Introduction “Setting up” a race kart chassis seems to be as much art as science. Even major championship repeat winners often differ greatly with regard to set-up solutions. The manual is based on both the specific recommendations of the CRG Factory Race Team and the dominant, if not exclusive, opini ons of kart racing champions. All recommendations come from reliable sour ces, but keep in mind that when making chassis/kart adjustments, “If it doesn’t get better going one way, try going the other”.
Basic Chassis Setup Base Setup (Normal Track Conditions) The following settings are recommended as a starting point for a dry track with normal levels of grip (not “green” or slippery and also not with high amounts of rubber on the track, causing high grip). Weight distribution should be 43.0% front, 57% rear and 50/50% side to side. Front toe should be set out to 1/16” to 1/8” (1-3mm). For hard compound tires, set toe out at 1/8” to ¼” (3-6mm).
Basic Chassis Tuning If front end of kart is not gripping in corners (understeering): Move out one wheel spacer on both spindles. If front of kart becomes too wide, move wheels back to original spacing and change caster/camber adjusters from II/II to II/III or III/III (be sure to re-check toe settings). Fit shorter hubs to rear axle. Be sure to measure from the hub face that meets the wheel to the chassis first (typically around 8-3/4”), so you can keep the same rear width measurement.
Advanced Techniques and Theory General Theory To enable us to properly set up a kart chassis, we must first understand the most basic principals of the racing kart, which is a unit made up of tubes and front steering geometry, propelled through a live axle (one without a differential). Making adjustments to enable the race kart to turn without oversteer or understeer is difficult and challenging. Achieving a well-balanced chassis set up is part art and part science.
It is best to work on the end of the kart that is not handling well. If, for example, the problem is understeer, try to solve the problem by first adding more grip. If that is not successful, try taking grip away from the rear to balance the chassis. When a kart is properly set up, steering effort will be reduced and it will seem to “float” through the corners. Remember, the front and rear of the kart must be in balance, with neither end too tight or too loose.
General Set Up Conditions Chassis Attitude The chassis attitude (frame in relation to the ground) should slope from front to rear, the front being slightly lower than the rear. Adjusting the ride height with axle carriers in the rear and/or kingpin shims up front, attains this. Engine Types Generally, 100cc karts will be set up to control understeer, as they do not have the power to require maximum rear grip. Excessive grip will slow the kart down overall.
Terminology Axle run-out: The variance of an axle from being perfectly round. This is usually measured with a dial indicator. Ballast: Weight, normally lead, added to raise he combination of kart and driver up the minimum legal weight for the racing class. Bearing Carrier: The element, normally three, in which the rear axle bearings are mounted. Caster: The tilting to the rear, of the top of the kingpin on which the front wheel spindle pivots.
Oversteer: A tendency for the rear of the kart to slide outward at corner entry or mid-corner. It’s important to understand this tendency must be occurring as the kart enters the corner, not on corner exit when application of power can cause “power induced oversteer”. Power Induced Oversteer: A tendency for the rear of the kart to slide outward at corner exit, under hard power application. Steady state throttle should not upset the chassis balance.
Front End Adjustments Some of the most important handling adjustments are made at the front of a kart. Problems that occur when entering a corner are frequently due to an improperly adjusted front end. Front end bite and steering response can be corrected by simple adjustments and toe setting is a good place to start.
Caster/Camber Adjusters: The adjusters at the front spindles should start at a II/II (top/bottom) setting. Refer to the CRG caster/camber chart at the end of this manual for the effect of various settings. Generally, karts are quire sensitive to caster adjustments and are not as sensitive to camber changes. Caster has the greatest effect at corner entry and during the first third of the corner. Camber has the greatest effect in the middle third of the corner.
Front Width: The most common adjustment made to change the handling of a kart is by working with its front track, or front end width. Widening the front track will create more of a jacking effect when the wheels are turned. This will result in more front end grip and quicker turn in. Narrowing the front track will have the opposite effect. This will result in slower turn in and less front end bite.
Rear End Adjustments The rear end adjustments include wheel hub length, track, rear ride height, axle stiffness, bearing locations and seat struts. Changes to these settings are usually made when handling problems occur on the exit of the corner. Some have said that the entire kart should be regarded as a tuned spring. When you change the rear axle stiffness, hub length or rear width, you’re actually tuning the spring’s “frequency”.
Generally, it’s best to start at 54-3/4”, as this gives the ability to narrow or widen the rear for slightly more or less grip if needed to balance the chassis. Each side is only 1/8” away from the maximum of 55”. It becomes necessary to narrow the track when the rear of the kart has too little grip. Keep the operating range of movement on the rear width in a fairly small range.
Wheels: Wheel stiffness has a smaller effect on grip (at both ends of the kart) than axle stiffness. Softer wheels such as spun aluminum will have less grip than cast or forged magnesium wheels. Softer wheels can also promote uneven tire wear. A soft wheel will tend to wear the inner portion of the tire. It is generally best to run a stiffer wheel.
Bearing Carriers: The axle bearing carriers can have an influence on the axle stiffness since the portion of the axle between the bearing and the hub is the part that flexes. If you widen the rear track, you are losing a bit of traction because the distance from the bearing carrier to the hub is greater. The normal installation is with the long bearing race (carrier) pointed inward. To effectively soften the rear axle a bit, the third bearing can be set loose in the frame housing.
