In the Back - Axles and Hubs

This is the first of a two part series about adjusting the rear end of your kart.  When a kart is properly set up and optimized to race day conditions, steering effort will be reduced.  The driver will be able to maintain maximum speed as the kart floats around the corners because it is neither too loose nor too tight.  The driver will also fatigue less because he or she is not fighting against the kart.

The rear end of the kart has the majority of the weight along with most of the moving parts so when tuning your kart for performance, that is a great place to start.

When approaching a corner, you turn the steering wheel, the rear inner wheel lifts and grip is transferred to the outside rear wheel.  The stiffness of the rear end is a big factor in how much grip is transferred to the outside tire and how fast that is done. 

The rear end of a kart may seem simple, but the axles, bearings, hubs, torsion bars, seat struts, rear bumper, and even the seat will impact stiffness. The stiffness of the axle will make the biggest impact so it is one of the most important things to get right before changing other things. When conditions are cold or the track is slippery, use a stiffer axle to transfer the weight to the outside tire more quickly. When the track is hot and sticky, use a softer axle to flex more.  This will be a recurring theme throughout the process.  More flexibility is needed when you have more grip.

Next up is the rear hubs which manage the weight transfer to the tire through the axle. The hubs work like a stiffener on the axle with longer hubs overlapping more axle and therefore making the whole system stiffer. Use long hubs on cold slippery days when the kart feels loose and you have oversteer.

Next time, we will move on to the rear track and torsion bars.

The Test

No, you do not need a #2 pencil and there will not be a grade assigned at the end.  We are talking about testing to improve your kart performance and ultimately your race times.  So, how do you test?

First separate out testing and lapping.  Testing is determining how changes on the chassis or the engine setup affect performance. Lapping is the process of making lap after lap around the track to improve the driver's line and consistency.  As we have said before, the biggest change from race to race is the driver so do not underestimate the benefit of lapping.

For a day of lapping, you will want to have the kart set up at a pretty much baseline configuration for both chassis and engine and have your fuel can ready.  The idea is to pound over a hundred consistent laps until the driver can hit his or her marks every time.  The point is to learn to drive the kart near its limit of control, and do it every single time.

For testing, you also want to start with the baseline configuration.  Get the baseline setup that your chassis manufacturer recommends, put everything back to that, make sure your engine package is solid and consistent, and you are ready to start.  Next make a list of the parts and changes you want to test.  The goal is for the driver to learn what the system does when a change is made - determine how it affects the turn in, apex grip, exit handling, etc. so that he or she can maximize the kart's performance.

Start with changes on the big things (seat position, axle, ride height) and then move to the small fine tuning adjustments.  Be cautious however,  and understand that the track changes throughout the day and from day to day. While speed and lap time is the ultimate measure of success in the race, it is more important to note what exactly was changed and how the kart felt.  Although there is no measurement unit for how tight or loose the kart feels, try to quantify it on say a scale of 1-5 or 1-10. That way, as you change each thing and note its effects, you will be prepared to tune for the conditions.

Some suggestions of possible things to test:

How does seat position effect handling: recommended, forward, backwards, raised?

How does a softer and harder axle effect handling?

Third bearing hooked up or loose?

Second set of seat struts?

Rear ride height: neutral, high, or low?

Front ride height: neutral, high, or low?

Different front bars?

Addition of rear and/or side torsion bars?

Increase/decrease front and rear track width?

Increase/decrease Caster?

Increase/decrease Camber?

Toe in/out 2mm from stock?

+/-3 psi of tire pressure: front/back?

Different wheels: aluminum vs. magnesium?

Karting Brakes

The following is an excerpt from an article by V. Hill which you can read in its entirety at www.KartPartsDepot.com in the Depot Depository.

From the very beginning, karters seemed to focus more of their attention on the go portion rather than on the stopping portion of kart racing. Brakes have seemed to take a back seat to the power plants and chassis in the search for speed.

With the advent of the very large penetration of European karts, mainly Italian made karts, the number of brake choices for the karter is even larger. Every brand of kart seems to have their own take on brakes and the parts are not interchangeable from one brand to another. For the karter, this means that he or she may need to keep more parts in their own selection to support if they have more than one brand of kart they use in their racing arsenal.

The science of brake design and developing brake technology is more about the materials used in the manufacturing of the brake rather than any new or fundamental changes in the mechanics of the brakes. The basic design parameters are pretty much set for the karter.

The disc is one component you can tune to tailor the brake system to suit your individual needs. Karters have made discs out of everything from Detroit wonder metal, Cast Iron, Steel plate, Aluminum and even exotic metals like Titanium and Beryllium. But the material of choice seems to always gravitate back to Cast Iron. Nothing seems to be able to beat this material for it ability to under go many heat cycles without distorting. It is relatively inexpensive and it has great wear capabilities. Carbon-Carbon was even tried for a short time. It offered great performance and it was incredibly light - often the disc would weigh less than the nuts and bolts used to hold the disc to the hub. But it was very expensive; really expensive, a single disc could cost $200.00 to $500.00 dollars depending on the application. The Carbon-Carbon disc also required special Carbon-Carbon brake pads so the cost was really astronomic.  But no matter how much things change, they still seem to be the same. Cast Iron is the material of choice and that holds true in 90% of the racing series around the world, not just karts.

More about Kart Dynamics

First let's define caster and camber. 

According to Wikipedia, "the caster angle or castor angle is the angular displacement from the vertical axis of the suspension of a steered wheel in a car, motorcycle, bicycle or other vehicle, measured in the longitudinal direction.  
Camber angle is the angle made by the wheels of a vehicle; specifically, it is the angle between the vertical axis of the wheels used for steering and the vertical axis of the vehicle when viewed from the front or rear. If the top of the wheel is farther out than the bottom (that is, away from the axle), it is called positive camber; if the bottom of the wheel is farther out than the top, it is called negative camber."

Clear as mud, right?

Let's start with camber, also known as toe-in and toe-out. Toe in, or negative camber is when the wheels are mounted so that the front of the tire is angled slightly inward toward the center of the kart. castor is the angle, from vertical, of how the wheel is supported. See the photos below from intraxracing.

Now that we have that basic understanding of terminology, I am going to point you to a detailed article by driver coach Chris Livengood at

http://www.kartpartsdepot.com/EXIT_OVERSTEER_KARTING_p/029.htm

He walks you through what to look for and the adjustments that you need to make to your kart to maximize your cornering capabilities.