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Weight Distribution

Discussion in 'Building tips' started by mitso, Mar 14, 2017.

  1. mitso

    mitso Bent Axle

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    First off, thanks to all of the great support contributed by the members and the top pros! This forum and members are top notch.

    Using the tips and techniques along with the DD4H supplies my son made it to the district race. We have to remove a little weight from the car for the district race and need some advice.

    The car is uses the standard (slotted) wheel base and is a 3 wheeler with a left DFW that has about a 5 * bend in the axle and drilled 3* cants in the rear.
    For our den race the car had approx. 4-5" of steer over 4ft.

    As for the weight there are 10 cubes behind and in front of the rear axle with an additional 0.42 oz of putty above the front cubes with a bias to the DFW.
    The following are the weight measurements (in ounces):

    Left DFW 0.710
    Left RW (DRW) 1.750
    Right RW (NDRW) 2.500

    The COM is approx 5/8 in.

    Unfortunately, we do not have access to a track to test on. Both our den and district races use an aluminum tracks.

    Are there any suggestions or recommendation on the above weight distributions?

    Since there is some putty to adjust, should we try to bias the weight in the rear?

    Prior to removing some weight the distribution was 0.83, 1.72, and 2.54 respectively.
     
    Last edited: Mar 15, 2017
  2. B_Regal Racing

    B_Regal Racing PWD Royalty Pro Racer

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    That is a loaded question and for some, a closely guarded secret. I would say that in a league context, the FDW has too much weight, but this assumes perfect tuning. I also try to balance the rear weighting between the wheels to whatever extent possible (there are varying opinions on this), without overly weighting the FDW. For a scout car, I would still run a bit lighter on the FDW, being more in the neighborhood of 16 to 18 grams, but again, I'm assuming that car tuning and track are properly addressed. I'm also going to probably be in the minority here, but for new builders, builders who make 1 car a year, those without the availability to test the car and for those who do not have direct access to a seasoned veteran, I would recommend 5 to 6 inches of steer to be safe. This accounts for the wiggles of surrounding scout cars as well as to account for weighting, gap, wheel prep, and possible alignment issues on a scout car. It is better speed-wise to have a bit more friction from rubbing on the rail (especially with the inside edge of the FDW being properly prepped) than it is to have the car wiggle down the track.

    Just my opinion...
     
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  3. King Racing

    King Racing Rail Runner Pro Racer

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    I would slide about .200 to the left and take a little off the front if possible.
     
  4. Crash Enburn

    Crash Enburn PWD Royalty

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    It's probably too late for you now, but I would just leave it alone and make sure the wheels and axles were lubed.
     
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  5. mitso

    mitso Bent Axle

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    Thanks B_Regal, I appreciate your comments (opinion). I can see from the lack of detailed posts on the topic of rear wight bias that it is part of a racers secret sauce
    .
    I know each car is different but I was thinking there must be some conservative starting point for weighting. Obviously with experience, the good builders will have a better idea of where the optimal settings will end up and plan accordingly, so I appreciate your guidance.

    My initial concern was the rear wiggles, so we biased more on the DFW and ran a gap of about 0.15 in the rears. Now that we have to make a weight change and know how the car ran, we can make some adjustments that are slightly more aggressive, and with guidance, optimal for our conditions.

    I'll work on making the weight adjustments to bring them more in align with your recommendations.
    With it lighter on the DFW, what wheel gap do you suggest?


    You mentioned the prep or in our case it will be a re-prep.
    We plan on pulling the axles and wheels and re-preping them by wiping down the axles, pledgeing them, blowing out the wheels and burnishing with graphite again. Do you think that is overkill or not worth the risk (compared to just re-graphiting and re-gapping)?

    As for re-tuning, we will recheck the steer and probably get it close to the 5" setting. Also, check that the rear wheels are migrating correctly. Any other suggestions?

    Thanks again, much appreciated.
     
