I have learned something new and interesting – the difference between hot-casting and cold-casting of polyurethane wheels (I did not even know there were two processes for making polyurethane wheels).
There have been a growing and significant number of posts on various e-board forums about how the polyurethane of hub-motors is cracking and breaking up far too quickly; and not just the usual budget companies, top end boards like Entertion’s Raptor seem to also have batches with the issue (Entertion aparently identified a bad batch). A few companies, inc. Backfire, Entertion and Verreal, offer replacement polyurethane for the motor; however, there is a concern, which I share, that there is a fundamental problem here with a lot of the hub-motors in the market right now.
Part of the challenge, and why hub-motors require high-quality and not cheap low-quality polyurethane, is that the polyurethane unlike with a real wheel is effectively just a wrap or sleeve around the hub-motor. Not only this the amount of polyurethane much less than a real wheel (why there is more vibration to the ride), but the hub-motor will also be getting hot and heating up the core of the wheel.
One of the posts on /r/electricskateboarding highlighted (thanks Predator Boards) that the potential biggest issue is how the sleeve is made, namely if the polyurethane has been cold-cast or hot-cast. In summary (and I am far from being an expert here): hot-cast, where the wheels are baked in an oven, is more expensive but produces high-quality polyurethane wheels (all duros); as opposed to cold-cast, where it is set in a mold at room temperature. In addition, cheap cold-cast wheel often don’t use a vacuum as part of the process, to take the air (micro-bubbles) out of the wheel.
And, in response to “how do we spot if a wheel has been cold cast or hot cast?”:
This isn’t a guarantee, but hot-casted thane usually goes through a vacuum/compression process. You can inspect the inner edge of the wheel and see if there are any air bubbles. If there are, then it’s likely cold-casted. If there aren’t any, then it may still be cold-casted and vacuumed.
I have not 100% understood all of this, and I need to do more reading, but it has first-off helped me with the question: “why don’t I just buy those cheap wheels from Ebay?“. As for hub-motors on e-boards, I just think that you have to accept it as part of the downsides (against their upsides), especially if you are buying a budget board which will almost certainly use cold-cast urethane sleeves. Having replacement sleeves is a distinct advantage with some makes, although there is an argument that just replacing the whole hub motor is actually the right/safer option. I think it all just reinforces the recommendation to only buy an e-board where you can fix and replace the parts easily. Cold-cast wheels are just going to damage easily and need replacing.