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Weighting questions ?

Discussion in 'Building tips' started by todd venoy, Sep 12, 2018.

  1. todd venoy

    todd venoy Pinewood Ninja Pro Racer

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    I know it’s a big secret but any help would be appreciated. I am wondering should you try to balance your rear weight for a faster car or just put as much weight in front of the axle really struggling with this concept.
     
  2. Wolfram Racing

    Wolfram Racing Rail Runner

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    Take my opinion for what it's worth... I can never exactly balance the weight on the rear wheels but I can get it close (~0.25oz different). I think the answer is that it CAN make a faster car, but there is more to it than just weight balance. I doubt anyone would argue that you want to have a COG as far back in the car as stability will allow. So weights in the rear. But that doesn't say anything about the weight distribution from side to side.
    I've found that all the cars that I have good balance on are faster than the one I don't. My conception (or rationalization) of this is from considering the friction that each wheel experiences. If my prep is good and consistent...I would expect to have very similar coefficients of friction between the two rear wheels. So the frictional force experienced will be proportional to the weight. If one wheel is experiencing more friction than the other...what would that do? Well, it would create an unbalanced force around the COG..and that generates a torque that causes the car to turn. For a rail runner, I want to turn into the rail as gently as possible to minimize that friction. Normally I do this by adjusting the steer. If I've got an extra torque from imbalance on the rear weights...I've got extra frictional losses and a slower car.
    Just my two cents. Someone with more experience can chime in their perspective.
    In addition, I've also found that my balanced cars take much less damage from hopping off the stop section. Think about what happens there if your COG is shifted too far to one side.
     
  3. B_Regal Racing

    B_Regal Racing PWD Royalty Pro Racer

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    Wow! That is a ton of research. I do not understand that theories in place, but I do know that you absolutely can get the weight on the rear wheels to be balanced and I do believe that is a faster setup. Chances are, if you get the weight balanced in the rear, the car will be plenty aggressive.
     
  4. Wolfram Racing

    Wolfram Racing Rail Runner

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    Boy, I'd love to find out how. Short of extending weights off the side of the car, I'm always a bit more heavy on the non-dominant rear than the dominant rear. Of course, I am working under the assumption that I'm not inserting weight into fenders or...god I don't want to say it in this forum...using a wheel weight. I hope I didn't just start another poop storm.
     
  5. bracketracer

    bracketracer PWD Royalty Pro Racer

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    gphall, I don't know what kind of weights you are using, but with just 1/4" tungsten cubes it should be pretty easy to get equal or nearly (within 2g on each rear wheel) equal readings. Easier still if you apply a tungsten plate under the car and offset it. The cubes in front of the rear axle may end up three rows deep and staggered offset towards the DFW side depending on how heavy the bare body turns out.

    Couple things to consider-

    If you draw a line from the DFW to the opposite rear wheel, everything in that triangle that contains your raised wheel is cantilevered weight. It takes load off the diagonally opposite rear wheel. So you'd like to see that area as light as possible within reason for the track you have to race on. In other words, don't try to go crazy light on a rough scout track or you may end up with a "two piecer"!

    If your car has a slight alignment issue in the rear axles you may find, through track testing, that biasing the weight toward the better aligned wheel will add speed over having the weight split equally. So if you have access to a track, try equal vs offset left vs offset right and go with what works on that particular car.
     
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  6. Wolfram Racing

    Wolfram Racing Rail Runner

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    Thanks bracket racer! There is one feature of every car I built that might explain that now. I was always focused on the part of the balance where the weights go and was TOTALLY ignoring the cantilever effect you are talking about. Ugh. I think I know what's going on now...it's a feature I've built into every car for the last 10 builds. Damn. I was so focused on what made the weight increase, I wasn't thinking about what made it decrease. THANK YOU!!!!
     
  7. todd venoy

    todd venoy Pinewood Ninja Pro Racer

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    Thank you all for all the information it clears a lot of the smoke in my head.
     
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  8. txchemist

    txchemist National Contender

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    The feedback I get from some very fast racers is the same as Bracketracer mentions.
    Many start with the following set up, and then adjust with track testing for best speed.
    You get a great head start by offsetting the back weight to the DFW side.
    upload_2018-9-13_7-49-18.png
     
  9. Wolfram Racing

    Wolfram Racing Rail Runner

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    Thanks for the picture TX. I think my problem is how I cover the car.
     
  10. txchemist

    txchemist National Contender

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    Finished car, Packing tape on both sides and a BMW skin does not add much weight at all.[​IMG]
     
    Last edited: Sep 14, 2018
    Jimmy & his 2 Kids likes this.

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