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How to use Weight Transfer to Increase your Speed in an Indoor Go Kart

Posted by admin on September 26, 2018 @ 10:11 am
in Uncategorized |

Weight Transfer is probably the last thing you will develop a sensitivity to when learning how to be competitive in a go kart. It’s one thing to be aware that there is an advantage to managing the shifting of the weight, quite another to make use of it consciously. It took me years, but I’m going to save you years of head scratching and give you the secrets.

The problem is that our reflexes are not really fast enough to deal with changes in inertia. I mean the average person has a visual response time of about 0.250 seconds. We see something happen, it enters our brain, gets converted into some kind of neural pattern, we concoct a plan to deal with it, signals shoot down our nervous system and we execute the plan. Then we gather input from our actions, visual, audible and tactile, another plan is concocted and we shoot more signals down the nervous system to the controls. By this time another 0.250 seconds have passed. So 0.500 seconds have passed between situational awareness and the beginnings of adaptation.

So how far do we travel in half a second?

Just 22 mph is about 30 feet per second. You’re going to travel about 15 feet in half a second.
Even at just 2.2mph you’re going to travel about 1.5 feet in half a second.
That’s pretty slow, and 1.5 feet is an eternally long distance to be off line in a go kart.

If you are 1.5 feet off a line, or late to a turn in, off from an apex, you are WAAAAY off pace.

late and off apex
IF you turning in 1.5 feet late, and maintain the exact same arc (because you’re travelling at the exact same speed), then you would add 1.5×2=3 feet to the length of your track. Whatever the case, you’re going to add length and time to your lap time.

So reflexes can’t possibly be what the top drivers use to maintain consistent laps that are within 0.250 of a second of each other on EVERY lap.
And it also can’t be what you use to manage weight transfer.

So what’s weight transfer about? How do we manage weight transfer?

First of all, let me give you a little secret here, the primary tool in the expert drivers toolbox, is timing.

The more perfect your timing, the more perfect you are going to hit your marks. And really that is the secret to being online and it’s also the secret to managing weight transfer because weight transfer is part of having a consistent plan for how you are going to navigate the track.

How is that? Well weight transfer is NOT something you manage by the seat of your pants when you are in the moment. I’m not sure if that is a surprise to you, but for the longest time, I thought that’s what it was all about. But it’s not.

Managing weight transfer really happens off the track, when you’re analyzing what is happening after the fact.

Managing weight transfer is all about having a technical awareness of the geometry of the kart, and being able to model in your mind how the inertial mass is being shifted and displaced as you go through different sections of the track. Then, knowing how the weight is being shifted in your model, you work out how that is affecting the traction levels and grip through those sections. Invariably that’s where time is gained and lost, from loss and gain of traction.

So managing weight transfer is all about modeling the effects of inertia and this usually happens in analysis, while off track.

Now it is possible to do this somewhat while you are on the track, and it makes a huge difference to your ability to be adaptable to new conditions and different karts. But usually the answer to a problem section of the track doesn’t come until you’ve got off track and thought to yourself, ‘what the hell is going on here?’. Some of my biggest ‘ah ha!’ moments have come when I examine slow motion helmet video, frame by frame, of my fast laps. Often I will examine a corner where I was exceptionally quick for some mysterious reason, and ask myself, ‘why was this fast?’. At this point I start to model in my mind how the inertial displacement is unfolding and what I am doing that is causing this, and how I might repeat it. Quite often I realize the answer and driving inputs change for that section.

By driving inputs I mean this. There are many ways you can shift the inertial mass of your kart around, here is the arsenal of your weight transfer toolbox.
Acceleration (blips and pulses on the gas)
Deceleration (throttle let off, coasting, slight frontal down force)
Coasting (gentle and gradual re-centering of weight displacement)
Steering input (left and right displacement – but also when under load of a turn, forward and rearwards weight displacement when you increase and decrease steering input)
Brake input (jarring frontal down force)
Body position, (leaning forwards and backwards, head up, head down, leaning left and right, hopping in seat)

Sometimes giving an input that does not seem necessary at the time can give you an advantage in RPM, or traction, and both.

