Start Owners Manual Area: This setup tutorial is designed to do just that by familiarizing you with your Ultramax Chassis and giving you the necessary information on chassis preparation and setup analysis that will put you ahead of the pack for the next racing season. Although this tutorial Mentions just one of our chassis designs, the instructions do apply generally to all of our chassis. In the following pages we are going to break down the process that we have found to be most successful in assembling a chassis once it is received from the factory. We will cover topics like squaring and alignment, front end geometry, seat and body mounting, at the track setup analysis and several other important issues that are necessary to keep you out front for future racing seasons and beyond.
1 - Out of the Box
The first thing that should be done when you receive your chassis is to make sure that you have received all of the necessary equipment from the factory. We try very hard to include everything needed to put the finishing touches on your chassis once you receive it but hey, we tend to make mistakes from time to time just like everyone else. So, keep us in check and go over this quick check list to make sure that you have all of the necessary equipment to make your assembly process a quick and easy one. The following things should be included in every chassis purchase:
• Left and right side seat strut along with 4 bolts and nuts for each strut and seat hook up point.
• Steering wheel with hub, three bolts, three nuts and three cotter keys.
• 12 wheel nuts and 6 sprocket hub nuts.
• Steering column lock and pin.
Once you have made sure that all of the necessary components are there, you are ready to move on to step two which many consider to be the most important step in assembling a new chassis.
2 – Squaring and Alignment
One of the most important parts of assembly on a new chassis is making sure your chassis is square from front to rear and that all of the front end geometry is set to your desired specifications. It is very important that a certain process is followed when setting your front end geometry and squaring your chassis. If the process is not followed, your front end may get out of align with itself and the rear axle giving you poor scaling consistency and on track performance. In this section, we will outline this step-by-step process, breaking down each step for a better understanding of its roll in your chassis on track performance.
Step 1 – Leveling your Chassis
It is a good idea to level your chassis when setting your front-end geometry so you can take accurate measurements when setting up your front-end. A surface plate used when scaling a chassis works well in completing this step.
Simply level your surface plate and leave the scale plates off. Without wheels or tires, place the chassis flat on the surface plate and make sure that it is stable and level on the plate.
You are now ready to move on to step two.
Step 2 – Setting Your Pitman Arm
Front-end geometry consists of a series of angles that set your caster, camber, king pin inclination and Ackerman. Each angle must be set correctly and work together with one another in order for your front end to work at its optimum level. The first step in doing this is making sure your pitman arm is set perpendicular to your level surface as shown in the picture on the left.
A digital smart level that can be found in any hardware catalog is a good tool to have when completing this step. To check its alignment, simply place the smart level parallel to the pitman arm on each side and turn the steering shaft the necessary direction to get the two angles to equal. The angle that you are looking for is around 4° - 5° on each side. Once this is completed, lock your steering lock down on the steering shaft and place the locking pin in it. You are now ready for step three.
Step 3 – Setting your Caster
Each chassis comes with the right front caster set at 10° and the left front caster set at 8°. These settings are obtained when both sides have the center notches lined up on the caster blocks as shown with the left front in the center picture below. For almost all conditions, these caster settings will be a good starting point. However, there are certain situations where a different setting may be desired for a better weight jacking effect. For this case, both the right front and left front caster blocks come equipped with three lines both forward and backward from the original notch. Each line forward or backward is a 2° change in caster. Therefore, on the right front you can go as low as 4° of caster or as high as 16° of caster. Similarly, on the left front you can go as low as 2° of caster or as high as 14° of caster. The following figures illustrate how this works using the left front as an example with the picture on the left set at 6°, the middle at 8° and the right at 10°.
Caster is built into a racing chassis to promote weight transfer, which is a major factor in producing the bite necessary to negotiate each corner on the track. Generally, more caster will produce more weight transfer and more bite and less caster will produce less weight transfer and less bite.
So, on high speed, hard biting racetracks, less caster will be needed since the racetrack itself will be producing most of the necessary bite. Similarly, on low speed, low biting racetracks, more caster will be needed in order to produce the necessary amount of bite in the chassis.
