Recently I received set 42107 Ducati Panigale V4 R.

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I noticed that this set includes a new spring - part 65151c01 Technic, Shock Absorber 11L with Internal Spring, Dark Bluish Gray Shaft, and Light Bluish Gray Tip - as well as a “regular” spring - part 731c04 Technic, Shock Absorber 6.5L - Hard Spring.

Part 65151c01:

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Part 731c04:

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Why did LEGO create this new spring, and what makes it different from other LEGO springs?

1 Answer 1


Over the years the LEGO group has made a number of different springs, dampers and suspension components. The most widely known ones are the springs in the 731 series, such as the above mentioned 731c04 (Hard Spring) and its cousins 731c05 (Normal Spring) and 731c06 (Soft Spring), but there are other more specialized springs as well, such as 32181 (which comes in a soft and normal spring version) and even this “cute” little brick-sized spring (part 2695c01 Brick, Modified 1 x 2 x 2 1/3 with Spring Unit (Shock Absorber)):

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Let’s take a look at the two springs from set 42107, and compare them with a few of the above mentioned ones, namely 731c05 (Technic Shock Absorber 6.5L with Normal Spring in Light Gray), 731c06 (Technic Shock Absorber 6.5L with Soft Spring in Teal) and 32181c04 (Technic, Shock Absorber 10L Damped - Soft Spring in Trans-Clear).

Here are these 5 springs side-by-side:

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As you can see, there is some variance in dimensions. From left to right, the springs length in studs is 11, 6.5, 6.5, 6.5, and 10 respectively. Note that the three 731-series springs are 1 brick wide, whereas 32181 and 65151 are 2 bricks wide at their widest point, with 65151 being asymmetrical due to the top connection point sitting 1 brick lower than the top, and offset by 1 brick from the main shock absorber shaft.

Now let’s look at how far these springs compress:

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It was quite the struggle to get this group picture taken, as the power exerted by each spring was almost too much for the Technic pins holding them in place (and the half-a-stud offset of 731 is a bit of a challenge). As you can see, the compressed length of these shock absorbers is (from left to right) 9 studs, 5.5 studs, 5.5 studs, 5.5 studs and 7 studs.

So there are more differences: while the 731-series only compresses by 1 stud, 65151 compresses by 2 studs, and 32181 even compresses by 3 studs (even though the uncompressed shock is 1 stud shorter than 65151!).

Finally, let’s see how stiff these springs really are. As I am not a physicist, nor a mechanical engineer, my test setup is a bit archaic, but using baking weights I hoped to get an idea of how much weight it takes to fully compress the spring in each shock absorber. Here are some shots of various shocks undergoing testing:

The new absorber from 42107 (part 65151):

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One of the 731 series springs (part 731c04 in this case):

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As you can see, some shocks needed more weight to fully compress than provide by my wife’s entire collection of baking weights, so I had to resort to more drastic solutions, such as adding dental guard cleaning powder jars.

The results of this test surprised me - it turns out that (at least with the springs I tested) the normal and soft spring versions of 731 both take about 500-600g of weight to fully compress. I had expected the soft spring version of 731 (731c06) to be able to carry less weight than the normal spring version (731c05), but my test shows it was able to carry a bit MORE weight than its Normal spring cousin.

With my methodology (placing too much weight on the springs, and then slowly removing weight until the spring started lifting the contraption up again) both 32181c04 and 731c04 handled up to 1.1kg in weight, while the other springs handled about half that weight.

Net, the front shock absorbers (there are 2 shocks in the front fork) in 42107 have the same combined strength as the single shock absorber in the back, but they have different features - the front absorbers can travel 2 studs while the back absorber only travels 1 stud), and due to its offset connection point the front absorber (65151c01) has a rotational ability that the traditional 731 series shock absorbers miss. Also, as 65151c01 is manufactured with 3 different colors (pearl gold for the upper part, dark bluish gray for the shock and light bluish gray for the lower connection point) it blends better into the build of the Ducati Panigale. So why did LEGO create this part? Likely because it needed to look like the actual bike’s suspension, and no existing and in-production spring had the characteristics and looks needed to make the front assembly look proper.

Finally, a few notes about part 32181. Did you know:

  • Even though it has a soft spring, it is able to withstand the same weight as the Hard spring version of 731?
  • It is a damped spring, so where the other springs jump back to their uncompressed state almost instantaneously, 32181c04 (and 32181c05) take about a second to do so.
  • Out of all the springs I’ve tested, 32181 is the only spring that allows for rotation on its main axis, which allows you to turn the lower connection point out of alignment with the upper connection point. This can be very useful for constructions where the shock absorber needs to connect to 2 parts that are perpendicular to each other.

Here are the full test results, for those who are interested:

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         |                                                     | Spring Type
65151c01 | Technic, Shock Absorber 11L with Internal Spring... | Gold      
731c04   | Yellow Technic, Shock Absorber 6.5L - Hard Spring   | Yellow
731c05   | Technic, Shock Absorber 6.5L - Normal Spring        | Grey
731c06   | Technic, Shock Absorber 6.5L - Soft Spring          | Teal
32181c04 | Technic, Shock Absorber 10L Damped - Soft Spring    | Clear

         | Length (studs) | Length (cm) | Compressed (studs) | Compressed (cm)
65151c01 | 11             | 8.8         | 9                  | 7.2
731c04   | 6.5            | 5.2         | 5.5                | 4.4
731c05   | 6.5            | 5.2         | 5.5                | 4.4
731c06   | 6.5            | 5.2         | 5.5                | 4.4
32181c04 | 10             | 8           | 7                  | 5.6

         | Platform Weight (g) | Load Weight | Total Weight (g) | Notes
65151c01 | 19.82               | 513         | 533              | Offset connection
731c04   | 19.82               | 1126        | 1146             |
731c05   | 19.82               | 531         | 551              |
731c06   | 19.82               | 643         | 663              |
32181c04 | 19.82               | 1081        | 1101             | Slow release (damped), able to rotate
  • 3
    "no existing and in-production spring had the characteristics and looks needed to make the front assembly look proper" — not least because no existing spring lets you fix the direction, whereas in that set the front wheel is supported entirely by the springs (using any of the existing springs would make it rather wobbly!)
    – Dave
    Commented Oct 4, 2020 at 19:45
  • Of possible interest, even though the 731 series springs only compress one stud, almost all models that use them have them arranged for some form of oblique compression relative to the direction of movement, resulting in an actual movement of the wheels (or other spring-loaded part) of greater than one stud. They're also the most widespread of all the springs, so most MOCs prefer to use them instead of other options. Commented Oct 5, 2020 at 1:20
  • @Dave Look is probably most of it, there are at least three springs that you could fix the direction of using additional components (95292, 2902c02, and 2902c03), but they don't fit the look of the real thing, require a lot of extra bulk to fix the direction (you need stops above and below the mounting points), and are all rather old (most recent set with any of them was in 2015). Commented Oct 5, 2020 at 1:24
  • 5
    I signed up to this stack for the sole purpose of being able to +1 you for this ludicrously detailed response. You're a madman.
    – KlaymenDK
    Commented Oct 5, 2020 at 15:19
  • 1
    @Phil B. Hey you listed only compression springs. This one, Spring for Forklift Wide and Crane Bucket is a tension spring. How about an update for the "other" kind of spring?
    – Dan1138
    Commented Oct 5, 2020 at 17:40

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