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Old 07-22-2010, 12:01 PM   #1
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Default Rear diff question

I know this subject has been flogged to death but I have a question about the rear diff.

I understand diff action and tunning quite well . But I see people running setups with a very heavy rear diff in truggies and buggies .

If thinner diff oil improves rear traction and thicker oil decreases rear traction going into the corner , how does a heavy rear diff oil help ?


A couple of weeks ago I was running on an astroturf track and the rear end was skidding about all over the gaf (i was running 7f 7c 3r) . Someone suggested moving up to 5 or 7 in the rear. 7 in the rear really calmed the rear end down and made the car more drivable . Why did this work when a heavier rear diff should in theory have made it worse?

I then ran the same setup at a different track a week later which was also astroturf and the backend was loose again so I dropped to 2 in the rear and the back end was good again .

Whats going on?

Thanks

Pete
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Old 07-22-2010, 12:17 PM   #2
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Pete, I think it is one of those driving style things, track grip, and layout.
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Old 07-22-2010, 12:19 PM   #3
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A heavier oil doesn't decrease traction, it increases it by sending more power to both wheels( like posi-track ) vs one wheel getting most of the power ( open-diff ), in effect giving you twice the traction..but the catch is this, if you are throttle happy and spinning your wheels from excess power, the 'posi effect' will tend to kick your car sideways more than an open-diff ( light oil ). Hope that makes sense.
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Old 07-22-2010, 12:32 PM   #4
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Quote:
Originally Posted by NitroFreakManHo View Post
A heavier oil doesn't decrease traction, it increases it by sending more power to both wheels( like posi-track ) vs one wheel getting most of the power ( open-diff ), in effect giving you twice the traction..but the catch is this, if you are throttle happy and spinning your wheels from excess power, the 'posi effect' will tend to kick your car sideways more than an open-diff ( light oil ). Hope that makes sense.

thanks

I does make sense but the setup manuals etc say heavier = less grip. Astro has some crazy grip though.

Why did the heavier oil not work on the second track though when dropping down to 2 in the rear gave the rear loads more traction than the heavier oil ? was it because the second track had less grip ?

Even though the second track had less grip , it was still way more grippy than a dirt track would have been . its a little confusing , especially when the front and centre diffs are so easy to tune .

appreciating the help

Pete
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Old 07-22-2010, 01:34 PM   #5
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The way i see it is that when using thicker/heaver oil in the rear, you loose traction in turns and corners, but you have lots of traction when going straight.
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Old 07-22-2010, 01:58 PM   #6
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The way i see it is that when using thicker/heaver oil in the rear, you loose traction in turns and corners, but you have lots of traction when going straight.

yeah this what i thought which is why it baffles me why heavier worked for me the other week on one track and was garbage on a similar track afterward . Also why some pros use really heavy rear fluid on dirt tracks . I would have thought the car would 180 all the time
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Old 07-23-2010, 11:48 AM   #7
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a lot of cars now have a lot less weight in the rear, sometimes theres not enough weight in the back to come around in a corner so a "looser" rear is needed or else you are stuck with the push. some tracks have a lot of sharp turns like 180's and some are a bunch of 90's. i've been running 777 in my rc8t since january and have always gone back to that after testing. shock weight and angle also affect rear traction.
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