.
Everyone who has pushed a shopping cart understands caster. Caster wheels, when placed on heavy objects that need rolling, allow the object to maintain momentum in a straight line. In other words, once it gets going, it likes to keep going. Think of it as a way to love Newton’s First Law of Motion: an object in motion tends to stay in motion. Newton would’ve loved caster wheels.
Caster helps the old lady push her three bags of cat litter through the grocery aisle without breaking a hip. It also allows me to move 55-gallon steel tanks of liquid nitrogen with two fingers. (Getting it started is a two-handed requirement.) However, what we know as caster wheels are just half the trees of the proverbial forest.
So what does caster do? Well, to understand why something works, it’s good to know how it works. Caster is a measurement of how far “pulled back” a wheel is from its center. It’s measured in the same degrees found on a circle, and the more the wheel is pulled back, the more degrees of caster that wheel has. Conversely, if you can pull a wheel back (+ caster), you can also push a wheel forward (- caster).
So how does that translate to what you feel? Think about what caster does to wheelbase. Positive caster shortens wheelbase, and negative caster lengthens wheelbase. Custom-chopped motorcycles have an extreme amount of negative caster because they lengthen the wheelbase from neutral. Ask anyone who drives a motorcycle, and they’ll tell you that the steering on these bikes is very, very sensitive and does not correct itself. However, on a shopping cart that has a lot of positive caster, if you turn the cart and let go suddenly, the wheels will correct the line of travel and allow the cart to more naturally travel in a straight line.
Shorter wheelbase cars can turn much easier. This is why if you look in the street stock pits at your local bullring, most of the cars are shorter wheelbase models, like vintage Camaros. The late ’70s model Camaro was (and still is) an extremely popular racing car simply because its wheelbase is the shortest allowed by many local rules. It’s so ubiquitious around the country that iRacing based its street stock on this car model!
So wouldn’t it serve best to pull both wheels back to maximum caster and shorten the wheelbase? Well, yes and no. Caster feels different to a driver than what a setup may show, and most of it has to do with the camber and toe settings. However, what most drivers feel when they say “caster” is actually a “caster split.” Think of it this way: maximum caster split would be the LF hub pulled back as far as possible, and the RF hub pushed forward as far as possible, causing the shortest wheelbase on the left side, and the longest wheelbase on the right side. So what does this do to the feel of a car in the corner? Well, try it out in a test session. You’re going to find the left side of the car is going to “pull” the chassis in the corner nicely, but it’s also going to turn a little too nicely off the corner as well as the front tires fight each other to gain grip!
Caster split is a mean devil. It can cause massive headaches with setups, but it can also be just the thing you need to make your setup even better.
Usually, drivers have a feel for a certain caster setting, and leave their setups alone in this regard. Dale Earnhardt, Sr. was known to prefer a higher caster split, and I’m sure there are top-tier drivers from all backgrounds who prefer different caster settings. Although caster does make an impact upon dynamic toe and camber, it is often adjusted according to driver feel.
So then why do nearly all circle-track setups have a LF wheel at negative caster and a RF wheel at positive caster? It has to do with the self-straightening tendencies of positive caster and self-turning tendencies of negative caster. As the car is cornering and the tires are under stress, the LF will want to turn itself MORE (because of the increased toe-out) and the RF will want to straighten itself (toe-in). If you can see this in your mind, the caster is actually working to toe the front-end around the corner by itself!
Colt trooper mark iii serial numbers. So, in short:
Positive caster in both front wheels will make the car slightly unresponsive in the steering, and will heed less to setup changes (less dynamic toe-out).
Negative caster in both front wheels will make the car feel responsive, more “touchy” and sensitive to track changes and tire temperatures (more dynamic toe-in).
Positive caster split (LF more + than RF) will make the car turn-in easily, and turn-out easily. Drivers complain of too much caster split as having no control with the steering wheel, and the car wants to fight itself into and out of each left-turn.
Negative caster split (LF more – than RF) will make the car turn less easily in the corners, but drivers will feel like they have significantly more control with the wheel; less “slop” in the steering. The dynamic toe will also be helping the chassis to turn throughout all parts of the corner.
Understanding caster is just one more trick to have in the bag when it comes to finding that extra tenth or that comfort level in the setup. After all, confidence makes you faster, right?
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Thanks for these articles! For those that read them they’re invaluable information about the hidden aspects of setups. Great work George.
Jonathan Wimbush
November 15th, 2013 at 11:25 am
November 15th, 2013 at 11:25 am
Keep these articles coming!
Scott Kelly
January 6th, 2014 at 12:31 am
January 6th, 2014 at 12:31 am
do these theorys apply to straight axles
Name
August 3rd, 2019 at 5:06 pm
August 3rd, 2019 at 5:06 pm
In article 5.5 we’ve covered ride height, and with this article we’ll continue the setup adjustments on the suspension, namely camber and toe. We’ll go over both of them together, as their effects are tightly coupled.
Camber
Camber is the vertical inclination of the tire. Zero camber means that the tires are straight, perpendicular to the road and parallel to each other. With positive camber, the top of the tires points outwards of the car. With negative camber, the top of the tires points inwards.