Lets consider parts of the track where you might often lose traction, or where it is easy to lose traction.

A brake zone where you come in hot and often lose traction.
If you find the back gets loose under brakes. Well there’s always the suggestion that you’re just braking too hard and too late, and so lighten up a bit and brake earlier. Often the problem is related to trail braking, where you are turning and braking instead of straight line braking. Our suggestion to newbies is to straight line brake and don’t brake and turn the kart at the same time, this means you brake earlier and straight, then let up and coast into a turn, and wait to get back on the gas at the apex. But for an expert driver, trail braking is definitely where you want to be. The thing that makes braking more effective in a kart is to lean far back in your seat and lift your head up high and back in the seat, because it adds downforce to your rear brakes (and you don’t usually have front brakes in an indoor kart). Doing so can give you a surprising boost in traction. This is managing weight transfer to a degree. You’re shifting weight to give you an edge.

But in the above scenario your modeling of the shift of inertial weight, shouldn’t end there. As you enter a trail brake scenario, the bulk of your inertial mass starts to move from the front center to the outside front wheel, while your rear wheels get light. If you are ever to get out of this turn with any kind of advantage in acceleration, you need to think about how you’re going to transition the inertial mass back to the rear wheels and how you will return down force to the rear of your kart. This is invariably why you tend to slide in these corners, because there is no down force in the rear.

Consider a turn where you came in under brakes and need to accelerate to get out of it, and you tend to slip a little as you go through the turn.
The easy and natural fix for this kind of problem is to wait wait wait after braking as you go through the turn, coast, coast, coast, and get on the gas later, typically at the apex. This works, full traction, and no slide. And this is what we tell newbies to do, because we know it’s just timing, and it will absolutely work. But this is not what the expert drivers do.

Note that the weight is loaded up to the outside front of the kart. Now note all the tools in our arsenal. There are several tools that can shift the weight from front to rear. Releasing brakes, releasing steering input, coasting, acceleration, and blips and pulses on the throttle. They will all displace the weight to varying degrees, some more aggressive than others. Note that the most aggressive would be to just accelerate, say by pushing your foot to the floor. But this wont work, because the back is light, so the back will just slide out from under you. So the next thing you can do, is blip and pulse the throttle. It turns out, if you do this on the entry of a turn, for a split second, you wont slide out of control. In fact you’ll push the weight back to the center and rear of the kart, and you’ll gain rear traction. From this point you can squeeze on the gas and be accelerating out of the turn, a full kart length earlier. The blip technique I just described we came to call ‘the double blip’ because you apply the throttle in a 1 and 2 motion.

There are other tricks you can use to finesse the weight transfer to the rear wheels, like in some instances it helps to release the steering pressure slightly as you apply the gas. If you find yourself in a loose kart, say during the cold of winter, you can try to add this as well. Some drivers don’t pulse the throttle at all, they just use a release of steering input to assist the rear loading, then they reapply steering input as they come on the gas and pass the apex.

Consider the sweeper. I have a whole article dedicated to the sweeper here

A sweeper is corner where you can enter under full throttle and can usually power all the way through.
The standard trap of a sweeper is where you chicken out under load and release the throttle in the middle of the turn, this shifts the weight forward and makes the back wheels light, and you invariably go into a slide. This is known in racing circles as ‘snap oversteer’ and is a rather fundamental lesson in weight transfer.

As I outline in that article, the trick to the sweeper is to manage your weight transfer by causing your weight to initially lurch forward on the entry by letting off the gas just before you turn in. This allows the front wheels to bite. Then you stomp back on the gas and hold everything steady all through the turn. Without this set up, the kart will often slide out and break loose in the middle of the turn.

So all throughout these examples you should be picking up a pattern here. If you have a problem you need to be asking, ‘okay, what is my weight transfer doing? what am I doing to cause this?” And whether you have a problem or not, you should be asking, “what is my optimum weight distribution going to be in this situation, and what can I do to help achieve this?”. Where you answer these questions correctly, is where you gain an edge over the other drivers on the track. And that’s going to take mental visualization and modeling in your mind.

