Vmax Tire Cutter©

Tire Cutting Made Easy

 

 

 

 

Table of Contents

 

1.  Introductory

2.  Why do we cut tires?

3.  Tire Profile

4.  How can you cut compound curves

5.  Setting up your machine

6.  Rim offset

7.  Mounting the wheel on the machine

8.  Aligning the cutter head

9.  Setting the cut radius

10. Measuring tire camber

11. Cutting your tire

12. Baseline Tire profiles

13. Setting camber

14. Machine maintenance

15. Measuring That Secret Tire Profile

16. Notes

 

 

 

 

Introductory

            Hi my name is Terry Parker and I would like to welcome you  to VMAX Racing Engines And Machine. During the many years I have spent in the karting industry there has been, and always will be a need, to go faster. The VMAX TIRE CUTTER © is but just one of many  ideas to help you  go faster. I would like to thank my wife Sherry and daughter Samantha for all their patience. They both know just how weird I really am and choose to accept it as normal. Most of all I praise an almighty and merciful GOD who sent his son JESUS to die for me on the cross at Calvary.  John 3:16

 

Why Do we Cut Our Tires?

Do any of the examples look familiar? I believe anyone that has been in karting for more than 5 minutes has run into these problems. Along with profile problems comes the out of round and balance problems. Wear can also create the excess camber problem. Have you ever seen a kart that looked to have 10* of camber in the right front but still handled great. As the tire cambers up you have to add more and more camber to the kart to stay with the tire profile.

 

            Above is an example of a tire profile as it goes around the racetrack. In A the kart is going down the shoot and is riding on the contact patch. That is where the least rolling resistance occurs. In B the kart is starting to turn in and the tire is racking over from the side load. You will notice it is not yet using all of the tire and has a little slip to it by not using all of the corner of the tire. In C the kart is at apex and maximum side load as the kart turns through the corner. If the track was still green or lacked traction from all the reasons they do, the process would be perfect and as you rolled out of the corner the tire would unload about the same way it loaded, At C at apex at B as you rolled off the corner and back to A down the shoot again. If the tire profile is not right for the track D may occur and the edge of the tire digs in or C can occur with a very sticky track and bind the kart up and slow you down.

            In the past we either let the tire wear in on its own or ground it down or put it in a pipe and stretched it halfway straight. Usually combinations of magic tricks were needed.

Another problem on fast tracks was having too much rubber on the tire and it would bind the kart up as soon as the rubber built up on the track. Back to letting it wear down or out with the grinder again.

Now we have solutions for the problems at hand, Tire Cutting101. There are many cutting designs available. Some use Profile plates, some do straight cuts and finish by hand, some are done completely by hand and some use a radius bar to control the profile.

 

Tire Profile

 

The tire profile is broken down to 3 or 4 parts as shown below.

 

 The contact patch is basically from dot to dot. You can make it wider but normally not narrower. This part of the profile is determined from the total weight of the kart and the air pressure you run. It is best determined by tire temperatures. The higher the number the flatter the contact patch.

 

            The slip angle starts from the edge of the contact patch over from ½ to ¾ of an inch. This part helps to control the amount of side slip the tire has. A higher number less slip, a lower number more slip.

 

            The next section is the lead in. It helps the slip angle and starts to blend in the edge of the tire. The same holds true for the angle number as does for the slip angle, higher number less slip, lower number more slip.

 

Last but not least is the edge of tire. It helps keep the very edge of the tire from digging in and over biting and rolling the tire under while cornering.

            A balanced profile is the answer to the search for speed.

 

 

 

How can you cut compound curves?

 

 

 

            Remember back in math class when you took a bunch of straight lines and made a curve. Well with using arcs instead of straight lines you do not need near as many lines to make the curve because the lines are already bent somewhat. If you decrease the radius on each arc and start it at the end of the previous one you will draw a compound curve as show above. We use the same principle to cut our tires. It gives us control of every aspect of the tire profile so that we can win that NATIONAL. (RIGHT?)

            Using the same radius numbers and width of section numbers we can now accurately repeat that profile to another tire or modify the profile to suit our needs.

