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NTC3 Light In The Rear End

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Old 05-03-2012, 05:48 PM
  #1
ZStein
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Default NTC3 Light In The Rear End

I recently bought a used NTC3, and I can not get the car to go streight. As soon as I hit the throttle the car goes right or left and spin in circles. I have tried to "set it up" by making sure that both tires leave the ground at the same time when a long screwdriver lifts the center of the front and rear. Unfortunately, with it balanced so that both tires (front and rear) leave the ground simultaneously when lifted in the front and rear center, its worse! The chassis is in good shape (carbon fiber) so I can't figure it out. Can anyone help me with this? If I turn the car left or right at low speed the rear end will slide around as if it's on ice!! What is causing this and what can I do to correct it?

Thanks,
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Old 05-03-2012, 06:02 PM
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Default RE: NTC3 Light In The Rear End

You need more junk in your trunk!

Seriously though, a few things come to mind that you can check for. Are the tires in good shape? You're not using drift tires, are you? Are the diff's too tight causing a locked axle effect? How is your camber setup? You say you balanced the car but is the weight distribution biased too far to the front?

Can you include a few photos of your setup to help us out?
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Old 05-03-2012, 06:11 PM
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Default RE: NTC3 Light In The Rear End

The diffs may be tight because when I turn a wheel all four will turn at the same time in the same direction. Also, I have no idea where the weight (front to rear) is at. I have been drag racing nitro and electric cars over 30 years and this is my first on road car. As for pictures I don't know how to post any. The tire are matching foams all around.
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Old 05-03-2012, 06:52 PM
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Default RE: NTC3 Light In The Rear End

I assume you're driving in the street or in a parking lot. I'm not a seasoned on-road racer, but Iunderstand that foam tires work very well on indoor carpet tracks but not so on pavement. There may be some traction addiditive tricks for them, but rubber is the tire material of choice on pavement.

I say your tires are the culprit. The diffs may or may not be a factor but you'll have to see how the car feels after you mount a set of rubber tires on it. You're weight distribution is probably fine as is your suspension geometry.

As for photos, there is a blue link at the bottom of the text box just above the OK and CANCEL buttons that reads "Click here to upload images and files!" Click that link and another window will pop up and allow you to select a file from your computer. Just be sure to wait for the file to load and the "File uploaded" cofirmation appears in the pop up window before you continue.
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Old 05-03-2012, 10:15 PM
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Default RE: NTC3 Light In The Rear End

Ok, good feed-back. I have tried rubber and foam tires and its the same. I'm thinking its in the shocks? The rear seems as if its on ice. Should the rear shocks be stiffer or softer than the front. As I previously stated, I know knowing about on-road cars, but this seems like a good platform for a "pro street" set up. The car has a modified 18TZ on it and when I get out a ways and hit it (whenever it stays straight) its quick and fast. I just want to get it to launch and track straight.
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Old 05-04-2012, 01:03 AM
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Default RE: NTC3 Light In The Rear End

Tow the rear wheels in a little and lower rear ride height. That should help. Your ride height should be aroung 5 - 6 mm.
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Old 05-04-2012, 01:39 AM
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Default RE: NTC3 Light In The Rear End

Lowering only rear ride height will make the problem worse (decreased suspension travel when loading up, or worse, ground contact at the rear under acceleration), but increasing rear toe is a very good call.

Here are the steps to take in order of effectiveness...

Softer rear tires or foam tires all around (a good set of foam tires on a good surface will last as long as rubber due to less wheelspin). Don't be tempted to use softer foam (lower 'shore' rating) in the rear, this will just make them wear faster. Use the same or slightly harder shore on the rear. Also use the wider foam tires on the rear if you have clearance (28 or 30mm).

Lift the car off the ground, turn ONE of the rear wheels. The opposite wheel should turn in the opposite direction with little resistance. If it appears to be locked (both wheels turn in the same direction), then this is no doubt the problem, look at the rear diff to determine what the problem could be. If using ball diffs, loosen them, if using gear diffs, check the internal gears or oils used inside.

Increase rear toe-in, it is normal to have as much as 3 degrees of toe in at the rear, but for a touring car, I would suggest starting at 2 degrees on each wheel and work from there. If the wheels are pretty much in line (parallel) then this is what is causing the problem.

