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Old 06-19-2014, 06:59 PM   #1906
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Originally Posted by homerthefourth View Post
Most corners though the car turns in, rear end slides 6 inches at the apex and hooks up and off you go. I haven't had this issue before. First I thought I was entering the corner too fast but I think it's more of a setup issue.
- What surface?
- Is it smooth or bumpy?
- What's the ambient temperature?
- What's the track temperature?
- Do you have ECS/DCJ's in the front?
- Is it doing this on the way into the corner, off power, on the way to the apex?
- Does it do it right from the start of the heat, or does it start OK and get worse as the heat goes on?
- Does it behave the same in both left and right turns?
- Is the chassis bottoming out? If so, and on carpet, are you cleaning it between heats?
- What rear diff oil do you have?
- Have you checked that your shocks are properly filled and aren't full of air?
- Have you made sure that you don't have bent hinge pins, cracked suspension mount inserts, tweaked suspension mounts, broken outer hinge pins, cracked c-hubs, etc?
- Are you sure the car isn't actually understeering and getting all bound up, and then suddenly releasing all at once?

Assuming you don't find anything mechanically wrong with the setup, one very simple thing to try is .5mm to 1mm more droop (lower number on droop gauge).
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Old 06-19-2014, 11:46 PM   #1907
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My bad. I should of stated all of this earlier.

Quote:
- What surface? - Med to High grip carpet
- Is it smooth or bumpy? - Smooth
- What's the ambient temperature? - 72
- What's the track temperature? - 72
- Do you have ECS/DCJ's in the front? - ECS
- Is it doing this on the way into the corner, off power, on the way to the apex? - Off power
- Does it do it right from the start of the heat, or does it start OK and get worse as the heat goes on? - On one pack I noticed it was in the first 3 minutes but it still seems to happen all the time.
- Does it behave the same in both left and right turns? - Both left and right
- Is the chassis bottoming out? If so, and on carpet, are you cleaning it between heats? - Not bottoming out.
- What rear diff oil do you have? - 1K
- Have you checked that your shocks are properly filled and aren't full of air? - Freshly rebuilt. No air.
- Have you made sure that you don't have bent hinge pins, cracked suspension mount inserts, tweaked suspension mounts, broken outer hinge pins, cracked c-hubs, etc? - Yes. Two cars same set up same results.
- Are you sure the car isn't actually understeering and getting all bound up, and then suddenly releasing all at once? - I don't think so.

Assuming you don't find anything mechanically wrong with the setup, one very simple thing to try is .5mm to 1mm more droop (lower number on droop gauge).
I'm running 1.5mm droop. I tried 2.5 and 3 tonight. It seemed to help. But not enough.

I also noticed tonight that the car, low speed is very touchy. Twitchy. When you let off the power and turn, the rear end wants to give out. The opposite of the problem I usually have.

Everything is mostly the stock carpet set up which usually does really well here. Ride height front and rear both 5.5mm.

The car for sure looks loose compared to the other cars out here. Mod sedan is planted and here I am whipping the rear end out on most all the corners.
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Old 06-20-2014, 01:14 AM   #1908
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Drop the rear end 1mm.

If rules don't allow, raise the front 1mm. If it's too much (car starts to push), try 0.5mm.

Either way, try to have the rear end 1mm lower than the front.
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Old 06-20-2014, 02:39 AM   #1909
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Originally Posted by homerthefourth View Post
My bad. I should of stated all of this earlier.



I'm running 1.5mm droop. I tried 2.5 and 3 tonight. It seemed to help. But not enough.

I also noticed tonight that the car, low speed is very touchy. Twitchy. When you let off the power and turn, the rear end wants to give out. The opposite of the problem I usually have.

Everything is mostly the stock carpet set up which usually does really well here. Ride height front and rear both 5.5mm.

The car for sure looks loose compared to the other cars out here. Mod sedan is planted and here I am whipping the rear end out on most all the corners.
Consider looking at some of the changes recommended for Metalnut on the previous page.
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Old 06-20-2014, 09:31 AM   #1910
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Originally Posted by niznai View Post
Drop the rear end 1mm.

If rules don't allow, raise the front 1mm. If it's too much (car starts to push), try 0.5mm.

Either way, try to have the rear end 1mm lower than the front.
Thanks I'll give this a try for sure.

