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Old 09-13-2017, 07:26 AM   #1
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Default No rear end grip.

Hi guys.

I race an old Schumacher MI4 with Lipo and spec r rear diff.I am having issues indoor on carpet with foam, with no grip from the rear whatsoever.

even on the start if I hit the power it will just 180 so I have to start off real slow. after 3 laps or sp it is better, but I have to catch the rear end almost every corner. I am using CG carpet setup and have tried the following.

red front springs
green rear springs
washers below the rear mount plate
no washers below rear mount plate.
loser belt
tighter belt
laying down rear shocks more
wide translink (makes even worse)
thinist translink plates (best so far)

Im not sure what else to try next.maybe less rear camber? widen the rear track width and narrowing the front?
lightest rear springs?

thanks
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Old 09-13-2017, 08:36 AM   #2
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Quote:
Originally Posted by stuartkeith View Post
Hi guys.

I race an old Schumacher MI4 with Lipo and spec r rear diff.I am having issues indoor on carpet with foam, with no grip from the rear whatsoever.

even on the start if I hit the power it will just 180 so I have to start off real slow. after 3 laps or sp it is better, but I have to catch the rear end almost every corner. I am using CG carpet setup and have tried the following.

red front springs
green rear springs
washers below the rear mount plate
no washers below rear mount plate.
loser belt
tighter belt
laying down rear shocks more
wide translink (makes even worse)
thinist translink plates (best so far)

Im not sure what else to try next.maybe less rear camber? widen the rear track width and narrowing the front?
lightest rear springs?

thanks
Try more front droop. (Lower number on droop gauge)
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Old 09-13-2017, 08:49 AM   #3
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Quote:
Originally Posted by stuartkeith View Post
Hi guys.

I race an old Schumacher MI4 with Lipo and spec r rear diff.I am having issues indoor on carpet with foam, with no grip from the rear whatsoever.

even on the start if I hit the power it will just 180 so I have to start off real slow. after 3 laps or sp it is better, but I have to catch the rear end almost every corner. I am using CG carpet setup and have tried the following.

red front springs
green rear springs
washers below the rear mount plate
no washers below rear mount plate.
loser belt
tighter belt
laying down rear shocks more
wide translink (makes even worse)
thinist translink plates (best so far)

Im not sure what else to try next.maybe less rear camber? widen the rear track width and narrowing the front?
lightest rear springs?

thanks
I would revert back to the "KIT" set up and completely rebuild the chassis. Sometimes these little race cars will have a good enough tweak that will remove the majority of rear mechanical grip, making the chassis spin out when turning off power and slightly on power. FYI: Laying down the rear shocks will take away rear traction, raising the rear shocks will add rear traction but there is a limit to everything. Revert back to KIT setup and completely rebuild the chassis and your problems should be resolved.
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Old 09-13-2017, 09:03 AM   #4
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You have a clear problem, don't try subtleties like belts and stuff. You sound like there is absolutely no weight on the rear.

Put some weight on it, make sure the rear loads up nicely on throttle, and then tune with small changes in subtle adjustments. Increasing front droop can help, but not if you don't sort all other issues first.
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Old 09-13-2017, 09:05 AM   #5
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Thanks. I will try rebuilding rear end, I did rebuild almost fully during off season. I had it almost perfect on the manual CG setup a while ago, with grip roll being the issue.

how dose oil weight affect it? I have schumi 80cst in there at present. and 6000cst in the diff.
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Old 09-13-2017, 09:35 AM   #6
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Yeah there is something way wrong probably. Spring not seated properly, fucked angles, heavy binding, tweak.. empty damper :P
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Old 09-13-2017, 09:42 AM   #7
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Originally Posted by stuartkeith View Post
Thanks. I will try rebuilding rear end, I did rebuild almost fully during off season. I had it almost perfect on the manual CG setup a while ago, with grip roll being the issue.

how dose oil weight affect it? I have schumi 80cst in there at present. and 6000cst in the diff.
Sounds as if you have too much front traction and not a good balance on the setup. Try the following: * Go back to exact kit setup, * raise your front inner camber link 1mm from Kit Setup, if still aggressive feeling on the nose go 1.5mm or even 2mm higher than kit setup and drive the car - NEXT: Go one step stiffer on the front springs. Also if your not gluing the sidewalls on the front tires I would honestly start there. Always start with 2mm negative camber front/rear and 1mm front positive toe and 3mm rear toe-in. Think you'll be happy with that my friend
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Old 09-13-2017, 09:44 AM   #8
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check your front CVD's
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Old 09-13-2017, 10:07 AM   #9
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check your front CVD's
Just fitted new cvds all round as all were bent and car shook lol, we race foams on carpet, contact tyres. so pre glued.
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Old 09-13-2017, 10:19 AM   #10
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i'd deal with droop and rear toe
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Old 09-13-2017, 10:20 AM   #11
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Just fitted new cvds all round as all were bent and car shook lol, we race foams on carpet, contact tyres. so pre glued.
Maybe I should have remembered you already mentioned you race on foams lol. I'm thinking the chassis is digging to much on the nose. Try raising the front inner camber links. That will take away forward bite and should settle the chassis for you.
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Old 09-13-2017, 10:32 AM   #12
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With foam tires we always ran a much, much harder rear spring than fronts, like 30lb/in on the front and 17lb/in on the rear.

