2 broken front suspension forks


1 mW
May 28, 2015
Hi, i've learn the hard way, how bad idea is having a front suspension fork made of magnesium, and a 350w 36v front hub.

I bought my second hand e bike, with recipe and 1 yr warranty still available ( <---thx to God or whatever...). It's an Adriática Boxter GS21v. 28 Platinium H. 55, i think mine it's a resell from Ciclotek, you can see the bike on sale http://www.ciclotekstore.com/b2c/producto/0202023/1/adriatica-boxter-gs21v-28-platinium-h-55 ( spanish warning ).

Anyway, i was pretty glad with my 600€ bought, a 50% disccount for a fairly unused item with warranty, seemed ok. I actually ride very joyfully the first 200 kms, i had a few punctures, but nothing worrisome. It was not too powerfull ( 36v 250w nominal - 500w peak), and i'm 200 pounds, so i knew that i would have to pedal a lot, more in the hilly area i live, but that was the healthy part and i was ok with sweating a bit.

I tested the e-bike, on some mild off road tracks in my city, Madrid (Spain), and the response was awsome, big wheels actually gives you wings, more when you come from a 20 inch foldable :). I rode 4 days, with 0 incidents, i barely used the accelarator, but to push me on the traffic lights and uphills. But...the 5th day, i was starting my easy 35 kms ride, and when i confronted a fairly steep part of road, i used the manual accelerator, and my Suntour SF-NEX4610 failed on me big time, it broke on the fork end and i almost facepalmed, glady i was able to put my hands before my face, but because of the hill, i rolled back miserable, not big harm done but to my pride.

I thought i might be some faulty fork, and asked my bike's workshop to ask Suntour for a warranty replacement. They took pictures of the broken fork, asked for the recipe warranty, after a couple of days, the Suntour's guys in Spain, took the broken fork back and get me a new one, a newer version actually, so i was fairly happy. I rode again, like 200 kms for the same routes, but this time, with some fear in my heart, i rode slower and more gently. I rode for a few days more, and just when i was regaining my trust on the ebike, it broke again !!!!. Just getting out of my home, using very midly the accelerator, on flat ground, i lowered from the pavement into the road, like 16 cms, and it broken again, as soon as it touched the floor, on the front ends, the very same way the other broke.

Boy, this time i was mad, i kicked the shit out of the suspension and shouted some spanish very nasty words...but the kicking didn't help me much to get the fork out, also hurt my feet, and the some neighbours complained coze my profanities, so no bike, hurt even more than i was from previous fall, and bothering people, great move.

My bicycle mecanic, whom does not have much exp on ebike, told me that, he had seen some broken forks coming from ebikes, but 2 in a row, was pretty unique for him at least. Doing some research i found you guys, and the world of torq arms. I've learnt that suspension of alumium or magnesium on front ebike hubs, is dangerous and i have one torq arm coming from the same company that sells the ebike, Ciclotek ( http://www.ciclotekstore.com/b2c/producto/1701029/1/torque-arm-pequeno-motores-xf-unidad ).

I wonder after reading hours and hours on this very forum, why they sell the e-ebike, without torq arm and also, with no brakes cutt-off. I wrote the company, about this issue, and the answer was, that this kind of situation was not common, and they suggested me to buy the torq arm. Is it me, or this combination of weak suspension and no break levers, it's the perfect cocktail for a facepalm on the move?. This is one the their lower front hub motors, they've got up to 1000w i think, i they just suggest to install it, when it should be mandatory even with steel forks.

Sorry for the long post, it's been like 2 months with changes and surprises, and i think i've fallen in love with e-bikes, so it's very hard not be able to roll, i even bought a new 13ah battery to increase the range and addiction. Now, i'm having some issues finding a 700c ahead rigid steel forks, so my only option, to ride this weekend, it's to get the 3th replacement from Suntour ( they must be curious....), wait till the torq arm arrives and ride with eyebrow rised....

I hope my english didn't make you want to pull your eyes out, but i needed badly to talk to some e-rides, i gladly take advice and thx for the time

Update ( pics of the front end )


Welcome and please consider adding your location Madrid (Spain) to user profile.

Experience teaches us front motors in particular should really never be mounted to anything other than steel. I cringe when I see front hub motors installed into alloy suspension forks.

Yes, it “can” be successfully done but so can jumping out of the way of a fast moving train. It’s just not a good idea to allow yourself to ever be in that position in the 1st place.

Chinese customer service sucks. No way around it and they know if we want cheap, take it or leave it. I suggest always use as much purchase protection (credit card) as possible.

Likewise about my English, LOL…
Hi Y, thankfully it was a legal pourchase from a well known dealer, i guess Ciclotek it's the main seller on this part of the world ( Madrid ), also Suntour reacted very well, so i can't really complain but on the basic design of that e-bike
You mention a steel fork. In the US, most steel suspension forks are poorly made and I wouldn't trust them (other opinions will vary). Surly makes a fine (I own two) 700c steel fork if they're available in your country. If not, Salsa ans other companies have them too.
Welcome to the wonderful world of Ebikes :wink: .There is alot of info on Endless sphere and you can figure out a safe way to use a hub on the front wheel.
HI Bicimad,
Thank you for your post. I was going to put a 350W motor on a Trek Shift 3. It has the same type of front fork. You saved me a face plant.
From my experience, a motor up to 350w in an alloy suspension fork is OK if properly installed with a central axle or eccentric washers. I bet OP'S bike didn't have either. Without seeing it, it's impossible to comment further.

