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Mike Smith

Tech Time with Mike Smith: Managing Weight Transfer

By | Mike Smith, Spec13 Knowledge Drop, Tech Time | No Comments

I’m sure you hear a lot about being smooth and managing weight transfer (in fact, I’m sure I’ve already preached that to you myself), and in this installment, we will revisit the importance of both those things (and it won’t be the last time, either). We also spend a lot time talking about braking; when to brake, when to get off the brake, should I be trail braking? How much brake pedal pressure should I use? etc. etc. but rarely is how you get off the brakes discussed. This may seem trivial, but it plays a big roll in vehicle dynamics during turn in and mid corner, and can make an oversteer prone car understeer, and an understeer prone car infuriating to drive.

First, let’s think about what’s happening with the front suspension during a braking event. Upon the initial application of the brakes, weight is transferred to the front, which is translated to a downward force on the front suspension. This downward force compresses the front springs, and as a result, a large amount of elastic potential energy is stored. Once the force compressing the spring is removed (i.e. you begin to release the brake), this elastic potential energy will be released. According to the first law of thermodynamics, “energy is neither created nor destroyed.” This is notable because it tells us that the rebound (decompression) force of the front suspension when you release the brakes will have as much force as the compression of the front suspension. If you think about the amount of braking force you can produce and how much the front suspension deflects, this is a lot of force we’re talking about here! It’s easy to see how releasing the brakes too abruptly can cause an unloading of the front suspension and a loss of grip. This loss of grip will be especially noticeable in a vehicle with underdamped front suspension (i.e. stock suspension, or stock shocks with lowering springs), as a rapid unloading of the front suspension will cause oscillation. This unloading of the suspension can be an issue even in vehicles with properly damped suspension. The damper is designed to control the rate at which the spring is loaded and releases its stored energy. However, even in a car with a great set of coilovers that were well setup for the application (such as the Ohlins I had on my Evo X), there can still be some degree of unloading of the front end when releasing the brakes due the front end load accelerated upwards from the spring releasing its stored energy. The shocks can’t necessarily stop the mass of the front from accelerating upwards, although they will reduce it significantly.

To completely avoid the unwanted effects of the front suspension unloading, think of using the brake pedal as an additional shock absorber to control the front end loading. In general, you want to release the pedal somewhat slowly and as smooth as possible, especially towards the end of braking. As you gain a feel for how your suspension reacts to the release of the brake, you can begin to increase the speed of your release. Ideally, a passenger wouldn’t be able to pin point exactly when you let off the brake pedal by feel.

This is an important skill to master in a car that has a propensity towards understeer. For example, watch a few minutes of the video (link below) of me driving my Evo X at Watkins Glen (skip to turn 8 for a good example at 1:35). Notice the incredible amount of finesse associated with releasing the brake. If I were to come off the brakes any faster or more abruptly, the car would most certainly plow.

 

Tech Time with Mike Smith: Heel-Toe Downshifting

By | Mike Smith, Spec13 Knowledge Drop, Tech Time, Uncategorized | No Comments

I’m sure many of you are familiar with the term heel-toeing, but some of you may not know that it serves a purpose (other than to impress your passengers). One of the most important skills you need to learn as a high performance driver is how to manage weight transfer/tire load. As I’m sure you remember from last week’s article, tire load management is very important due to a tire’s non-linear lateral grip to normal (vertical) force relationship. When threshold braking (when the car is producing the maximum amount of braking force without locking up the tires), it is very important to be smooth. Any weight transfer during threshold braking can lock up tires which can induce a spin, or cause you to not make the turn (after all, a locked up/sliding tire has a much lower grip potential than one that remains rolling). When you downshift by simply letting the clutch up slowly (which is how everyone is taught to drive initially), you cause a weight transfer and change the attitude of the car. This unweights the rear tires (which can cause them to lock up) and transfers weight to the front (which could potentially cause them to lock up since you could very well be at the limit of the front tires load capacity). Heel-toeing, if done properly, will eliminate this weight transfer and will allow you to threshold brake and maintain control of the vehicle by matching the engine RPMs to the transmission speed of the next lowest gear. Heel-toeing is a simple concept and will eventually be second nature for you, but it requires practice. Lots of practice. Practice every time you come to a stop light, or are slowing for your exit on the highway (don’t practice the threshold braking part though, that could be bad). Your first track day isn’t the time or place to be experimenting with heel-toeing. Here’s a simple step by step of how to heel toe:

  1. Firmly and quickly apply the brakes (without “slamming”) until the threshold is achieved (this will also take some practice, but eventually you’ll be able to detect when the tires are just about to lock up)
  2. With the brake pedal still depressed, engage the clutch pedal and select the next lowest gear (Don’t skip gears as this creates a large difference in RPMs which can make the maneuver unnecessarily challenging).
  3. Now pivot your foot on the brake pedal while (maintaining a constant brake pressure) so that it makes contact with the gas pedal and give the gas pedal a quick jab or “blip” while letting the clutch up. you don’t actually have to use your heel for this either. If your foot is big enough, you can do what I like to call big toe-little toe (which is demonstrated in the graphic and video below). if done correctly, you shouldn’t feel any weight transfer at all and the shift should be perfectly smooth. The amount of blip you give is different in every car, and is something you’re going to have to get used to and feel out.

