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    Front Hub Motors Dangerous?

    Been doing a bit of research and it seems that front hub setups are inherently/potentially very dangerous, is this true? The bike I have claims to have a steel front fork and I heard aluminum forks are the worst type of metal to do a front hub conversion for. I am just looking for more information on this kind of conversion and ways of doing it safely. I honestly am discouraged from doing it though right now unless I can find some information to tell me otherwise. I heard you need torque arms. I was reading some people who installed them and even on steel forks and still had breaks. Just seems like a recipe for disaster is all I'm saying. If anyone has any input on this let me know, thank you.

    #2
    If it is a low power system like 350w or less you wouldn't necessarily need torque arms, but why take the risk when adding a torque arm is so easy?

    Personally I would avoid front more due to how it will spin out at high power due to load transfer, so it is kinda useless for high performance. But if it is for a medium to lower powered build and you value how much easier it is to do the build with front then it is not a bad way to go. Course even if you go with a rear hub and it's high performance you would probably want at least one torque arm, reinforcing the motor is always a good idea in that situation regardless of motor type

    Comment


      #3
      How much runout is acceptable on front brake rotor? Does not appear to be scuffing, but is visible, have not put an indicator on it, what is the best way to shim?

      Comment


        #4
        Originally posted by paxtana View Post
        If it is a low power system like 350w or less you wouldn't necessarily need torque arms, but why take the risk when adding a torque arm is so easy?

        Personally I would avoid front more due to how it will spin out at high power due to load transfer, so it is kinda useless for high performance. But if it is for a medium to lower powered build and you value how much easier it is to do the build with front then it is not a bad way to go. Course even if you go with a rear hub and it's high performance you would probably want at least one torque arm, reinforcing the motor is always a good idea in that situation regardless of motor type
        Well I was just reading this story of a 250w front motor causing this guy to fall and break his nose, kind of freaked me out. Some other guy on a forum said front hubs should be banned. I'm sure it is fine but there is really no way of actually knowing, its a steel fork from what I was told. If I do it I want to kind of be sure its not ever going to fail on me, no idea how though.

        I would want it for hills mainly, the extra motor in the front. But a mid drive would be perfect for that just would cost me more money for that.

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          #5
          What quality of steel fork are we talking about here? I would totally trust say a 1995 Trek steel fork or any past or preset Surly. Or are we talking about a wal mart quality bike here?

          If its a cheap or older bike that you already own maybe changing the fork would be a reasonable option because not only would you be able to up the quality you could also upgrade to a disc brake.

          Comment


            #6
            Originally posted by 73Eldo View Post
            What quality of steel fork are we talking about here? I would totally trust say a 1995 Trek steel fork or any past or preset Surly. Or are we talking about a wal mart quality bike here?

            If its a cheap or older bike that you already own maybe changing the fork would be a reasonable option because not only would you be able to up the quality you could also upgrade to a disc brake.
            Its a 700 dollar Ancheer Amazon bike. Its got premium quality parts on it, brakes, wiring etc. I even think it has a Bafang motor but i'm not sure. Here is the bike fork and listing. Idk tho.

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              #7
              Whether that counts as premium seems debatable, but if you are questioning whether that actually is steel you can always hold a magnet up to it.

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                #8
                I hate to break it to you but $700 is the bottom end of E bikes. I'm not saying that a $700 e bike can't be a good fit for some peoples needs but its for sure a bottom end bike quality wise. What a lot of us that have been in the e bike community a few years see is people buy these sub $1000 bikes and are expecting the performance of a $2500+ bike.

                A low end low power no name hub motor kit is going to cost about $500. That leaves you $200 for the rest of the bike. $250 I think is about the start of a Wal Mart bike and even with proper assembly which doesn't usually happen that is going be a barely ride able bike. Again I'm not saying that MAYBE there is a use case for a bike like that but I don't think you can get anything cheaper. Look at the prices of pretty much any parts. Lets say a bunch of parts cost $10 each which is also bottom end of much parts, you only get 20 of those which there are at least 20 major components on a bike and that doesn't count larger items like say the frame.

