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Old 12-03-2012, 08:59 AM   #3721
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What are you guys using for rear diff fluid. Medium bite carpet fairly tight track.
1000 or 2000 diff oil.
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Old 12-03-2012, 10:17 AM   #3722
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Thanks. Anyone prefer the ball diff to the gear diff? For the cxl?
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Old 12-03-2012, 11:16 AM   #3723
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Thanks. Anyone prefer the ball diff to the gear diff? For the cxl?
A few of our guys run the CXL, and the gear diff is preferred. We've been running 1000 to 1200 with great results.
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Old 12-03-2012, 12:00 PM   #3724
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Originally Posted by Blitzrockey View Post
What are you guys using for rear diff fluid. Medium bite carpet fairly tight track.
1000
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Old 12-03-2012, 12:02 PM   #3725
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Originally Posted by Blitzrockey View Post
Thanks. Anyone prefer the ball diff to the gear diff? For the cxl?
i only use the ball diff in very low traction track, but 98%of the time i run the gear diff
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Old 12-17-2012, 10:55 AM   #3726
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I just got a MI4cx pretty cheap and was looking to getting into either the VTA or USGT class. And was curious if anyone could point me in the right direction with gearing for both a 21.5t and 25.5t. The track is on the small side 40x70. High bite

I have been racing off road for a while now and was just looking for a change.
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Old 12-17-2012, 11:42 AM   #3727
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Did the worlds mod to the bulk heads. Ran the car this last weekend and you could defenatly tell a difference , it seemed easier to drive, a bit more grip also. I would recomend it to anyone with a cxl.
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Old 12-17-2012, 03:50 PM   #3728
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I just got a MI4cx pretty cheap and was looking to getting into either the VTA or USGT class. And was curious if anyone could point me in the right direction with gearing for both a 21.5t and 25.5t. The track is on the small side 40x70. High bite

I have been racing off road for a while now and was just looking for a change.
With a track that small, as a safe starting point, go for about a 3.7 with the 25.5, and about a 4.0 with the 21.5. Depending on your driving, motor timing, and layout, you can will likely be able to add a few teeth on the pinion from there.

With the Novak Ballistic 25.5 in my club, there's a couple schools of thought. We've got a 104x48 med-high grip carpet track, with a lot of fairly tight corners, and only one long straight. The drivers with a little more corner speed are running down in the 3.1-3.4 range with 35-40* motor timing and it's working. They say more than 40* makes it slower again. I'm finding that with my setup not quite there for corner speed, that I prefer the feel with 3.6 FDR and 45* of motor timing, as it gives me more speed out of the corners. I've tried it both ways, and overall pace is about the same, but the higher FDR is a bit more consistent. But either way, with the 25.5, you don't necessarily have to get the motor hot in order for it to be fast.

-Mike
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Old 12-17-2012, 04:43 PM   #3729
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With a track that small, as a safe starting point, go for about a 3.7 with the 25.5, and about a 4.0 with the 21.5. Depending on your driving, motor timing, and layout, you can will likely be able to add a few teeth on the pinion from there.

With the Novak Ballistic 25.5 in my club, there's a couple schools of thought. We've got a 104x48 med-high grip carpet track, with a lot of fairly tight corners, and only one long straight. The drivers with a little more corner speed are running down in the 3.1-3.4 range with 35-40* motor timing and it's working. They say more than 40* makes it slower again. I'm finding that with my setup not quite there for corner speed, that I prefer the feel with 3.6 FDR and 45* of motor timing, as it gives me more speed out of the corners. I've tried it both ways, and overall pace is about the same, but the higher FDR is a bit more consistent. But either way, with the 25.5, you don't necessarily have to get the motor hot in order for it to be fast.

