LEGO Brick Inspired 10" Flat Free Utility Tire

I, and I'm going to assume many of my fellow Instructable-ers, grew up playing with LEGO® bricks. Heck, who am I kidding... I still play with them!

I also recently found out my wood splitter ate another set of tires. The 10" pneumatic utility tires seem to last me about 2ish years before they wear out which is mildly irritating. There are flat free tires, I've used them but they're not great because they have essentially no flex.

So basically I'm stuck with either replacing the tires every couple of years or dealing with a rougher riding tire.

Until now.

To solve this mildly irritating issue, what would happen if we scaled up a LEGO® tire to fit a typical 10" utility tire?!?!?! 🤔 Would we get a better "flat free" tire that also had that certain "je ne sais quoi" style?!

Lets fire up the 'puter and find out!

*I'm doing my best to try not to step on any legal trademark toes here. Disclaimer: LEGO® is a trademark of the LEGO Group of companies and is not in any way affiliated with this project. https://www.lego.com/en-us/legal/notices-and-policies/fair-play

1. We need a LEGO® wheel or four to measure.
2. We also need a typical 10" utility tire to measure.
3. I'm using this one from Harbor Freight. https://www.harborfreight.com/10-inch-pneumatic-tire-30900.html
4. Digital calipers to do the measuring. Also having a ruler or tape measure wouldn't hurt.
5. Computer with 3D modeling software
6. I'm using Autodesk Fusion. Here is the link to try it out if you're curious https://www.autodesk.com/products/fusion-360/personal
7. Digital file from later in this instructable.
8. 3D printer that can print flexible filament with a 10 inch or larger bed. I'm using a Bambu Labs X1C.
9. Flexible TPU Filament.
10. I'm planning to use Bambu HF-TPU 95A because I'm impatient...https://us.store.bambulab.com/products/tpu-95a-hf
11. Ha... I thought I was going to use HF-TPU, but future me found out I didn't have enough left. So I used YOYI brand black TPU.
12. 1/2" or 13mm wrenches to take apart the utility tire hub.
13. Optional: Yellow spray paint

The brick wheels appear to be fairly simple so I've decided to go the physical measurement route to create the model instead of trying to 3D scan or trace one.

Using millimeters in this instance also seems to make more sense to me for two reasons. First, since there's going to be quite a few teeny tiny measurements I sometimes find it's just easier to keep track of mm's instead of trying to keep track of what 64th of an inch I'm on. And second I'm not trying to create an EXACT replica (draft angle, ect), so I'm planning on rounding to the nearest 1/2 mm for my sanity. (Metric for my sanity... did I really just say that?!?! 🤣)

I measured all the wheels I had because I was curious if there was some sort of obvious relationship/scale between all the brick wheels. However at first glance they all have a different number of treads and the treads are different sizes, so if there is a relationship it's not immediately obvious to me (IE. all of them are some % larger or small, or all have same size tread, just add or delete treads as needed to fill the diameter). I've attached the measurements if you want to try to crack the brick tire code?!?!

Allrighty, pick your favorite tiny tire, fire up Autodesk Fusion and lets get onto the CAD's! I chose to go with the "Medium" size tire from the LEGO® Technic series for this experiment.

To start, create a new sketch on your favorite construction plane, I chose top plane so it will automatically orient the way I want it to when I export it to the 3D printer (face of the wheel down/Z up). There are a number of ways to create the base profile of the tire, since I have OD (outer diameter) and ID (inner diameter) measurements I'm going to sketch two circles and use a symmetric extrude so the origin point stays in the very center of the tire. This tire does have two ID's, use the smaller one for the main extrude so we can use the chamfer feature to cut in the slope down to the larger ID once the extrude is finished.

I chose not to model the little nubs on the inside of the tire. They won't be needed for the larger utility tire and my intent is to create a brick-esque model not an exact replica.

