Crankset Failure and Deceptive Specifications on Giant Electric Mountain Bikes

Tom W

New Member
The following is a summary of my experience owning, albeit briefly, a 2017 Giant electric bike. To cut to the end, it did not go well. I returned the bike to Giant after the events I describe below, but feel that I have an obligation to let other riders know what happened, as I believe there are serious safety and honesty/integrity issues involved.

Based on a successful test ride of the Giant Full E+1 electric mountain bike, I purchased a 2017 Giant Full E+0 in mid-June 2017. My only major reservation was the square taper crank interface, as these have not been used on real mountain bikes well over a decade. But given Giant’s size and reputation, our satisfaction with the three Giants we've owned over the past 15 years, and the fact that their website listed the crankset supplier as Praxis Works, I mistakenly believed that Giant had done their homework.

After a thorough check-over to eliminate the standard shop assembly issues (under-torqued bolts, no grease or washers on the pedals, chain with only storage lubricant on it, etc), I took it out for a first ride. Minutes after starting the first downhill trail, on an innocuous 60 cm drop over some rocks to a smooth, downhill-sloped landing (shown in the photo), my brand-new Spank Spike pedal ripped completely out of the drive-side crankarm.

I was very lucky that the pedal provided just enough support as it came out that I didn't lose control. As I skidded to a stop, my immediate thought was that the square taper interface must have failed, but only the pedal was on the ground. The failure had nothing to do with the pedal, it was the crankarm internal threads that had failed catastrophically.

The cause of the failure was simple: Giant made a choice years ago to partner with Yamaha for their motor technology. Yamaha only makes a square taper interface for their power unit (until the 2018 model year). Giant chose not to specify and procure a proper crankset for the intended service of the bike (i.e. enduro mountain biking). Instead they specified an FSA CK-745 crankset. I have no idea what testing Giant did at the time, but that crank is designed for a different market (commuter ebikes that are used to buy groceries and ride around in the city). And it is made very cheaply - full retail is $38 on FSA's website. The design of the crank is probably fine, but I believe that the material is not. I didn't have the resources to have it tested, of course, but I strongly believe that the aluminum used would not come close to the strength required by the 6061-T6 specification, which is the standard aluminum for an MTB crank of this type and application. The FSA webpage on the square taper CK-745 just says the material is 'alloy', which is meaningless and likely indicative of the very low quality aluminum used.

Beyond the quality of the part is Giant's misleading specification sheet. You'll remember that the crankset was supposed to be a Praxis Works according to Giant's website (quoting Giant Canada’s website when I bought the bike: “Crankset: Praxis Works Custom Forged, 38”, where 38 is the number of teeth on the chainring).

In reality Praxis Works had nothing to do with the crank at all. They had provided only the chainring. So Giant was using Praxis Works' name to mislead consumers, by suppressing the FSA part number to hide the low quality of the crank. When I confronted Giant Canada on this, they said it was a simply a mistake.

It is curious to think how often such 'mistakes' are made when the advantage goes to the consumer rather than the company.
1 - The small drop .jpg 2 - Trailside after failure.jpg
To Giant Canada’s partial credit, they quickly changed the crankset description on their website to "Giant Custom Forged by FSA" after my initial complaint and warranty claim, with a separate note about the Praxis Works chainring.

However, this new wording is still clearly intended to deceive the public, as there is no doubt that the actual crank installed on the bike is an FSA CK-745. The only 'custom' thing Giant did was to take FSA's logo off the visible side. When I confronted the Canadian brand manager with this, he said he was completely comfortable with the ‘custom’ wording and would not change it. Two weeks after leaving numerous voice messages and sending them an email with a version of this posting attached, Giant USA has not had the courtesy to even reply to me.

Some of Giant’s international websites have an additional line in the crankset description saying that the cranks are 'minimal Q-factor'. While the deception attempted here is less important, the claim is ridiculous. A properly designed crank for the Yamaha drive system could easily reduce the Q-factor (the perpendicular distance between pedals) by 20-25 mm compared to the supplied FSA cranks.

So here are my conclusions: If you own or are considering buying a Giant ebike from any model year, you are in danger of crank arm failure at the pedal interface. In this mass-produced world, the chance that my bike had the only defective crank arm is essentially zero. Giant's specification of such a low-end crank on an otherwise high-end (US retail $7700) bike is, in my opinion, unforgivable. And may be worthy of a lawsuit in the unfortunate but almost-inevitable event that someone does lose control and is seriously injured when their properly-installed pedal rips out of their crankarm. I was very lucky to walk away uninjured, and under no circumstances would I recommend that anyone trust such a low-end crank for real off road riding.

