So, I cracked the rim on my Veteran Sherman. It sucked, but I’m okay and survived without falling off the wheel. Here’s the story of what happened, and what I’m doing to prevent it from happening again. Actually, I’m not 100% sure if I’m taking all the necessary precautions to avoid fracturing my EUC rim again. But, it’s a balance between enjoying the ride and avoiding the hassle (and danger) of breaking an electric unicycle (EUC’s) most important component while it’s moving at speed–its only wheel.
Tools You’ll Want for Replacing an EUC Rim or Tire Change
There are host of tools you’ll need for replacing a broken rim or changing a tire–many of which you may already own from other household projects. Here are a few kits and tools that I recommend you have around when you need to do some work on your EUC.
- 24mm pass through spanner wrench (x2)
- Metric hex/allen wrenches
- Rubber mallet
- Philips head screwdriver
- Pliers
- Razors
- Silicon sealer (for waterproofing motor cover and shell)
- Block of wood (helps with roll cage removal)
- Work bench
- Markers
I’m certain you already have most of these tools already. But, if you’re starting from scratch and want to know what essential tools and supplies you’ll need to repair anything on your electric unicycle, the list above is a great start! See more about this below.
What Was I Doing When my Electric Unicycle Rim Fractured?
I was riding my Veteran Sherman (an amazing electric unicycle for long range cruising on streets) with a group of other riders at night. As a 160lb rider (or about 170lbs fully geared up) I’m not light or heavy. I’m about average weight I think for a performance electric unicycle.
My stock knobby tire pressure at rest was at 38psi, which is above the 30-35psi most riders say protects the rim from cracking. Suffice it to say, this tire pressure did not save my rim from failure. More about this below.
With about 1500 miles on my stock rim and tire, it shattered.
Where Was I Riding During this Rim Breaking Event?
I was riding on normal roads, paved with asphalt with your typical cracks and worn surfaces here and there–nothing off road or technical. This is your typical city or township street where you may ride a bicycle or an e-scooter with little issue.
We were cruising at speeds of between 20 and 30 MPH cruising through downtown Wallingford, Connecticut. I forget the exact street, but it’s a typical three or four lane road with a bit of evening traffic.
At the moment I hit the pothole I was following my buddy riding a Gotway/Begode Monster Pro. He had the best light setup to see ahead of him and he also knew the directions. So, naturally , I was following him. Being in front of me, he may not have seen the dip in road as it was hidden as a sewer manhole cover with sand on top.
I was off to his right a bit, and because it was too dark I didn’t have any time to swerve. Given that the sewer manhole cover had sand on it, there was not enough contrast to see the depth of the dip in the road.
Here’s the video captured of the event.
I knew another rider was behind me–who video recorded the whole incident–so, stopping suddenly wasn’t a good option. My instincts told me that going straight and hoping to stay on the wheel was the safest option.
Crack!!
My heart skipped a beat, and the breath in my chest stopped. The gunshot of shattered metal grinding around the inner shell of my Veteran Sherman shook me, literally and emotionally.
The Veteran Sherman has an Achilles Heel, Literally
In Greek mythology, Achilles was a neigh invincible warrior. He defeated enemies large and small, and overcame insurmountable odds where other men failed, miserably.
But, as we all know, this veritable demi-god was brought low by a single poisoned arrow shot to his heel. In the same way, the tire on my Chinese-made electric unicycle rim was destroyed by a single hit.
The catastrophic failure of the rim shattering allowed the high pressure of the tire to expand against the inner shell’s dimensions. As the tire spun, the friction of the rubber against the shell of the EUC created enormous heat!
For the 100 feet or so that I was able to ride the broken EUC to a controlled stop, the spinning tire literally melted the inner part of my Veteran Sherman shell.
The heat actually “cooked off” the plastic inner shell, creating an acrid smell like burning hair. It’s difficult to describe. Smoke poured out from my Veteran Sherman, wafting through the front headlight beam like in some low budget music video with smoke machines and strobes.
I gagged at that smell of burning rubber. Not sure if it lead me to tears, or I was just sad as I inspected my now fractured identity and deflated ego–as certainly, we are all bound to feel this connection to a machine that takes us places in such a unique and incredible way.