                The lower end E bikes that seem to get good reviews seem to be more in the $1000-1200 price range. These still more or less probably have the $500 motor setup maybe with a few slight upgrades so lets call it $600 which still isn't the $700 bafang branded hub motor kit cost. That now leaves $400-600 for the rest of the bike which makes a huge difference. At this level you are probably not getting a better frame but you are getting a little upgrade on everything else which makes a big difference. $400 is the high end of a wal mart bike or mid range for a sporting goods store. $600 gets you into the bottom end of a bike shop bike which is the first level I would start talking about good quality components. You look at a low end E bike from a bike shop its going to be in the $2000 range. For that you are getting that $600 Trek bike and something like a $1400 Bosch motor system.

                On the subject of forks the least expensive name brand suspension fork you can get is from SR Suntour and cost about $150. Rock Shox there are a few in the $350 range but $500-700 is more of an average. Lots of forks $1000+. If you don't need suspension then a quality steel fork would be a Surly and those are about $130. So using $150 as the base line for a cheap for how do you think the fork that comes on a $200 bike compares to that? Heck lets say its a $300 or even $400 bike..... still no room in the budget for a $150 fork yet.

                Comment


                • Retrorockit
                  Retrorockit commented
                  Editing a comment
                  E bikes are fast and heavy. Don't forget wheels, tires, and brakes.I equate entry level Bike shop MTB parts with street level E bike use.But looking at the fork can tell you a lot about what level the other components will be at.I personally look for older lightly used MTBs with a high level of components in a no longer popular wheel size. Good wheels, brakes, and fork for the price of a Walmart bike.A 3x8 speed 26" high end hardtail with disc brakes can be a screaming deal and will make a nice 1x8 speed E bike.

                #9
                Is everybody done running down the OP's bike? Are we ready to offer answers to reasonable questions/concerns posted by the OP?

                Originally posted by ViciousCyclist7 View Post
                Been doing a bit of research and it seems that front hub setups are inherently/potentially very dangerous, is this true?
                Reports on the 'net pretty much prove they are not safe on their own. Luckily torque arms make them MUCH safer but only when done right. So let's talk about how to do it right. Because gittin road pizza all over ya is no fun!

                Originally posted by ViciousCyclist7 View Post
                The bike I have claims to have a steel front fork and I heard aluminum forks are the worst type of metal to do a front hub conversion for.
                Test your fork with a magnet. Steel is magnetic; aluminum is non-magnetic. In other words a strong magnet will stick to steel but not aluminum. A weaker magnet might not stick solid but it will try to stick and you will feel it pulling toward the steel though it might ultimately fall off. If it's steel then skip the next 2 paragraphs as they deal with aluminum.

                Common grades of aluminum have lower tensile strength than steel. It is also more ductile than steel which means it bends easier than steel. So the problem with an aluminum fork when doing front hub conversion is that aluminum's higher ductility allows the dropouts to spread open easier compared to a steel fork. So yes, an aluminum fork would be the worst candidate for front hub conversion if torque arms are not used BUT torque arms might mitigate all that and make it safer. I say safer rather than safe for a reason and the reason is nobody knows for sure when safer adds up to safe enough for the kind of riding you do, your weight, the torque your motor outputs, etc.

                Originally posted by ViciousCyclist7 View Post
                I heard you need torque arms.
                Absolutely do not attempt it without torque arms, not even on a steel fork. No matter the watt rating on the motor do not attempt it without torque arms. Anybody who advises otherwise is willing to gamble things they cannot afford to lose (their life/health) on the prospect of a small reward (they save $15). That's a fool's bet, don't listen to them.

                Originally posted by ViciousCyclist7 View Post
                I was reading some people who installed them and even on steel forks and still had breaks. Just seems like a recipe for disaster is all I'm saying. If anyone has any input on this let me know, thank you.
                Did they install the torque arms correctly?
                Did they inspect the installation regularly to look for signs of impending failure that could have been prevented simply by re-tightening a loose nut or clamp?
                Or did they think torque arms are magic bullets immune to failure so don't bother with regular inspections?

                Like everything else torque arms have evolved over time. Manufacturers learn from failure and improve their products. Don't be discouraged by a few bad reports. My friend has had great success with his front hub motor plus torque arm. Mind you he's a very experienced automotive mechanic who knows how to do things right, how to look for signs of failure and when it's time to upgrade to a better design, replace a part. It's not a matter of luck but rather a matter of being informed, staying current and getting a little grease on your hands when you need to. You can learn from his experience and share the same success if you're willing to learn and work at it. You'll need good tools too. Read on if still interested.

