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Color0's Micro RC Blog -- A technical brain dump from the mind of yours truly...
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Happy July 4th! Now Back to MOD. :)

Posted 07-05-2011 at 02:21 AM by color0
Happy July 4th everyone! I myself just got back from a fireworks showing on the Charles river (between Cambridge and Boston), looked great.

Now continuing on where I left off last week, my changeover from RCP to Carpet Mod racing.

First of all, I was gently reminded that the carpet at Kyosho and Cruzin is LOOOOW grip, no matter what tires you use -- the surface itself simply feels too powdery to let any kind of tire stick too much. I suspect there is a lot of internal slip between the carpet fibers, so even if your tire can grip the surface layer, it still has to go through the rest of the thickness of the carpet before the track exerts any moving force back to the tire. It's also soft, which lends an advantage to heavier cars that sink better into the carpet (giving you mechanical leverage as well as chemical adhesion). RCP is like this too, but to a MUCH lesser degree, so it feels more like a road surface (though still not true tarmac at all).

Thus I quickly learned two lessons:

1) Low CG is not the king on carpet! On RCP with Mod power, there's enough load on the tires to warm up the tires to the point of overheating, so avoiding traction roll is priority #1, finding steering response is priority #2, and preserving the tires is #3. A low CG promotes all of these things quite well under the given conditions. My light, low and flat setups are therefore good on RCP, I just need to find the right tires for the day and then drive the wheels off the car. Carpet is different. Because there is so little grip, I've found that the tires don't warm up enough, no matter how soft and squirmy the tire is. So what can you do? You can try "forcing" the tire into the track, raising its load and thereby warming it up, to try and obtain better grip. Without changing anything else, the easy way to go about it would be to raise the entire car. This would increase the magnitude of weight shifting as you pitch the car in a corner, loading the outside tire more, warming it up more -- exactly what we want. Warmer tire = more grip = faster car.

2) Low weight is also no longer king! Because RCP usually has ample grip, we often try to reduce the load on the tires by reducing the weight of the car, keeping the tires from getting overloaded and fading. Once again, this logic is broken by racing on carpet, when you find that your tires are not being loaded enough! As I suspected and EMU tested, heavier cars will sink better into the carpet, load the tires more, and generally produce more grip, for the same tire combination, than their lighter opponents.

Now you could then reach into your book of tire physics and tell me "but Brian, doesn't that mean you could get the same effect by running narrower tires?" This would, as you might imagine, reduce the contact patch of the tire against the carpet, increasing the pressure on the rubber and warming it up more. I.e. exactly the thing Grant recommended that I try at RCX. And you know what? Theoretically I think you'd be right. More grip should be able to be generated without purposely adding weight to the car. That said, I personally feel that carpet tires right now are too soft and squirmy already, leading to a very mushy steering response which I honestly don't enjoy. Although the carpet surface is more consistent than RCP, the way the tires squirm actually negates that gain and my car feels no more precise than it was on RCP with stiff-carcass PN RCP tires.

So if not narrower tires, why not make even softer compounds? Again, my comment about tire squirm. Right now Atomic has recently released an uber-soft 7-degree compound silicone carpet tire, and meanwhile PN has had 6- and 8-degree silicone carpet tires for a while. I've ordered some of each to test, but my suspicion is that they're all just going to feel way to squirmy to have positive steering feel. In which case, however, I'm not entirely out of options. Gluing the sidewalls of the tires, as Grant M. taught us in the past, would stiffen up the sidewall enough to provide more positive steering response, but without affecting the compound of the contact patch actually touching the track, so it should be the best of both worlds as I continue to refine my carpet Mod setup.

If the tire dilemna weren't enough, carpet offers an interesting opportunity to tune the traction balance via scraping off the surface gunk that accumulates on the tires after a while. At Kyosho less gunk accumulates because there's less silicone run into the track (mostly, just whatever percentage is inside Kyosho 30 and 20 "Racing" Radials). But at Cruzin with RC's, WOW the stuff builds up within two runs and lowers grip considerably. So as you might imagine, scraping the gunk off will temporarily increase traction at the tire. I figure this could be used in multiple ways:

1) Scrape both rear tires right before the main of a race. This will give better traction at the start buzzer, and calm down the car a little bit while you settle into your rhythm.

2) Correct tweak (what a hack! ). I'm always running a side-shock setup of some sort now, but for those of you on disk dampers and on carpet, if you feel the tweak, try scraping tires to balance it out! It won't be permanent, it's crude and you'll laugh at yourself as you do it, but hey, if you need a quick fix after you got hit and can't find the source of the tweak, why not give it a go.

One quick note about driving differences: Mod on carpet feels waay more relaxed than Mod on RCP. This is clearly due to the low grip slowing things down. I'm no slouch on the driver's stand, but I'm no god either: Mod racing on high-grip RCP like Kenon just feels frantic to me, there's no time to actually adjust and refine your cornering line, and it's all point and shoot, and you better have your car setup perfected to a "T" or it's just not going to go where you need it to go on faith. Meanwhile, on carpet, it's slower, you have more time to make corrections, blip the throttle, adjust your line, pick where to go, and it's a mental driver's game much, much more than on RCP where it's extremely technical. At least that's how I see it at the moment. Once I go back to RCP after this summer, and run Mod again, surely I'll be less overwhelmed and begin to see the finer points of driving such ballistically fast and agile cars on a high-grip surface.
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