           

 

 

Setting Up Your Machine

 

            If your cutter was picked up or delivered to you by us, it will be ready to cut as soon as you plug in the power cord. If it was shipped to you it will come in a crate. You will need to uncrate the unit. The radius bar and slide will have been removed to allow for crating. You will simply set the slide bar it the slot shown below and screw the feed rod into place. Then place the bottom plate on and insert the bolt and snug it up. Next feed the slide bar over to the lineup marks that are on the frame. That will put you close to the centerline setup. Next remove the cinch bolt from the cutter head and slide it over the cross bar. Next line up the radius bar to the slide bar and insert the pivot pin making sure the hole patterns line up and the end of the bars are equal. Next connect the traverse rod and the assembly is complete. All that is left to do is align the cutter head, which is covered shortly.

 

 

           

 

           

 

            Included with you machine will be the following accessories

 

A         Aluminum Square

 

B         Reference stop

 

C         Straight edge

 

D         3’ Tire tape

 

E         Indicating Head assy

 

Rim Offset

Rim offset is the distance the mounting flange of the rim is from  the inside outer edge of the rim. There are many different combinations of wheel offset available and we have made provisions to realign the centerline of the tire to the cutter bit. 

 

Mounting the Wheel on the machine

 

 

 

The tire and wheel mounts on the machine just as you would install it on your kart. It uses the same hub as your kart so all standard wheels will fit perfectly. I recommend to tighten down the lug nuts by hand and not to use an impact gun as this can wear out and strip the stud threads. Using an impact may also cause the threads to seize and gall, which makes replacing the stud very difficult

 

Back out the cutting bit to clear the outside of the tire. It is very sharp and if you tighten the wheel down against it, it may put a hole in your new tire.

 

Do not move the hub on the axle to try to adjust for wheel offset. That adjustment will be made at the radius bar slide mount and will be explained later in the manual.

 

Tighten the lugs as you would on your kart

 

After the lugs are tightened spin the wheel and check for excessive runout. If the runout is excessive recheck the wheel to see if it seated correctly on the hub. If all is well it is time to proceed.

 

 

 Aligning The Cutter Head

 

The machine uses a full floating cutter head system, which allows it to be adjust for different wheel offsets as well as camber and radius changes.

 

Install the wheel and tighten down the lugs.

 

Take the square and hold it against the outside of the wheel. Now while holding the square place the straight edge against the inside of the wheel. Note the measurement as read from the inside of the square. This will give you the overall wheel width. Now set the reference bar to an amount equal to ½ of the overall width. Place the square back against the outside of the wheel and make a mark on the tire at the edge of the reference bar. This will be the centerline of the tire. I use a white paint pen to mark the tire. They can be bought at WalMart in the crafts section.

 

Now rotate the wheel so the mark is at the cutter bit side and swing the bit to line up with the mark

 

Next while holding the square against the outside of the wheel slide the end over to the lineup mark on the radius bar. This will tell if the wheel offset is the same as the last tire you cut.

 

 

 

 

If it does not line up simply loosen the bolt on the radius arm slide and rotate the adjuster wheel to move the bar left or right then retighten the bolt. Now the tire is centered with the cutter head and it will cut the same on both sides of the tire with no camber. Camber cuts will be discussed later.

 

 

 

 

 

Setting The Cut Radius

 

You can set the different radius by simply unscrewing the pin and moving it to a different location. The hole closest to the tire is 13” and goes up 1” per hole as you move out to the end of the bar which is 50”.

 

 

Measuring Tire Camber

 

 

Measuring the tire camber is very simple. Take your tire tape and measure the circumference of the tire just inside the dots on each side. To have no camber would mean that both sides are the same circumference. (+/- 1/32 or so)

 

Cutting Your Tire

 

You can always cut more rubber off but you can never put it back on

           

