Long waits for a car delivery apparently bring out the obsessive part of me almost as much as the physics of racing. I placed a deposit for the new Lotus Emira back in May of ‘22, in Hethel Yellow of course, and still don’t have a definite delivery date. During the long wait, I can’t help but regularly dig for the latest info, and one subject I often see brought up is questions and opinions on the steering feel of the Emira. Lotus is renowned for having great steering in their cars, but even most professional reviewers seem to get quite vague when discussing steering feel. So in this article, I wanted to look at this subject more in depth and learn what exactly the steering wheel is trying to tell us.
A kart's extreme steering geometry helps it unload the inside rear during corners. What is “Good” Steering Feel?
First off, what exactly does “good” steering feel mean? That can obviously be quite a subjective question, but one fairly universal goal is to have a light (in weight) and tight steering system that transmits forces more directly between tires and hands. A quick test I like to do on a racecar is to jack up the front and manually move a front tire from side to side. If it moves easily, that means you will be able to more directly feel the forces from the tire as they make their way through the steering system. Heavy components, friction, and compliance all dampen the forces from the contact patch.
Manual steering systems as found on older cars and many racecars will often give the most direct steering feel, but at the cost of greater steering effort. Most newer cars use an electronic power assisted steering system (EPAS) which reduces steering effort but at the cost of more inertia and friction which dampens the forces sent to the steering wheel. Many of these systems then purposefully further filter out forces with the aim of increasing driver comfort. Some more recent electronic steering systems have started going the other way however, and aim to use the electronic controls to enhance steering feel and I’m interested to watch the development in this area. Although not seen much on new cars anymore, the other common power steering system is hydraulic based and Lotus is one of the few manufacturers to still use this. Hydraulic steering systems typically have lower friction and inertia compared to EPAS and manufacturers like Lotus feel this provides a more direct link between the contact patch and hands.
Having a very direct steering system does require that the vehicle designer pay close attention to forces about the steering axis however, because they can’t hide them behind an electronic steering system that filters them out. An example of where pure and direct steering feel is not necessarily a good thing is with racing karts. These have a very light and tight steering system, but also large amounts of caster and scrub radius along with a very quick steering ratio. This results in very heavy and twitchy steering, as well as lots of steering kickback when hitting bumps and curbs. A kart’s steering geometry was designed to overcome the limitations of the platform, not to improve steering feel. In this case, top kart racers are fast despite the direct steering feel, not because of it.
First off, what exactly does “good” steering feel mean? That can obviously be quite a subjective question, but one fairly universal goal is to have a light (in weight) and tight steering system that transmits forces more directly between tires and hands. A quick test I like to do on a racecar is to jack up the front and manually move a front tire from side to side. If it moves easily, that means you will be able to more directly feel the forces from the tire as they make their way through the steering system. Heavy components, friction, and compliance all dampen the forces from the contact patch.
Manual steering systems as found on older cars and many racecars will often give the most direct steering feel, but at the cost of greater steering effort. Most newer cars use an electronic power assisted steering system (EPAS) which reduces steering effort but at the cost of more inertia and friction which dampens the forces sent to the steering wheel. Many of these systems then purposefully further filter out forces with the aim of increasing driver comfort. Some more recent electronic steering systems have started going the other way however, and aim to use the electronic controls to enhance steering feel and I’m interested to watch the development in this area. Although not seen much on new cars anymore, the other common power steering system is hydraulic based and Lotus is one of the few manufacturers to still use this. Hydraulic steering systems typically have lower friction and inertia compared to EPAS and manufacturers like Lotus feel this provides a more direct link between the contact patch and hands.
Having a very direct steering system does require that the vehicle designer pay close attention to forces about the steering axis however, because they can’t hide them behind an electronic steering system that filters them out. An example of where pure and direct steering feel is not necessarily a good thing is with racing karts. These have a very light and tight steering system, but also large amounts of caster and scrub radius along with a very quick steering ratio. This results in very heavy and twitchy steering, as well as lots of steering kickback when hitting bumps and curbs. A kart’s steering geometry was designed to overcome the limitations of the platform, not to improve steering feel. In this case, top kart racers are fast despite the direct steering feel, not because of it.
