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Owners Manual Page 5:

Setting Your Weight Percentages continued...
Nose weight is also proportional to the amount of bite in a track as well as front-end settings, rather than driver size. For a track with a lot of bite and speed you can generally get by with the least amount of nose weight that we recommend, 43.5%. This is due to the strong influence of the high biting track conditions on the front end of the kart. On the other end of the spectrum, a track with a low amount of bite can generally take on a little more nose weight, 45% or so, due to a lack of track bite to help the kart turn. In this case, you will generally have to tighten the kart up a bit to keep the rear end underneath you at the apex of the corner however, once this is done you will generally have an overall better handling kart. We are now ready for the always debatable, cross weight setting.

Over the last several years cross weight has become an increasingly complicated topic that has had many different cases of debate to go along with it. So for this section, we will primarily give you a set of constraints that we feel are a safe range to stay in. This is an area of chassis setup that you will just have to play with and learn what you and your driver likes for different situations. For the 2003 Blaze we recommend a minimum of 55% and a maximum of 65% cross weight. Yeah, I know, we really helped you out there didn’t we? This is simply one of those areas that you are just going to have to work at and see what works best for you. We have found that generally a track with a lot of bite and high speed tends to like a lot of cross weight for two reasons: 1) excessively loading the right front tire making it carry all of the work and thus, pivoting the kart very quickly in the center of the corner and 2) relieving the right rear tire from excessive tire temperature and stress. Given the previous two reasons, it should be obvious to you that cross weight is very dependent upon other settings in the kart such as front end geometry (remember, we said that a lot of cross weight loads the right front tire excessively) left side weight, as well as and most importantly, driver preference. With this brief explanation of weight percentages we are now ready to go to the track and tune on those miscellaneous chassis settings.

7 – At the Track Tuning

In this section we will simply discuss several different chassis tuning techniques such as axle lead and air pressure. This section is simply designed to familiarize you with the rest of your 2003 setup options.

Axle Lead
Axle lead has become quite a hot setup-tuning tool over the past several years for all of the top karting manufacturers and riders. Your chassis is leading the way of top manufacturers by giving you that same tuning tool. Axle lead is designed to assist the kart in turning from the apex to corner exit much like a fork lift turns. Maximum axle lead will generally be ran during those fast hard biting track conditions where the kart tends to get tight from the apex to corner exit and becomes very hard to steer under other karts to make that all important pass getting into the next corner. Be careful with axle lead, as it will tend to give the driver a sensation of spinning out on corner exit. This sensation varies depending on track size and condition but is definitely something that takes a little getting used to. We recommend running no less than the standard axle lead of 1/8" for most all track conditions.

Tire Pressure
Tire pressure is yet another thing that greatly depends on track conditions and situations. However, for dirt and pavement we recommend starting with 1psi less air pressure in the left side tires than the right and working on your own from there. On dirt, race air pressures can vary anywhere from 5psi to 11psi depending on the amount of speed and bite in the track. The more bite a dirt track has, generally the more air pressure you need to run to keep the kart free. On pavement, we recommend starting around 10psi for most all track conditions. Going up in air pressure will tighten the kart along with making it "come in" quicker (which is good for qualifying) and having the long lasting effect of "locking down" late in a run. We recommend going no lower than 9psi and no higher than 13psi for most pavement conditions.

Tire Selection
This is a touchy subject that can rarely be simplified as we are trying to do here. However, We will lastly try to give you an idea of what to do when you see that dirt track go through a "face lift" or that pavement temperature go up or down 25°.

A dirt tire is primarily dependent on two things; spring rate and rubber thickness, both of which tie into one another. The thinner the rubber the less natural spring rate a tire has and the more air pressure you would have to run to get "x" as a desired spring rate. Likewise, the thicker the rubber on a tire the more natural spring rate a tire would have requiring you to run less air pressure to get the desired spring rate "x." Now, we aren’t saying that you have to calculate spring rates and rubber thickness for every track condition; we are simply trying to give you an understanding of the basis behind the following statements.

The more speed and bite a racetrack has, the more tire temperature that will be developed which will require you to run a thinner amount of rubber to dissipate that excessive temperature build up. Running a thinner amount of rubber will require you to run a little bit more air pressure to get the necessary spring rate needed for that particular tire and those particular track conditions. As speed and bite decrease in a track, tire temperatures become less and less and you need more and more rubber on a tire to create bite in the tire. Because of the larger amount of rubber, you need to run a little less air pressure to get the desired amount of spring rate for those particular conditions. The more speed and bite that is produced in a track, the harder the track is on tires requiring a harder tire selection. This can be compared to sand paper being rubbed on bare skin versus sand paper being rubbed on wood. The bare skin, like the soft tire, is too soft for the sandpaper and just gets ripped away while the wood is harder and therefore cannot be torn up by the sandpaper as bad. In the same way, the harder tire can resist the harder biting track conditions better than the softer tire, producing better overall grip.

Pavement tires have all of the same conditions as mentioned above. However, the one thing that is generally most important on pavement is a new tire. With this being the case, we don’t have near as much influence over the spring rate of one tire versus another due to each new tire having roughly the same thickness of rubber as the other. This is an issue that many tire manufactures has already taken care of and calculated for while building their tires for pavement conditions. So, that leaves us with the easier, yet in some financial ways harder, job of just bolting on a new set of tires and picking the right air pressures.

For most pavement conditions, either Firestone YGF’s or YGH’s will be ran with the F being the softer of the two. The more rubber that is laid on a racetrack, the less and less abrasive the track becomes, allowing you to generally run the softer tire. This is likely opposite of the way you would think it would be. With this being said, for most pavement conditions we recommend running the YGF with a DAM Dunlop on the left front and a DAH Dunlop on the left rear.

In closing, we would like to thank you for your purchase of the Ultramax chassis and hope that you get as much out of it in your racing seasons, as we have put into it. We hope that in some way this setup tutorial has helped you become more familiar with your chassis as well as becoming better acquainted with chassis preparation and analysis in general.

Here at Ultramax Racing Chassis, we try very hard to give you the very best product and customer support that we can and we look forward to helping you in any way that we can for the 2003 racing season and beyond.

Ultramax Racing!

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