Running more caster in the right front than the left front assists the kart in turning left on corner entry, this is known as caster split. The more caster split that is ran, the more the chassis wants to pull to the left thus, helping the kart turn on corner entry. In a situation of too much caster split, the kart will generally turn in very well on corner entry but pick up a push at the apex of the corner due to an insufficient amount of weight jacking by the left front. If there is not enough caster split in the front end, the driver will have to apply a lot of input to get the kart to turn getting into the corner, making the kart feel tight in the front, or possibly twitchy in the rear, on corner entry.
A few good rules of thumb on caster for those who are less experienced with it are as follows:
• 2° of caster split is a safe amount of split for most all conditions. If you are not experienced with caster or simply don't like to adjust it much, this split will be the best overall setting for you. It is our recommendation that you don't exceed 4° of split and never run less than a 0° split.
• Using the right front as a baseline, we have found that you will generally not need to run more than 14° of caster. Most times if you run more than this you will create too much weight jacking to quick and will be unable to keep the kart consistent. Likewise, 6° of caster is the least amount we recommend running. Lower settings than this tend to cause a pushing condition due to a lack of weight jacking.
Naturally, these are simply guidelines to follow. Every racetrack is different and may require caster settings outside of the parameters we have outlined above. However, if you stay within these parameters, we feel confident that your front-end settings will be within a safe range and should be sufficient under most conditions. Now that your Caster is set, we are ready to move onto step 4.
Step 4 – Setting your Ackerman
For this season, Ultramax Racing Chassis has implemented Ackerman adjustability on our chassis. The function of Ackerman in front-end geometry is to turn the inside tire at a higher rate than the outside tire. This is based on the geometric understanding that the left front tire is traveling on a tighter arc than the right front tire.
In most cases your desired Ackerman setting will be with the left front tie-rod end one hole closer to the king pin bolt than the right front tie-rod end. In unison with the correct Pitman arm angle, this will give you the correct amount of left front steering lead for most conditions.
Although this setting will be ideal for most track conditions you may encounter certain situations that you will benefit from a change in Ackerman. On a fast, hard biting racetrack, moving the left front tie-rod end forward another hole may free the front-end up from the apex to corner exit, allowing for you to exit the corners lower without binding the chassis or engine RPM's (picture above). Likewise, on a slower racetrack that lacks bite, you may find it helpful to move the left front tie-rod end back a hole to stabilize the chassis on corner entry to the apex.
As with all adjustments on our chassis, if you are not comfortable with the adjustments or just like to keep your adjustments simple, we recommend that you run the settings that we recommended above. These are settings that will be ideal for all situations and will not hinder performance under certain track conditions like the other settings may, if the wrong adjustment is made. Now that we have discussed Ackerman settings we are ready for step 5, squaring the chassis.
3 – Axle Preparation
The axle in a chassis is a very important structural component. It is very important that the axle is secured in the chassis and that it is in the least amount of bind that is possible. In order to complete this step, you will need 6 axle locking collars, lock tight and a set of sprocket guards.
First, remove each set screw one at a time from the axle bearings, place a drop of lock tight on them and place them back into the axle bearings tightly. Next, make sure that your brake rotor is spaced evenly away from each brake pad to ensure free rotation without drag. Once this is done, make sure the rotor hub is tightened securely. It is now recommended that you place sprocket guards on your sprocket hub to ensure that the chain stays in position even in those tight altercations that we all tend to get into from time to time on the track.
Finally, we are ready to install the axle collars. One collar should be placed on both sides of each axle bearing and tightened securely to assist the set screws in ensuring the axles position in the axle bearings. Next, set your right rear wheel hub spacing by placing a 10" wheel on the right rear and moving the hub to where the wheel is a ¼" off of the frame. Once this is done, place an axle collar just inside the hub and tighten it down securing your hubs position on the axle. A collar should be placed just inside the left rear wheel hub to ensure its position on the axle. Its spacing will be discussed later in the final setting up of the chassis. Once your axle work is complete, it should look like the picture above. We are now ready to move on in our chassis preparation.
4 – Mounting the Seat
Another very critical step in your chassis preparation is the picking and mounting of your set. The seat holds the driver and in karting, the driver is the single biggest piece of ballast and therefore, the largest portion of weight transfer on the chassis. With this understanding, it is clear that the type of seat used and its position on the chassis is very significant in your chassis handling characteristics. We recommend using a heavyweight seat with a good lip around every edge. This lip and thickness will prevent a large amount of flex in the seat and give the chassis the amount of stiffness and stability that it needs to perform at its optimum level.