Next up is the tire tread. I'm going to make an extrude cut to form this. Create a new sketch on the front face of the tire. I sketched in a construction centerline to align this sketch to so offsetting the next cut for the other side of the tire will be easier. This is tread spacing and depth from the tire measurement table. Tread length is how far this sketch needs to be cut into the face of the tire.

From here we'll use the circular pattern command in the create menu. Object type should be set to feature and for object select the extrude cut we just did. You can select it from the model, I find it easier to select the whole feature from the timeline on the bottom of the screen. Enter the number of treads from the measurement chart and voila, tread 1 is complete.

To create the second set of treads, start with a sketch on the bottom face of the tire. I chose to use a sudo shortcut and project (shortcut Ctrl+p) the front face that already has the treads on it into this sketch and then sketch in the offset tire tread. The picture of the sketch probably makes more sense. For me this was faster than calculating the the treads are offset by 9 degrees.

Then it's rinse and repeat with extrude cut and circular pattern. Now we have a 3D model that looks like a brick tire!

Since scaling the tire up to size is really easy, I'm going to include that here as well.

The print bed of the Bambu Labs 3D printer I'm using is 256mm square, so I'm going to scale the 30mm tire to 255mm OD, or 8.5 times. Pick the origin as the scale point to keep everything aligned to the center (you may have to use the little eyeball next to origin in the design tree on the left side to make it visible).

And BOOM! We have a 255mm/ 10" tire! (Fine, 10.0394"😅)

The Fusion model that is attached to this step is only the scaled tire, it hasn't been modified to fit the wheel rim yet. I thought this might make it easier to follow along. To toggle between the brick size tire and the larger tire you can drag the timeline bar forward or backwards. The next steps will add to this model.

I see two ways to go here. 1, just mod the tire to fit the 10" rim. Or 2, create a whole 10" rim model.

I'm tempted to just mod the tire since I'm just doing this for funsies and should probably be doing other things... But on the other hand the honey-do-list isn't getting shorter anytime soon and maybe it would be worth having a model of the utility wheel for future use?

First, the wheel needs to come apart. Remove the four 1/2" (13mm) bolts to split the wheel hub apart. Now the tire and tube can be removed. The clamshell halves appear to be symmetrical but there are differences on the inner wheel faces. I'm not adding anything to in inner "dish" so I'm ignoring that for now. OK, time to take more measurements!

First, OD/ outside diameter. I'm getting 127mm (yes, sticking with mm, not looking to have a Mars Orbiter imperial to metric mixup...)

Next, width. With the two halves bolted together finger tight I'm getting 57.6mm, which rounds up to 58mm. It would be better to have the new tire slightly "squished" instead of slightly too loose on the rim.

Metal thickness of the rim is 1.75mm. I'm not going to round this one up.

ID is a little tricky since the wheel doesn't look like it's a constant radius bend. The point where the wheel flange radius meets the start of the center hub radius is the most important IMO since this is were I'll probably want the tire ID to stop. This measures 42.39mm. I'm going to round it to 42.5mm. I have a plan for how to use Fusion to sudo cheat the rest of the ID, I'll show you in the next step.

Since it's easy to measure and may be helpful, we'll call the wheel halves 27.5mm thick/tall.

That should do it for the wheel/rim measurements. Time to jump back into Fusion.

To create the 3D model of the rim start with a reference sketch of the OD and diameter on the front plane. This sets us up with reference geometry for the next step.

In the insert menu select the canvas feature. Select the front plane again and pick one of the top views of the wheel to insert. I chose the one with the half wheel dimension shown. Don't worry about scaling it perfectly when you first insert the image, but do try to get the image aligned vertical and center.

Right click on the canvas image from the design tree and select calibrate. Pick two points that are a known dimension, thin this instance I'm picking the width, 58mm.

This is where we run into one of the limitations with this technique. You can see that the left side is more "fish eye" curved than the right. This is due to trying to take a picture of a curved object perfectly straight on and not quite getting it perfect.

Since we're experimenting, what do you say we just go with it and see how close we get?

