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.



  1. Pingback: ▷ Calendrier de l'Avent #13 : Un set LEGO Technic 42099 4x4 X-treme Off-Roader à gagner ! - HOTH BRICKS

  2. So is stage 2 in addition to what was done in stage 1? Or don’t worry about stage 1 if you’re doing stage 2?

    • It is independent, Stage one is only swapping the gears, stage 2 is replacing one set of gears for each axle.

      • Thank you for your quick reply. I thought as much but I wanted to make sure. Happy New Year!

      • Hey racingbrick,for me doing a measure,how many kph has each version got?

        i havent got the 42099 assembled yet and idk how slow is it,i want to do just stage 1 but i also want to be able to crawl.

        can you help me,i mean,kphof original,stage 1 and super slow

  3. Hey there,
    I have a question about the mod… I’ve done the two 16t gears on each axle but I’m not too sure if I swap the other gears. If I need to swap the other gears around, can you give me a guide sorta thing. (How to access the other gears I need to swap without having to destroy and rebuild the whole thing again).
    Thankyou from Australia!

    • The other pair of gears are not easily accessible once the model is built, I highlighted here in this post at which step they are added. Unfortunately there’s no easy way to replace them without stripping down the car since they are added at the beginning of the axle’s building process.

  4. stage 1:
    1:1,667 * 1,667:1 = 1
    78:82 * 131:145

    stage 2:
    1,667:1 * 1:1 = 0.6

    18:19 * 154:176

    replace stage 1 with 16:16 * 16:16
    or undo the stage 1.

    so it is either I do stage 1 or stage 2?

    so if it is a new build,
    stage 1: replace steps 78:82 * 131:145 with 16T
    or swap parts for 78:82 * 131:145 if I dont have 16T yet.

    stage 2: swap gears 18:19 * 154:176

    is it recommended to do stage 1 and stage 2?
    or stage 1 only or stage 2 only?

    Thank you in advance! just got the 42099 so this will greatly help! appreciate it!

  5. Hi,

    Thank you so much for your videos. I’m sure my story doesn’t really matter, but, I was camping recently with a friend who had an RC that was a climber, and I thought, I bet there is a LEGO, and I found this beauty. It hasn’t arrived yet, but after watching your videos, and reading your instructions I am really excited to challenge my friend’s “real” RC.

    Just a few questions, is the 16T a part included in the box? Or is it something I will have to order from LEGO? I am sure I can find this out on google as well, or the brick site I’m on, but I was just curious if I might get a swifter answer here. And, I also wanted to say “thank you” for your awesome videos.

  6. This is very chaotic. I got to the step 145 and don’t know where I am with this upgrade.
    I turns out that I need 8x 16T gears ?
    Step 131 – should I have two big cogs on then?
    It would be easier if you just say what step what cog to use and where we swap places and where we replace with 16T.

    • Don’t think it is chaotic, you need to read the description carefully, it worked for a lot of people. There are 4 pair of gears, 2-2 for each axle. For the stage 2 mod 2 pairs needs to be swapped, and the other 2 pairs needs to be replaced with 2 pair (4 pieces) of 16T gears. it does not really matter which one is swapped and which one is replaced until you do 1-1 for each axle.

      • Thank you Racingbrick for reply.
        So I had to strip it down & re-do it in the end :/ Here’s a simple instruction from myself for those who may struggle with a new build:

        – if you just go for simple upgrade:
        Step 78 & 82 + 131 & 145 – cogs black and beige swap places

        – if you go for full upgrade (very slow but torquey – as the one from video):
        Same steps above but don’t swap cogs – replace them with 2x 16T (4x altogether)
        Additionally steps 19 + 154 & 176 – cogs black and beige swap places.

  7. Hi RacingBrick,

    I just wanted to ask about your thoughts on swapping the diffs in this set for the new ones that come in the 42109 and 42114 sets…? This would be a further gear reduction and give the crawler more power but also make it even slower. If you could test this and possibly show it in a post or video that would be great! This could be another option for mixing speed and torque with your already discussed options or just as one extra change to the stock drivetrain of the model.

    • It is an option, but with the demonstrated gear swapping options you can already make it slower than enough so investing in the new diffs just for gear reduction is not really worth it.

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