We recommend using a heavyweight seat with a good lip around every edge. This lip and thickness will prevent a large amount of flex in the seat and give the chassis the amount of stiffness and stability that it needs to perform at its optimum level.
Every driver obviously has different size characteristics: short, tall, big, and small and with every case a different seating position may be needed. With this being the case, it is hard to state a universal truth on how to mount your seat. However, what we will discuss in this section is some things to look for and do on a consistent basis when mounting your seat.
The seat can be mounted on the stand without wheels and tires. In order to do this you need to find a flat board or plate of some sort and place under the center section of the chassis for the bottom of the seat to sit on as is in the picture on the right. The first step in mounting a seat is to place the right side seat strut on the rear cross member and snug it up just enough to hold it in position but not so much that it cannot be moved.
Next, loosen both front seat struts up and push them forward out of the way of the lower portion of the seat for now. Now place the seat on the kart with the bottom of the seat lying on the board we placed under the chassis. Move the rear of the seat around with the right side seat strut getting the spine of the seat to line up with the center of the brake rotor. Line the right side seat strut up with the seat with a slight lean towards the front of the kart of roughly 5°.
Now for the part of the seat mounting that greatly depends on the driver's height, weight, seat style selection and the type of track. 8 ¾" from the top of the seat to the top of the axle will give you the 14" WKA minimum seat height (shown to the right).
A lot of the newer style seats on the market are built in a way that the 14" minimum cannot be reached due to the severe curvature of the upper rear portion of the seat (consult your nearest dealer or Ultramax Racing Chassis for further information). For these style seats, add 1" to every number that is getting ready to be discussed. The following list is a list of different driver sizes and track conditions that will mandate seat height positioning.
|Track Type||6' and above, 150lbs and above||Below 6', 150lbs and above||Below 6', below 150lbs|
|Pavement||8 ¾" from axle||8 ¾" from axle||8 ¾" from axle|
|High speed/ high bite dirt||8 ¾" from axle||8 ¾" from axle||10" from axle|
|High speed/ medium bite dirt||8 ¾" from axle||10" from axle||11" from axle|
|Low speed/ medium bite dirt||10" from axle||10" from axle||11" from axle|
|Low speed/ low bite dirt||11" from axle||11" from axle||12" from axle|
As always, this chart is designed to give you an idea of where to mount your seat. There are several variables that can effect where your seat needs to be mounted to transfer weight correctly. However, with the assistance of this chart, you should be able to get your seat height close for every track condition.
Now that you have your seat height set, drill your right side seat strut hole while maintaining proper seat height. Place the bolt through the seat hole, the seat rubber on the bolt and then place the nut finger tight on the bolt for now. Next, put the left side seat strut on the chassis and align it with the left side of the seat and snug it up as you did the right side seat strut. Now make sure the back of the seat is near level from left to right and that you are still maintaining your desired seat height, then drill your left side seat strut hole and place the bolt through the hole, place the seat rubber on and finger tighten the nut.
You can now slide your front seat struts up towards the bottom of the seat and align them with the seat leaving enough clearance to place the rubbers in between the seat and the strut.
Once they are aligned and tightened down, take a marker and mark the two holes to be drilled, take the seat back off and drill the holes. Now you can put the seat back on and place all four bolts through the holes and finger tighten each nut.
Check one last time to make sure you still have your desired seat height, the seat is still level from left to right and that the bottom of the seat does not hang underneath the chassis.
Then tighten the seat bolts and seat struts down. Once your seat is mounted it should look similar to the picture above. Now that we have the seat mounted, we can move to hanging that body.
5 – Hanging the Body
There are three important issues that must be addressed in hanging your body: ground clearance, hanging it squarely to the frame and connecting it freely to your chassis. If you are using the Ultramax Racing Chassis body kit it should be an easy job for you since the bodies come pre-cut for proper clearance and fitted for easy joint connections. There are many different techniques that can be used to hang a body on a chassis. In this section we will discuss what we have found to be the easiest and most consistent way to hang a body.
The first step in hanging a body is to connect the nose to the right side panel squarely to ensure that your body will be square to itself throughout the installation. As shown to the right, you can connect it in three separate places using either pop rivets or small button head bolts.
