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Tire Truing

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  • Tire Truing

    I think there are five basic types of tires used in 1/32nd. That is, silicone, sponge silicone, rubber, sponge rubber and urethane.

    I'm not going to ask about silicone and sponge silicone -- the IHSR club I race with doesn't allow them, and sponge rubber is easy to true with sandpaper, so no issues there.

    But the surface of many rubber tires tends to come off as eraser crumbs when sanded. I've not found a good way to prevent that, even if I feed the tires into the sandpaper a thousandth of an inch at a time. (Yes, I'm set up to do that!)

    Am I doing something wrong? Maybe I need to turn down the RPM's while sanding?

    One thing I have considered is using a lubricant -- oil or water -- while sanding. It will make a real mess, I'm sure. But it's the only thing I can think of besides reducing the speed.

    As for urethanes, I'm not sure what to do except keep sanding them at a very slow feed.

    Ed Bianchi

  • #2
    I've not found a GOOD method either.
    I use a 6 volt power supply on my Hudy machine. even that much slower drum speed doesn't help. I've tried sort of cold air from a "dusting" (shaking it gives colder air) compressed air can, not much real good luck there either,
    One thing I have found that sort of works, is after you do the truing, just rub the tire between your thumb and fingers to remove most of the balled up rubber, pick off the stubborn pieces with your finger nails, then a couple of laps on the track, and all seems good.
    While it may look horrible off the machine, it seems some manual manipulation and laps cleans them off. Really bad ones, I've tried lighter fluid, this helps a little too, along with a few laps.

    Anyone else ?



    • #3
      I do not have much experience with rubber tires but i have been working with some NSR supers. On my hudy i run 6 volts and go very slow if you have an adjustable power supply watch the amp draw if it goes to high it adds too much heat to the tire I let it come down to neutral for a minute or so then dial it down again very little. I get the tire close to my desired size then i let it set/rest for a day or 2 then finish it. I also round the outside with 600 grit sand paper with a little Simple Green on the paper.
      Your Mileage May Vary

      Courtney S
      Chatt TN


      • #4
        Very soft rubber tires are difficult to true. I have a Hudy, but I have not trued NSR tires myself. One of the guys in my club has been entering a proxy series that uses rubber tires for a couple of years and I believe that his tires were not optimal last hear, however he has been doing better this year. The last that I heard he was grinding at 5 volts with his Hudy. Possibly he is using some sort of lubricant, like soapy water, but I am not sure about that. My own experience with truing tires is that you should not use a lot of pressure. What you need to do is to remove the high spots, if you use too much pressure you will reduce the diameter of the tires without removing the high spots. An indication of the pressure would be the amp reading on your power supply. The motor in my Hudy pulls an amp when it is not grinding. I adjust the pressure to see 2 amps and that has worked well with silicone tires.


        • #5
          Try baby powder when truing NSR TYRES


          • #6
            Hi Ed, I hope you are using a tire truing machine for rubber tires,????... especially aftermarket tires from NSR, ThunderSlot, Slot-it etc. While sandpaper is passable for truing the stock RTR tires from Scalextric, Fly, Carrera, etc, and is also reasonable for truing any urethanes, you won't get satisfactory results without a tire machine. It is just nearly impossible to hold the tires steady enough and with light enough pressure to avoid them grabbing/chewing up.
            Tire machines that counter rotate the tire against a rotating sanding drum are much better suited to truing rubber.

            I don't true rubber tires at anything more than 4/5 volts, and I use the knob on the Hudy or my Wrightway machine to continually move the tire in/out, cutting/sanding for only a few seconds at a time.....and with an absolute minimum of pressure,.....I don't go above a 2amp draw,.....any more and the tires easily overheat and will not cut cleanly, It is a slow process, but, I don't know any good racers that have found truing rubber tires to be anything other than a long process. You can use water/lighter fluid/kerosene to cool the tires, but you can still only cut them for a few seconds at a time before they overheat.

            By contrast, urethanes are a snap to true/profile.........I can easily do 5/6 pr in the time it take to do a pr. of rubber tires......they are much less susceptible to heat/pressure than rubber, but, I still true the same way........4/5 volts, cutting for 5/10 seconds at a time with minimal pressure.

            Hope this helps
            Chris Walker


            • #7
              I do not use a conventional tire truing machine. I use my benchtop milling machine with digital readouts. I chuck an axle, wheel and tire assembly into the spindle and grind the tire surface against 80-grit sandpaper glued to the side of a machinist's vise bolted onto the horizontal bed. I can adjust my 'X' axis manually by 0.0005 inches at a time (0.013mm). I can adjust the spindle speed with the electronic speed control from a bit over 100 RPM to about 15,000 RPM. So far I have been using about 1,200 to 1,300 RPM.