Increase rear droop. Droop is most easily translated as the amount by which you can lift the rear of the car WITHOUT the rear wheels leaving the ground. Think of it as negative suspension travel. The bumpier the surface, the more of this you need. It is normally adjusted using grubscrews in the rear arms which contact the chassis, shortening suspension extension. Start by taking the screws out, or making sure they do not contact the chassis (full droop), and go from there. The right amount of droop is a tricky setting to get, but for stability you want as much as you can get.

Raise the ride height a little at the rear for more squat absorption. If the car is lower at the rear, then try making it level by only raising the rear a little.

Use softer springs in the rear shocks, or softer oil, or an extra hole in the rear shock pistons.

Put a stiffer anti roll bar on the front or stiffen the existing one (move the silver retainers along the ARB toward the center of the car). Anti roll bars affect traction at the OPPOSITE end of the car. A stiffer front gives more rear grip, a stiffer rear gives more front grip. Don't go too stiff though, this can have a dramatically detrimental effect on the handling.

Reduce your toe out at the front a little. Toe out is necessary at the front to get good turn-in, but more toe out makes the car turn more aggressively, encouraging the rear to step out.

Lastly, try to avoid wheelspin.

Hope that helps. Once again let me stress that droop is very important to understand and can make a HUGE difference to rear traction, it is the most overlooked setting in my experience.
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Old 05-04-2012, 05:25 AM
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Default RE: NTC3 Light In The Rear End

WOW!! Now that's knowledge. Thank you, thank you and thank you! This should be a sticky. I was up most of the night messing with that little car (on vacation) per your directions, and I took it out this morning and its running perfectly. However, I don't have a sway bar in the front, but I do have one in the rear. Should I remove it, or put it on the front? I copied your post and put it on my desk top for all future set-ups. Thanks again.
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ORIGINAL: Foxy

Lowering only rear ride height will make the problem worse (decreased suspension travel when loading up, or worse, ground contact at the rear under acceleration), but increasing rear toe is a very good call.

Here are the steps to take in order of effectiveness...

Softer rear tires or foam tires all around (a good set of foam tires on a good surface will last as long as rubber due to less wheelspin). Don't be tempted to use softer foam (lower 'shore' rating) in the rear, this will just make them wear faster. Use the same or slightly harder shore on the rear. Also use the wider foam tires on the rear if you have clearance (28 or 30mm).

Lift the car off the ground, turn ONE of the rear wheels. The opposite wheel should turn in the opposite direction with little resistance. If it appears to be locked (both wheels turn in the same direction), then this is no doubt the problem, look at the rear diff to determine what the problem could be. If using ball diffs, loosen them, if using gear diffs, check the internal gears or oils used inside.

Increase rear toe-in, it is normal to have as much as 3 degrees of toe in at the rear, but for a touring car, I would suggest starting at 2 degrees on each wheel and work from there. If the wheels are pretty much in line (parallel) then this is what is causing the problem.

Increase rear droop. Droop is most easily translated as the amount by which you can lift the rear of the car WITHOUT the rear wheels leaving the ground. Think of it as negative suspension travel. The bumpier the surface, the more of this you need. It is normally adjusted using grubscrews in the rear arms which contact the chassis, shortening suspension extension. Start by taking the screws out, or making sure they do not contact the chassis (full droop), and go from there. The right amount of droop is a tricky setting to get, but for stability you want as much as you can get.

Raise the ride height a little at the rear for more squat absorption. If the car is lower at the rear, then try making it level by only raising the rear a little.

Use softer springs in the rear shocks, or softer oil, or an extra hole in the rear shock pistons.

Put a stiffer anti roll bar on the front or stiffen the existing one (move the silver retainers along the ARB toward the center of the car). Anti roll bars affect traction at the OPPOSITE end of the car. A stiffer front gives more rear grip, a stiffer rear gives more front grip. Don't go too stiff though, this can have a dramatically detrimental effect on the handling.

Reduce your toe out at the front a little. Toe out is necessary at the front to get good turn-in, but more toe out makes the car turn more aggressively, encouraging the rear to step out.

Lastly, try to avoid wheelspin.