                Googling the phrase torque arm ebike yields a plethora of info on the "are front hub drives safe" issue. I found an article at https://ebikes.ca/product-info/grin-...rque-arms.html to be very informative. Read it carefully and read it more than once. Note they use hose clamps to fasten the torque arms to the fork. Note also that in the TorqArm_V1 section they state "While this design did work, we did run into several instances of failure from the hose clamp in cases where a motor controller had shorted mosfets." Ignore the part about shorted mosfets and concentrate on the fact that it was the hose clamp that failed rather than the torque arm itself. So let's talk about hose clamps. Specifically let's talk about the type of hose clamp in the pics at that site. I call them "helical gear clamps" and I believe that is the name the industry uses. Let's use the acronym HGC to refer to helical gear clamp in this discussion.

                If you ask any experienced automotive mechanic they will tell you HGCs are prone to failure. Indeed the automotive industry has opted for much stronger hose clamps, you will find none on new vehicles. They are popular because they are inexpensive, easy to use, available at most hardware stores, etc. but the fact is they are more likely to fail than other designs. Most auto mechs won't use them unless a quick repair is required and they have nothing better on hand.

                The primary reason HGCs fail is because users over-tighten them to the point where they literally begin to tear themselves apart. I recommend destroying a few on your own by overtightening them. They're inexpensive and you will get a much better understanding of what they can take and what they cannot take. You will quickly learn that when overtightened, the rack (the band with the slots against which the helical gear pushes) distorts and fails to engage the helical gear properly. Or else the housing that holds the helical gear in the rack distorts and the gear no longer engages the rack.

                Another reason HGCs fail.... installation on something that is conical rather than cylindrical, for example, a tapered fork. When installed on a conical shape the rack MUST deflect sideways as you tighten the clamp. The more you tighten the more it deflects. Eventually the sideways deflection prevents further tightening or, worst case, tears the clamp apart. Even the best quality clamps fail on conical shapes.

                Another reason HGCs fail... using a bigger clamp than necessary. An example would be using a clamp designed for a 5" diameter on a 3" diameter. Yes, the 5" clamp is wider and therefore stronger but it's not designed for a 3" diameter. Forcing a 5" clamp to wrap around a 3" diameter will distort the housing that holds the helical gear in the rack. It won't fail if you don't force it too much but it will definitely fail if pushed too far.

                Your fork is cylindrical so that eliminates a common failure mode. If you use the proper size clamp and don't over tighten you eliminate the other mentioned failure modes. Still, common sense tells us 2 clamps is better than 1 so Grin's TorArm_V1 is not recommended. Nor would I recommend Grin's TorqArm_V2 which uses the fender eyelet holes because those holes are too close to the region that will distort and they're designed to take whatever force a fender will produce not the much larger force a torque arm will produce.

                I would recommend without reservation something like Grin's TorqArm_V3 which uses 2 hose clamps and places the clamps further up the fork which gives the assembly a greater mechanical advantage (leverage) against the axles's torque compared to the shorter TorqArm_V1. More leverage = less stress on the HGCs. Just be sure to place the clamp as shown in the picture. Note they place the clamp's gear opposite the torque arm rather than close to the torque arm. That's because an HGC is designed to clamp best on a curved surface. If you put the gear close to the torque arm then you either force the weakest part of the HGC to go flat when it wants to be curved.

                A final thought.... ditch the HGCs as they are considered to be the weakest least robust clamp on the market. Googling hose clamp types yields numerous links, here's just one that catches my eye:

                Supra clamp T-bolt, very popular with auto mechanics, very strong and robust, likely available at your local automotives store

                Comment


                  #10
                  First I'm going to say Grin Technology says they sell a lot of them, and people are happy. Second I've never bothered to ride one, so IDK what I'm talking about.
                  I have ridden my BBSHD mid drive a lot, and I am a retired mechanic. So I know something about how things work.
                  On my bike when taking off from a traffic light my front wheel is barely touching the ground. Acceleration will be limited by weight transfer with a front drive. So the useful power for acceleration is self limiting. This is very important to me but maybe not to everyone else. The frame of bicycles is designed to be powered from the rear axle. No bicycle fork is designed for this. But strength for braking is there so it's probably not disastrous at the lower power levels that make sense for this. The question I would ask is why get a front hub motor when a rear dive hub motor is an option?
                  I can understand some resistance to the complexity and maintenance issues of a powerful mid drive. But rear hub motors seem like a fairly benign option.