 

Check out the foot cam in the video of Mike Smith at Watkins Glen below to get a sense of the timing/rhythm of this technique.

https://www.youtube.com/watch?v=vneiWDEidVo&list=UUlCknQ0K88q5J6HYif55QYg&index=7

Tech Time with Mike Smith: Weight Reduction

By | Mike Smith, Spec13 Knowledge Drop, Tech Time | One Comment

Today on Tech Time with Mike Smith, I’d like to talk about why weight reduction is so important in a performance vehicle. It is common knowledge that a lighter vehicle will handle better and be able to generate higher peak G-Forces in a turn when compared to an identically prepped car that is heavier. But why is this the case? It seems counter intuitive since you can easily drag a piece of paper across a desk, but then once you put a paper weight on it, it becomes harder to drag. The friction force between the paper and desk increased with the additional load of the paper weight, so the same should happen with your car, right? Well, lucky for us, tires aren’t made of paper, and therein lies the difference in this scenario. Tire dynamics is a very complicated topic, involving adhesion, cohesion, friction, hysteresis among other principals. It is these principals that allow engineers to develop tires capable of producing greater than 1 lateral G without the assistance of aerodynamic components. If a car’s lateral grip was generated only by friction, it would only be possible to generate 1 g of lateral force. Like all complicated things, tires have specific optimal operating parameters; temperature, pressure, slip angle and load just to name a few. With racing tires, it becomes even more important that these parameters are within the optimal operating range, due to the fact that a racing tire’s grip comes mostly from adhesion and cohesion rather than friction. Below is an example of a racing tire’s load vs lateral grip graph. As you can see, the grip increases linearly with load until a certain point, beyond which the amount of grip per unit load begins to fall off. This is something that you can easily test on your own. Go to a skid pad with your car and test it with varying amounts of ballast (keep careful control of other parameters such as tire pressure/temperature and fuel load). Time how long it takes the car to do laps around the skid pad (trying to keep the car tight) with various loads.

Tech Time with Mike Smith: Where to Hold the Steering Wheel

By | Mike Smith, Spec13 Knowledge Drop, Tech Time | No Comments

We already talked about how to hold the wheel, so now let’s talk about where to hold the wheel. keep in mind, this may not totally apply to Auto-X (definitely doesn’t apply to drifting) as there is generally a great deal of steering angle required in this type of driving. Now, I know this isn’t what you learned during driver’s ed, but the proper hand position is actually at 9 and 3 o’clock with NO shuffling. Here’s why:

1) This gives you a full 180 degrees of steering angle input in both directions

2) You are able to give smooth, consistent inputs to the steering wheel

3) You have better leverage on the steering wheel

4) Your brain is automatically calibrated to where straight is in the event of an oversteer attitude

5) If the car does start to oversteer, you have a greater range of motion in the countersteer direction than if you shuffled your hands. This gives you the ability to correct more quickly/smoothly and give plenty of input (try shuffling vs. 9 and 3 on a skid pad. you’ll feel the benefits immediately)

6) **This is kind of a bonus reason** While this gives you plenty of steering angle (of the 10 different tracks I’ve driven, I’ve never NOT had enough steering angle using this method), sometimes it can seem like it’s not enough. If you encounter the sensation of it not being enough steering angle, that typically indicates that you’re not taking an efficient line through a particular turn and may be scrubbing speed. Try to find a line through the turn that allows you to turn the steering wheel less.

#SpeedSecrets #TheMoreYouKnow #NeverLift #TrackDayBro#Spec13Motorsports #CantechAutomotive

Tech Time With Mike Smith: Holding the Steering Wheel

By | Mike Smith, Spec13 Knowledge Drop, Speed Secrets, Tech Time | No Comments

Today, we’d like to talk a little bit about how you should grip the steering wheel (next week, we’ll talk a little about proper hand position). As our friend Ross Bentley describes in the Speed Secrets link below, it’s important to use a light grip (but not too light so as to allow the wheel to slip through your hands). If you think about it, you drive a car entirely based on sensory inputs; visual, auditory, tactile (even olfactory sometimes). If you have a death grip on the steering wheel, you will reduce the amount of vibration and feedback through the wheel, thereby limiting your ability to gauge the car’s proximity to the theoretical limit. If you watch closely, some of the Spec13 drivers will actually wiggle their fingers periodically throughout a session to remind themselves to maintain a light grip. Check out Ross’s article below for a more detailed explanation.

Tech Time with Mike Smith: Vehicle Rake

By | Mike Smith, Spec13 Knowledge Drop, Tech Time | No Comments

Let’s take a second to talk a little about car setup; in particular, vehicle rake. This is something that’s often overlooked when installing a set of new coilovers (or adjusting old ones). Sometimes, a car that’s setup with proper ride heights and rake isn’t the most aesthetically appealing. And conversely, a car with an appealing rake/ride height usually isn’t optimized for performance. So, let’s get down to it. When you adjust front or rear ride height, you are effectively moving the center of gravity of that axle (see picture below) up or down. And as I’m sure you already know, increasing the center of gravity will effectively increase the moment “arm” associated with that center of gravity and less force will be required to induce roll on that axle (or that axle will roll more with the same amount of force). For example; let’s say you have two rectangular objects of similar mass distribution and density with the same size base, but one is much taller than the other. Which will be easier to push over? The tall one (see example below)! That’s exactly what you’re adjusting when you change ride height. If your car is oversteering, you could lower the rear ride height while leaving the front the same, giving the rear axle a lower center of gravity. This will provide more mechanical grip to the rear (provided the car isn’t already ridiculously low to the point where the roll center is way off). If the car is understeering, you could raise the rear to help loosen the rear end. This is generally a trial and error process that requires testing. Thisexplanation was meant to be quick and dirty and in no way covers all the intricacies of adjusting ride/corner heights. So, if you’re interested in getting the most out of your performance vehicle with adjustable ride height but maybe want to skip the physics lesson (or if you want an in depth physics lesson), make an appointment with us to have your car corner balanced. We will be sure to address your concerns about rake among other things!