Do You Need Good Steering Feel to be Fast?
This last part is key because it’s important to understand that good steering feel is not required to be fast. While a well-designed steering system that allows a driver to feel every bump and nuance of the road might subjectively feel good, it’s actually possible for a driver to turn competitive lap times without having any steering feel whatsoever. For instance, I can take an elite level driver and turn off all steering forces when they are training in a simulator and they can still drive effectively. This is because in order to achieve that level of performance, they are driving based primarily on precise visual cues, not steering wheel forces. It's important to understand that the steering wheel is integral to driving at the limit, but it’s not primarily the forces felt that matters, it’s the way the driver turns the wheel and reacts to the vehicle’s response (or lack thereof) that does. Those constant small movements of the steering wheel you see top drivers make as they negotiate a corner is how they find and then stay at the limit. This process of making a driver input change and seeing how the car responds is called testing for the limit. What you typically can’t see is that, depending on which portion of the corner they are in, these drivers are also testing for the limit with the throttle and brakes as well. So although good steering feel won’t necessarily help you drop your lap times, having a nicely weighted wheel that accurately reflects the forces at the contact patch can certainly improve the experience. So let's look now at what exactly all those forces and wiggles you feel through your hands are even trying to tell you.
This last part is key because it’s important to understand that good steering feel is not required to be fast. While a well-designed steering system that allows a driver to feel every bump and nuance of the road might subjectively feel good, it’s actually possible for a driver to turn competitive lap times without having any steering feel whatsoever. For instance, I can take an elite level driver and turn off all steering forces when they are training in a simulator and they can still drive effectively. This is because in order to achieve that level of performance, they are driving based primarily on precise visual cues, not steering wheel forces. It's important to understand that the steering wheel is integral to driving at the limit, but it’s not primarily the forces felt that matters, it’s the way the driver turns the wheel and reacts to the vehicle’s response (or lack thereof) that does. Those constant small movements of the steering wheel you see top drivers make as they negotiate a corner is how they find and then stay at the limit. This process of making a driver input change and seeing how the car responds is called testing for the limit. What you typically can’t see is that, depending on which portion of the corner they are in, these drivers are also testing for the limit with the throttle and brakes as well. So although good steering feel won’t necessarily help you drop your lap times, having a nicely weighted wheel that accurately reflects the forces at the contact patch can certainly improve the experience. So let's look now at what exactly all those forces and wiggles you feel through your hands are even trying to tell you.
Steering Wheel Forces (Scrub Radius & Trail)
What you feel through the steering wheel is directly related to the forces at the contact patch and their relation to the steering axis. Looking at a kart is a good way to visualize this, because on a kart, the steering axis is an actual kingpin. Modern cars don’t have a kingpin anymore and instead use various complex suspension assemblies, but the sideways tilt of the steering axis is still often called the “kingpin angle” and from the contact patch’s perspective, it works the same way.
If you draw a line through the steering axis, the sideways distance between where it hits the ground and the center of the contact patch is called the scrub radius. Try to visualize how with a greater scrub radius length, the tire will move forward and backward more in relation to the car as you turn the steering. What this forward and backward movement also means is that if a tire hits a bump, the tire will be pushed backwards creating a turning force at the steering wheel. If you have a large scrub radius such as on a kart, these steering wheel forces can sometimes be quite high, but on most modern cars, the scrub radius is typically measured in millimeters and so you only feel a small tug at most. While you will primarily feel scrub radius forces from bumps, any uneven longitudinal force on the front tires such as a single wheel brake lockup will also create a force that can be felt through the steering wheel.
What you feel through the steering wheel is directly related to the forces at the contact patch and their relation to the steering axis. Looking at a kart is a good way to visualize this, because on a kart, the steering axis is an actual kingpin. Modern cars don’t have a kingpin anymore and instead use various complex suspension assemblies, but the sideways tilt of the steering axis is still often called the “kingpin angle” and from the contact patch’s perspective, it works the same way.