Any thoughts on bump steer or roll steer? Thinking about this logically if traction is getting lower at the track, and the car seems to give out when the front has the highest amount of G forces applied, it could be that the car is rolling and with that inducing roll steer which the track can't handle right now.

I'll try taking out or putting in 1mm shims.

Last edited by homerthefourth; 06-20-2014 at 09:44 AM. Reason: spelling
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Old 06-20-2014, 11:36 AM   #1911
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Quote:
Originally Posted by homerthefourth View Post
My bad. I should of stated all of this earlier.



I'm running 1.5mm droop. I tried 2.5 and 3 tonight. It seemed to help. But not enough.

I also noticed tonight that the car, low speed is very touchy. Twitchy. When you let off the power and turn, the rear end wants to give out. The opposite of the problem I usually have.

Everything is mostly the stock carpet set up which usually does really well here. Ride height front and rear both 5.5mm.

The car for sure looks loose compared to the other cars out here. Mod sedan is planted and here I am whipping the rear end out on most all the corners.
You might want to try a little pro-squat, ( raise the RR by . 5 mm ). It helped my tail happy little puppy by helping the weight transfer to the rears under power. Also make sure you're running the Hard A arms and not the Graphite ones.
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Old 06-20-2014, 03:22 PM   #1912
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You might want to try a little pro-squat, ( raise the RR by . 5 mm ). It helped my tail happy little puppy by helping the weight transfer to the rears under power. Also make sure you're running the Hard A arms and not the Graphite ones.
I'll be conducting a few test this week. Still trying to get the hang of this.

I took the graphite arms off last week. Seems to help a bit.


On a different note is there an android app that is like the windows app that give car dynamics? It'd be great to have a app that did an if then type of process.
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Old 06-20-2014, 06:06 PM   #1913
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@homer

I think bump steer is definitely worth playing with. Generally you want fewer shims on carpet.

Also, based on what you've posted:

- Thicker rear diff. I'd jump right to 3K and see how you like it. This should help the back end resist kicking out off power a bit more. EDIT: It will also give you more on-power steering.

EDIT: If you're running thin (<400cst) shock oil, try going thicker. If you have some associated 40wt lying around, throw that in and see what it does for you.

- Maybe try anti-dive. It will make the car very crisp and precise into the tight corners, but can make a bit of a mid-corner push. But it might make things worse because it might let you develop more rotational momentum.

- If you're running short camber links, try medium. This should really smooth out the car.

- If you're running 2mm inside and outside on the front camber link, try 1mm outside. Again, this should smooth the car out a bit.

If you're running Sweep wheels, make sure your camber links aren't rubbing on the inside of the wheels. That could definitely cause some nasty behavior when the car is heavily loaded in tight corners.

-Mike
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Old 06-20-2014, 06:18 PM   #1914
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Originally Posted by grippgoat View Post
@homer

I think bump steer is definitely worth playing with. Generally you want fewer shims on carpet.

Also, based on what you've posted:

- Thicker rear diff. I'd jump right to 3K and see how you like it. This should help the back end resist kicking out off power a bit more. EDIT: It will also give you more on-power steering.

EDIT: If you're running thin (<400cst) shock oil, try going thicker. If you have some associated 40wt lying around, throw that in and see what it does for you.

- Maybe try anti-dive. It will make the car very crisp and precise into the tight corners, but can make a bit of a mid-corner push. But it might make things worse because it might let you develop more rotational momentum.

- If you're running short camber links, try medium. This should really smooth out the car.

- If you're running 2mm inside and outside on the front camber link, try 1mm outside. Again, this should smooth the car out a bit.

If you're running Sweep wheels, make sure your camber links aren't rubbing on the inside of the wheels. That could definitely cause some nasty behavior when the car is heavily loaded in tight corners.

-Mike
Thanks for the info Mike.

I did play with 3K in the rear diff. Seemed to help but didn't eliminate the issue. Perhaps this is a multi step fix rather then a one shot deal.

Currently I got 1mm on the camber links.

Not running Sweeps so no issues there.

Logically from what I feel the first thing I'll try is Camber link length. Increase that and see what happens. Then throw in a 3K diff.

Good deal. Thanks again.
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Old 06-20-2014, 07:01 PM   #1915
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So it's kicking out at the apex, but at which point are you getting on power?