Create a new sketch on the front plane and project the edge of the reference rectangle sketch into it (if it's not visible go to that sketch in the design tree and toggle the eyeball on). Next, use the offset command (Ctrl+o) to account for the metal thickness we measured, 1.75mm. Now, zoom in further and start sketching the profile of the wheel in the image. I used the line and spline sketch commands.

Add a centerline to connect the profile sketch then offset the curve again by 1.75mm. Next close the sketch using the line command. The profile created with turn blue if it's closed when the mouse hovers over it. I also chose to turn the intersecting horizontal line into a construction sketch (select line, right click, select construction) so it doesn't interfere with the next step of turning the sketch into a solid. Exit sketch mode.

Now, in the create menu select revolve. Then select the profile that was created in the last step. Next select the centerline to revolve around and poof, the wheel profile is now a solid body! (Turn off the canvas using the eyeball in the design tree to see the new solid body better).

I'll admit it looks more like a dog dish right now than a wheel rim 🤣.

Save the file. Now lets 3D print a small slice to see how close we actually are to the profile. Looks like we're close enough for what we need: height is correct, width is correct, flange/tire bead profile is very close, the inside sweep to the hub is off though (which sorta makes sense, this would be the furthest from the camera lense and possibly the most distorted area?).

The TPU print is probably going to take forever, so I should probably get going on the tire and come back to refine the rim hub more later.

Is there a better way to model this, absolutely. Is there an easier/faster way to model it, maybe, but I couldn't think of one at the time when I was making it. Since this is just something for funzies, this approach is fine IMO. It doesn't work for everything, and I'm definitely guilty of going down a rabbit hole or two... but I still like the quote from Voltaire - “Don’t let perfect be the enemy of good.”

To start finally kitbashing this rim and tire concoction I decided to start with tire width first. Uninflated, the 10" utility tire is roughly 80-82mm wide. The scaled brick tire is coming in at 93.5mm wide, I think this could be too wide in some instances where the wheel rides close to the equipment it's attached to. Since the wheel rim is 58mm wide, I'm thinking I'm going to go 78mm wide for this tire, or 10mm extra "meat" on each side of the wheel rim. Will I regret this later? Dunno yet, that's future me's problem!

Again, many different ways to do the width mod, you could do 7.75mm deep extrude cuts on the top and bottom faces of the tire. I want to do it in one step and have it symmetric to the origin, so I'm going to sketch a 78mm center rectangle on the front face and make a symmetric, extrude, cut, all, and select everything outside the 78mm rectangle.

Next, there's no more putting off mating the utility tire rim profile to the brick tire profile. So, right click on the rim model and insert it into the tire model. Since we're modding the tire, not the rim (yet...) its easier to do it in the tire model instead of the rim model. Now a joint needs to be added to put the rim into the center, center of the tire (as opposed to centered concentrically but on the top or bottom face of the tire). Go to the assemble menu and select joint (or Ctrl+J). (You may be prompted to "unground" the model from the parent, right click on the rim and select unground). Make sure a rigid joint is highlighted and select the center of the bottom face of the rim. Then select the center, center of the tire, it may help to turn on the origin and select that.

With the rim inserted into the tire model, it's obvious the chamfer I created earlier in the tire model is not helpful. To remove it right click on it in the timeline and suppress it.

At this point it's going to be helpful to have a section/cut out view. Select this from the inspect menu and then select the front plane.

OK, another sketch on the front plane (aren't we glad everything is center centered now!), project the top and bottom of the tire and the inside profile of the rim into the sketch (Ctrl+p). Then create a closed sketch up to about where the wheel flange ends. And now revolve join the sketch to the tire body (might help to eyeball off the rim in the design tree). Sooooo close, in the create menu select mirror, set it to features and select the last revolve feature and select top plane as the mirror plane.

Holy Guacamole, do we have a life size LEGO® utility tire?!?!?

OK, that's pretty cool, I just need to do one more thing... Turn the rim yellow. Back in the rim model, right click on the body in the design tree, click appearances and change it to paint/glossy yellow.

YES!!! Finally getting there!