To do this, first hold the two pieces together and see how the joint will fit. Once this is done, clamp the two pieces together with C-clamp vice grips or something similar and step back and eye it up to make sure that the nose and the side panel are square to one another. Once the two are adjusted to square with one another, go ahead and drill your holes through both the nose and the side panel and bolt or pop rivet them together.
We are now ready to fit this portion of the body onto the kart. To do this, put wheels and tires onto the chassis and place it on the floor where you are going to hang your body. Now, slide the nose/ side panel combination onto the chassis and block it up where it is flush to the bottom of the bumper. You can do this using a level, 1" x 1" box tubing, plywood or something similar to this. Next, place the seam where the side panel and nose are connected together directly over the right front king pin bolt as shown in the picture on the left.
This should ensure the proper wheel clearance for both the front and rear tires. Now, move the body directly left or right on the chassis to get the side panel about even with the right rear rim. Once this is done, step back and make sure the body is square to the chassis. This can be done by sighting down the right side panel and checking its square with the right side tires or by looking at the left side panel joint with the nose making sure it is directly over the left front king pin bolt.
Once your body is square to the chassis and is located from front to rear via the king pin bolts, you can mark your front bumper connections points with a marker and drill each hole, one at a time, placing a bolt and nut finger tight in each one after its drilled. After each bolt has been placed in the nose, tighten them all down. Now that your nose is located, step back and make sure the body is still square on the chassis. If it is still square, relocate the right side nerf bar, if necessary, to fit flush against the right side panel. You are now ready to mark each hole in the right side panel and drill each hole one at a time, placing a bolt and nut on finger tight after each hole is drilled. You can now pull your 1" spacers out from underneath the body and again step back to ensure that the body is square on the chassis and located properly from front to rear. Once this is done, you can tighten each bolt and nut down and move on to mounting the left side panel.
With the hardest part of mounting the body behind you, we can quickly locate the left side panel and move on in our setup process. Place the left side panel up to the nose and space it up with your 1" spacer as done before. Again, check the joint to see that it fits well and then clamp the panel and nose together. Now, step back and look at the side panel to see if it is square with the chassis from front to rear. Be careful to check the clearance from the left rear rim making sure that the rim is no farther than 1" inside the side panel in order to comply with WKA rules.
Once the above has been done, move the left side nerf bar in or out if necessary to get it to fit flush against the side panel. With this done, you can now mark and drill each hole, one at a time, placing a bolt and nut through after each hole is drilled. When all four holes have been drilled, tighten each nut and bolt down and remove your 1" spacer.
When your body is fit and secure, it should look similar to the body in the picture above. Now that we have finished hanging the body, we can move on to getting your new kart ready for the race weekend ahead!
6 – Preparing For Race Day
With all of your necessary preparation work done to your new Ultramax Chassis we are now ready to do the necessary setup work to get you ready for the race weekend ahead. The following section will be a generalized discussion of the pre-race setup process. Because there are so many different track types and conditions we will not discuss specific setup numbers, rather, a general set of parameters for each setup item and a systematic approach to your pre-race setup process.
Step 1 – Tire Positioning
Your chassis should now have its caster, Ackerman and seat positioning set from the previous sections above. Now all we have to do is get an engine on there, pick out the right starting four tires and get it on the scale plate. Because of the unending variations in possible track types and conditions, we will not discuss specific types of tires to run and when to run them. We will only discuss their positioning on the kart. Tire positioning is a very critical aspect of chassis performance since they transfer the chassis information to the track and visa-versa. For that reason, we recommend leaving the positioning of your tires at the factory recommended settings that we are getting ready to list. There will be times where moving a tire slightly in or out here or there may help you, but as we have stated before, you will generally be better off if you run these recommended settings as the incorrect positioning of your tires can negate any chance of optimum chassis performance.
We recommend running the right rear, right front and left front a ¼" off of the frame or spindle at all times. The left rear is where any moving in or out will generally occur depending on track conditions and tire selections. For dirt, we have found that in almost all cases a 6.00 on the left rear is the way to go. As we have stated before, there may be times where this is not the case however, by keeping this constant you eliminate certain variables that can greatly hinder your on track performance. As a starting placement for the left rear, we recommend running a rear tread width (measured from outside of the right rear tread patch to the outside of the left rear tread patch) on dirt of 38 ¾" and on pavement, 39 ¼". Any time you change from one left rear tire to another, always recheck this measurement and move the left rear in or out to regain this measurement.