Maximum Grip Setup (Low Grip Track) The following settings are recommended as a starting point for a dry track with little grip. These types of tracks are often referred to as “green”, given the inherent lack of grip in them. The attempt here is to gain more grip from the kart. The following recommendations should aid in this. Weight distribution should be 43.0” front, 57%.0 rear and 50/50% side to side. Toe should be set out to 1/16”-1/8” on each side. Caster should be at maximum.
Minimum Grip Setup (High Grip Track) The following settings are recommended as a starting point for a dry track with a high amount of grip, perhaps one with a lot of rubber laid down. The attempt here is to lose grip from the kart. The following recommendations should aid in this. Weight distribution should be 43.0” front, 57%.0 rear and 50/50% side to side. Toe should be set out to 1/16”-1/8” on each side. Camber should be set at -1/2 degree (negative ½) to 0 degree Caster should be at III/III settings.
Rain Set Up Obviously the first change is fitting rain tires. Beyond that, racing in the wet is extremely challenging, even more so if you’re stuck with a dry set up. The changes below will serve to soften the chassis and improve adhesion in the wet. First, a word or two about driving in the wet. Get some RainX for the outside of your visor, a good anti-fog agent for the inside of your visor and a plastic rain suit to wear over your driving suit. The typical racing line contains oil, water and rubber.
Chassis Set Up Procedure Measuring the Chassis In order to effectively determine if the chassis is straight, it will be necessary to remove the seat and set the kart on a stand. First measure the parallel relationship between the front stub axles and the rear axle (with the wheels set straight ahead). Measure each side of the kart from the back of the rear axle to both the bottom and the top of the kingpin bolt. Both sides should be equal.
Progression of Tuning at the Track While there are many different ways to troubleshoot a chassis handling on the track, the essence of what you’re trying to do is just simply figure out where the chassis is lacking.
Kart Scaling & Weight Distribution Weight distribution on a kart has a huge influence on the final performance of the kart on the track. The mass of the driver is often greater than the kart itself, so this mass must be positioned properly. Scaling the kart is perhaps the most important thing a driver or team can do to ensure proper handling of their machine. When the kart is scaled properly, ideal weight distribution is achieved. Therefore, the kart will have the potential to perform at its optimum level.
Scaling the Kart The following steps are very important to the scaling accuracy of your kart: Use digital scales for highest accuracy and repeatability. Be certain the floor is level. If necessary, place shims under the appropriate corner scales. This is very important. Set caster and camber evenly on both sides of the kart. Set spindle heights evenly on both sides of the kart. Set toe (always after setting caster, camber and ride height).
Tires (Care & Feeding) Tire Pressures The first thing that must be determined for a kart tire is correct inflation pressure, if you want to get the best performance. That is easily said, but the real problem is the word “correct”, because its meaning varies with conditions such as driver, frame, course layout, road surface, weather and temperature to name a few variables. The manufacturer’s approved pressure is usually from around 10 to 18 psi.
Pyrometers An even better means of evaluating pressures is the use of a digital pyrometer to measure tire temperatures across the tread face. These should be taken immediately upon re-entry to the pits after a little to no cool down lap. While laser type pyrometers are easier to use, the surface probe types are more accurate as they are not measuring a rapidly cooling surface, but they actually “probe” a bit beyond the surface of the tire tread, where the heat is better held.
Change in Atmospheric Temperature: The general rule is to raise inflation pressures slightly as the temperature falls and lower it as the temperature rises. If there is a significant difference between morning and afternoon temperatures, raise the inflation pressure a little in the morning for better grip by increasing the load to generate heat. Lower it in the afternoon to reduce generation of heat by the tire. This rule applies for summer and winter also.
The Moving Target of Proper Pressures: Ultimately, one of the difficulties in setting correct tire pressures lies in the condition of lower pressures producing more grip once the tire is up to proper operating temperature. However, higher pressures bring the tire up to operating temperature sooner, ultimately at the expense of grip later in the race (compared to a lower pressure at that same tread temperature). Therefore, proper pressures are often based on how soon and how long optimum grip is needed.
Troubleshooting Guide Adjustments recommended for different handling problems. Always make only one change at a time. The back end is loose at the entrance of the corner or there is too much front end bite.
Kart is tight at the exit of the corner or the front end is understeering at the exit of the corner. Put shorter wheel hubs on the axle Move in the rear track by up to ½” Raise the air pressure in the rear tires by 1 psi Install a softer axle Lower any ballast at the rear of the kart to a lower vertical position Remove one set of seat struts (leaving 1 on each side) Lower the rear ride height Kart understeers or oversteers, but only in one direction.
Quick Troubleshooting Chart Remedies are listed in approximate order of relative effectiveness with most effective listed at the top. Many of the items below are of similar effectiveness to those adjacent in the list.
CRG Caster / Camber Chart CASTER CAMBER Maximum More More Central Central Central Less Less Minimum Central More positive More negative Max. negative Central Max. positive More positive More negative Central UPPER LOWER III II III 0 II II II I I III III II II II 0 I II I REMARKS Maximum Caster . Maximum negative camber Factory neutral setting Maximum positive camber Minimum caster Fixed Bottom Carrier: Position I on top carrier will give more negative camber and less caster.