Obviously, steel forks are more robust than alloy ones, but you can't get decent suspension ones on steel.
True, no decent steel suspension forks but what good is any suspension fork once you stuff a couple lbs of motor w/torque in a telescoping fork? Using a steel suspension or non-suspension fork is simply for safety. Definitely not suspension compliance.

Of course, alloy forks “can” handle low power hub motors with proper washers, hardware and careful installation but how many times have we seen alloy dropouts snapped by motor axles due to improper installations?

Over the years, more than I can count on both hands…
I have also seen some smaller, 350w or less ebikes that were sold without a torque arm, using alloy forks. My thoughts? Morons.

You can get away with it a long time, btw. But the first instant a nut loosens, then the axle will rotate even with very low power, and break or wallow out the forks.

What happened to you, is the new forks likely allowed the axle shoulder to dig very slightly into the soft metal. That in effect, made your axle shift a half mm to the outside, and now the nut is not tight anymore.

ANYTIME the wheel is off the bike, tighten nuts, wait 15 min, tighten some more. Ride around the block, tighten again if it needs it.

And the obvious, to use alloy forks in the future, get yourself two c washers and two torque arms.
It seems that the only available 700c a-head 1 1/8 rigid forks are in Germany, besides weak, also my Adriatica seems to have pretty unique size for the spanish standars, and i was told that it would take like 3-6 weeks for the fork to arrive Madrid.

I think my option it's going to be use an aluminium suspension fork, because it's mostly the only thing i can buy, use the torque arm and also get the brake leavers. But does not seems to be the best solution, more like a temporal fix.

I'm quite dissapointed with the bike design, it's doom to fail, and the ebike manufacturer ( Ciclotek ), seems all suprised, also, now, the fork manufacturer, SR Suntour, it's not answering my bike's guy emails, so it's been 3 weeks with no answer ( search on Google for Sr Suntour 125k units recall ). I bought the ebike, hoping to help me to smoke less and go out more, and im not, i´m putting down hundreds on repairs and sitting ducks.

I'm thinking about selling the ebike, i feel bad to give this piece of shit to another person, but i don't know what to do, i don´t trust the ebike, spares are very hard to get, very fragile, and with some sort of lame warranty. Maybe it'll be better for a smaller person or someone with interest on fail industrial designs.
Good news!, i bought a new steel fork, and it's comming thursday, so hopefully i'll be able to ride this weekend, after almost 3 months, f...yeah !

Suntour distributor still has to say something about the 2nd broken fork, but i asked to give me something different, paying the possible difference, but still not news. I guess i'll keep it for emergency spares and about the torq arm, it arrived, better than the picture, with 4mm think plate, fits well so i'll use it, just in case.

But i´m curious, now, that without the front suspension and with my hard-to-ride marathon plus tour tyres, my ass it's going to pay the extra security, so i hope it's not too harsh.

Also, i've been talking in other forums, with people who has the same bicycle, and they didn't have any problem, so i'm going to recheck the c washer installation and make sure everything it's tight and well placed, yes, it's overkill with a 350w motor, but after my ordeal, i need to feel safe riding.
"C" washers are not the solution.....common sense says you shouldn't put any amount of torque onto that cast alloy drop out.
Wasn't someone on here making steel "drop outs" on steel tube sleeves that fixed over the bottom of (modified) alloy forks .... for just this purpose ?
And wouldn't the clamping "through axle" type of fork be an even better solution ?
C washers AND two torque arms to clarify.

The torque arms will not fit into the axle cup, steel or alloy fork, and so some kind of filler washer is needed. You can make your own c washers by grinding down tabbed torque washers that usually come with a motor kit.

Too funny the manufacturers of the bike seem all surprised by the busted forks. Shows the level or their R&D.

Without a c washer, or other filler washer, many hubmotor washers and nuts will crack an alloy fork, just by cranking down on the mis fitting, oversize nut. A really legit Ebike manufacturer would at least start by having forks made that fit their axle bolt washers and nuts.

You could also do a motocycle like through axle. Two bolts secure the bottom half of the through axle mount. Again, it would take an actual commitment to manufacture an e bike, vs just slapping whatever motor on whatever bike parts.
d8veh said:
Hillhater said:
And wouldn't the clamping "through axle" type of fork be an even better solution ?

How do you get your motor in?
With remove able axle caps,..similar to these..