Lastly concerning tires, we recommending running no less than ¾" of rear stagger and no more than 1 3/8". With front stagger we recommend running no less than 1" and no more than 1 ¾". Again we stress that these parameters are merely a gauge to work off of. By no means will they work for every track condition in the country. However, we feel that if you stay within these parameters you are running a reasonable amount of stagger that should allow you to be fast at most any track.
Step 2 – Setting Your Camber
Now that the tires and engine are on the kart, we are ready to get your chassis on the scales! The first step once the chassis is on the scales is to check the camber and get it roughed in. Some drivers like to check camber with the driver in the kart and others like to check it with the driver out. There really is no right or wrong way to do this, only a consistent way. In other words, whichever way you choose to check it, check it that way every time you check the camber. With that said, lets discuss some numbers.
Right front camber can be related to how much the kart is being loaded by the given track conditions. If the track is very fast and is producing a lot of bite, then the right front tread patch will be deflecting quite a bit and therefore will need more negative camber in it. If the track is not biting very hard then likewise, the right front tread patch will not be deflecting very much and will not need as much negative camber. Right front camber is also very dependent on the tracks banking. If the track has a lot of banking in the corners it will then go through a very strenuous load on corner entry due to essentially being driven into the racetrack. Because of this you will have a rapid amount of right front tire deflection and will need to run more negative camber. We recommend running no less than -1 1/2° and no more than -4° of right front camber.
The left front tire can generally be considered as the tire that holds the kart in the corner. Relating the right front to the left front, the right front is the tire that accepts the load of the racetrack and the left front is the tire that directs the load put in the chassis. Left front camber can also be related to tire deflection, as was right front camber. If the track is very fast and producing a lot of bite, the left front tread patch will be deflecting quite a bit and will therefore need more positive left front camber. If the track is not producing a lot of bite the left front tread patch will not be deflecting as much and will therefore not need as much positive camber. Left front camber is not generally affected as greatly by banking as right front camber although it does depend on it a bit. We recommend running no less than +1/2° and no more than +1 1/2° of left front camber.
Again, these numbers are merely meant to give you parameters to work within. You may find situations where you need to run outside of these parameters. However, these parameters will almost always hold the correct amount of camber for your given track conditions. There is one final note on changing your camber settings.
We mentioned before that you would need to recheck your toe after checking your camber. With every camber change the toe will be effected, depending on how much the camber was changed. Whichever tire you are changing the camber in is the side that you will need to readjust your toe with. In other words, when you make a right front camber change, place the toe plates back onto the front end and readjust your toe by lengthening or shortening the right front tie rod. Once the right front camber is set you then do the same with the left front camber. By doing this after each change, you can prevent having to redo the squaring process mentioned earlier in the tutorial. The same process holds true for changing caster and Ackerman. Whichever side you change either of these on is the side that you need to readjust the toe on. We are now ready to place your chassis on the scales.
Step 3 – Setting Your Weight Percentages
We are now in the home stretch of pre-race preparation, its time to scale your chassis. We will again only be able to talk general numbers since there are so many varying track conditions as well as driver weights and sizes. The following paragraphs will give you some starting percentages as well as some pointers on when to change you weight percentages.
Left side weight is directly proportional to the amount of bite the track has and the size and positioning of the driver. We mentioned the positioning of the driver in great detail in the previous section on seat mounting. With that being addressed, we will now tie the amount of bite the track has to the positioning of the driver. The more bite a racetrack has and the bigger the driver, the more weight that will be transferred from left to right in the corners requiring more left side percentage to offset the amount of weight transfer. Likewise, a track with a small amount of bite and a little driver will not transfer very much weight in the corners therefore not needing very much left side percentage to offset the small amount of transfer. With this being briefly explained, we recommend running no higher than 58% and no less than 54%. The higher percentage will be needed for tracks that are very fast, have a lot of bite and have a bigger, but more importantly taller, driver. The lower percentage will be needed for the tracks with the least amount of speed and bite and a driver of a smaller build. Too much left side weight will generally make a kart quite lazy on corner entry sometimes creating a pushing condition due to lack of weight transfer from the left rear to the right front tire. Not enough left side weight will sometimes yield a very twitchy kart on corner entry causing an over biting condition of the right side tires making the kart overall, unstable.
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 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 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.
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.