Lets look at some other scenarios.

Consider a very slow turn where you need to accelerate all the way through it, from start to finish. This is where you run into problems with the solid rear axle, and binding. The problem is that the solid rear axle wants to turn both wheels at the same velocity and when the kart goes through a turn the inside circumference is always shorter than the outside. If your weight is rear biased, because you are under acceleration, and you have come in flat to the ground, the rear wheels are going to go into a battle. Basically your inside rear wheel will act like a brake, and it will fight your engine.

bind

So what can we do about this? Well go karts with solid rear axles are designed to tip over onto 3 wheels when you turn the steering wheel. This works better when the kart is slowing down, than when the kart is accelerating, because the inside front wheel is designed to push down, while the outside front wheel lifts up. When you are decelerating and turning the forward weight bias causes the kart to tip over onto 3 wheels and the inside rear wheel pretty much lifts into the air. I call this ‘The Tripod Effect’. But when you accelerate into a turn, from a very slow start, all your weight goes to the back of the kart onto the solid rear axle, you can lose steering control, but usually it just puts the brakes on and you don’t really realize it, because it seems like the kart engine is powering away and accelerating. You’re often slow, and you don’t know it.

So there are several things in the weight transfer toolbox to assist the tripod effect. In a particularly bad kart, that tends to ‘push’ that is, you turn the wheel and it just wants to go straight, you can jab on the brake slightly to throw the weight forward and to force frontal down force. If you have to do this, you’re going to be slow anyway, you have a junk kart, but it’s often going to be faster than just trying to drive through it.

The first technique that we offer to new drivers is to just release the gas a split second before you turn the wheel in. This causes the front wheels to bite down and tips the kart over. Then you reapply the gas and drive through the turn. This is usually quicker, but doesn’t always get a good lift.

My favorite technique for managing this situation is the ‘snap in’ steering technique. This is where you aggressively and quickly snap the wheel into your turn, with the goal of throwing the kart up quickly onto it’s outside wheels, you can often do this, without lifting the gas at all. To execute it, you kind of over steer your input way beyond where you would want your natural steering input, then you release the steering input back to your ideal. It plays out like a quick 1, 2, 3. You then rely on the lateral inertia to hold your kart up in the tripod position. I used this technique to give me an edge back during the Oregon State Championship, it freed my kart up all through the infield giving me a huge edge. I used a regimen of weight lifting off track to build the strength needed to sustain the ‘snap in’ during the 30 minute race.

Sometimes it is advantageous to lean forward in a kart. I discovered this once while watching a video of driver who pulled off a freaky fast lap. He gained his magical moment in a chicane. A chicane is a complex of turns that create like an S in the track as it leads onto a straight, it’s usually used to slow the track down a bit. Now normally he leaned back through the chicane and leaned out relative to the entry of it, but he was chasing a very fast kart that had twice his horsepower, and for some reason he sat up on this particular lap and threw his head forward as he exited the chicane, not only that, instead of leaning out when he entered the chicane, he leaned in. That’s very odd, it seems the very opposite of what we would expect and it was the very opposite of what he did usually. When we examined the delta for his time through the chicane, he had picked up 0.100 of a second in that section. Well well? why did this happen? We wondered. When we modeled in our minds what could possibly be going on it started to come together.
First it became evident that leaning out on the first turn, was not helping him at all, it was better than he tried to set his weight up for the exit of the chicane, because the displacement of his weight from left to right while navigating the middle of the chicane was too unsettling. He might not be in the optimal position for entry, but being in the optimal position for exit gave him an advantage as he pulled onto the straight. So we learned there that leaning into a chicane in prep for the exit is the key to a fast chicane. Next his head thrown forward put his weight more towards the front of the kart and off the rear of the kart. This would give him bite as he turned into the final turn and onto the straight that followed and would free up any potential binding that might happen because of the weight transfer from the left rear to the right rear. The exit wasn’t enough to induce any kind of slide, instead he had rear binding problems that were retarding his ability to accelerate out of the final turn. So leaning forward gave him bite, and freed up the bind. After this examination we both started doing this in this section, and it was a consistent 0.100 seconds for us every time. We were in different weight classes at the time, but we both won our racing seasons easily. Little secrets like this in every turn gave us the edge.

