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  1. #1
    RC Enthusiast
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    4s mid motor speed rustler rear downforce?

    Hey all, I have a mid motor rustler that I recently just converted to 4s to get into the speed run scene. I was doing some test runs on 3s and the extra weight from the 4s system gives the front of the car way to much grip compared to the rear when turning, and even though itís supposed to go in a straight line, it is still way to squirrelly for me. Just a small over correction can make the car go sideways. I donít want to add more weight to the rear because it hardly wheelies now and hooks really well during launches/pulls, but when off-throttle or braking at speed it is really sketchy. I was wondering if anyone had some suggestions for some downforce for the rear of the car? Would mounting something to the shell be strong enough for ~90mph or would I need to mount to the shock tower or chassis? I have a spare bandit wing and was wondering about putting it on an old shell. Anyone know if the bandit wing provides any actual downforce or is it too steep?

  2. #2
    RC Champion Acidic01's Avatar
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    Does your rx have tsm? That may help?

    Sent from my Pixel 3 XL using Tapatalk

  3. #3
    RC Racer
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    Hows your toe and camber angles? Could also try to turn down your steering sensitivity if possible.

    Sent from my SM-G970U using Tapatalk

  4. #4
    RC Turnbuckle Jr. Squeegie's Avatar
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    Can you set your steering expos? You can also add an adjustable wing in the rear and angle it for some downforce. Test & tune... repeat if necessary.
    Creativity is intelligence having fun. -Einstein

  5. #5
    RC Competitor
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    Jan 2018
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    sounds like the rear is unloading off-power. you can try stiffening the front or softening the rear to help. Either of those will help keep weight on the rear. if you don't have any springs to tune with you can use the shock mounting holes on the arms to make minor adjustments. Moving the lower shock mounting point further in on the arm is like going to a softer spring, further out on the arm is like going to a stiffer spring.

    with all that said, you're fighting the basic physics of how 2wd cars react to deceleration. You'll always have a certain amount of load transferring from the rear tires to the front tires when you let off the gas or start breaking so you'll always have this problem to a certain degree.

  6. #6
    RC Qualifier
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    Can you post some photos of the car so we can see the existing set up and narrow down what can be done?

  7. #7
    RC Enthusiast
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    Quote Originally Posted by TwoBelugas View Post
    Can you post some photos of the car so we can see the existing set up and narrow down what can be done?
    https://imgur.com/gallery/mW0MSqu
    Never got imgur set up until now, so hopefully this works. Iím not at home right now so this is the best I have for pics. The RPM bumper is to act as a simple wheelie bar (donít mind the mismatched screws lol). The suspension is stock rear shocks with the rods from a set of front suspension, two of the retainers usually used at the bottom (one on top and one on bottom of spring now so there is less travel so the car wonít bottom out) and 1/2 of a rear spring.
    Edit: I meant to add that there is no front suspension, just camber links in its place, so I canít make that any stiffer

  8. #8
    RC Qualifier
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    So a couple of thinking out aloud ideas

    1 definitely add a wing or at least piece of thicker lexan bolted to the rear deck to create down force
    2 related to (1), foams do poorly without downforce so that would account for a lot of the wiggle
    3 related to (2), I donít often run foam and usually run grpís, for 4s especially you are probably not going fast enough to warrant foams
    4 I donít like rpm for on road, they bend and twist too much for my taste, ymmv. I run stock arms for my on road builds
    5 not sure what you are running for the diff, but I use the hot racing sealed diff with fairly heavy fluids for more straight line stuff
    6 double check your steering bellcrank, servo, servo horn and turnbuckles to make sure everything is tight.
    7 if you do add a rear wing or spoiler, make sure you add front aero aids too, else you may risk the opposite of catching air.

    Good luck!

  9. #9
    RC Enthusiast
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    Quote Originally Posted by TwoBelugas View Post
    4 I don’t like rpm for on road, they bend and twist too much for my taste, ymmv. I run stock arms for my on road builds
    5 not sure what you are running for the diff, but I use the hot racing sealed diff with fairly heavy fluids for more straight line stuff
    7 if you do add a rear wing or spoiler, make sure you add front aero aids too, else you may risk the opposite of catching air.
    RPM will be switched out, I’m just keeping it on there for now because I’m still getting the feel for it on 3s, I have that hot racing diff and it is awesome, even for off-road stuff, lastly I won’t be having any wheelie problems because it hardly would wheelie with the mid-motor setup, and my lipolock weighted bumper just came in so the front should have no problem staying down, just need to figure out the back now

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