Maybe you already know this but it looks like a fracture propagating at the 6:00 Position
1 Like
Haha beat ya too it
3 Likes
Yes, looks like you beat me by 2 minutes.
1 Like
So with injection molding, the molds typically have many part cavities in a single mold. It could be 4, 12, 48… There might also be more than one mold. So with each cavity not being identical, it is not surprising that some wheels have very pronounced part lines and others are relativley clean of part lines.
Even though there is varibility in the parts and where they split, there does seem to be a general pattern.
The plastic that forms the bearing socket does not seem resilient enough to hold the bearing in place so the bearing socket fractures either at the weakest point ( a large part line) or at the thickest points that stretch the least (spokes). Spoke fractures seem to be the most frequently occuring. In some cases the socket has split wide open before the customer mounts the wheels.
The pictures that zoom in to the bearing sockets seem to show some extremly poor quality plastic that is pitted and riddled with defects. We don’t know if the problem is low grade plastic or poor temperature control during the molding or just the fact that there is no glass fiber re-inforcement.
Whatever the cause, it does seem that any core could fracture at any time and in more than one place.
2 Likes
It’s not this lol. Look at what I just did in the pics thread
@isabar
Thanks for the info on what the rest of the industry is using for wheel cores and also for your perspective on what the limitations of PC are for wheel cores & bearing sockets.
I have already talked to my contact at iWonder and suggested they changed to TPUs. They said they will forward to their engineers.
3 Likes
Is TPU is good on it’s own without glass fiber? I’m curious because @jeffwuneo stated that the mold for the I-wonder core does not use a steel that is hard enough for GF. I supose it would be a good thing for future customers if I-Wonder could quickly switch to an appropriate plastic – without having to re-do all of their molds. And hopefully customers with cracked I-wonders could get stronger replacements. That would be a good outcome for everyone.
1 Like
with a properly designed hub, most wheels do not need TPUs with glass fiber. the idea is that you want the hub to be an additional shock absorbing element beyond just the urethane. also since bearings are pressed into the wheels, you need a material with some give. too much glass will result in the bearing seat cracking as you press the bearing in.
1 Like
Thanks. Your a good teacher.
in case you are not aware, I am Ilan… the founder of Metroboard!
8 Likes
Oh hey, its “crank wheel bearings down with no spacer until hard stop then back off one turn” dude! Welcome!
6 Likes
I still stand behind that. you can do whatever you want, but I have never had any failures from this method.
2 Likes
and I have been building Electric Skateboards since 2003!
3 Likes
Why does it pertain to electric skateboard? lol. My question is 1) how do you get a hard stop in plastic core? You’ll crush the core before it hard “stops”. 2) bearing damage? hard stopping a bearing will pit the races. Ask any quality machinist. 3) why not just use spacers.
Idk what you imagine hard stop means, but by definition it means the nut stops at a definitive point, any further torque will only turn the nut marginally while increasing clamp pressure drastically. This is how torque to yield concept works. Additional tightening will strip said fastener. I guarantee on a plastic wheel, the nut will keep going until it bottoms out on the axle and the core is destroyed.
2 Likes
Totally agree and this is aided by the spoke design.
The issue is the material used or the method of making the hubs thay currently follow. Wether that’s temps and cooling, material or mix % of material I’m only able to speculate, for this reason I have not.
But this is a Issue several people have had so fare. I wonder have trying to hide it by banning and deleting posts and denying it in press realises with out right lies of only case reported to them. and this is not ok in my eyes and as a community should be in uproar and vocal about. (Remember any other company that did this?)
Company’s stating lies as to maintain profit at the neglect of safety is why the law has to be constantly updated closing as many loopholes as posible
2 Likes
I must ask why are you so bent on the material. First it’s they must switch to gf nylon, now its tpu… What makes you think PC/ABS is not strong enough if properly injected? what makes you think if they switch to TPU that they will learn how to inject it correctly? For all we know they can switch to titanium and have it crack out of the forge because it’s the procedure they have wrong.
Jeff had mentioned pc/abs is strong enough, and ian is right that it needs to be flexible, which is what the abs is for.
1 Like
you don’t need a bearing spacer to keep you from overtightening. just like any other nut in this world that you may need to tighten. you use sensory feedback from your fingers as you tighten that goes to your brain and tells you to stop turning. It’s not rocket science! you don’t need a bearing spacer to idiot proof this process!
5 Likes
You’re absolutely correct! I snug up nuts often, or I pre-load bearings with proper angular tension. However I have never seen one spec sheet ask for “hard stop” on a bearing preload… Nor have I seen hard stop + back one turn. Seen plenty of torque specs even, or preload pressure ranges. Hard stop means lock that bearing until it cannot move.
because TPU is tried and true by all professional wheel manufactures in the US (including AEND and LABEDA). These two companies manufacture 90% of the US brands out there include ABEC11, Seismic, Loaded, and pretty much all other US brands. TPU is chosen because it has the best adhesion to Urethane (which is another source of wheel failure, aka urethane separating from the hub), and it’s also a very elastic material, which means it will flex and not break. Glass filled materials are not good for wheel hubs as they are at risk of becoming too brittle, since forcing a bearing into a bearing seat with a press fit, requires a material with give. And also the repeated impact of riding on skateboard wheels with too stiff of a hub material can also cause them to crack.
5 Likes