So hopefully by now you have an idea of what it means to manage weight transfer to your advantage. It’s all about modeling in your mind how the shift of the inertial mass of the kart is affecting the handling of the kart. You can model to fix problems, and you can model to imagine the theoretical optimal weight distribution. With this in mind, you can concoct unique and optimal tactics for each turn.

With that I will leave you with a problem to ponder. Let’s say you have drawn a random rental kart and upon driving it, you realize that it wants to veer off to the right. What could possibly be causing this? And so what would the optimal place for your weight be? You can be sure that one of those wheels is dragging against the others when you try to drive in a straight line. Taking away down force for that wheel is not going to solve the problem, but it will give you a better time than if you just left things be.

The trick to winning an indoor racing season is that you just need to be able to drive the junk karts better than everyone else can drive them. Weight transfer will give you that edge.

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How to Stop your Indoor Go Kart from Sliding in a Sweeper turn.

Posted by admin on September 26, 2018 @ 12:40 am
in Uncategorized |

If you find your kart sliding in a sweeping turn, (a long steady turn of maximum throttle from entry to exit) even if you are breaking loose slightly, then you’re losing time to the guy who makes it stick.

So you need to start thinking about WHY the kart might be slipping at that spot. In racing parlance we’re about to enter the realm of ‘weight transfer’. The first thing to ask is, “what is your inertial mass doing?”

More precisely, ‘is your inertial mass shifting about? (of course it is) and what are you doing to cause it to change?”

What is inertial mass? Think of it as the direction of force on your kart. Under deceleration the inertial mass is biased towards the front, and under acceleration your inertial mass moves towards the rear. But there is also down force which exerts itself on your tires and is a combination of the total mass and your center of gravity.

The first rule for increasing traction in a go kart, is LEAN OUT of a turn, DONT LEAN IN
If you lean into a corner then you move your center of gravity towards the inside wheels, this lowers the downward pressure on your outside wheels and raises the downward pressure upon your inside wheels, this in turn creates an increased lateral (sideways) g force on your outside wheels. This effectively creates a lower center of gravity, and with less down force on the outside wheels and an increased lateral pressure the kart is more inclined to slide, than it is to tip over.

leaning
Direction of force relative to rear wheels due to center of gravity.

The counter to this is that as you lean outwards you shift your center of gravity over your outside wheels which lowers the lateral g force on your outside wheels and creates more down force, because it effectively raises the center of gravity relative to the outside wheels. This effectively increases the grip. So we might only be talking the difference of a few pounds, but when you are at the limits, this makes all the difference between being able to ‘stick it’, and ‘busting loose’ such that you have to deal with a slide.
With respect to leaning, you want to lean out BEFORE you begin the turn, because you want the lateral shift to happen while the inertial stress of the kart is neutral, which means lean while on the straight. If you lean after the turn in, it causes a shift in the inertial mass AFTER the tires are loaded, and that is a good way to bust yourself loose too. Some drivers place cushions in the side of their seats to stop their inertial mass from sliding around in the seat for this reason.

So while leaning out before all kinds of turns will help, it is not so much the ‘positioning’ of your inertial mass that causes or fixes sliding in a sweeper, the real enemy is the ‘changing’ of inertial mass while you are in the middle of navigating the turn.

A very common cause (but not the only cause) for sliding in a sweeper is Snap Oversteer. This is a condition where the back wheels break loose (usually slightly) in the middle of a turn. Particularly a turn that *should* be able to be taken at full throttle. Lets call this sliding area the drift zone. The primary cause for snap oversteer is a shift in the inertial mass that causes the tires to lose traction. And the number one culprit for this shift in the mass, especially in a sweeper, is releasing from full throttle while in the middle of a turn.