If you draw a line through the steering axis, the sideways distance between where it hits the ground and the center of the contact patch is called the scrub radius. Try to visualize how with a greater scrub radius length, the tire will move forward and backward more in relation to the car as you turn the steering. What this forward and backward movement also means is that if a tire hits a bump, the tire will be pushed backwards creating a turning force at the steering wheel. If you have a large scrub radius such as on a kart, these steering wheel forces can sometimes be quite high, but on most modern cars, the scrub radius is typically measured in millimeters and so you only feel a small tug at most. While you will primarily feel scrub radius forces from bumps, any uneven longitudinal force on the front tires such as a single wheel brake lockup will also create a force that can be felt through the steering wheel.
Most cars have a steering axis that hits the ground on the inside of the contact patch (positive scrub radius) and so a backwards force on a tire will pull the steering to that side of the vehicle. Some cars are designed with a steering axis that hits the ground outside the contact patch (negative scrub radius) however, so this causes the steering to be pulled in the opposite direction. I’ve driven and raced both designs and in my experience it doesn’t really make a significant difference either way as long as the scrub radius, and therefore force, is small enough to not cause unwanted steering movement. I’ve also driven cars that aim to have zero scrub radius, but you will still feel some scrub radius forces because bumps aren’t necessarily going to act directly along the centerline of the tire where the scrub radius zeroes out. For example, clipping a curb with the edge of a tire is still going to create a force through the steering wheel because the force imparted is offset.
| So while longitudinal forces act through the scrub radius, there will be lateral forces as well and these act through trail. It's important to understand that there is only one steering axis, but separating it laterally and longitudinally makes the forces easier to visualize. While the scrub radius length is determined by the left/right placement of the steering axis in relation to the contact patch, the trail length is determined by how far in front of the contact patch the steering axis hits the ground. The contact patch then “trails” behind and is pulled to the center as the car moves forward like a water skier being dragged behind a boat. While trail will allow you to feel bumps that impart a lateral force into the tire, it primarily adds a self-centering effect to the steering, and the greater the trail length, the more steering effort will increase as cornering forces go up. |  |
A Responsive Steering System Will Naturally Countersteer Into a Slide. It would make sense to think that maximum steering effort would occur as the front tires were providing their maximum force at the limit of adhesion, but this is actually not the case. The reason for this is that the contact patch does not just stay centered in the middle of the tire. As cornering force starts to build, the center of force is actually more toward the rear of the tire and this additional trail length from the center of the tire to the center of force is called pneumatic trail. From a steering effort standpoint, it’s important to take this additional trail length into account because, as the tire nears the limit, the rear of the contact patch starts to slide moving the center of force forward, reducing the pneumatic trail. The end result is that, from the driver’s standpoint, you may feel a reduction in steering effort just prior to the front tires reaching the limit.
This reduction in steering effort was one of the earlier cues I experimented with when trying to find the best way for a driver to sense the limit, but it didn't work very well. First off, as mentioned, a driver only may be able to feel the drop in steering effort as a tire nears the limit. The reduction in pneumatic trail is typically only a small part of the total trail and so the drop in steering effort is usually quite small. This is one area where Lotus seems to differentiate themselves, as they specify lower than average caster angles, and therefore trail, so you are more likely to be able to feel the change in pneumatic trail. Even if you are able to feel the change however, there isn’t a good way for a driver to separate steering effort variations due to pneumatic trail from changes due to track features or load transfer. For example, as a driver goes through a corner, the load will transfer onto and then off the front tires, and this will increase and then decrease steering effort. Then add in the steering effort variations due to bumps, track camber and elevations changes. Even in ideal circumstances with a flat and smooth constant radius turn however, there is still no way to know exactly where the peak lies after the steering effort starts dropping and you only get a general sense you are near the limit.
But although trail forces won’t tell us much about finding the maximum limits of grip, we can use it to find the minimum, and that is more useful than it may seem at first. As we’ve learned, trail causes a tire to want to straighten out in the direction of travel. When you are driving normally, this causes the steering to straighten out toward the center of the car. When a car starts to oversteer and takes a sideways attitude however, the direction of travel is no longer straight ahead. Because of this, the steering will now try to center itself in this new angled direction of travel. This is quite useful, because it means that if a car has a sufficiently responsive steering system, it will naturally countersteer into the slide. While this doesn’t usually allow a driver to completely let go of the wheel and have the car correct itself, it can certainly help guide a driver as they work to correct and control an oversteering car.