            Now your are ready to cut your tire. Mount your tire on the cutter. Set you tire pressure to 10PSI. Turn on the machine and check for excessive rim runout. If it is ok then we are ready to start. The first section to cut would be the contact patch. Set your Radius setting to the number you are going to use. Bring the cutter over to the dot area on the tire. Now ease the bit up to the tire so that it just barely touches. Snug the tension screw on the cutter down lightly. Now swing the cutter over to the edge of the tire using a slow and steady turn on the handle. The quality of the cut is determined by the speed of the handle. A fast cut is quicker but a little rougher, a slower cut gives a finer finish but takes longer. I use a fast cut to get a lot of rubber off, and then slow down for a finish cut. You should have made a very light cut to the edge on the tire, now swing the cutter over to the opposite side making a light cut across the tire. After the first cut I always take time to look at the tire to check the surface to see how bad the tire looks as far as true and consistent. I also double-check for camber by measuring just inside the dots on both sides of the tire they should be the same. If not double-check your alignment. If needed you can adjust the camber by moving the slide bar slightly to one side or the other as needed. If you want to zero out the camber move the slide bar towards the small side of the tire. If you want to add camber move the slide bar to add either positive or negative camber to the tire. Move the bar towards the side you want to be bigger. Record the distance and which side you moved it to for your records. Now you are ready to begin cutting the tire down to the rubber depth that you want. Each ¼ turn of the adjustment wheel equals 8-9 thousands cut. Make ¼ turn cuts until you get use to the feel of the cutter then you can cut more as needed. Keep a check on your depth often as you can go by your number very quickly. You can cut in both directions, Left and Right I always stop at the setting plus .010 to give room for a light slow finish cut before I get to my number. On the contact patch area cut all the way across the tire from side to side. The extra you are removing is just rubber you will not have to cut off later and it gives a better finish to the final product. After each pass STOP the machine and remove the cut rubber from the tire. DO NOT DO THIS WITH THE MACHINE RUNNING AS IT CAN PULL YOUR HAND INTO THE CUTTER BIT.

            Now it is time to start the slip angle portion of the cut. Back the cutter away from the tire surface. Reset the radius setting on the bar. Swing the cutter over to the dot. Ease the bit in until it just starts to cut. Lock down the cutter and start a slow cut over to the edge of the tire. I always cut from the inside out. That way I always know where the section will start at. If you cut from the outside in it is a guessing game as to where it will end at. This will be a finish cut so make a slow cut. When you get to the edge you can swing back across the tire to get the other side.

            Next set up your radius setting for the lead in cut. Back the cutter away from the surface of the tire.  Make a mark on the tire the width of your section over from the outside of the dot towards the outside of the tire on each side of the tire. This is the beginning of the lead in angle. Move the cutter over to the mark and ease the cutter in until it just starts to cut. Now swing the cutter over to the edge of the tire slowly until it cuts over to the edge. Now you can swing the cutter over and do the other side. Now you can see all the angles blending in to form a curve.

            Next set up the radius setting for the edge of tire cut. Back the cutter away from the surface of the tire. Make a mark on the tire 1 ¼ “ over from the dot towards the outside of the tire . This will start the edge of tire cut. Swing the cutter over to line up with the mark. Ease the cutter in slowly until it just starts to cut. Now swing the cutter slowly over to the edge of the tire. Now you can swing the cutter over to do the other side of the tire.

            On certain tire sizes the edge of tire cut may not be necessary as the tire is not wide enough to need that cut. You have now cut a profiled tire that will be true and fast.

 

           

 

Baseline Tire Profiles

 

 

            The following is a list of baseline profiles that we have found to work well. You can use them to start with and then adjust them to your needs.

 

 

LF                                                                               RF

4.5,5.0,5.5                                                                  8.0

CP= 18                                                                      CP= 43       

SA=  13   From dot to edge                                     SA=  25   from dot to edge

                                                                                    LI=   18    ¾ over from dot to edge

                                                                                    EOT= 13  1 ¼ ‘ over from dot to edge

 

 

LR                                                                               RR

6.0                                                                              8.0

CP= 36                                                                       CP= 43

SA= 22   from dot to edge                                       SA= 25   From dot to edge

LI= 18     ¾” over from dot to edge              LI= 18     ¾” over from dot to edge

EOT=13  1 ¼” over from dot to edge                      EOT= 13  1 ¼” over from dot to edge

 

** Note that the LF tire only uses 2 angles due to the tire width.

 

 

 

 

CP  is determined by total weight of kart and air pressure raced with.

            Novice, Jr. Sportsman, with 5-10 psi = 44

            Jr. stock. Stock light, Medium, with 5-10psi = 43

            Heavy, Super heavy, with 6-12 psi = 42

 

SA  is used to help the tire side slip a bit. It basically is used to fine-tune the cp under

         cornering loads. The higher the number the more grip the tire has cornering. The

         lower number the more slip the tire has cornering.