Furthermore, as far as I am aware owners of Giant ebikes have no other viable crank options at this time. Nobody in the world makes mid- or high-quality square taper cranks for the Yamaha drive.

Giant is the world’s largest bike manufacturer and they could easily have had a proper set of cranks manufactured for this line of bikes. They should have been made of at least 6061, and preferably 7000 series, aluminum, with proper Q-factor for the Yamaha motor. But they chose not to bother.

Giant should now be taking a whole series of actions, including a thorough investigation of the pedal interface strength of this crank and others like it, warnings to consumers, and, if testing shows similar defects in other cranks, then a recall should be initiated.

And no more deceptive specification sheets. Every one of Giant’s global websites should list FSA CK-745 as the crank on this bike, and similarly for the specifications of all their other bikes. If a manufacturer customizes something they have to say what they’ve done, not hide low quality parts behind a ‘custom’ façade after changing only the graphics.

This issue is not isolated to just Giant bikes either – there are many other ebike companies using low quality drivetrain parts. And it is probably not isolated to just 2017 and earlier model Giants. Some of Giant’s 2018 ebikes will have an ISIS drive interface, but the quality of the cranks they use will probably be the same (the advanced sales literature still refers to them as ‘custom forged’). So they will probably be just as likely to fail at the pedal interface as earlier models.

The following are more detailed technical notes, and are included only for those with an interest in the minutiae of the failure. I’ve included them on the basis that unusual claims require a higher level of proof:

• First, keep in mind that all the photos were taken after the trail-side incident was over. At the time the pedal came off I was stranded on the trail, and the crank was clearly destroyed. As darkness was falling, I tried to screw the pedal back into the deformed threads so I could limp home. However, the first few threads just ripped out completely. So the photos show the outer section of the pedal thread in the crankarm torn out, but this did not happen at the same time as the crankarm failure.

• The Full E+0 has 140 mm travel with a Rockshox Super Deluxe shock, which was pressurized to 190 psi. It did not bottom out on the small drop, and neither did the Lyrik fork. I did land the drop with my weight biased to the right side (probably 80%) when the crankarm failed, but there is nothing unusual in that. The drop is tiny by enduro mountain bike standards.

• The cranks did not suffer any rock strikes prior to the failure. The pedals and cranks are unblemished except for a dent in the pedal bearing housing that must have happened as the pedal flew off the bike. It could not have happened during the failure (if it struck a rock as I landed, for example), as the dent has a distinct direction - about 25 degrees sideways - which is completely inconsistent with a rock strike while moving forward at ~15 km/h. And beyond that, there is no matching mark on the crankarm.
3 - Damaged pedal.jpg
• Many of you are probably thinking that the most likely cause of such a failure is a pedal that has become partially unscrewed. However, I installed them myself to 35 ft*lb (with grease), and pedals are threaded so that precession acts to tighten them, so the probability that they were partially unscrewed is already extremely small. But evidence inside the crank arm proves the failure occurred when the pedal was fully threaded into the crank. With the Spank pedal and pedal washer in place there are two unengaged threads inside the crankarm.

The photos attached show that the damage starts at the third thread (subtle damage, paint is missing), which is the first internal thread that engages with the pedal. And there is progressively more damage on each successive thread, moving from the inner side of the crankarm to the midpoint. The fourth thread is clearly deformed. From the midpoint on the threads are stripped away completely as I described earlier.

The pattern and orientation of the damage to the crankarm threads is consistent with the back of the pedal thread levering itself up into the top of the crank threads as it came out, with the crank at the 4:30 position (looking at the drive side of the bike). This is consistent with my right foot being forward as I rode over the drop. At the time of failure, vertically upward corresponded to the direction from the pedal centerline toward the ‘4’ in the ‘CK-745’ logo printed on the crank.
4  - Damaged threads 1.jpg 5  - Damaged threads 2.jpg 6  - Damaged threads 3.jpg
In contrast, the other side of the crankarm thread (which was facing down as the pedal ripped out from the opposite side of the crank) appears to be undamaged.
7 - Undamaged Threads.jpg
• For completeness, the OD of the pedal thread on the Spank pedal exactly matches the stock Giant pedals (14.0 mm on my cheap micrometer, nominal is 14.022 mm). So there was nothing wrong with the pedal. The pedal threads do not appear to be damaged but the dent in the bearing housing has effectively destroyed the pedals. And no, Giant did not offer to replace them. Spank, however, has offered a crash replacement at reduced cost.

For the record I have no financial interest in, nor any social ties to, any other bike company.

