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Old 2011.10.11, 10:05 AM   #1
briankstan
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Mini-Z Tire Truing / Grooving / Cutting

I've done a lot of searching but came up with very little information regarding this subject, other than what people are running, but not really specifics as to why or what they do.

I know quite a few people have been running trued tires, and also cut and grooves in the tires. Iíd appreciate some information on what specific things do.

Truing: the obvious thing is to correct the true of the tire so itís a consistent diameter. So what does truing them down to a specific diameter do? Bigger, smaller, etc. Also whatís the difference in running different diameter of wheels, is it just to keep the tire wall taller while maintaining a smaller overall diameter?

Grooving: changing the pattern of the tires from slicks to grooved. This is more obvious as it can affect the traction of the tire for the specific surface. Any other benefits?

Is gluing the tires to the rim a must? Would it defeat the purpose if you didnít?

Thanks for the help, Iím sure others will benefit from this as well.
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Old 2011.10.11, 12:01 PM   #2
geeunit1014
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Quote:
Originally Posted by briankstan View Post
I've done a lot of searching but came up with very little information regarding this subject, other than what people are running, but not really specifics as to why or what they do.

I know quite a few people have been running trued tires, and also cut and grooves in the tires. Iíd appreciate some information on what specific things do.

Truing: the obvious thing is to correct the true of the tire so itís a consistent diameter. So what does truing them down to a specific diameter do? Bigger, smaller, etc. Also whatís the difference in running different diameter of wheels, is it just to keep the tire wall taller while maintaining a smaller overall diameter?

Grooving: changing the pattern of the tires from slicks to grooved. This is more obvious as it can affect the traction of the tire for the specific surface. Any other benefits?

Is gluing the tires to the rim a must? Would it defeat the purpose if you didnít?

Thanks for the help, Iím sure others will benefit from this as well.
This is my take

Truing- Smaller diameter = less front grip essentially (if everything else stays constant). Typically you see bigger front tires in less grip/slower classes, and smaller tires in more grip/faster classes. Smaller diameter wheels will make the car react faster (for the same amount of tire sidewall). The wheel size also changes how much the rubber is stretched which will change how it reacts (although im not too sure how...). Normally its a preference of 19/20mm in stock, but mostly 20mm in mod

Gluing the tire to the wheel- Essentially, the more the tire is secured to the wheel, the more energy you put into the tire and the more grip you will have. You can tune this with tape/glue ( glue>246 tape>pn tape in stickiness). I typically will use 246 tape, and if feel the car is pushing a lot in high speed corners and I see a funky wear pattern on the sidewall, I know the sidewall is rolling over and ill glue the outer edge down.

You can also glue the sidewall of the tire if you really want to take away some front bite, but this is typically a last ditch band-aid effort to eliminate traction roll, and can make the car push quite a lot (especially when the center of the tire wears down below the glued sidewall since the glued sidewall doesnt wear essentially).

My educated guess on grooving is that if all you do is add a groove around the circumference, you will take away grip. If your getting more tricky than that and changing the tread pattern, your playing with some black magic there haha.

Something else you can play with is how much you round the sidewall after you true it. The more you round the front sidewalls, the more steering you get (helps maintain tire contact as the car rolls vs a square edge)
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Old 2011.10.11, 03:54 PM   #3
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I swear I've written a blog post on this before lol. Anyways, I agree with most everything Mike Gee has said except for the grooving process.

Grooving basically reduces the contact patch of the rubber as well as increasing the amount of flex in the rubber touching the ground. This creates more heat in the tire, which will lead to improved grip on low-grip surfaces, and severe overheating on high-grip surfaces. I usually groove tires of harder compounds, such as PN 8 slicks and Kyosho 20 slicks, while leaving softer compounds -- PN 6, Kyosho 20 radial, etc. -- alone.

Truing tires, while reducing flex in the tire, also reduces the amount of rubber that's actually in there. At a certain thinness of the tire, you stop losing traction because the tires are actually heating up more than before you cut them down, so the rubber gets warmer and you actually get MORE traction with LESS sidewall flex. This doesn't apply to silicone tires, which are not nearly as temperature sensitive and rely mostly on flex to generate grip. But for rubber tires, there's a reason why we're all cutting down the fronts, and that is the triple benefit of increased steering response AND absolute grip AND less traction rolling.

I'm a cheapskate, I normally don't cut my tires below 23mm because I want them to last longer; but for important races I've seen anything from 21-22.5mm, the smaller tire on a normal 20mm rim makes the cars very quick and responsive.
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Old 2011.10.11, 04:28 PM   #4
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Thanks for the info guys, Brian, if you find that write up point it my way.

I purchased a Hudy tire truer and will be playing around with it, I just wanted a little more info before I start so any other input is appreciated.
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Old 2012.06.23, 07:04 PM   #5
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This is a perfect place to revive a topic and bring up some questions:

I have a friend's Hudy truer with the sanding drum for material removal and I'm having a go at trueing and grooving. My first attempts have created a surface on the tire that can best be described as graining...I'm not getting a smooth cut surface at all.

The only thing i can wonder is if the sanding drum needs a certain rpm supplied via the power supply to cut clean without building material in its cutting surface.

Is it the nature of the sanding drum to give me a "grained surface"? Is there a tire truer at this scale that has a diamond bit cutting tool?

Grooving seems to be going OK except for the fact that holding the PN grooving tool is a bit of a PITA...I might build a grooving arm but I'd like to find out more about the surface graining before I invest time into this thing.
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Old 2012.06.23, 09:26 PM   #6
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i run my truer with a 7.4 lipo. running it at 12v heats up the tire to much and will cause the tire to get chatter marks on the trued surface. you should see a little graining but a few laps on the track and they are fine. i did find a diamond sanding disk on a slot car site a while back. a google search may yield it for you.
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Old 2012.06.24, 02:07 PM   #7
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Another aspect of truing your (rear) tires that is not mentioned that often is the effect on the "gear" ratio and its implications for torque and speed. Essentially, running a 22 mm sized rear tire means that for every full turn of the axis the car will move 69,1 mm forward (assuming no slip). For a 23 sized rear tire this distance would be 72,3 mm (still, no slip), which is roughly 5% more. This means that a car with larger (rear) tires could be faster than one with smaller tires. Just like when changing gears though, this additional speed comes at the expense of reduced acceleration.
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Old 2012.06.24, 06:29 PM   #8
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i run my truer with a 7.4 lipo. running it at 12v heats up the tire to much and will cause the tire to get chatter marks on the trued surface. you should see a little graining but a few laps on the track and they are fine. i did find a diamond sanding disk on a slot car site a while back. a google search may yield it for you.
I'm with Chad on this one -- 7.4V is the way to go for Mini-Z tires. When you first cut into the rubber, go very slow, and keep the RPM's of the truer from dropping too much. That will heat up the rubber minimally. Then just slowly work the tire down to the diameter you want, all the while keeping the RPM's up and light cuts only. Once you're down, you can take off the graining by edging the tire towards and away from the drum -- extremely light, short-duration cuts. After that you can finish off the outside edges to prevent traction rolling the first couple laps.
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Old 2012.06.24, 07:31 PM   #9
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another thing i did not mention that i do sometimes is use a large nail file to smooth the tire after truing. also to round the tires if needed
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Old 2012.06.26, 08:59 AM   #10
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Thanks for the info, guys.

I was able to try 7.4 volt and was able to refresh some rears to good effect.

I'll try the extra methods to improve my trueing efforts.
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