LEGO Technic 42099 4X4 X-treme Off-Roader stage 2 upgrade – even more power with only 4 extra gears!

After the first crawler upgrade of the LEGO Technic 42099 4X4 X-treme Off-Roader set here’s the next level – by replacing the other gear sets the vehicle becomes a real crawling monster:

Update: I immediately received lots of questions about this so I’ll try to clarify things.

  • For each axle there are two set of gears between the motor and the wheel hubs, two pairs of 20T and 12T gears, gearing up the motor’s output by 1:1,667 * 1:1,667 = 2,778.
  • Here are the gear ratios at the different stages:
    • Original – 1:1,667 * 1:1,667 = 2,778
    • “5 minute upgrade” (swapping one set) – 1:1,667 * 1,667:1 = 1
    • Stage 2 upgrade (replacing one set with two 16T gears) – 1,667:1 * 1:1 = 0.6
    • Super slow (swapping both set of gears) = 1,667:1 * 1,667:1 = 0.36

One set of gears is easily accessible, the other one is more difficult to swap.

For the 5 minute upgrade which is a balance between speed and power, you can either follow the video if your set is already assembled or you need to perform the following swaps during building:

For the “stage 2” upgrade you need to swap the two sets of gears that we did not touch in the first upgrade:

Then the other set that was swapped in the 5 minute upgrade needs to be replaced with 2-2 16T gears. You can do it after the assembly as there are the gears that are easily accessible or you can do it during building by replacing the gears in step 78-82 and 131-145 with the 16T gears.

And that’s all 🙂 Now your 42099 has slightly less speed but enough power to deal with most obstacles. If you want to get back to the state of the 5 minute upgrade, simply replace the 16T gears with the original ones in their original setup. This way the inner gear set will be still swapped, the outer set will be in the original gearing so you’ll have the 1:1 gearing from the motors to the wheel hubs.


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