Also ..see here ..http://endless-sphere.com/forums/viewtopic.php?f=2&t=7185&start=15&hilit=20mm+axle
apologies if slightly off topic...but i think relevant.
I only recently realised how many new bike frames , BMX, MTB, Road Race,, Cyclocross, etc...are being made with "through axle" forks AND rear wheel location,
20 mm axles seem to be the standard, but i am sure other sizes exist.
Obviously this will cause complications for us fitting hub motors unless something changes.
we all know the issues hub motors have in drop outs ( ref this thread), so i feel it should be the motor manufacturers who move away from the current standard of 12/14mm axles with flats on, to some new 20 mm axle designed to lock securely into the new "through axle" locations on the bike.
A 20 mm dia motor axle would also offer big advantages for heavier wiring and better insulation.
Thoughts ?
I'm not sure such a configuration could reliably handle the torque from a high-powered hub motor. Under ideal circumstances (no dirt/grease and good precision [roundness] on both parts) it would do better than most would assume (just look at Morse Taper fittings for machine tools or shrink-fitted pulleys and gears for power transmission) but I think the diameter is just too small for the torque involved and the frame material too soft. I could be wrong.

Unless the motor manufacturer want to put an extra ~10mm/1/2" of length on each end of the shaft, with a spline on it, which would hang out of the frame dropout and take a torque arm.
Front motors have been mostly a fail since the invention of the ebike.. you are very lucky if your front setup is not slipping on gravel/drt, torque steering, or breaking suspension forks that are typically made out of strong yet brittle materials..

Just say no.. :mrgreen:
I thought i would the bike fixed today, bu i forgot today it was local holidays, so...doing some research till tomorrow.

I've been doing some accounting about how much i've spent since i bought the bike 5 months ago, some expenses are due to the broken fork some other are just the use of an e-bike, which is higher than a regular bike.

-600€: E-bike cost:
- 50€: Security, Bulldog U-Lock, steel wire, second u-lock, lock steapost, secured wheels
- 50€: Front white light and back red led. Front 1500lm, back 400lm.
- 25€: E-bike insurace ( partial theft, injuries, legal assistance, etc...): 25€
-320€: Battery li-ion 36v 13ah ( Samsung ) + 4,5A Charger
- 40€: repair of old battery and installation of second wire charger on new one
- 40€: First change of fork and some other direcction changes ( warranty paid the fork, just workshop expenses)
- 90€: Installation Marathon plus tour tyres and Kenda Ant-Flats tubes ( after 6 flats in 1 week....)
- 20€: Change of chain for a Shimano one.
- 90€: Second change of fork and installation of steel rigid fork and steel torque
- 25€: XLC Suspension seat post
1350€: TOTAL

Wow, it actually looks more than i thought for a second hand e-bike, 1350€, like 1517$. But just related to the fork, are like 200€, which beside the time i've been off the bike, stings like damn hornet. 200€ extra expenses, insecurity&falls, no time riding, all this because a obviuous faulty design.

This is one video i found on Youtube, from a guy who also broke 2 front forks, and speaks about the wonders of the torque arme
How C washer (without tab like torque washer) is different from normal washer? It does not take any torque anyway...
Is it just spacer like normal washer?
Punx0r said:
I'm not sure such a configuration could reliably handle the torque from a high-powered hub motor. .
For sure a 20 mm shaft CLAMPED in a 20+ mm wide frame could handle all the torque required.
Add in a simple single 3mm woodruff key and it's bulletproof.
If you needed more , install a Taperlock bush system or similar.
These are proven industrial power transmission systems.
The current 12/14mm shaft with flats on, is a pathetic failure for a torque drive connection.
As I said, someone is going to have to figure this out in the next few years, because "drop out" frames are gradually being phased out, just like rim brakes have almost disappeared .
I get the current shafts are far from ideal, but it's not progress to replace one compromised solution with another ;)

The only way I can see the clamped solution being viable is to knurl the motor shaft so it can bite into the frame. That damages the frame, though, and repeated applications would make a bit of a mess of it.

I can't recall an example of an aluminium-on-steel clamped arrangement used in industry for power transmission, but there could well be one. It might work in the real world, it might only work under ideal circumstances or it might be hopeless.

Whatever the solution it needs to be able to handle Cromotor levels of torque. What's that likely to be? 200Nm? More?

A woodruff key would help, but I can't see frame manufacturers including a slot of one...

Taperlock bushes: I just looked up the spec for a random 20mm one and it's 70mm OD, 32mm wide and has a torque capacity of 100 ft.lb (135Nm). As before, I can't see a frame being made to accommodate that...
Current axles are fine for "bicycle" power levels. It's when attempting to build mini-motorcycles which run into problems...
Motors like the Cromotor etc won't dictate a frame/axle standard, ...they are a minority.
( incidentally, the Cromotor has a Kt of 1.027, so torque won't be over 100NM)
there have already been several adaptations of them onto through axle frames. https://www.electricbike.com/cromotor-monster-hubmotor/. But obviously still retaining the "axle flats" of the motor.
Ultimately, it's down to the motor makers to get together with the frame designers to sort out solutions.
...it should be easy for Cromotor with their own frame , but they need to ensure independent motor buyers can use other frames also.
meelis11 said:
How C washer (without tab like torque washer) is different from normal washer? It does not take any torque anyway...
Is it just spacer like normal washer?
The C washer allows for the eccentricity of the axle when you have dimpled drop-outs. Without them, your drop-outs will pop when you tighten the nuts before you even switch the motor on.