-Mike
What Mike said. In fact, if you can keep pace with a cooler motor, the better off you are. The 25.5's, like any motor, don't like heat. I'll most likely be changing gearing next time for that reason.
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Old 12-17-2012, 04:49 PM   #3730
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Exactly what i was looking for thank you very much!
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Old 01-01-2013, 10:46 AM   #3731
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Default Checking for tweak

I have an Mi4 that I've been running for a while but it's been driving me nuts, as it's loose no matter what I do ... I've laid down the front shocks, stood up the rear, went as firm as I could in front and soft as I could in the rear, spool in front, etc. and it keeps spinning. I was wondering if maybe the front belt was too loose and I'm essentially running on RWD only, but I don't think that's the case (although I'm going to try a serpent 167 tooth belt instead of the Schumacher 171 tooth belt and will also try retrofitting a belt tensioner). Talking with one of the track pros (who doesn't run Schumacher ... I'm the only one running Schumacher at my track), he suggested it's time for me to check the chassis for tweak. So I'm tearing the car down to rebuild it and also check for tweak, but I have a problem ... most of the holes in the bottom of the chassis aren't countersunk deeply enough for the screws to be fully flush with the bottom of the car. I have a countersinking drill bit ... any reason for me not to drill out some of these holes a bit while tearing down the car? Don't want to weaken the chassis, esp. at the point where I'm attaching vital suspension pieces that must be firmly and securely attached.

While I'm at it, any thoughts on the handling issues? I'm running 17.5 blinky on HPI X-Pattern belted radials with Sticky Fingers traction compound on the inside half of fronts and entire rear tires at a medium sized indoor carpet track (RC Excitement in Fitchburg, MA).

Thanks in advance,
John
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Old 01-01-2013, 11:21 AM   #3732
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No there is no problem to do a little extra countersinking - as long as you are VERY careful. On a 2mm chassis, it's difficult, as the official (from an engineering point of view ) countersinking depth for an M3 screw is 2mm!! If some of the screws happen to have a slightly thicker head (i've seen this) then it makes it an even bigger problem.

The front belt shouldn't be too loose - remembering there is belt tensioning on the front diff mounts. It shouldn't be possible to fit a belt that is 4 teeth shorter - that's 12mm!! 171 is the correct length belt.
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Old 01-01-2013, 11:54 AM   #3733
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I would just sand the screw heads. I had the same issues with my car too
i sanded the few screws that were sticking out a little at a time, checked them and sanded more if needed. Make sure the chassis is flat when you attach the top deck, camber links and shock towers. That could be where the tweaking is coming from.
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Old 01-01-2013, 12:14 PM   #3734
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I like that idea ... I'll feel more comfortable sanding a $0.10 screw than drilling out 10 holes on a $70 chassis. I do think that some of my screws have the thicker than usual head.

Even with a brand new belt, with the front diff on the center setting, I can push the belt down a good centimeter easily, probably more (not at home now to do the measurements). I think belts can be run a lot looser than people often think and I'm probably dealing with chassis tweak more than the belt issue. It's just that my old belt (which admittedly had been in there a while) was pretty beat up, but it could have stretched too.
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Old 01-02-2013, 12:48 AM   #3735
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Quote:
Originally Posted by JohnPrz View Post
I have an Mi4 that I've been running for a while but it's been driving me nuts, as it's loose no matter what I do

...

While I'm at it, any thoughts on the handling issues? I'm running 17.5 blinky on HPI X-Pattern belted radials with Sticky Fingers traction compound on the inside half of fronts and entire rear tires at a medium sized indoor carpet track (RC Excitement in Fitchburg, MA).
Can you give more detail on your setup? I've got some experience with the X-Patterns on carpet with 25.5, which may or may not be helpful, but your shock angles alone sound funky. You're probably way outside the setup window. I usually have good results with just a base carpet setup, dropping ride height back down to 5mm, and adjusting droop so that I have about 1.5-2mm uptravel in front and about 2-3mm in the rear. Honestly, though, the 25.5 is slow enough that I can drive around setup issues.

Be sure to include weight, what body you're running, and even your spur/pinion combo (motor position can affect handling quite a bit).

-Mike
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