XRAY - Model racing cars

Hello, bought an Xb8-tq kit, and planning to built it.
In the supp. sheet, it mentioned, that i NOT have use the extra 0-rings.

It says i could use it to fine tune it, but what do they exact do ???
Is it better to put them direct in, and why only in the front diff ???

I'm a little confused right now.

Thnx in advance.

If you put the O-rings in the spider gears they will swell and make the diff feel like it has a much heavier oil in it. It's better to not use them, as it makes for a more consistent differential. With the O-Rings in, it will gradually feel like the front diff oil is getting thicker and make the car harder to drive.

-Adam

Thnx!