Adjusting your rear links to have more camber-gain would probably help as well.

I would run nearly 0 droop all around to prevent the car from being able to "load up" on one side and cause it to break traction.

Also, I would guess that you are dragging the chassis in the corners. Do you have buildup on the chassis edge?
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Old 09-13-2017, 10:50 AM   #13
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i would go in this order:
1. go back to kit settings
2. check for binding at all points in drivetrain and suspension. check for tweak
3. 6000cst in rear diff sounds heavy (at least where i run). see what others are running at your track
4. try different front rear droop settings
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Old 09-13-2017, 11:05 AM   #14
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80 cst?!?! What are you trying to run? I would suggest you go down to about 40cst or so and take it from there.

Try this test. Push the car down all the way to the ground and let go abruptly. Does it come back up all the way in a short time (imagine it's driving around and has to roll from side to side or transition in a chicane, around a switchback or hairpin, whatever). If it takes a while, well that's what it will do on the way down as well, so basically you will have no roll, dive or squat (within reason). It will be a brick sliding around the track (which sounds like your description). Add to this some other problems and you now understand why your car doesn't transfer any weight around to load the tyres.

Remember, the car needs to be able to roll more in the rear than at the front, so you need a softer suspension at the rear. You need to have weight transfer to the rear to make use of your accelerating power, so you need to have some weight and some squat action happening.

I would first check that everything is within spec, there's no binding, etc.

Adjust rear toe in and camber to your preferred values (3deg toe in, about 1.5-2 deg camber max) and leave it alone.

Then adjust the rear suspension to be softer but react quickly.

Then make sure your car can roll enough (more at the rear). This means adjusting rear droop/down travel, rear ground clearance, set and leave alone for now.

Then check squat (look form the side and try to take off). If the car doesn't squat at all, you have no weight transfer. Remember, you don't need to see the front lift a lot or the rear go down a lot, but you need to see clear signs of pitch.

Adjust the front and/or rear end accordingly.

This is where first you need to give the front a bit more droop.

If you find you need to give it loads of front droop, you don't have enough weight on the rear (i.e. too much on the front).

Move some weight back (move shims on the suspension hinge pins to have the rear arms further in front).

If that is not enough, you need to physically move some weight towards the back (weigh the car on two scales front-rear, ideally you should have as close as possible between front and rear, a little rear bias is okay, perhaps up to 60-40 rear-front).

If you get to 60-40 after all that and it is still not enough, you can give the car a bit of squat using the rear hinge pin inclination (very rare, not exactly ideal, perhaps you should go softer in the back springs/oil first and keep the squat adjustment as a last resort).

As a rule of thumb, you should have the car set up such that you have a higher ground clearance at the front of the car or equal all around. The other way around (raked stance) is not your friend save for some special situations (shouldn't be the case on carpet indoors).

This is part of the preliminary set up before you start the whole process, perhaps I should have put it at the top. You can start with the car level at your desired ride height (ground clearance) and try everything that way, and then, only after your car starts behaving, you can experiment with giving it a bit more ride height at the front and check it is beneficial. If things improve, give it some more and so on until things get worse. If you find you can give it loads, with no adverse effect (unlikely) go back and put some more weight on the rear and take some of the front ride height out (perhaps 1mm difference front to rear is more than enough).

That's pretty much the process, ideally after each adjustment I would test (for my home track, I have a good feel based on experience so I can get the car in the ballpark on the bench, no need to test).

First test acceleration in a straight line, and when you have the car going like a cut cat and straight as an arrow, I am willing to put money it will go around corners pretty well too.

It will still need fine tuning.

If the car squirms under acceleration from a stand still, you have a very stable car (squirming as in trying to get out of shape, but self correcting without your steering input, and without you needing to back off the throttle). For comparison, what you describe right now is the exact opposite.

At this point, the car is actually too stable, and you are not using all the power to take off, some of it is lost at the rear wheels as they fight each other to correct the car. A bit of squirming is acceptable, as long as the car self corrects and doesn't fishtail for umpteen meters until it stabilises.

Ideally you should only see a twitch when the car moves off the line, finds the equilibrium pitch angle once all the weight that can be transferred on the rear is transferred and then it just goes like mad. All of that should happen in a flash and be indistinguishable to the untrained eye. That is the sign you are on the very edge of using everything you've got to take off.

Once you achieve that, you can start tuning for cornering with sway bars, laying shocks down or standing them up, roll centres, you might touch the camber a bit, or perhaps the toe in (both front and rear), Ackerman, whatever else have you but it's all fractions of degrees and (imperatively) followed by testing after each change.

I didn't mention caster, I don't normally touch it, not sure if it is adjustable on your car, I just leave mine at 4 and tune around it (my cars only have set caster blocks and I don't feel like buying a million of them just to try; never felt like I needed them). Use your best judgement, or perhaps ask at the track what the fast guys use and go with that.

At this stage, you shouldn't need to touch springs, shocks, wheelbase, ride height, droop, etc., everything else you have adjusted above.
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Old 09-13-2017, 11:23 AM   #15
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What tire compound are you running front and rear? Are you using traction compound?
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