I do know I was disappointed, especially seeing the melted rubber and plastic on my inner shell like some sort of modern art installation at Burning Man where you don’t know whether to laugh or cry.
In hindsight, of course–after the initial shock wore off–I was quite pleased that I lived through that experience and that the Veteran Sherman did not self-implode all things considered.
I was riding at 25mph and hit a 2″ dip in the road. The edges of the depressed manhole cover were relatively sharp edged, so there must have been quite a bit of force exerted on my rim as the tire sidewalls compressed to absorb the impact.
Later on, my inspection of the wheel showed no other damage to the wheel except to the rim and a bit of burned off plastic shell casing that you barely notice after I cleaned up the debris.
How Do I Think the Veteran Sherman Rim Fractured?
All electric unicycle rims bend or break when placed under forces they are not intended to withstand. Given the cost of constructing an electric unicycle, I’m not surprised that the alloy in these rims aren’t of a more durable quality.
As I understand the engineering, all electric unicycle rims are made with cast alloy. Basically, an EUC rim is made of molten metal that is poured into a rim-shaped mold. When cool, the cast part is removed from the mold and post-processed with different methods to strengthen it (maybe a heat treatment?) and make it look good.
RELATED: VETERAN SHERMAN EUC (MY FULL REVIEW)
Of course, an EUC rim needs the right tolerances for the tire to fit properly, as well as have all the fittings, e.g., screw holes, for the hub motor and magnets.
To keep costs down with manufacturing productivity up, these processes are reduced to their lowest common denominator. Steps are skipped, or processes applied with the fewest care for outcome and resilience in the metal rim.
What Do Manufacturing Cost-Saving Processes Mean for What Happened to My Cracked Rim?
I can only speculate that 3 things happened:
- The rim had intrinsic flaws from the factory, which made it vulnerable to breaking with repeated impact
- The metal component slowly degraded with with repeated stressors from riding my Veteran Sherman
- The force of impact was too great for the rim to handle
1. Intrinsic Metal Flaws
If my rim was manufactured with flaws due to poor quality control or sub-par processes, e.g., bubbles, fissures, then it would only be a matter of time before a sufficient impact exploited this weakness.
The alloy metal heat cast and cooled with improper temperature could lead to a poorer quality product. When it comes to constructing metal parts through a casting process, properties like “compressive yield strength” and “tensile yield strength” are important to the structural integrity of the resulting part.
Compressive and tensile strengths vary with different types of alloys, which would affect the overall durability of a metal part. In general, tensile strength qualities are more important for e-unicycle parts that will be exposed to repeated stress from tension when in use.
In heat treating, the alloy is heated in an oven and cooled rapidly in a furnace with a large flame or quenching bath to produce a material with superior tensile strength. Since high heat temperatures are required to achieve the desired results, which often warp or change the alloy chemistry of any metal parts that contain different mixes of alloys (like castings), increasing the cost and complexity of manufacturing processes–all things I’m sure EUC manufacturers like Ninebot/Segway try to avoid.
I believe our rims were made with sub-par alloy materials, which made it prone to cracking when stressed over time by riding the unicycle.
2. Metal Fatigue and Fracture Point
The metal alloy in my rim could have started out with an intrinsic weakness that eventually led to fracture during repeated stressors like all electric unicycles go through when in use.
Another possible cause of metal fracture is metal fatigue , which occurs in materials subjected to cyclic stress over time. Metal fatigue is a process in which tiny cracks propagate slowly, causing the material to fail after it’s been stressed many thousands (or millions) times. As the crack grows, the material will eventually fail (see above).
I’d like to think that my rim reached its fatigue point during an especially violent impact when I hit that pothole.
Your electric unicycle might be especially vulnerable if it falls in such a way that stresses one part of your rim more than other parts. In this case, the alloy material would slowly degrade from repeated stress in that localized area until it eventually cracks from accumulated fatigue.
3. Strong Force of Impact
Finally, I think my rim cracked from a combination of intrinsic metal flaws and metal fatigue points but could have been saved if the impact wasn’t so violent or not concentrated on one localized spot of the rim.