Please spread the word on this issue so that it creates real change. And if you work for Giant or another company that uses cheap drivetrain components on mountain ebikes: do something about this before someone is seriously injured.


Tom W

Burnaby BC
1 - The small drop .jpg
2 - Trailside after failure.jpg
3 - Damaged pedal.jpg
4  - Damaged threads 1.jpg
5  - Damaged threads 2.jpg
6  - Damaged threads 3.jpg
7 - Undamaged Threads.jpg


New Member
Thanks for sharing. Just wanted to post a quick reply that a few weeks ago, I hit my pedal on a rock (hidden in grass) at 12+ mph and it spun me and the bike around and threw me off the bike. My crank arm was bent from the impact with the rock. In my case, it seems like if I had a inferior crank arm, the pedal might've ripped out.

Tom W

New Member
I'd like to follow up on my earlier post about my bike's crank failure with a related issue: lack of proper ground clearance for enduro mountain biking.

As far as I am aware the Giant Full E+ bikes have the lowest motor-to-ground clearance in their segment. Compare the side view of the Giant Full E+ against virtually any of its enduro-level competitors and you will see that the Giant motor projects further downward, below the bottom bracket axle, than the others. I haven't completed measurements myself (most of the competitors aren't even sold here), but the difference is several inches compared to the best-in-class, as shown in the photos attached. Be aware when looking at photos that the Bosch drive uses a much smaller chainring, so while it may appear to stick down a similar amount below the edge of the chainring, the actual ground clearance is much better than the Giant.

Ground clearance means little if you are riding simple forest paths, but for any real black- or double-black trails like we have in my part of the world, it is critical. Having the motor hang up on an obstacle means potential motor damage and, much worse, the potential for getting bucked forward off the bike. At the very least it means that you'll have to be constantly aware of the low clearance available, and either adapt your riding or simply walk over obstacles that could otherwise be ridden.

As a note to anyone in the bike review industry: Please consider adding ground clearance at the motor casing as figure of merit used to rate off-road electric bikes. It should be measured both at rest and at full suspension compression to take travel into account, and should be measured at the lowest point that isn't hidden behind the stock chainring.

The reason that the Giant bikes have such low ground clearance is because they started with a compromised drive system. As I mentioned in the earlier post, the Yamaha motor was developed for the commuter and street bike market. The Yamaha's square taper bottom bracket axle, the cheap crankarms, and the low ground clearance don't matter at all for that market.

However, when you start with all those compromises and try to stretch the performance envelope all the way to enduro MTB, as Giant has done with the Full E+0, you end up with a highly compromised and, in my opinion, dangerous, bike.

@ Akhim: The fact that your crank bent, rather than the pedal threads ripping out, could mean a number of things. Highly dependent on the geometry of the impact and, of course, whether your crank was made from inferior material. The failure on my bike could be batch-specific at the manufacturer, who knows. But unfortunately if you replaced the crank in kind (as you almost have to do, there are very few other options), then your new crank could be from a defective batch. No way to tell, unfortunately.

Tom W


  • Enduro ebike ground clearance comparison.pdf
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New Member
I have the 2017 Full-e+1
with the syncdrive sport, Canadian websites were full of blab about the Pro version for 2017, but it was not available in my country.
I certainly see the square taper drive as a nightmare to remove at some point in time.
I guess if the shop hammers it off and wrecks the motor they will pay? HAHAHA
I must very much agree with the report that the bike does not have the ground clearance for logs more than 5 inches, it seems a nice stack of logs forming a ramp is OK.
It is embarrassing that I must get off my bike and walk over what I used to ride over with my nomad.
Sometimes if I slow to a crawl I can mount the obstacle and not smash the motor shield into the rock or log.
Scares me as I see "dollar signs" at every bash.
I use the Eco and Normal range most often, the highest setting is goofy the cadence range it works in is very narrow.
Any others have opinions on using the power setting?

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New Member
I have the Full-E+1 and just love it. Most of my riding is light trail and pavement (with an occasional curb or staircase), so I don't anticipate the type of failure that you experienced. However, the only issues I have is that these things want to constantly go their top speed under motor power which is 20mph, and I actually only use maybe 3-4 of the 22 speeds available.


New Member
I think I understand and agree, the cadence maintained is very important, especially in the highest mode, if the rpm drops or exceeds a very narrow band the assist drops and strands me on the hill.
So speeding up cadence ends the climb, a constant careful speed and torque in the high mode seems to be needed.
I can climb most stuff in normal mode, slowly, sitting.
I wonder if anyone had a technique for log climbing.
I do all but the most crazy trails.
Any input?