This reduction in steering effort was one of the earlier cues I experimented with when trying to find the best way for a driver to sense the limit, but it didn't work very well. First off, as mentioned, a driver only may be able to feel the drop in steering effort as a tire nears the limit. The reduction in pneumatic trail is typically only a small part of the total trail and so the drop in steering effort is usually quite small. This is one area where Lotus seems to differentiate themselves, as they specify lower than average caster angles, and therefore trail, so you are more likely to be able to feel the change in pneumatic trail. Even if you are able to feel the change however, there isn’t a good way for a driver to separate steering effort variations due to pneumatic trail from changes due to track features or load transfer. For example, as a driver goes through a corner, the load will transfer onto and then off the front tires, and this will increase and then decrease steering effort. Then add in the steering effort variations due to bumps, track camber and elevations changes. Even in ideal circumstances with a flat and smooth constant radius turn however, there is still no way to know exactly where the peak lies after the steering effort starts dropping and you only get a general sense you are near the limit.
But although trail forces won’t tell us much about finding the maximum limits of grip, we can use it to find the minimum, and that is more useful than it may seem at first. As we’ve learned, trail causes a tire to want to straighten out in the direction of travel. When you are driving normally, this causes the steering to straighten out toward the center of the car. When a car starts to oversteer and takes a sideways attitude however, the direction of travel is no longer straight ahead. Because of this, the steering will now try to center itself in this new angled direction of travel. This is quite useful, because it means that if a car has a sufficiently responsive steering system, it will naturally countersteer into the slide. While this doesn’t usually allow a driver to completely let go of the wheel and have the car correct itself, it can certainly help guide a driver as they work to correct and control an oversteering car.
Steering Forces Around Center (Toe In & Toe Out)
While trail primarily effects steering feel as lateral force builds, toe affects steering feel right around center because it determines how quickly those forces start building. For instance, if a vehicle has toe in at the front, where the tires are angled toward each other, the vehicle will turn in quicker for a given amount of initial steering. When a car with toe in is traveling straight, the front two tires are slightly turning into each other and so the forces cancel out. As the car starts to turn however, the outer tire becomes more heavily loaded because of load transfer and so starts to supply a greater percentage of the turning force. Since toe in means this outer tire is already turned into the corner somewhat, this essentially gives it a head start and the turning forces start building quicker. From a steering feel perspective, these turning forces building quicker causes a greater self-centering force on the steering wheel. This is one reason why road cars are often setup with some toe-in at the front, as most manufacturers prefer to have a car that tends to track straight and has a stronger centered feeling in the steering.
While trail primarily effects steering feel as lateral force builds, toe affects steering feel right around center because it determines how quickly those forces start building. For instance, if a vehicle has toe in at the front, where the tires are angled toward each other, the vehicle will turn in quicker for a given amount of initial steering. When a car with toe in is traveling straight, the front two tires are slightly turning into each other and so the forces cancel out. As the car starts to turn however, the outer tire becomes more heavily loaded because of load transfer and so starts to supply a greater percentage of the turning force. Since toe in means this outer tire is already turned into the corner somewhat, this essentially gives it a head start and the turning forces start building quicker. From a steering feel perspective, these turning forces building quicker causes a greater self-centering force on the steering wheel. This is one reason why road cars are often setup with some toe-in at the front, as most manufacturers prefer to have a car that tends to track straight and has a stronger centered feeling in the steering.
Camber thrust makes a tire act as a cone rolling across the ground creating a force in the direction the tire is leaned. On the other hand, if you have a car setup with toe out in the front, where the tires are angled outward, the car's initial turn-in will naturally be slower. The dominant outer tire will have to turn more before it starts building force in the direction of the turn. The side effect of this slower buildup of turning forces is that the steering will have less of a centered feel. What’s interesting here is that, although toe-out might make a car feel more responsive and twitchy because the steering has less of a centered feel, it is technically less responsive and will turn in slower than with more toe-in.