Buuuuuuuuutttttttttttttttttttt... There's more CAD'ing to do before we can 3D print it.

Fricken spoilsport...

I know, I know... All CAD no play makes Makerneer a dull, um maker?!

Alrightly, focus... The tire model as it sits right now is a pretty excellent representation of a life size brick tire. But it has massive flat overhangs for starters, which will generally 3D print like fecal matter. Especially with TPU.

Speaking of fecal matter, don't forget to save everything right now!!!

For this project I'm willing to compromise exact replica-ness in exchange for a tire that will have better 3D printability. So first order of business is to add chamfers (or angles) to the flat overhangs. This will eliminate the need for support material on the tire treads and I don't think it will really detract from the overall look. So, pick two opposing treads, click on the chamfer button, I was expecting it should be an equal distance chamfer of 12.75mm, but Fusion wants 12.74mm and I'm not in the mood to fight with it 😂. An Den, you guessed it - circular pattern, pick the chamfer feature and Bob's your uncle!

(Where did that phrase come from, it's odd right? Woah, way more to it than I thought! https://en.wikipedia.org/wiki/Bob%27s_your_uncle ).

The next thing I want to change is to add a slight radius to the tire tread corners. It might be fine as-is, but sharp corners tend to be good places for warped edges to start in my experience. It's probably a good idea to have this as a separate feature so it can be modded without impacting the chamfer feature. Anyhoo, right next to the chamfer button is the fillet button in the modify menu. Put a 2mm fillet on the inside corners and a 1mm fillet on the outside corners and yep, circular pattern - you're getting the hang of it!

Last, a fun cosmetic touch. Tires usually have their makers mark on the side, so I think these need to say "MAKERNEER" on the sidewalls. Create a sketch on the top face of the tire. I want the text curved, so I made a circle that's 1/4 of the distance from the inside to the outside of the sidewall. I used a construction center line and then another line between the center of that line and the inside edge. This sounds overly complicated, I know, but I did it this way so it will update itself to always be 1/4 of the way up the sidewall even if I change the diameter of the tire later. Couple extra clicks now saves future me a little bit of headache.

Anyway, I'm rambling aren't I? I need to 3D print something STAT!

Focus... Almost there... In the create command, select text, on path and select the circle. Type in the text and hit ok. Then it's extrude cut that sketch 0.3mm into the face of the tire (emboss feature would also work here). Repeat for the otherside, except project the 1/4 circle from the first sketch and they'll all update together. Why .3mm? This ensures at least one 3D printed layer will have this feature (Assumes a standard .4mm nozzle). Some slicers do funny things. But regardless, that's all the CAD! Finally lets GOOOOOOO!

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Oh right, Fusion File attached. And .step, and .stl. We'll need that for the next step won't we... Got ahead of myself there... To export these files out of Fusion, right click on the model in the top of the design tree, select export in the menu and pick your favorite flavor of digital file.

YES! Finally, this idea is about to come out of my head and into real life!!!

Grab the file from the previous step and pop it into your favorite slicer. I'm using Bambu studio. I want this tire to do tire stuff, so it needs to flex some, but not too much. I'm guessing at the goldilocks ratio here, but I think 5 walls, 5 shells and 5% infill is going to be about right. The center hub area needs to match the profile of the wheel, which means support material is a necessary evil here so turn that on. Also, since nearly all of the print bed is being used, I added a pause at layer one before the print starts so the purge and calibration lines can be removed. Otherwise this would print over the top of them and we don't want that.

I unfortunately found out somebody used more of the high flow TPU than I thought they did (It was me...) so I will be using the "generic" YOYI TPU filament. My exact settings are in the attached .3mf file. Slice and dice and wouldn't you know it will take about two days to find out if we did the dang thing right or not...

How about we compromise and print a proof of concept in something faster?!

Good plan.

While we're thinking about it... since I'm not 100% confidant in the hub profile, lets also print just a portion of the wheel to triple check things. This is really easy to do in the slicer with the cut command. And will only take about 30ish minutes to print for the test.

