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JK21 chassis help

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#1 cck42


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Posted 03 December 2020 - 12:33 PM

I have a JK21 chassis, Pro Slot 2002 motor, 12 tooth pinion, McLaren body. 


It is super loose in the corners. The back slides out bad if you go into the corner fast or if you get on it too fast coming out of the corner. My other one works fine. I've flattened the chassis, reset the motor, etc. Still doesn't work. Any ideas or possibly tire suggestion? We need to start the race with .050" clearance. There are four different types on the Alpha site: supernatural, Wonder, Piranha. 


We run on a 145' hillclimb. Looking for suggestions.



Chris Kapell

#2 MG Brown

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Posted 03 December 2020 - 01:14 PM

Sure sounds like the wrong tires for conditions to me. Have you tried swapping the tires and rear axle on both chassis to see if the "problem" is there?

If the C21 with the handling problems is older, it might be time for new bushings.


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#3 mreibman


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Posted 03 December 2020 - 01:16 PM

if you have a duplicate car that works then I would suggest the difference is in the tires.


Step 1: measure the tires on the good car.
Step 2: measure the tires on the loose car

Step 3: compare results, document.

Step 4: take the tires from the good car and put them on the loose car. Try the car. If the car works, then tires are the answer. if the car is still loose then it's not the tires.


If it is the tires, then try to get the same hub size, diameter, and width on your new set of tires. Of the tires you mentioned, the Piranha should be the grippiest, and the Wonder should be the loosest. But hub size will also influence handling.


A larger hub will go faster on the straights with the sacrifice of grip in the corners.


Let this be your starting point, and beyond that, observe and ask the locals what works for them... all tracks and raceways are different, and the local guys usually have a good handle on what works.


Good luck!

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#4 Dave Buchholz

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Posted 03 December 2020 - 03:08 PM



Tire diameter is a possible source of problem as well. Many of the tires over the counter are around .750". On that same track, I have reset the bushing position lower to use .720" that will pass tech. Using a .730" tire will get in some practice laps before the tire is useless for Tuesday night at .710". Smaller hubs seem to help, more sidewall to flex perhaps, not as stiff as the big hub. A wider tire gives more contact  for less slide in the corners, but at the expense of straightaway speed.
Check out this article:
Slot Car Handling & Tire Selection
 See you Tuesday,

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#5 Pablo



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Posted 03 December 2020 - 05:35 PM

Try an 11T pinion with stickier tires, naturals with smaller hubs maybe.

Paul Wolcott

#6 Dan Searcy

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Posted 03 December 2020 - 09:55 PM

You didn't say what tires are on the car and how old they are.  Old tires won't work well.  Alpha Piranhas are pretty sticky.  Smaller hubs offer more grip than larger hubs.  Like Mike said above, swap out the tires and see if the handling improves.  You might want to play with the bite bar diameter as well, but I'll bet the problem is the tires.

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