Hollow Wheel Manufacturing & Shipping Update #18

Hey Everyone,

Sorry for the delay in the update. I have been busy durability testing. It's going really well. Planning for production now.

Durability issues are fixed as far as I know so far. I'm pretty happy with it. Since the last update, we created 2 more custom compounds; there were two rounds (batches 6 and 7) of material optimization. Batch 6 (shown in Update #17) was the Hollow Wheel made from our first attempt at high temp formulations. While there have been no durability failures and I am confident I fixed the durability issues, the grip was not great. We took this data to optimize and create batch 7 compounds to maintain durability and improve grip.

I have validated that a low melting point and low strength at high temp of the material was the direct cause for the failures that I was seeing. 

I was able to simulate a 600lb person (170lbs on one wheel) for hundreds of miles and it went without a hitch with batch 6&7. Also a lot of ride testing with heavy friends. This took a very long time. 

Where is the timeline?

I am waiting from the factory to understand the exact timeline. They just had a week long national holiday. Also, there are some global supply chain challenges that we are working around (keep reading). But the silver lining is that I will have one very soon and there isn't much left to do.

I will be back in about a week with a timeline. Sorry. I know. This is very annoying.


We won't be using urethane for the wheel because with urethane you can't get very high melting points and it breaks down very easily. So I have been focusing on the new rubber compound. Read more below.

At this point, I feel like I have done everything I can do with the resources I have. I am confident in these wheels and I will begin with the initial batch to make sure all the suppliers can work in unison and maintain high standards of quality. I am not saying there will be 100% perfection and 100% of the wheels will be free of defects because that is impossible, but I am comfortable in the design and the materials to begin on the first production batch. If there are, I will replace it and make it right.

There are some global supply chain challenges ahead but this was the biggest step. See below.

Fixing the Grip from Batch 6:

From Batch 6, we increased the melting point of the compounds. Usually when you increase melting point, you end up making the wheel harder and/or you add other chemicals that have different molecular structures. It's hard to predict how it can change grip without a lot of experimentation. This is the case for batch 6 where we started experimenting with a different rubber compound that had a different molecular structure than urethane. Grip isn't usually measured in standard mechanical property tables, so we had to experiment.

How does a wheel generate grip? Here is a little chart that explains it:

In laymen terms, the road is sort of like one giant piece of sand paper. It has a lot of very tiny crevices. To get more grip, the wheel basically needs to latch onto these little crevices. Generally speaking, the softer the rubber or urethane, the more grip it will have - because it can reach into these little crevices. At the same time, if you have a wheel that is softer, then you have more deflection of the structure of the wheel. When you have more deflection (movement), the wheel starts to get hotter. With more heat, you have degradation of the material. After the material gets hot, then it becomes greasy and then your grip degrades. It is a very fine balance in (including but not limited to) how you tune the structure, what temperatures it can endure, and also what material your wheel is made of.

Once I had figured out that the melting point and heat deflection temp was the route cause in my issue, I had to focus on grip testing. So I had to do a lot of skid pad testing (basically driving in a circle as fast as you can and recording your lap time). Actually, it is a half of a skid pad because it is only one circle. With a full skid pad, it would be a figure 8.

For those that don't know what a skid pad is and why it is useful for assessing grip:

Here is a quick video of my half of a skid pad:

Here are some skid pad times (going in a full circle). Compound 2 is part of Batch 7 and an evolution of compound 1. I didn't bother too much with the urethane that we developed with both Batch 6 or 7 because, well, urethane doesn't have the durability that I needed. See the durability section as to why.

How to read the table: The major things are just to take a look at the average time and the standard deviation (STD Dev) time. A wheel with the highest grip will have the lowest time. A very low standard deviation will mean the time is consistent. I have an infrared lap timer that is supposedly accurate to .001s. The new compound 2 is 5.5% faster than Compound 1 and 4.31% faster than a urethane Hollow Wheel. As I am writing this, I really should have tested against a popular urethane wheel so you can see the difference. I'll do that very soon.

Other things left to do:

There are not many things left to do.

  • Changing thread color to black and core to white. Awaiting time estimate.
  • Adding printed logo to the cover. Awaiting time estimate.

The suspension insert molds have to be modified due to me changing the internal geometry back in Update #14 (https://momentum-boards.com/blogs/news/manufacturing-and-shipping-update-14). It is very likely that I will ship the wheels first and those that ordered the suspension inserts will ship those separately. I didn't want to change the suspension geometry till I figured out the reliability issue. Right now, I am trying to get the wheels out as fast as possible.

