Post by Chuck on Feb 18, 2012 1:19:32 GMT -5
"Torsion bars / "Magic Wands?"
This article will focus upon the large-gross- macro picture for the kart racing chassis and roughly how the chassis functions as a unit composed of various tubes weld \ constructed together to form an infrastructure know as the kart racing chassis. The basic layout of the chassis will be addressed, also the way the chassis functions. However we will take a micro approach upon how the removable\ additional, and bolt on sub-components can substantially change the desired outcome of the overall chassis character and performance in specific conditions and applications.
The basic kart racing chassis has a given wheel base, bearing hangers for the rear axle assembly, king pin receptacle \ spindle hangers for the stub axles. Steering uprights and seat mounts, either welded on, or bolted on. These basic components are all connected via several bent tubes of given diameters and strengths.Various types of tubing in terms of tinsel strength and yield. Essentially, their own working character of properties inherent to their design. Together they form the kart racing chassis when welded in a design determined by the chassis manufacturer or the designer of the chassis.
The chassis designer has created this elaborate configuration based upon what they feel is necessary to arrive at a given race kart conception to handle the track character, karting division, racing application or classification he has intended the chassis to excel in. The biggest thing in which the designer is confronted with is how to make the proper chassis design to perform at maximum potential for the specific classification in all applications and conditions which the driver will be potentially raced in. Once the classification has been established and the designer has rendered his version of how all of these tubes can be combined into the ultimate racing chassis, he soon realizes that anything he does will not function perfectly under all potential adverse, or ideal conditions. Basically anything that he has designed is optimum for only one given set of parameters. If anything changes such as ambient temperature, track temp, different track surfaces, rain, etc. the driver is faced with a chassis which is not perfect. In fact, the duration of the event can seriously change the chassis set up, such as a qualifying set up verses a final, or main event setup. In any case, the chassis as we once knew it, has slowly become more technical in nature and requires more adjustability to achieve a well balanced set up for the particular race conditions. Somehow changes must be made to accommodate the changing conditions.
Even with everything the designer has done to manufacture an optimum racing chassis, conditions are rarely optimum. Basically a set chassis is not as efficient as it needs to be. To make the chassis more adaptable designers have begun to utilize some of the perhaps non traditional and now somewhat accepted, traditional chassis accessories, or bolt on and removable components,. He can now optimize the handling character to accommodate any and all variable conditions. Our goal is to utilize the chassis to its fullest capacity. In order to do this, manufactures adds on these peripheral items.
Let us explore these devices, or what most would probably consider "magic wands". These bolt on items consist of the following but are not limited to: inner rails, rear torsion bars, removable transverse front axles, removable/adjustable first cross members and "K" struts. Almost everything that is bolted onto the chassis including tie rods, front/rear/side bumpers, rear axle, the seat and seat struts, wheel hubs, and wheels all have and affect on the performance of the chassis. But we will address those later.
In order to understand what a manufacturer is trying to accomplish, we must first understand the most basic principal of the racing kart, and without becoming to elaborate in our description. The racing kart is a unit made up of tubes and front steering geometry and coupled with a live axle, (one without a differential) to be able to make turns left of right properly, and hopefully with out oversteer, or understeer. This is a very very difficult task to accomplish without a differential. Therefore the chassis must be designed in a manor to be able to turn, the only way the chassis can turn without a differential, is if the inside rear tire can lift up and then the outer rear tire acts as a pivot and the chassis can now turn because the inner tire is up, verses its position down (with both wheels driving), if the inner wheel does not lift, no matter how much you turn the steering wheel, the front of the chassis is just going to keep going straight and therefore creating an understeer, or a push condition. When a chassis lifts up the rear wheel properly, then the chassis can pivot and turn.
Now that we have established that, we can go forward and find out why it is necessary to make chassis adjustments. The total combined effect of these additional devices, or adjustments will basically net a desired affect as to how long or what duration of lift is given to the inner wheel when the steering wheel is turned either one direction, or the other. At this point we will leave out geometry, and assume that we do have some sort of fixed geometry in the front of the chassis. I.e. king pin inclination and caster.
Traditional, inner removable rail, or commonly called the fourth rail. It is called the fourth rail, as it is one of four rails. The two primary rails are the chassis outer most rails know as the main rails. Typically, the third rail is considered the inner most motor mount rail. Naturally, then the fourth rail is the rail between the first cross member located underneath the front of the seat, and attached to the most rearward cross member, know as the rear cross member. This fourth rail is on the brake side of the chassis. It has been traditional or normal, or most common in the past five to seven years to have this inner rail fixed in place, then as time and chassis progressed, it has become the normal to have this tube in place, however, it could be either made to be stiffened, or somewhat rigid, or if the driver desired, he is able to remove this tube. This has quite an effect upon the chassis general handling character.
To start with, the inner rail can be utilized in two positions, either fixed or welded in place. Fixed in place, however, joined to the outside mail rail via long bolts with bushings in between, or simply a removable inner rail with sliding clamps to keep it in place, or remove it completely, thus leaving the chassis as a two - three rail configuration. The net effect of installing the fourth rail is a chassis which has now become stiffer, as we have beefed up the integrity of the chassis. This may be desirable depending upon what the track conditions, and how the chassis feels to the driver. The basic rule is, the stiffer the chassis in this section, the less the rear wheel is to go up or the sooner it is to come down depending upon the drivers steering input, however, based upon the character in the fourth rail it can either help with the following.