  6. mitso

    mitso Bent Axle

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    Thanks King Racing.
    Based on the replies, it sounds like that is what I need to focus on.
    I will make the front lighter and have try to have a more balanced setup in the rear.
     
  7. mitso

    mitso Bent Axle

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    Thanks Crash Enburn. Since I have to reduce weight anyway, I wanted to get experienced opinions. That said, I understand what you mean. I should have reached out before adding the weights and having the car configured.

    From experience, I know changing too many variables can really work against the goal.

    Would you suggest pulling the wheels and prepping as in burnishing the wheels and axles? Or just get leave the car together and re-graphite, gap, and tune?
     
  8. B_Regal Racing

    B_Regal Racing PWD Royalty Pro Racer

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    For wheel gap, I do it by feel. I really have no idea what gap I'm running other than it's as small as possible. When tuning a car, I may try slight differences in wheels gaps for the best results, but it usually is very small. I use K-House grooves to make minor adjustments. I would not know if graphite cars need a larger wheel gap or if it is essentially the same as an oil setup. Same goes for burnishing. I REALLY dislike working with graphite, so I could not say if re-burnishing graphite is necessary. Personally, I would re-pledge, re-graphite (without burnishing a second time), and call it a day.

    I'm looking to hear from King and Crash on graphite. Both are very good racers and Crash has been here as long as I can remember.
     
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  9. Crash Enburn

    Crash Enburn PWD Royalty

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    Depending on how the car has been handled since last race, I'd just add more graphite and spin and call it a day. But, since it seems you've already taken it apart, I'd say repack* with graphite and treat it as though this is the initial install on the wheels.
    *That is, hold the wheel with one finger covering the inside hub. Partially fill the bore with graphite. Take your axle, and stick it into the wheel until it stops. In one quick motion, move your finger, push the axle through, and turn it all over so now the nail head is covering the bore opening. Spin. Add a bit of graphite. Spin. Put the axle into the car. Repeat for the other wheels.

    I am confused by your weighting... Did you have 5 cubes behind and 5 cubes in front of the rear axle? Or was it 10 and 10 like I originally read it? And if there is indeed 2-3/4 oz. of putty on top, I can see where that is a very heavy car and needing a diet regimen. :) If it's 5 and 5, you should be able to make more room under the car for moving the putty/adding weights.


    Dang, B_Regal, you're right. I am getting rather long in the tooth. You'd think I'd do better... :D
     
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  10. mitso

    mitso Bent Axle

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    Thanks B_regal. The graphite is definitely messy!
    I also use a K-House groove on the front to make the adjustments. Its amazing how a slight turn of the axle makes a large change in steer. I assume that is typical but wonder how a slight bump or a not so soft track stop can cause a change between runs.


    Crash, thanks for the tip on the graphite process and a BIG thanks on the comment on the number for the putty! I edited the original post with the correct value - it would have been a heavy car!

    As for the weight, there are 10 cubes behind and 10 in front of the wheel and 0.42 oz of putty. I was able to remove one of the cubes over the RRW to see if that would help in the weight shift more towards a balanced amount over the rears. I am thinking of adding that and another cube in place of some of the putty over the LRW. Do you have any recommendations in that shift?

    As for the car sitting, it has been a little over a month. I would have like to get to it sooner but wok and life tend to get in the way:). That is why I thought re-pledging would be in order.

    As for the gaping, I can understand that with experience, B_Regal and others can do it by a 'feel' for the car - I am not there yet.. Do you use a starting or max gap setting? As for setting the gap on the DFW, since there is a cant, should the gap be set/measured so that closest part of the hub to car reflects the gap setting?
    The reason I asked is when I recheck the gap, it was closer to .10 at the contact point (maybe the wheel got squeezed during handling).
     
  11. King Racing

    King Racing Rail Runner Pro Racer

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    Check your gaps at the contact point. I don't have a lot of experience with graphite but recommend .015-.020 on the rear and .015 on the front depending on your axle/wheel bore clearance (slop). if the back of the car sways side to side tighten the rear gaps up.
     
