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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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