Whooops... it hits the rim. Good thing we tested. Back to Fusion to fix it. I see two ways to fix this. 1, change how far the hub extrude extends down the profile of the wheel, or 2, add a fillet to that edge. I'm going for #2, so drag the timeline slider on the bottom of the screen back to the hub revolve feature. Add a fillet, my eyecrometer says 10mm is too much and 5 isn't enough so I went with an 8mm fillet. Update the mirror feature to include the revolve and the new fillet, slide the timeline back to the end and bam, done! Easy peasy.

(That's another weird saying isn't it? Is it British too like "Bob's your uncle?" https://en.wiktionary.org/wiki/easy_peasy_lemon_squeezy it is British again, and it appears to be from a detergent commercial - "Easy peasy lemon squeezy.")

(Note - the models in the last step are the updated versions with the fillet added)

One more small profile test print (being able to test and iterate quickly with 3D printing is awesome!) looks good! OK, lets print a whole proof of concept tire in high flow PETG!!!!!!!!!!!!!!!!!

One sleep later and it's now real! It's undeniably brick-like, it fits great and I love it!

That means it's officially time to load up some TPU into the 3D printer and send it on it's 2 day journey. My .3mf print file is attached to this step.

After seeing the proof of concept tire mounted on the 10 inch utility wheel, I knew I had to do one more thing to sell the Brick-esqe-ness of the thing.

Paint it yellow!

I gave hub halves a quick clean and hit it with a couple coats of yellow spray paint. Yes! I love it when a plan comes together!

Just need to wait for the paint to dry and the 3D printed tire to finish now...

Aaaannnnndddddd... They're done! Assemble!

Note: Removing supports from TPU can be a PITA. Do the best you can, sometimes a little heat helps too. Fortunately this area will be covered by the wheel hub.

I also decided the wheel hardware needed a quick polish for it's photo shoot so I hit them with a wire wheel real quick (don't tell the other wheel... 🤣). Bolt the wheel back together again. No need to put air in the tire this time though!

Now, the only thing left to do is put it on the log splitter!

YESSSSSSS!

It's glorious, I don't quite know how to explain how happy this makes my maker brain!

But I know what you're going to ask next: How tire-y is the tire?! Surprisingly tire-y, which turns out to be really hard to quantify so checkout the video attached!

Well, before I clean up my brick mess, I wanted to share one more "hack" with you. Not only are LEGO® bricks fun to play with, they make really good temporary jigs. This is one I made to hold clothes pins so I could laser engrave a decent size batch repeatably. It worked great! (I'm not showing the finished clothespins because they haven't been delivered yet and I don't want to spoil the surprise for the friend I made them for).

Doggo "helped" with this one a little bit, but was not impressed when she found out the bricks weren't treats... My last instructable at least had sticks so I think she liked that one better 😅.

Something else I probably should have figured out sooner than now... what do the numbers on the side of the tire mean? 4.10/3.50-4 seems odd, this doesn't seem to align with car tire numbers (width in mm, sidewall ratio, diameter in inches) so what's the deal? OK, it is similar https://lappwagons.com/blog/how-to-read-tire-size/ So according to that info this is supposed to be a 4.1" (104mm) wide tire with 3.5" (88.9mm) tall sidewalls and a 4" (101.6mm) diameter rim. This is way different than what I measured! Am I going insane in the brain? Nope - Double checked the measurements on the hand truck I have that uses the same tires: Overall tire diameter is 10"-10.25" (whew!), tire is ~3"-3.25" wide when inflated, not anywhere close to 4.1" and the sidewall is closer to 3" than it is to 3.5". And we know from step 3 that the rim is 127mm or 5" diameter not 4". That's way off!?!? And I'm not finding any good explanations online... Anybody out there know what the deal is with tire size not matching IRL measurements?!

OK, I think the honey do list is calling... and that means I should wrap things up for today. Thanks for hanging out and giving me an excuse to play with my LEGO® bricks again!

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