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Old 10-21-2019, 05:12 AM
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Join Date: Dec 2005
Location: Cheltenham, Gloucestershire, England
Posts: 1,059

Originally Posted by fastev View Post
Can someone give me the rundown on running two gears in a diff vs four? I was searching this thread but itís length has become overwhelming. Necessary to adjust oil viscosity or run the same as a 4-gear?

New 6.1 build for stock (21.5) class. Fixed gearing.
Not easy to give a concise answer but I will try.

2 gears bind more on load (throttle or brake) but are freer off load.

This means that the car will want to push a bit more (slightly less on power steering due to more stable rear) then when you get to something like a hairpin the rear will rotate nice and freely, then as soon as you get back on the throttle it is back to having a little more push than it would have had. Basically the driving feel is a bit more like a ball diff would be.
You would mainly use this for tight high grip indoor tracks.

As a rule of thumb it isn't double the oil viscosity when using 2 gears, more like 50-60% higher.

My go to builds are 2 gear with 7k-10k oil on high grip carpet, 4 gear with 5k-7k on high grip astro outdoors, every other situation is ball diff.
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