Hope that helps. Once again let me stress that droop is very important to understand and can make a HUGE difference to rear traction, it is the most overlooked setting in my experience.
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Old 05-04-2012, 05:55 AM
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Default RE: NTC3 Light In The Rear End

You're very welcome, I'm glad it helped. If I had an ARB only in the rear, I would probably remove it entirely (I might also experiment moving it to the front, but I doubt you'll reap many real benefits except a little more understeer, which may or may not be desirable). If you move on to racing, use one at both ends. On the other hand, if you are happy with the setup as it is (your rear arb is effectively increasing front grip), leave it in place.
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Old 05-04-2012, 07:18 AM
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Default RE: NTC3 Light In The Rear End

I ordered new tires as well, 35/40 (front/rear) componds.Now if I can just get the diffs loosed up. All four tires turn in the same direction as one. Clearly to tight!
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ORIGINAL: Foxy

You're very welcome, I'm glad it helped. If I had an ARB only in the rear, I would probably remove it entirely (I might also experiment moving it to the front, but I doubt you'll reap many real benefits except a little more understeer, which may or may not be desirable). If you move on to racing, use one at both ends. On the other hand, if you are happy with the setup as it is (your rear arb is effectively increasing front grip), leave it in place.
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Old 05-04-2012, 07:27 AM
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Default RE: NTC3 Light In The Rear End

Sounds like it was set up for drifting (locked diffs front and rear). Just to confirm, with all the wheels off the ground and you turn ONE rear wheel only, it turns all the wheels in the same direction simultaneously? If so, then yes, you will need to do something about the rear one.

This isn't bad in a way, because when you buy an RTR touring car, it has free and open diffs both ends, which is arguably worse, and then people spend a lot of time and effort trying to find a way to either heavily restrict or lock the front diff. The best front diff for a touring car is a one way. The next best thingn is a gear diff (or a ball diff) HEAVILY restricted with either 50k oil or done up very tight in the case of ball diffs. Finally, in the absence of either of those options, a locked front diff is almost as good, all these diff configurations will give tremendous front end pull out of the corners for little sacrifice on turn in (0 sacrifice in the case of a one-way). So leave the locked diff in the front. Buy the rear diff parts bag as spares from somewhere and load it up with 10-15k diff oil. It'll be like a different car. You may even then find you are understeering now that the rear end has so much grip. If and when that happens, I'll be happy to provide more advice to balance it.
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Old 05-04-2012, 08:05 AM
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Default RE: NTC3 Light In The Rear End

Yes, that is correct. With all wheels off the ground, if I turn one wheel, doesn't matter which, all wheels turn in the same direction simultaneously! If I hold one rear or front wheel and turn the other front or rear, the non-holding wheel will rotate in the other direction, but its tight. So is it best to leave it as is?
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Old 05-04-2012, 08:39 AM
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Default RE: NTC3 Light In The Rear End

Yes, that is correct. With all wheels off the ground, if I turn one wheel, doesn't matter which, all wheels turn in the same direction simultaneously! If I hold one rear or front wheel and turn the other front or rear, the non-holding wheel will rotate in the other direction, but its tight. So is it best to leave it as is?
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Old 05-04-2012, 04:17 PM
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Default RE: NTC3 Light In The Rear End

Must be ball diffs wound down tight. Leave the front very stiff. See if you can free up the rear. There should be a method of adjusting it, you may be able to download a manual from Associated's site. Normally, it's a screw buried deep inside the drive cups, but I can;t be sure as I'm not familiar with that exact model. Until you find out what kind of diffs they are and how they are 'locked', its hard to offer solid advice.
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Old 06-24-2013, 01:29 PM
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Default RE: NTC3 Light In The Rear End

Ive partially read some of the responses. I have an HPI RS4-3 and have the same problem, its not the tire, suspension, nor weight dist. its the way the cars gearing is set up and its rotating to either the left or to the right and that will be the direction your car will twist to.

When I drag race there is usually VHT on the ground and that is what keeps me straight.
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Old 07-02-2013, 10:14 AM
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Default RE: NTC3 Light In The Rear End

It could be that you wheels is off. Or it could be that you need to mess with the steering knob on your remote.
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