In a low grip situation, (as in the rain, or a damp track, or such as a parking lot, or temporary circuit, perhaps street) the installation of the fourth rail in any capacity will net the rear end more grip. In the fact that it will not allow the chassis to transfer weight and lift up the inside wheel as much, or as long, therefore coming down and driving the kart off of the turn sooner.
Conversely, in a high grip situation, such as a long term event, high ambient temperatures, or just a large amount of entries creating a situation where the track is getting hotter and the grip is becoming more severe. The removal or reduction of tension on the forth rail allows the chassis to properly lift up the inside wheel, or the how long the inner wheel will stay up, allowing the kart to pivot on the outside wheel and turn in as if there was a differential. This is desirable a high grip situation, where you want the duration of lift to be increased to avoid too much grip.
The rear torsion bar, the bar which is transversely mounted between the two main rails, behind the axle bearing hangers.
There are a few different variations of the rear torsion bar. Basically, there is the fixed or welded in place bar.
Most commonly or versatile is the removable rear bar. With the removable rear bar, you have many options. Typically you see what would be described as a rear blade. The tube is flattened between each end creating a tube which can be attached with clamps. However, the character of the tube is changed when the middle has been flattened. When flattened the tube is now able to be flexible in the horizontal position. When positioned perpendicular to the ground, the bar becomes very strong and less capable of flexing like a normal tube, and strengthens the rear of the chassis. Other forms of the rear torsion bar can altered by using a conventional tube, however, changing the type of material, outside diameter, or, the wall thickness. I have even seen some manufacturers use alloy, or cast blades to arrive at a pre-determined characteristic.
Essentially, the rear torsion bars effect is as follows. When the track is low grip, or you have an oversteer condition, you can use the blade in it's most effective position, Perpendicular to the ground. This keeps the rear from lifting as easily, and sets the tire back down sooner, thus giving more rear grip. If you want a little less rear grip, you may consider just the installation of a standard tube, or even less, perhaps the blade in its least effective position, parallel to the ground. If you have an understeer condition, you would not install the rear bar. This would allow the chassis to function as normal and let the inside wheel travel its regular distance, thus creating a longer duration of lift and ultimately less drive, (or grip) off the corner.
Front removable axle, or torsion bar, or front transverse axle. Sometimes the front axle on chassis are removable. In most of the newer homologated for sure the front axle is removable. When the front axle was reintroduced, it was basically to make the front of the chassis stronger. At that time because of several factors, 40mm rear axles, tire compounds, and construction horsepower, etc... the chassis were suffering from a lack of front grip, generally producing an understeer condition. Some manufacturers utilize larger diameter front axles to strengthen the front of the chassis. However, this is still not enough. Then came the introduction or reintroduction of the transverse front axle. This made the chassis more positive on turn in and cured the problematic understeer. However, with every action, comes a reaction. The net was better when you have a severe understeer but, if you can work around the implementation of the front axle, the overall lap times are faster. It is just like the rear end of the chassis, if the front is too planted, you can loose lap speed just as if the rear end is too planted. Therefore, you will see most new chassis without a transverse axle, or with the front axle removable, or with the installation of clamps or some other variation of this system. Some manufacturers use different tubing diameters, or wall thickness in the front axle to vary the strength, as another part of refining the package, or tunability.
Other less conventional torsion bars are out there, such as the removable 1st cross member utilized by Tony Kart on their Extreme, model. They also had a blade where you had the ability to adjust it to give either more of less flex at this joint. This is a very critical chassis adjustment and would give substantial net change when utilized. However, on their newest homologation, they have gone back to a conventional tube in its place. Sodi Kart has used a form of torsion bar/blade on one of their models in what would be the lower "A" arm position to give a variable strength to the front of their chassis. Other manufacturers use a basic sliding clamp method over a tube which has been cut. So either the joint is able to flex freely, or it can be joined together to form a connection from one tube to another improving the integrity of a junction to net a specific desired effect.
A good example of this is where the new Paul Tracy Kart has taken latest technology of chassis manufacturing and made the triangulated waist section adjustable. This is achieved by installing a sliding clamp in the triangle section prior to welding. Then cutting the tube so that you can either have the chassis function as a traditional design, or create more grip in certain applications when you slide the clamp in place.
We can go further when we look at the race kart chassis as an entire unit. So many bolt-on items are critical to the chassis. Axles, tie rods, hubs, wheel, seat struts, seats etc.....
To summarize:
In the final analysis, Chassis all have a specific goal in mind by the designer, or manufacturer. The character can be altered via the implementation of torsion bars throughout the chassis. If you want to increase grip, the basic rule is stronger seems to produce the net result of more grip. If you want to reduce grip, reduce the integrity of the chassis at certain points and you will diminish grip in that section of the chassis. The thing to keep in mind is, that when you install a component that increases the integrity of a portion of the chassis, the net will be more grip. When you have more grip, you have a greater need for horsepower. Therefore, there is a happy balance of the chassis regarding understeer and oversteer, coupled with the lease amount of grip to produce the lowest lap times and robbing the least amount of horsepower from your racing engine. This is what all racers/designers must keep as the ultimate in desirable outcomes. Of course that is in a combination with the rest of the chassis package to try to achieve a neutral balance of the chassis, or whatever will suit the course conditions, or the driving style of the chassis pilot.