              While my mill cost about 5 times what a Hudy tire truer does, it is a far more versatile machine, and I use it a for a lot more than tire truing. If you have ever lusted after a benchtop mill, here's another justification for you. (Father's Day anyone?) What it does not do easily is true tires glued onto a full axle assembly. I had to build a special rig for that.

              I need to try greatly reducing the speed of the spindle when truing rubber tires, with frequent pauses for cooling. And I'll also try using baby powder as a lubricant. Soapy water, oil? Maybe.

              I have thought about freezing the tires, but I have no good way of keeping them cold. You can buy "freeze sprays" for electronics, which claim to chill circuit boards to -60F/-51C, but they cost about US$2.00 an ounce (28 grams). Pricey whot? Still, might be worth a try.

              I agree with Mike- that the graining on rubber tires can be removed manually. I have also found that simply running them on a car for a few thousand laps of my oval track will clean them up a lot.

              One thing I have tried is actually machining the tires with a sharp carbide cutter. I need to experiment with that more. Maybe chilling the tires and a quick pass with the cutter will work.

              I remember seeing full-scale pit crew members using rasp files to dress the surfaces of tires. Hmmm...

              Ed Bianchi

              Last edited by HO RacePro; 06-16-2019, 03:54 AM.


              • #8
                I use a diamond coated drum, approximately 180 grit, and take VERY light cuts. This allows me to even re-size silicone tires. If I'm just looking to radius the edges of a silicone tire, I use a diamond nail file. These work well for me.


                • #9
                  Have any of you guys tried putting the tires in the freezer to get them near ice-cold, and then trying to true them?


                  • #10
                    How about -60 degrees Fahrenheit (-50 degrees Celsius)? I just bought a can of "Super Cold Spray" to experiment with freezing tires and machining them true. The trick would be to do it fast, so the tire doesn't have time to warm up. I think I know how to do that.

                    And why machine rather than grind against sandpaper? To prevent friction from warming up the tire and making the freezing step pointless. I've got a lathe tool to do the cutting, and a benchtop vertical mill to do the turning. A Styrofoam coffee cup will be my dunk tank.

                    That "Super Cold" stuff is no way cheap -- US$20 for ten ounces (285 grams). It is used for both medical treatments and electronic testing. Won't be the first time I've raided the piggy bank to try something outlandish.

                    I'll report back here. Wish me luck!

                    Ed Bianchi


                    • #11
                      You could always move your operation to Antarctica! If the tires are frozen solid they could shatter if you tried to machine them. In the lab if I wanted to chill something down I could dunk it in liquid nitrogen. If really low temperatures are not needed powdered dry ice in acetone works well. Another alternative would be a small chiller bath filled with ethylene glycol solution, you might get down to -20C or so with one of those.
                      I have a Cobra commutator truing machine with a diamond bit that I also use with HO silicone and rubber tires. The machine only works with the older type of silicone like Tom Hiester uses. You can't machine Super Tires, those need to be sanded. The Cobra also does not work well with soft rubber tires. With very soft rubber the bit will just push, rather than cut.
                      Last edited by RichD; 06-21-2019, 07:20 AM.


                      • #12
                        No guys, LOL ... just cold like freezer for 10-20 minutes cold!


                        • #13
                          LN2 to you too!

                          Liquid nitrogen is an awesome plaything! Okay, yes, dangerous to play with really. But it can be used for cool tricks. (Oh jeez, sorry!) Boils at -321 degrees Fahrenheit (-196 Celsius). While still an undergrad I did a co-op stint at COMSAT -- Communications Satellite Corporation. LN2 was used in their space simulators. They trusted me with the stuff! Silly rabbits...

                          And yes Rich, I realize deep freezing tires may make them brittle. Only one way to find out...

                          Hadn't thought about dry ice. Cools to -109 degrees Fahrenheit (-78 Celsius). And didn't know about using it with acetone. Will dry ice sink or float in acetone? So many tricks to learn, so little time!

                          Ed Bianchi

                          PS - We ARE talking about serious cold here, like instant frostbite! If you try this at home I will deny any knowledge of your actions...


                          • #14
                            As I recall the dry ice sinks to the bottom. In a fit of ambition I looked it up, the specific gravity of dry ice is 1.4, acetone is only 0.79. Dry ice is good for -109F. If you glued your tires with cyanoacrylate acetone would attack that. Any liquid with a low freezing point could be used. Maybe methanol or naphtha would work. Methanol freezes at -143.7F and naptha freezes at -22F, not low enough. At work we had a machine for grinding dry ice, I sometimes just smashed up the dry ice to get small chunks, with the machine you get snow, which is easier to use. If you had the snow you could just bury your tires in that for a few minutes and not have to bother with a liquid.


                            • #15
                              Anyone try a skid pad with a sandpaper surface for truing rubber tires?
                              I recall someone doing that in the past. Surface was something like 400 grit sandpaper. He ran the cars at low voltage in both directions for a number of laps.