As I was riding straight on my EUC, the left side of my tire came into contact with a the edge of a pothole that I just couldn’t avoid–and this was enough force to crack my rim.
My rim may have been able to withstand multiple instances of less intense stress, including the hundreds of bumps I cleared navigating my local city streets. But when an impact exceeded its tolerance threshold, it broke under pressure. After that point–and with repeated stressors–the fracturing process could only continue until my rim reached metal fatigue point or developed more tiny cracks.
In my case, I think a combination of factors led to the quick demise of my rim . In other instances, unique to each rider and riding environment, it could be one problem or another that eventually leads to metal failure.
How Did I Get my Rim Fixed?
No EUC rims are covered under warranty by any distributor that I know of. I purchased my Veteran Sherman from eWheels.com, which have been my favorite vendor for a while now.
I informed eWheels of my fractured 60mm rim, and they quickly let me know that they had a few in stock. Given that I thought my inner tube or tire might have been damaged, too–they underwent serious heat and rubbing damage against my EUC shell when the rim cracked–I also asked for these replacement parts, too.
To my happy surprise, eWheel preinstalled the inner tube and tire for me on the new rim when they shipped it. For those that know how much can go wrong and the time it takes for changing a motorcycle tire and inner tube, this was a great service!
It took a week for the rim and tire combo to arrive from across the country. The package arrived packed really well and upon inspection, the rim was perfect and true (round as I could see).
Video Tutorial for Replacing Rim and Tire
I used Shawn Duffy’s video to learn how to remove my wheel from the Veteran Sherman, and how to remove and replace the hub motor into the new rim.
See the video here:
The entire repair process took me about 5 hours to complete from start to finish. I’m sure for first timers it’ll take around this long for you, too. With experience, you could probably do the job quicker.
Given that the Veteran Sherman is nearly 80 lbs, I was physically exhausted. Part of the repair effort requires that you lift the EUC and flip it over several times to access both sides of the wheel.
The Key Tool You’ll Need to Replace Your Veteran Sherman Rim or Perform a Tire Change
Of all the tools you’ll need to replace your rim, the one that most of us may not have an easy time finding in a local hardware store is the 24mm pass-through socket wrench.
Although there are ways to circumvent not having this tool available, it will save you a TON of time. The 24mm pass through socket wrench allows you to loosen and tighten the axle bolt around both sides of the motor wheel.
The pass-through aspect of the tool allows the motor wires to safely hang loose while you unscrew the bolts.
You’ll NEED TWO 24mm socket wrenches for an easier time with the bolts. The two wrenches let you use both your arms to torque the axle bolts with enough force.
Yes, I recommend two of these wrenches for the job. It’s a good thing they are affordable–and you’ll probably need them again when you do a tire change.
Other Essential Tools You’ll Need for Maintaining Your Electric Unicycle
- Metric hex/allen wrenches
- Rubber mallet
- Philips head screwdriver
- Pliers
- Razors
- Silicon sealer (for waterproofing motor cover and shell)
- Block of wood (helps with roll cage removal)
- Work bench
- Markers
Conclusion
Everyone will encounter an issue with their EUC. It’s a machine after-all, and they will break or need maintenance at some point.
In this case, breaking my Veteran Sherman rim may have been a blessing in disguise as the process taught me a lot about my EUC. It forced me to learn how to ride more carefully to avoid obstacles for one thing.
I also have a new found respect for the fragility of this new class of personal electric vehicle. Though I’m disappointed in the sub-par resilience of the wheel rim–among other parts in the EUC–I also realize that this is a new industry for us.
It’s growing and improving all the time. In this optimism, I’m glad there is a community of other riders out there that are helping each other out. If it were not for the forums and other internet gathering places, e.g., Facebook, YouTube, I would likely never have engaged with the EUC hobby/sport at all.
I hope you found this article helpful, interesting, or simply entertaining. While it may seem overwhelming in the beginning with working with these machines, start out slow. You’ll find that you can do it–whatever repair/maintenance project you’re working on!
Indeed, I cracked the rim on my Veteran Sherman. But, it hasn’t killed me, and I think I’m a much wiser EUC hobbyist for the experience now.
Thank you for reading! Leave me a comment!
Ride safe 😃