                  Comment


                  • AltaBrad
                    AltaBrad commented
                    Editing a comment
                    I think if front hub motors were causing fork damage we would be hearing about it in cycling mags. Maybe there are such reports and I'm just not seeing them?

                    IMHO the main reason to avoid front hub motors is what front wheel drive does to steering and control. Front wheel drive is fine for going in a straight line but not so great in turns. If you give it too much throttle and spin the wheel in a turn you're likely gonna hit the ground. I can handle the rear wheel sliding out but not the front.

                    I would go front hub motor only if I already had a rear hub motor or mid-drive and was getting stuck frequently in mud/snow or had a yearning to climb very steep hills.

                  #11
                  Originally posted by AltaBrad View Post
                  Is everybody done running down the OP's bike?
                  Yes I am here to run down the OPs bike. He has been here for a while insisting his $700 e-bike has premium components. There is no way a $700 ebike is anything but a collection of the cheapest components available. The last bike I bought new for $700 was in 1086s and that was a deal on a $1000 bike. As I look to build an e-bike for my wife I am starting with an $800 bike adding a $500 battery to a motor and parts that costs more than his entire bike. There is nothing wrong with his bike but he needs to quit making a high end bike out of a bike made from a collection of the cheapest parts available.

                  To the OP ride what you got add a second battery if you want to go further into e-biking buy a better e-bike or build a better one.

                  Comment


                  • AltaBrad
                    AltaBrad commented
                    Editing a comment
                    Thanks for your response.
                    Try one of those ultra wide super cushion seats with a gel filled cover over it for additional softness. That way your severely bunched up panties won't rub your arse raw.

                  #12
                  In his initial post he didn't say what sort of power front hub he was thinking about but then in a later one he mentions 250w. I have a 250 continuous 350 peak front hub bike and have zero safety or handling concerns about it. It happens to be on a later 1990's GT fully ridged steel mtb. I was used to my 1500w BBSHD on my Surly which was a $2000 (before the motor) fully ridged steel bike so when I was building this hub bike I had very very low expectations. Its actually a very nice riding bike. At first I thought the motor wasn't doing anything so I shut it off and which point I was reminded that I am no longer 20 years old and 120 pounds.

                  I took it on a 15 mile local ride I do a lot just to see how it did and it was fine. My average speed was lower than when I do it on my BBSHD . On that ride I maybe average 15 mph on a BBSHD, with this I think it was more like 13 which is fine for a recreational ride. Where the big differences are is if I was feeling lazy this could barely move my fat ass on throttle alone. My BBSHD's can move me fine on throttle only as long as its not up hill. Same thing when it came to climbing hills. With the BBSHD's and pedaling I could darn near hold my average speed still. With that little hub motor I didn't look like I was on an E bike. I was crawling up in the granny gear and out of breath by the time I got to the top. If I tried that with no motor I would probably have passed out about 1/4 of the way up.

                  If you just want a little help to ride at bicycle speeds on fairly flat pavement or hardpack a front hub motor is is a very attractive choice for a conversion. They are the least expensive, easiest, and most universal. Rear hubs and mid drives add a lot more variables when it comes to conversions and generally more expense just because you have to start dealing with possibly changing drive line parts. I think the conversion kit I bought lists for $600 and I didn't need anything else to make it work. With the BBS conversions there is always more things you end up needing which I assume would be similar with a rear hub. I had to buy some more spacers that didn't come with the kit. I had to buy a new longer chain. I didn't like the gear ratio I ended up with so different chain ring than came with the kit. Also got a new cassette but that didn't work with my derailleur so had to replace that too. It was all worth it and I got a great bike but it was a lot of extra time and money and screwing around that someone without a lot of time money and skills that just wants to make it easier to get out for a ride would not have to go through.