The key here is not THAT you lifted the throttle, its WHEN you lifted the throttle.

Here’s several ways that karters of various skill levels try to handle this situation.
Novice karters just keep their foot planted and ride out the drift zone, losing all kinds of control. They’re terribly slow even though they feel fast and create congestion out of the sweeper.

Intermediate drivers feel the drift coming on and THEN release the throttle to regain control. They experiment with timing for reapplication of power because if they try to get back on too soon, they drift more. Eventually they find their sweet spot and they can get through without sliding. So they basically use a coasting technique.

Advanced drivers pre-empt the drift and back off the gas slightly early BEFORE the drift zone, maybe going through the drift zone at 3/4 throttle to maintain control. They’re not coasting, they’re throttle modulating. It’s a bit quicker, and it’s really hard to execute.

Expert drivers blast through the drift zone at full throttle with no slide or slip whatsoever.

So how do expert drivers do it?

Well first of all, lets examine why the drift happens in the first place.
Snap oversteer is basically the consequence of the mass or weight of the kart being redistributed in the middle of a turn when the wheels of the kart are under maximum load. The redistribution causes a loss of down force and / or an overloading of the tires ability to hold traction.

While mass redistribution can happen in many ways, such as having unstable and shaky hands, the most common way that mass redistribution happens is when you let off the gas while your tires are under maximum inertial load.

That’s a bit counter intuitive to most drivers, surely letting off the gas slows you down and gives you more control?

But consider what happens to your weight distribution in the following scenario.
1. You come down a straight at maximum speed and hold your throttle at full power as you turn into your sweeper. No problem at this point, no slide, almost no lateral (sideways) pressure. Your center of mass is basically centralized but starts to slowly move to the outside center as you enter the turn.
2. As you enter the mass stays centered and your load starts to build up on the outside wheels. No problem holding traction at all at this point.
3. Now you start to approach the zone that the kart starts to get loose, usually somewhere near the apex. You’ve ran this corner many times, you just KNOW it’s going to get loose right up ahead. You’re almost halfway into the sweeper. So what do you do?
Most drivers will get off the gas.
But consider what happens next.
As you release the gas, the kart slightly decelerates and your centralized inertial mass starts to move forward. This causes the down force on the rear wheels to lessen and the forces on the front wheels to increase. Now in some vehicles (with suspension) under such conditions the front wheels might break loose if under maximum load, but in a kart what typically happens is the rear wheels lose their grip and back begins to step out. You just CREATED the very thing you KNEW was going to happen, by letting off the gas.
What you actually did wrong, was that you let off the gas, TOO LATE!

“Okay, no problem!”, you say. “so I’ll let off a bit earlier and maybe control my throttle through that zone”. Now you’re thinking like an Advanced Driver. So you change your strategy and at about a quarter of the way through the turn you back off the gas, and sure enough you are able to get through with no slide by modulating at 3/4 power through the trouble spot. This is REALLY hard to do consistently, especially in inconsistent rental karts, so I really have to commend the drivers that can pull this off. But guess what? You’re still going to be creamed by the Expert Driver.

All right, so here’s the secret. Let off BEFORE or AS you turn into the sweeper. “WTH??! thats waaay too early”, you say. Well I know this probably seems counter intuitive because you have absolutely no threat of losing control way back at the start of a sweeper, but let me explain what this does.

First of all, immediately after letting off and turning in, like within a split second, you want to stomp hard on that gas and hold it down hard with no intention of letting up all the way through the sweeper.

So here’s what happens to the kart in an ideal world.

As you let off the throttle, the mass that was centralized before now moves forward slightly and causes extra down force on your front tires right at the moment of turn in. This causes the front tires to BITE on the tarmac and the rear inside wheel becomes slightly lighter and causes the kart to tripod onto 3 wheels. This has several advantages, first it raises your center of gravity and distributes it BEFORE the tires are under any load, so there is NO chance of a sudden overloaded mass redistribution and displacement in the middle of the turn.
Next, because this strategy assists torque in the chassis, which assists the tripod affect, the solid rear axle lifts the inside rear wheel, allowing the kart to roll speed without bind.