When looking at your toe settings, it’s important to understand that due to compliance in the suspension and steering, what you see on the rack isn’t necessarily what you are getting at speed. Plus, you also have to take into account the effect of camber thrust. This is a tire’s tendency to want to turn in the direction it is tilted and makes negative camber act like toe-in. Lotus often specifies close to zero toe on their vehicles, where the tires are aimed straight ahead, but combined with the effect of having some negative camber, the front tires will generally still have a small net toe-in force. The camber thrust effect means that if you increase negative camber on a car, you also need to increase toe-out to compensate. This is one reason why racecars often run a fair amount of toe-out, because they also typically run a fair amount of negative camber and have to compensate for it.
Feeling the differences between toe settings is actually quite difficult during a standard turn-in, however. They are much more noticeable during back and forth steering motions because the tire providing the majority of turning forces quickly changes with each movement. Wiggling the steering wheel back and forth is a good way to test this, but keep in mind that while more toe-in might make a car feel extra responsive here, when driving at the limit, extra response is not necessarily a good thing. Take, for example, a high-power car coming out of a corner at the limit of oversteer. The driver will be trying to balance throttle application with movements of the steering right around center trying to keep the car under control. What the driver wants here is a toe setting that doesn’t give too much response… or too little. They want a toe setting that gives a predictable and seamless transition from one tire to the other as they move across the steering’s center.
When looking at your toe settings, it’s important to understand that due to compliance in the suspension and steering, what you see on the rack isn’t necessarily what you are getting at speed. Plus, you also have to take into account the effect of camber thrust. This is a tire’s tendency to want to turn in the direction it is tilted and makes negative camber act like toe-in. Lotus often specifies close to zero toe on their vehicles, where the tires are aimed straight ahead, but combined with the effect of having some negative camber, the front tires will generally still have a small net toe-in force. The camber thrust effect means that if you increase negative camber on a car, you also need to increase toe-out to compensate. This is one reason why racecars often run a fair amount of toe-out, because they also typically run a fair amount of negative camber and have to compensate for it.
Feeling the differences between toe settings is actually quite difficult during a standard turn-in, however. They are much more noticeable during back and forth steering motions because the tire providing the majority of turning forces quickly changes with each movement. Wiggling the steering wheel back and forth is a good way to test this, but keep in mind that while more toe-in might make a car feel extra responsive here, when driving at the limit, extra response is not necessarily a good thing. Take, for example, a high-power car coming out of a corner at the limit of oversteer. The driver will be trying to balance throttle application with movements of the steering right around center trying to keep the car under control. What the driver wants here is a toe setting that doesn’t give too much response… or too little. They want a toe setting that gives a predictable and seamless transition from one tire to the other as they move across the steering’s center.
Steering Feel Vs Speed
While we have primarily been talking about steering feel in this article, it’s also important to keep in mind that all of these settings have other effects on vehicle performance as well, and when you are chasing lap times, these other factors may override. For instance, while front toe settings dictate the vehicle’s response for a given steered angle, a skilled driver can always turn the steering faster or slower to get the same turning response provided by a different toe setting. So although a certain toe setting might subjectively feel better, if another toe setting produces lower drag and therefore higher straightaway speeds, it might be worth adapting too. The good news though is that most competitive setups often produce quite good steering feel, so this is typically not something that has to be compromised.
I hope you enjoyed this look at steering feel and the reasons behind it. If you are interested in a complete guide to the physics of racing, we also offer The Science of Speed book series, available through our bookstore or at popular retailers such as Amazon.
While we have primarily been talking about steering feel in this article, it’s also important to keep in mind that all of these settings have other effects on vehicle performance as well, and when you are chasing lap times, these other factors may override. For instance, while front toe settings dictate the vehicle’s response for a given steered angle, a skilled driver can always turn the steering faster or slower to get the same turning response provided by a different toe setting. So although a certain toe setting might subjectively feel better, if another toe setting produces lower drag and therefore higher straightaway speeds, it might be worth adapting too. The good news though is that most competitive setups often produce quite good steering feel, so this is typically not something that has to be compromised.
I hope you enjoyed this look at steering feel and the reasons behind it. If you are interested in a complete guide to the physics of racing, we also offer The Science of Speed book series, available through our bookstore or at popular retailers such as Amazon.