                  If you are a heavier person that wants to go faster especially up hills with less pedaling and do some off road stuff then a front hub motor is a terrible choice. I would also say the same thing about the quality of the bikes. If you are not that fat and just want to go at bike speeds on paved trails a wal mart quality bike is probably fine. You won't be stressing it much or at all. If you want to go faster and off road that is going to put more stress on the bike so you want to have a little higher quality there. I ride my wal mart conversion bike on the streets but would not trust it with my fat ass on it banging around the trails like I do on my Surly. Both have the same BBSHD's. One was $400 new and stock, the other $2000. I may break the Surly but its steel so hopefully it will kinda bend and give me some clues before it lets go. My $400 aluminum walmart bike I expect to just suddenly implode if I push it very hard.

                  Comment


                    #13
                    LArgh the computer just ate my first paragraph, anyroad here goes VII.
                    Just took the bike out for a test ride with the new (to me) 350 watt front motor, could not feel any difference in the handling, but it was my first ride since Oct,
                    The forks are aluminum and have shocks. I can now climb hills that were out of the question. The intent is that the front motor (no PAS) just throttle will be used pretty much for hills and maybe starts, today tried it every way I could think of and just love it. Bike is a heavy old monster with a 250 watt brushed rear hub so all up the bike now has about 600 watts with both motors wot.
                    Bike came with new LA batteries but I may build a battery with 5 of my Nissan leaf modules if I decide the bike can handle another 30 lbs.

                    Comment


                    • Retrorockit
                      Retrorockit commented
                      Editing a comment
                      Unless there's a special need for 2WD I would have put a 750W rear hub motor and called it a day.But if you get used to how it rides I would say it's not dangerous in and of itself.

                    #14
                    Thanks Retro, I had the bike and like it a lot, It is almost as old as me, in bike lives, brushed 250watt large diameter rear hub.

                    For a total of about $300 and some work put on the second motor. Mostly wanted the extra power for hills, wanted to get some experience as am installing hub motors on my freighter reverse trike, so for the money got some schooling and a much nicer bike. One problem am having is torque arms, there is just no room on the spindle, what do you think of welding a 19mm socket onto a bar to clamp to the forks and grip the nuts. as torque arms?

                    Comment


                    • AltaBrad
                      AltaBrad commented
                      Editing a comment
                      That will stop the nuts from turning but not the axle. Take a look here at the 4 diagrams at the top of the page. The diagram titled Torque Arm Absorbs Spinning Force shows the hole in the torque arm is NOT perfectly round, it has 2 flat sides that slip over the flats on the axle so no way the axle can spin unless the torque arm itself or the clamp fails.

                      If you immobilize the 2 nuts then the axle will tend to spin into the right side nut which will tighten it against the fork (no problem). However the axle will tend to spin out of the leftside nut which would tend to push the fork away from the hub if your bar-nut device doesn't break at the weld and the clamps don't break either. Or it could push the nut and arm off the fork if your nut-bar (no pun intended, not saying it's crazy) device does break.

                      Notice I said "could" and "tend to" rather than "will definitely". So I mean like "theoretically". In reality the fork likely wouldn't spread very far before you would notice something is loose. In reality, even if your weld and clamp aren't very strong the left side nut would probably have to back off 3 full turns before it breaks your weld or clamp. Probably you would notice something is loose and wobbly before it went that far.

                      The danger is that it will work perfect for such a long time you'll eventually figure it will never break. Then you'll forget about it and stop paying attention to it because that's just human nature. Then one day...

                    #15
                    Originally posted by ynot View Post
                    what do you think of welding a 19mm socket onto a bar to clamp to the forks and grip the nuts. as torque arms?
                    Wow, what a flash back that brought on... ;-)



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                    Agreed that any thickness on the axle is better than on the nut.

                    Pictures taken from this thread. It may provide inspiration for a proper solution...

                    Cross-posting these two threads so a search will turn up both: "Found an awesome torque arm" (3 pages) https://endless-sphere.com/forums/viewtopic.php?f=1&t=11570 xxxxxxxxxxxxxxxxxxxx Original thread died. Figured I'd help out and repost what I saved. Here is the album link...



                    My favorites on page 8.


                    Regards,
                    T.C.


                    See my completed Magic Pie V5 rear hub motor E-Bike build HERE.

                    Comment


                    • AltaBrad
                      AltaBrad commented
                      Editing a comment
                      Anybody can have vanity license plates. Your vanity torque arms are fly.
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