What about your belt tension? Although I haven't experimented with this myself, I believe you can affect driving characteristic with making one belt tighter than the other. A tighter rear belt will make the rear wheels more reactive to throttle and "ahead" of the front wheels in terms of what's happening. I think

Also, stupid question, but how are your bearings? Is everything spinning smoothly?
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Old 06-20-2014, 07:09 PM   #1916
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Originally Posted by metalnut View Post
So it's kicking out at the apex, but at which point are you getting on power?

What about your belt tension? Although I haven't experimented with this myself, I believe you can affect driving characteristic with making one belt tighter than the other. A tighter rear belt will make the rear wheels more reactive to throttle and "ahead" of the front wheels in terms of what's happening. I think

Also, stupid question, but how are your bearings? Is everything spinning smoothly?
Good call, I forgot all about belt tension. If brakes are hitting the rear wheels harder, it could get ugly.

-Mike
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Old 06-20-2014, 11:27 PM   #1917
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Originally Posted by metalnut View Post
So it's kicking out at the apex, but at which point are you getting on power?

What about your belt tension? Although I haven't experimented with this myself, I believe you can affect driving characteristic with making one belt tighter than the other. A tighter rear belt will make the rear wheels more reactive to throttle and "ahead" of the front wheels in terms of what's happening. I think

Also, stupid question, but how are your bearings? Is everything spinning smoothly?
Sweepers are fine, mid to high speed corners are fine. But the slow speed hair pins and such the car reacts too quick, or as you steer in it steers more and more. With that the hair pins it's when you let off the power in the corner that the rear end swings out. Especially in a chicane where I'm off power turning, on power then off power turning. Or something to that effect.

Having the rear act first braking because of belt tension make some sense to me. I'll add that to the list to try.

Bearings are good.

I'll test most all of this our tomorrow. Or at least that's the plan.

Thanks for the help.
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Old 06-21-2014, 12:37 AM   #1918
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When you say the car steers in more and more, I'm thinking that the rear end is rotating too much, perhaps enough so that it then suddenly snaps loose. In theory, in my head, I could see that happening. You could try to stand up the shocks in the back and see how that reacts. Though I don't know what position you have them in. I could be completely wrong and it could be that the rear is actually too stiff and thus suddenly lets go. Any way you could get someone to shoot a video of a few corners?
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Old 06-21-2014, 12:43 AM   #1919
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Quote:
Originally Posted by homerthefourth View Post
Sweepers are fine, mid to high speed corners are fine. But the slow speed hair pins and such the car reacts too quick, or as you steer in it steers more and more. With that the hair pins it's when you let off the power in the corner that the rear end swings out. Especially in a chicane where I'm off power turning, on power then off power turning. Or something to that effect.

Having the rear act first braking because of belt tension make some sense to me. I'll add that to the list to try.

Bearings are good.

I'll test most all of this our tomorrow. Or at least that's the plan.

Thanks for the help.
You said you are using the basic kit setup so I assume you are using the 2.5 springs all-around. I had a similar issue a few weeks ago where we had some pretty high traction. My car was to soft and was rolling to a point and had no where else to go so the rear was letting go when I was getting off power. I was told to stiffen the car up a little. I am running the aluminum chassis, but Ihave my top deck split completely down the middle to allow the car to have more flex on our lower grip track at home here in Dallas. I put on a stock 2.0mm top deck and stiffer springs and the car was much better. I am guessing you are not running the aluminum chassis and a top deck like mine. Since yours is prob kit stock I would try some stiffer springs like 2.7's and see how that does. It worked pretty well for me.
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Old 06-21-2014, 01:30 AM   #1920
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Given that you are battling with low rear end grip and assuming you have the maximum front end grip you can have I advised you against doing anything that takes away grip from the front end. This may be wrong if my assumptions are wrong, but I still don't see how heavier rear diff oil and stiffer springs (suspension) would help. You want more rear grip which none of these things will help you achieve.
Do one thing at a time and see where that gets you.
In short, I would make sure that 1) rear end is lower, 2) rear diff is free to allow wheels to turn independently (otherwise they'll try to go in a straight line instead of around corners), 3) allow the rear to roll a bit to move weight on the outside wheel, otherwise you'll have the grip on the inside wheel where you can't use it, 4) adjust rear end camber and camber gain to find the best compromise, 5) adjust rear toe to get the best compromise (too much toe will tend to make the rear want to go straight), 6) look at how much weight is transferred on the rear outer wheel (wheelbase adjustment?), roll centers. Not necessarily in this order, but pretty close to it. Use the coarse adjustments first to get it close, then use the finer adjustments to dial it in.
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