Camber is the vertical inclination of the tire. Zero camber means that the tires are straight, perpendicular to the road and parallel to each other. With positive camber, the top of the tires points outwards of the car. With negative camber, the top of the tires points inwards.
Toe
Toe is the angle the tires are rotated around their vertical axis, looking at them from above the car. You have no toe if the tires are parallel to each other, along the direction of the car. You have toe-in when the tires point in towards each other, and toe-out when they point away from each other.
Toe is the angle the tires are rotated around their vertical axis, looking at them from above the car. You have no toe if the tires are parallel to each other, along the direction of the car. You have toe-in when the tires point in towards each other, and toe-out when they point away from each other.
The effect of camber on available grip
As you go through a corner, the cornering force (as discussed more thoroughly in 5.3) causes the car to roll and the tire to deform, as it twists between the car which wants to go one direction, and the track that’s going the other direction. This is called lateral tire deflection.
As you go through a corner, the cornering force (as discussed more thoroughly in 5.3) causes the car to roll and the tire to deform, as it twists between the car which wants to go one direction, and the track that’s going the other direction. This is called lateral tire deflection.
With zero camber, the force on the tires are equally distributed along the contact patch when you’re standing still or driving in a straight line. This increases the available grip under straight line braking and acceleration (assuming no camber gain). Cornering with zero camber causes one side of the tire to unload, while the other side of the tire takes more load. This is unequal load distribution and lowers the overall available grip on the tire, just when you need it most: while cornering!
With negative camber, the force distribution along the contact patch is somewhat unequal while driving in a straight line. However, when cornering forces and carcass deflection come into play, they can negate the effect of negative camber, equalising load distribution along the contact patch. This maximises the available grip on the outside tires (which are the ones taking the heavier load), exactly the moment when the car is limited by its available grip. This is the exact reason why typically on road cars you’d use negative camber.
Tradeoffs of using camber
As always, nothing comes for free. Chromium based browser. While camber can help cornering, it causes additional heat, more tire degradation and uneven wear pattern on the tires. You should also realise that you are trading off traction on a straight line (braking and acceleration) with cornering grip. This means that the track profile is a determining factor on how much camber you want to run. In general, a track with mostly straights and low speed corners, you’d run lower camber; and on tracks with lots of bends or high-speed corners, you’d run more camber. And, as always with mixed profile tracks, you’d have to experiment different settings to see where you can gain more time; on the straights and low-speed corners, or high-speed corners.
As always, nothing comes for free. Chromium based browser. While camber can help cornering, it causes additional heat, more tire degradation and uneven wear pattern on the tires. You should also realise that you are trading off traction on a straight line (braking and acceleration) with cornering grip. This means that the track profile is a determining factor on how much camber you want to run. In general, a track with mostly straights and low speed corners, you’d run lower camber; and on tracks with lots of bends or high-speed corners, you’d run more camber. And, as always with mixed profile tracks, you’d have to experiment different settings to see where you can gain more time; on the straights and low-speed corners, or high-speed corners.
Camber and vertical stiffness
Vertical stiffness of the tire is hugely tied with tire pressures, as discussed in 5.2. This is mostly to be considered on tires with high sidewalls. Having the tire inclined at an angle may cause the sidewall to deform a little. The effect is that of a softer tire without changing the tire pressure. As of time of writing, this really is only something to consider with two cars on iRacing, the Williams FW31 and the McLaren MP4-30.
Vertical stiffness of the tire is hugely tied with tire pressures, as discussed in 5.2. This is mostly to be considered on tires with high sidewalls. Having the tire inclined at an angle may cause the sidewall to deform a little. The effect is that of a softer tire without changing the tire pressure. As of time of writing, this really is only something to consider with two cars on iRacing, the Williams FW31 and the McLaren MP4-30.
Effects of toe-in and toe-out
There is one more effect of camber that we haven’t mentioned yet. If you roll a free tire at an angle, it would want to follow an elliptical trajectory instead of a straight line. In other words: an angled tire wants to turn. The force that causes this effect is called camber thrust. This results in a bit more friction, heat and wear, which can be offset by a toe-out adjustment. You can also use a toe-out adjustment to get the slip angles of the front tires in a more optimal spot. So you’d typically run some toe-out on the fronts.
There is one more effect of camber that we haven’t mentioned yet. If you roll a free tire at an angle, it would want to follow an elliptical trajectory instead of a straight line. In other words: an angled tire wants to turn. The force that causes this effect is called camber thrust. This results in a bit more friction, heat and wear, which can be offset by a toe-out adjustment. You can also use a toe-out adjustment to get the slip angles of the front tires in a more optimal spot. So you’d typically run some toe-out on the fronts.
Toe adjustments on the rear tires also have an effect on car handling. Toe-in on the rear creates understeer, which can help with cars that are oversteery on exit. The tradeoff is wear and heat in the rear tires. Toe-out on the rear is generally wrong, as you’re likely to get more oversteer on exit.
Up to you
Iracing Correct Camber Wheel
While building a setup, go through the order of tire pressures, anti-roll bar, ride height and spring rates. If you have that set, experiment with the camber angles to find the optimal balance between speed in the corners and on the straight. Warcraft 3 tavern heroes. Use toe-out on the front tires to counteract camber thrust, and possibly toe-in on the rear tires, to optimise handling.