But that’s not all, provided that you are leaning out and not leaning in, BEFORE you turned in, the chassis torque creates extra down force on your outside tires, which means you not only have extra roll speed, you also have extra traction. That’s because a kart that is in a tripod configuration has a different center of gravity than a kart that has slipped out. Consider this, if a kart has slipped out, then it has no outside traction, and in that case the rear axle plants BOTH wheels flat to the ground, and a planted inside rear wheel in a turn can only act like a brake. That’s because the circumference traveled by the inside wheel in a turn, is ALWAYS less than the circumference traveled by the outside wheel. Remember that the solid rear axle means that BOTH wheels must rotate at the EXACT same velocity.

bind
The tripod affect is extremely important in a kart, because it frees up the inside rear wheel that is on a fixed solid axle. The steering geometry of a go kart is specially designed to create this effect, so that under optimal conditions only the outside rear wheel is touching the ground. You want this, and you want to lean out to help it.

The next thing you need is a pair of steady hands that hold your steering at a single angle and input. No shaking of the hands in the middle of the turn. or at least through the zone of highest g force. Shaky hands will redistribute your weight and upset any kart at maximal load. There are several things you can do to assist this. First have a consistent turn in point, use a mark or some reference on the track. You want a single hand movement through the turn, so if you find yourself adjusting the angle of the wheels through the turn, adjust your turn in point forward and backwards until you find the sweet spot.

Next, keep your eye focused on the apex, no matter what is in front of you, train yourself to observe everything you need to observe through your peripheral vision, while your eye is focused on the apex. The general theory goes that the kart will go, where your eye is looking, so look at the apex. This is important because when you look at the kart in front of you, you invariably end up driving like the kart in front of you. When that happens, you might have been quick enough to catch them, but now you’ll stop doing what made you faster, and start doing what makes them slower. This is a common trap.

Next use your peripheral vision to your advantage by focusing on your apex while you peripherally watch where your inside tire is actually pointing while you are in the turn. Point your inside wheel directly at the apex. This allows you to make adjustments for various changes in track conditions.

When you get it right, there will be almost no hand movement once you have initiated turn in. There will no sensing and correcting of inertial sway from left to right. You’ll just be balanced, steady and loaded with no slip. That’s how you get steady hands.

Finally DONT LIFT OFF THE GAS until you complete the sweeper. This is because any lifting of the throttle when you are under maximal load will shift your weight and upset your traction. And that lifting of the gas IS the essence of what creates the drift of snap oversteer.

Okay so one more bonus tip here. Many indoor karts have a foot stirrup that you can push your heel into, just below the brake and throttle. This stirrup allows you to create cross tension through the chassis. Cross tension allows you to change the down force slightly through the kart. I have tested this on scales in a flexible outdoor kart, and just by pushing your heel into the left front stirrup you can create a extra 10lb to 20lb weight on the left front AND right rear wheel, at the same time. Push on the right front stirrup and you create the extra weight on the front right and rear left wheels. It’s interesting how it creates down force across the diagonal of the kart.
The idea is to push your heel in the direction you are turning. So a left sweeper needs your left heel to push into the stirrup. Remember to keep it steady throughout the turn, don’t release, because you don’t want to upset the balance.
So what does this do for you? This assists the tripod effect on the kart, and releases weight, pressure, bind and drag from the inside rear wheel. Cross tension also gives you extra traction on your outside wheels.

The short version of this is. If you want to go full throttle through a sweeper then create a throttle lift off point before you stomp on the gas full throttle, and keep moving your lift off point earlier and earlier until you find the sweet spot that allows you to push full throttle all the way through that sweeper without sliding. The sweet spot is almost always way back on the straight before you even turn your steering wheel, and never when you are already loaded up and into the turn.

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