  12. mitso

    mitso Bent Axle

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    Thanks King Racer. I will keep it as tight as practical in the rear. I don't think we'll be able to get any practice runs in on the track so its the tuning board and table for us at this point.

    I notices some oxidation in the front axle (revell nail), any thoughts on how that can be addressed without creating a new one?
     
  13. davet

    davet League Racer

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    These are our numbers from 3 fast cars in the NorthernStar Council WITH OIL and extended wheelbase. Are you limited to stock axle slots? Maybe these numbers only apply if you can run extended WB. Gives you an idea of how light you can go on the DFW and be stable.
    The 2016 car listed is our avatar pic.

    These cars all had either 1 or 2 full cubes between the rear axles to help get weight to the rear. You can always drill a single 1/4" hole between the rear axles and epoxy (for strength) a cube in there since the rest of the weights are in. We added all of our adjustable weight (putty) across the very back on the underside of the back row of cubes. Spread a thin coat of CA or put tape over the putty so the stop section doesn't pull at it.

    These numbers were fast for the scout races we were in, no league races, so take advice from the pros before us. These cars were all very stable with no wobble. I would've been comfortable going with more weight to the rear but we weren't good enough at cutting the block to have room for that. Good luck.
    [​IMG]
     
    Last edited: Mar 17, 2017
    Dizzy and mitso like this.
  14. mitso

    mitso Bent Axle

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    Thanks All for the guidance with the weight and re-prep!

    We finished 3rd at the district race this past weekend and were very excited with the finish.

    We were able to shift some of the weight in the rear but only slightly lighten up the front. The final weight distribution was:
    (all in ounces)
    Left DFW 0.690
    Left RW (DRW) 1.930
    Right RW (NDRW) 2.380

    The COM computed using the http://jsfiddle.net/minionsracing/UUnT5/embedded/result/ tool was 0.6124, which was spot on with actual measured.

    We also had to use another wheel due to the wheel bore being scraped and some plastic lifted. Not sure how that happened.


    Davet, thanks for the details on your car builds! I really like the last car you and your son had in the race with the lights (your avatar).

    To answer your question, we had to use the standard axle slots, so the wheel base was shorter than what you have posted. All of our parts were stock; although we did you the SB Pro to drill the axle slots. We epoxied the slots with a 5-minute epoxy and drilled the axle holes into the hardened slots.

    Reviewing your numbers I can see how you are able to move more wight towards the rear with the extended wheel base. With the standard wheel base, I was concerned that the rear end would suffer from the wiggles if we moved too much weight to the rear.
    From a video of the race I could see a slight rear end wiggle from time to time in the race.

    Thanks again everyone for your support and guidance!
     
  15. King Racing

    King Racing Rail Runner Pro Racer

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    Congrats Mitso! you did all the work... We just answered a few questions.
     
  16. davet

    davet League Racer

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    Awesome job! Congratulations.
     
  17. mitso

    mitso Bent Axle

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    Thank you! I really appreciate the support and guidance.
     
  18. derbydentist

    derbydentist Council Champion Pro Racer

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    So I'm constantly amazed at all the new things I read on here - just when I think I am getting a grasp on things - what in the world are you talking about with the different weight measurements for the different wheels? How are you measuring how much weight you have over any given area? I saw the link to the calculator there but how are you getting the numbers that you are plugging into the calculator? Sorry this is something I've never come across on here somehow
     
  19. jatofau1

    jatofau1 Council Champion

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    I measure the weight on each the rear wheels and the DFW. And I measure COM using the cantilever method. My COMs come out around .5 or .6 inches.
     
  20. derbydentist

    derbydentist Council Champion Pro Racer

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    I'm really sorry I'm not picking up what your putting down. How do you measure the weight on individual wheels? I understand the com determination just not the weight distribution - how exactly is this determined
     

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