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  1. #1
    RC poster
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    Jul 2012
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    Tire adhesion and differential locking

    In the “Differential Locking” forum, I posted, that, with a 2S battery, any power setting over 52% causes the car to swerve to the left, including tipping the car over. And any braking percentage over 70% causes the car to swerve to the right, also tipping the car over.

    Thus it looks like the right drive tire has all the traction, both in acceleration and in braking, and thus tips the car over in opposite directions.

    I want to thank “billy Weeks” and “LightFighter” for their forum comments.

    I “locked” the differential with Silly Putty using the method described in this video. http://www.youtube.com/watch?v=zkO-0...eature=related

    With Silly Putty in the differential, there was no change in the cars swerving behavior. Everything was exactly the same as before.

    So I exchanged the right and left rear tires with each other, and now, with 52% power, the car swerves to the RIGHT rather than to the LEFT and it is definitely more stable during the run. (I did not test how much more power I could use before tipping the car.)

    Therefore, there is a significant difference between the two tires. One tire obviously has more adhesion than the other. I do not do burnouts and have not treated the tires with anything.

    I assume that an un-locked, or semi-locked differential, will magnify any adhesion differences between the tires, so I am going to totally lock it with JB Weld.

    I would appreciate any comments on the adhesive difference between tires. How do we detect such differences, and how do we deal with these differences.

    Thank you.

    Bob

  2. #2
    RC Qualifier
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    Apr 2012
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    Norf Cackalacky
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    Your problem could be from a different amount of rollout in each tire as well. Also, my car seemed to have a different wheelbase on each side of the car for some reason. Rear end was cocked a little.

  3. #3
    RC Racer
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    Jan 2011
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    in texas currently
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    first off i dont have a funny car but i was thinking about your rear end being cocked a little bit and was wondering could it be cocked to compensate for torque steering and try to help prevent spinouts and such? but to OP i have no official idea but even though the tires are putting out different amounts of traction would it be possible to add some sort of compound to the other tire to increase stickiness or to rough it up a little bit with say fine sandpaper? or what about the whole bleach thing for making tires sticky on 1:1 vehicles would it work the same in this scenario. i know these are all "what ifs" but they might be worth exploring. but thats my .02 so hopefully something works and or helps at least and if they do spread the word to others so they can improve their drag racing fun

    -Cody

  4. #4
    RC Enthusiast
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    Sep 2011
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    Fort Dix NJ
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    check your contact patch on both tires........ seems like one is more flat than the other...... you might have to buy a bunch of them to match them up!!!! or get some Foamies and you can true them

  5. #5
    RC Qualifier
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    Jan 2012
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    My friend told me that some one already makes a spool for the funny car

  6. #6
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    Sep 2011
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    Fort Dix NJ
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    Quote Originally Posted by slayer17 View Post
    My friend told me that some one already makes a spool for the funny car
    Thats awesome I knew parts would becoming soon.. A lightweight chassis would be awesome

  7. #7
    RC Enthusiast
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    Jul 2012
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    Idaho
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    Is there anymore info on who is making the locked diff.? Inquiring minds definately want to know!!!!!

  8. #8
    RC Enthusiast
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    Sep 2011
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    Fort Dix NJ
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    Quote Originally Posted by drive4fun View Post

    I would appreciate any comments on the adhesive difference between tires. How do we detect such differences, and how do we deal with these differences.

    Thank you.

    Bob
    One thing you could do is get some KOFORD slot Car Traction glue..... that stuff works and it works good better on FOAM tires but it works

  9. #9
    RC poster
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    Jul 2012
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    6

    FOLLOWUP -Tire adhesion-differential locking -

    This is a follow-up to my post (#1 on this forum thread).

    In that post I indicated that on heavy acceleration the car would veer in the direction opposite that of one specific tire, independent if the tire was on the left or right of the car. And on heavy braking the car would veer in the same direction that that specific tire was on. When veering occurred, it was always tire related as stated, and never once did it ever veer in the other direction.

    My conclusion is that one tire has more adhesion than the other and the differential was magnifying this difference.

    JB Weld in the differential made a significant change. I now get exactly 50% veering to the right and 50% to the left, independent of what side of the car the tires are on.

    Therefore, the locked differential is now mitigating the adhesive difference between the tires.

    Based on the 15 successful runs before and the 15 successful runs after the JB-Weld, the median ET decreased by 15% and the median speed increased by 16%. However, this is not a definitive improvement, because there are many variables involved. For example, one pre-JB-Weld run had a lower ET than any of the JB-Weld runs.

    However, the two 15% improvements would seem to be convincing evidence that an improvement has really occurred.

    The power generated veering is no longer a function of tire adhesion, there is a performance improvement, and even with the locked differential, it is easy to turn the car around at the end of the run.

    Bottom line, I am very happy with the locked differential.

    Bob

  10. #10
    RC Racer
    Join Date
    Nov 2012
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    123
    I run the factory setup and on 3s I am able to keep the car perfectly straight with no "torque steer".....unlocked. The car runs 2.4s@66mph(132ft) at 60% launch power....hoping to see a 2.2@70mph soon!

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