Next steps in production:

The molding factory is currently very busy producing products for the winter holiday rush, so we are trying to jockey for a production spot at the factory. Still waiting. Here are things that we have to do:

  1. Secure raw materials. Order and secure big batch of raw materials (thread and core). There are some production capacity shortages on plastics/rubbers. See below. Awaiting on this timeline.
  2. Get raw materials to molding vendor. Ship materials from material vendors to wheel mold vendor. All vendors are close to one another, so shouldn't take longer than 1 week.
  3. Setting up all the molds into machines. Machines need to be prepped ~2 days.
  4. Training the staff. We will be doing the first run so staff that have not been close to the project should be trained to keep on manufacturing process of the Hollow Wheels. Set up production. begin
  5. Molding of wheels. Awaiting timeline but this usually takes 20 days or so for the batch size I need.
  6. Quality inspection. We are 100% inspecting these wheels as best we can. To make sure all material specifications and molding parameters are not deviating, we will produce a batch of 200 or so wheels. I'm designing processes for visual inspection of wheels as well as random inspection to inspect for proper bond between the core and tread. After this is approved, then all the wheels will begin. Still awaiting alignment on timeline from vendor.
  7. Packaging into boxes. Preparing for sea cargo shipping 
  8. Sea shipping, Port, & Customs clearance. Get ahold of shipping container and ship. There is a big global supply chain challenge. See below for explanation. Usually 4-6 weeks, but it could be 6-8 weeks delay. Hard to tell right now. Will get better estimate when closer.
  9. Fulfillment. Arrive at my office in Southern California. Start shipping to you all. ~5 days.

I'll be providing this in a ghantt chart (like I have done in the past updates) in a week. Still awaiting timelines as seen above.

Some supply chain obstacles that are adding extra time.

I don't know why this had to happen when I'm trying to release the Hollow Wheels but a perfect storm has been created by COVID, natural disasters, radically increased appetite for consumer electronics (fueled by the pandemic), and the brief recession has manifested the following supply chain issues related to: 

  • Dramatic increase of Sea and Air freight shipping cost & lead times
  • Scarcity of raw materials related to anything plastic
  • Energy power outages leaving businesses incapable of running https://www.bbc.com/news/business-58733193
  • China had a one week national break from the 1st to the 7th. 

Mainly the China to USA shipping transit as well as shortage of anything plastic is a major contributor to some of the delays on attaining the timeline.

The obvious question is this: "Doug, why can't you just air ship the wheels?" Reasoning: I would love to but it would bankrupt me.

I priced it out and I unfortunately cannot afford to choose air freight. An equivalent size and weight package sent via sea shipment costing $195 would mean that same package could cost $1000 by air. See reference here: https://www.freightos.com/freight-resources/air-freight-vs-ocean-freight-making-the-decision/

Sea shipping can usually be 4-6 weeks. However, with big shipping time delays, it is looking more like 6 to 8 weeks as I have experienced such in other products I sea ship.

The other bad news facing is very long sea shipment transit times. Ports are backed up. Wall Street Journal says that there are a hundred thousand shipping containers just waiting outside the sea shipping port waiting to be picked up by customs. Customs departments are evidently spending up to 3 days per container. Reported back from the Wall Street Journal: https://www.wsj.com/articles/u-s-ports-see-shipping-logjams-likely-extending-far-into-2022-11630843202

    Just so you know I am not making this up...

    Rising chemical cost and shortage of raw materials.

    Taken from the Boston herald - "The root of the problem has become a familiar one in the 18 months since the pandemic ignited a brief but brutal recession: As the economy sank into near-paralysis, petrochemical producers, like manufacturers of all types, slashed production. So they were caught flat-footed when the unexpected happened: The economy swiftly bounced back, and consumers resumed spending with astonishing speed." 

    This means all the plastic pellets which makes up for basically everything you're looking and holding is on a shortage too. This adds difficulty when we are getting our materials and we are still waiting to hear back. With this scarce material, the price goes up but that's my problem and not yours.

    Reported by the Boston Herald: https://www.bostonherald.com/2021/10/02/from-paints-to-plastics-a-chemical-shortage-ignites-prices/

    Believe me, I am working around the clock to get these wheels out. Please do not hesitate to reach out at any time.





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    • I love the detailed updates and getting insights into the engineering challenges that go around producing the wheels. As an engineer I feel this has been a gift I’m getting for backing this product. Thanks for putting the effort in writing these updates!


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