 

LI   aids the slip angle and starts to blend the profile over to the edge of the tire. It reacts

       the same as the SA. The higher the number the more side bite. The lower the

       number the more slip the tire has cornering.

 

EOT  is used to blend the profile over to the edge of the tire. It can also help keep the

         very  edge of the tire from digging in with lower air pressures.

 

            It is Important to record all of the parameters in order to be able to reproduce the profile again. You need to know the tire pressure, 10psi. The radius numbers and the width of each section

 

There are many different combinations that your cutter can cut. Keep good notes and it will serve you well. You are only limited by your imagination and the number of tires you have to play with. Always remember you can always cut more off but it is tough to take that rubber on the floor and put it back on the tire. AGAIN, Keep Good Notes they are invaluable down the road.

 

 

           

Sample Tire Profile Record Sheet

 

 

Setting Tire Camber

 

 

In some instances you make want to camber your tires. First determine which way you want to camber them. Make note of which side of the tire you want larger. Next move the slide bar towards the side you want to be larger. Now test with a light cut and measure the amount of camber and adjust the slider bar as needed. When you have what you want record the side to which you moved to and how far from the center dot you have moved the bar.

 

 Machine Maintenance

 

 

The tire machine is very simple to maintain.

 

Check belt tension, adjust as needed

Grease axle bearings as needed

Keep excess rubber removed from machine in between cuts

Keep a very light film of grease on radius pin

Keep a very light film of grease under cutter head and support bar at wear point

Adjust tension bolt on cutter head if ever needed

Once a year relube the feed screw inside of cover tube

 

Measuring That Secret Tire Profile

 

            Included with you tire cutter was a dial indicating attachment. This gives your tire cutter the added benefit of being able to not only cut your tire to profile but also measure that super secret tire you have kept hidden away, not wanting to wear it out, using it only on special occasions. Now you can measure the profile and make another just like it.

 

 

            To start with you need to air up the tire to your cutting pressure and mount it on the machine. Now center up the cutter head and rim and check the centerline, adjust as you would to cut a tire. Make sure that you measure for camber so you can take it into account when starting to measure the profile. Next unbolt the cutter head by removing the four bolts that hold it on and set it aside. Now bolt on the indictor head and snug it up centering the roller on the centerline. Set your cut radius to a base line setting of 43 to start with. Now swing the cutter from left to right starting and stopping at the dot areas while watching the dial indicator. If the profile matched it would not move more than .010 from side to side. If the reading was more than .010 you need to move the radius pin to a new setting and measure again. A rule of thumb to follow is move the pin in the direction the indicator moves at the center of the swing. If the indicator moves toward you in the center move the radius pin towards you. Keep working with it until your readings are within the .010”. If the reading shows that the reading go up from one side to the other then you have to adjust for camber if you wish. Simply move the slide bar towards the smaller side to start with and remeasure. When you have worked it out measure the amount and direction you have moved the bar and record it on you setup sheet. Personally I do not use camber but that is an option for you to use. Now that we know the contact patch radius, record that number.

            Next swing the roller back to the center of the tire. Slowly move the cutter towards the outside of the tire. When the indicator has moved more than .010 and starts to drop off rapidly make a mark on the tire. This is where the slip angle has started. Now move the radius pin to 25 and reset the roller to the mark you just made. Now continue to move the cutter towards the outside of the tire. Readjust the pin to center up your reading as you did in the center section. Rule of thumb is as you move to the edge if the roller moves toward you move the pin away from you and vise versa. After you have gotten that measurement start from you mark and move to the outside and watch for that drop off again and mark the tire as before. This starts the next section or lead in area. Repeat the process until you have covered that half of the tire.

            Now you are ready to do the opposite side of the tire. Proceed as you did for the first half. It sounds complicated and time consuming at first but take your time and study the movements and after you have done it several times it will go very quick.  Again record all of the parameters on your setup sheet for future reference. Now you can do what no other tire cutter can do, profile that super secret, known only to a few, national winning tire profile and make another just like it.

           

Notes: