Torque arm on a suspension fork?

[DomW]

I'm glad I read this thread. I am not going to put a hub motor on the front of my wife's bike as we had planned. I reread the first five posts a couple times and I actually thought that 'the rude' post had been deleted, I guess my skin is pretty thick.

 

[glennb]

Uh-oh, I think I may be guilty of the last one on your list, glennb. Why is that bad, and should I get the hospital visit pre-authorized tomorrow, or wait until I can see the accident coming?

Most people probably are, but use typical heavy chunky faceplates that cope with it. The super thin ones with machined out fronts do not cope. We’re talking about four-bolt plates here.

Uneven torque on diagonally opposed bolts creates a racking stress that cracks the plate. (There’s a reason why some faceplates take the form of two separate vertical pieces - it avoids this stress).

Anyway, one corner breaks first, so on a flat bar you’ll be alright, but with drop bars ther'es enough leverage that when the plates clamping pressue is relieved by the crack the bars suddenly rotate 45 or more degrees downward. With your hands on the drops, you might just survive it, but from the hoods you're pretty well guaranteed to lose your purchase and be left grasping thin air either side of the front wheel. At least that's what happened to me, and I don't have a particularly heavy upper body or handlebar position much lower than the saddle.

To be serious though, riding in thongs? I gotta ask: how did you get hurt doing that?!

With hindsight I wonder how anybody does it witout getting hurt.

The method I employed was to head out on a hot summer day, riding out of the saddle giving it everything up a slight rise, when the front plug between my toes popped loose and my sweaty slippery foot scooted off the thong straight in between the fork blade and spokes. It happened in the blink of an eye, I was instantly on the ground in front of the bike not knowing what happened until I could piece together events based on the damage sustained. With a carbon tri-spoke you would not have a foot anymore, but steel spokes act sacrificially, so you can limp away with the wheel looking worse than your foot. Upper body injuries are guaranteed though.

In short, the foam rubber thong underside beds in to the spikey pedal ridges. There's very little friction between foot and thong, excacerbated by sweat, causing the foot to slide forward and put more pressure on the thong plug between the toes than it can handle.

Moral of the story. If you're riding in thongs and feel pressure from the strap between your toes, you're a blink of an eye away from a faceplant.

 

[glennb]

I'm glad I read this thread. I am not going to put a hub motor on the front of my wife's bike as we had planned. I reread the first five posts a couple times and I actually thought that 'the rude' post had been deleted, I guess my skin is pretty thick.

Front motors are very practical.

The significant risk is cast aluminium fork lowers.

It's easy and cheap to swap the fork. If the suspension's important to you, you can use a steel one. The weight difference isn't significant for a coil spring fork with aluminium crown and steel lowers by the time you've added a couple of kilograms in motor weight. You're looking at perhaps half a kilo weight difference, and even less if you forego 100 grams or more of torque arm hardware.

 

[glennb]

Yeah, I generally try to avoid the wet & icy. My bike has an internal gear hub on the rear wheel & is a belt drive, so I'm kinda locked into FWD unfortunately.

You'e got an awesome bike. For all I know you don't have room in an apartment for multiple bikes and therefore can't convert a different one, so I'm loath to suggest that option. What I would suggest is having a think about how important the front suspension is to you. Perhaps try a rigid fork for a while to see how you get along with it. Suspension stems have also made a bit of a comeback, there's a few different ones on the market now.

 

[DomW]

Front motors are very practical.

The significant risk is cast aluminium fork lowers.

It's easy and cheap to swap the fork. If the suspension's important to you, you can use a steel one. The weight difference isn't significant for a coil spring fork with aluminium crown and steel lowers by the time you've added a couple of kilograms in motor weight. You're looking at perhaps half a kilo weight difference, and even less if you forego 100 grams or more of torque arm hardware.

Hmm, I'll take a magnet out tomorrow and see if it sticks. Thanks.

 

[Chalo]

Front motors are very practical.

The significant risk is cast aluminium fork lowers.

All three of my e-bikes (750W to 1500W) use front hub motors, and they have for years. There are lots of advantages to them. But I use rigid chromoly forks and torque arms. The only near disaster came when I used one with a disc brake and a badly oriented fork tip slot. That one was 2kW+, but the failure was brake related and not motor related.

 

[gromike]

Moral of the story. If you're riding in thongs and feel pressure from the strap between your toes, you're a blink of an eye away from a faceplant.

And I thought you were talking about underwear! You're lucky to have toes! Most people new to ebikes have no experience at coming off a bike at speed.

 

[glennb]

Well, too much pressure from the strap between your legs might lead to a crash as well.

Sorry, forgot that flip flops is the American terminology.

 

[calab]

He's got a business to run with all its other costs involved, I'm sure the bicycle store mechanic would be happy to sell you a nice Shimano, or Bosch e-bike, thats what he's there for.

Am I missing something?

 

[glennb]

All three of my e-bikes (750W to 1500W) use front hub motors, and they have for years. There are lots of advantages to them. But I use rigid chromoly forks and torque arms. The only near disaster came when I used one with a disc brake and a badly oriented fork tip slot. That one was 2kW+, but the failure was brake related and not motor related.

Unfortunately I suspect you’re probably in a minority doing it safely. There’s sure to be an army of kids bolting motors into suspension forks that never publicise their failures. Once one kid has one done it, all his mates will want the same. And because the first installation didn’t (immediately) fail, they’ll take this single instance as proof of the validity, without understanding the material properties and forces involved. Or maybe I underestimate the average teenager and their proclivity to research these subjects.

 

[vmcroller]

You'e got an awesome bike. For all I know you don't have room in an apartment for multiple bikes and therefore can't convert a different one, so I'm loath to suggest that option. What I would suggest is having a think about how important the front suspension is to you. Perhaps try a rigid fork for a while to see how you get along with it. Suspension stems have also made a bit of a comeback, there's a few different ones on the market now.

Yep, it's a 675 square foot townhome, AND I live there with my girlfriend. DC real estate, man. I'd love to have a second bike, but am unfortunately stuck with this one alone for the time being. My bike has to live outside, which is why the "maintenance free" option of a belt drive + internal hub was so enticing to me.

The rigid fork that came with the bike is alright, but there are so many potholes on roads here that it often looks like a bombed out hellscape. Being constrained to the bike lane is further limiting since I generally can't swerve much to avoid things.

I assume higher end rigid forks might provide a bit of relief, but imagine that still pales in comparison by quite a bit to even a cheap suspension setup? If only they made worked & welded suspension forks

 

[vmcroller]

I'm glad I read this thread. I am not going to put a hub motor on the front of my wife's bike as we had planned. I reread the first five posts a couple times and I actually thought that 'the rude' post had been deleted, I guess my skin is pretty thick.

Yeah, same. Good perspectives in this thread. Has made me reconsider what sort of risks I'd be willing to take in order to smooth out my ride. Went from a "yeahhh, there's maybe some safety issues here, but a smooth ride " to "yeahhh, probably not worth it, should find an alternative solution".

The term "rude" is essentially personal VMCRoller shorthand for this: In my 10ish years of flight instructing (from total n00bs up to multi-engine instruction), I've found that when students ask me questions like "you said it's dangerous, but why exactly can't I do X/Y/Z, I don't get it?" it's 100% without-a-doubt counterproductive (also, inexplicably bizarre) to respond with a "WHAT, YOU THINK YOU KNOW MORE THAN ME?!?!?" (I know instructors that do this sorta thing!). People just wanna know the *why*! If you denigrate people for asking questions or expressing skepticism at advice that is in conflict with what they thought they understood, the outcome is never "oh thank you wise sage, you've humbled me with your wisdom!", it's "oooof, I'll just try it on my own when they're not around to tell me I'm an idiot" (or they learn to quit asking questions!). Not good! Am pretty confident all here who are of the opinion that this is a good approach to bike questions are NOT a fan of this approach as it would pertain to the way the airline pilot on their next flight had been instructed. Consider this a little bit!

Anyways, eminently grateful for the mass of follow-on messages that have opened my eyes a bit. I've also been trying to pitch my non-rider girlfriend on getting a bike, and I was contemplating a suspension fork as something that might lower the bar of entry for her. The many recent messages have totally nixed this for her, and almost assuredly for me. Very grateful for the many thoughtful and kind explanations.

 

[2old]

I'm glad I read this thread. I am not going to put a hub motor on the front of my wife's bike as we had planned. I reread the first five posts a couple times and I actually thought that 'the rude' post had been deleted, I guess my skin is pretty thick.

You might look at Grin's all axle system.

 

[vmcroller]

Intriguing! I definitely will have to keep the bike outside, which is a major bummer (but totally inescapable given my living situation for the foreseeable future) for maintenance and such, but if that could get my gf actually riding -- totally worth it. It still helps that my plan for her bike () is still very much in the nascent planning stage. Thanks for the idea.

 

[E-HP]

Intriguing! I definitely will have to keep the bike outside, which is a major bummer (but totally inescapable given my living situation for the foreseeable future) for maintenance and such, but if that could get my gf actually riding -- totally worth it. It still helps that my plan for her bike () is still very much in the nascent planning stage. Thanks for the idea.

Well it's good for her to know that you're researching diligently in order to keep her from an unexpected trip to the ER .
In any case, a belated welcome to the forum!
I just looked back at my first post on this forum, and even after researching ebikes for a year and looking at tons of YouTube videos, I probably tripled my knowledge by carefully reading the responses to that first post. And, it was the typical question that I see being asked as the first post of maybe half the newbies LOL. Here's what I've learned. The members of this forum come from all walks of life and professions. Food deliverers, car mechanics, physics professors; the breadth of knowledge is vast as is the depth. You will find that certain members have a great deal of knowledge and hands on experience in certain areas, while others have an amazing breadth of general knowledge, but even that has a lot of depth. But, in the end, it's a community of people, and personalities that you may get to know over time; and first impressions aren't always accurate.
When it comes to bicycle knowledge, I'd argue that Chalo likely has the greatest knowledge and experience out of the current active members. Other members have knowledge in specific technical areas as mentioned, and when I see any of their posts, I read them carefully looking for things I don't know to build up my own knowledge base. And the experience is real world, so when someone provides cautions about battery fires, it's even more impactful when delivered by someone whose house burnt down, or has first hand knowledge.
I see the most passion and tough love delivered around topics related to safety, and while the delivery may be off putting, the messages are absolutely necessary. If an expert hasn't chimed in, then I will do my best to deliver to tough message just so I can have a clear conscious in case something goes wrong. If you stick around the forum long enough, you may find yourself doing the same.
So, I would caution you against using the ignore button based on first impressions, or you'll likely miss out on a lot of good information. Besides, once you get to know the folks and the hot button topics, then you can just sit back, get out the popcorn, and watch when those topics come up.

 

[vmcroller]

Well it's good for her to know that you're researching diligently in order to keep her from an unexpected trip to the ER .
In any case, a belated welcome to the forum!
I just looked back at my first post on this forum, and even after researching ebikes for a year and looking at tons of YouTube videos, I probably tripled my knowledge by carefully reading the responses to that first post. And, it was the typical question that I see being asked as the first post of maybe half the newbies LOL. Here's what I've learned. The members of this forum come from all walks of life and professions. Food deliverers, car mechanics, physics professors; the breadth of knowledge is vast as is the depth. You will find that certain members have a great deal of knowledge and hands on experience in certain areas, while others have an amazing breadth of general knowledge, but even that has a lot of depth. But, in the end, it's a community of people, and personalities that you may get to know over time; and first impressions aren't always accurate.
When it comes to bicycle knowledge, I'd argue that Chalo likely has the greatest knowledge and experience out of the current active members. Other members have knowledge in specific technical areas as mentioned, and when I see any of their posts, I read them carefully looking for things I don't know to build up my own knowledge base. And the experience is real world, so when someone provides cautions about battery fires, it's even more impactful when delivered by someone whose house burnt down, or has first hand knowledge.
I see the most passion and tough love delivered around topics related to safety, and while the delivery may be off putting, the messages are absolutely necessary. If an expert hasn't chimed in, then I will do my best to deliver to tough message just so I can have a clear conscious in case something goes wrong. If you stick around the forum long enough, you may find yourself doing the same.
So, I would caution you against using the ignore button based on first impressions, or you'll likely miss out on a lot of good information. Besides, once you get to know the folks and the hot button topics, then you can just sit back, get out the popcorn, and watch when those topics come up.

Haha thanks, the candor here in this message is noticed & appreciated. This community really does seem to have a ton of knowledge to share, and I'm grateful that I get to pick up this knowledge for free. As a bit of context for where my head is at, I teach woodworking classes & help run a makerspace in the DC area as a little side gig to my full-time job. I see a steady stream of folks that show up all wide-eyed with excitement but lacking any real background or knowledge-base. Usually, the response to my "have you ever done any woodworking?" opening question goes like this: "Have I ever done any woodworking? No, but I still really want to build that heirloom quality 19th century chifferobe!" . I'm simultaneously cognizant of the pitfalls of this mentality, and concede that I'm equally subject to it myself (also ). In my own little leadership capacity there, I bristle at the way others at the makerspace sometimes scornfully treat new folks earnestly trying to learn, which often takes the form of asking questions that (to an expert) seem trivially easy to google or are bonkers dangerous (other than doing howl-at-the-moon crazy & reckless things with a tablesaw or bandsaw, being unkind to unknowledgeable people is about the only way to draw my ire there). I don't have that power here, but I do generally think my assessment of tone and intent is fairly well-calibrated.

Much of the difficulty in "onboarding" people to both makerspaces and woodworking in general is getting individuals to the point of being self-sustaining -- knowing why you can do X with the bandsaw (but only if you do A, B, and C first), Y with the router, and *NEVER* Z with the tablesaw. If some n00b told me they'd taken a class at Rockler and had asked the instructor if they could rip a board without the fence, and the instructor's correct-but-insufficient response ("that's a terrible idea") didn't make sense to them or was contrary to what they'd previously understood to be safe, I can't even wrap my head around responding "Don't believe them? Fine, figure it out for yourself. See how that works for you. And also, maybe think about why someone way smarter than you would think that's a dumb question in the first place. Don't expect me to treat you kindly when you come with questions like that." 100% unnecessary. 100% unhelpful. Kindergarten level stuff. Major bummer that this is the mentality of a super-poster here. It doesn't make sense to me how people don't understand that this is totally severable from providing help. Relatedly I seldom find a person's "tough love" explanation to be much more than a post-hoc rationalization of "I am intentionally curt and short with people".

Anyways, I want to learn! I'm receptive to being told I'm dead wrong! Just... not really seeking to be taken down a peg for not understanding -- no one is.

 

[99t4]

I'm a little worried I'm going to have to really flex the fork a bit to get it properly seated with spacers for brake alignment, even if they're only ~1/8" thick. I figured that'd possibly be a doable task, but your comment has me second guessing it.

If you're talking about spreading a front suspension fork to force fit a hubmotor axle's wider O.L.D. (Over-Lock-nut Distance)-- Not a good idea. Picture the telescopic sliders having to now slide in unison when not in plane with each other. You can get away with this to a certain extent with steel non-suspension forks.

I hear you about riding on poorly maintained rough irregular road surfaces. For me, I finally found a good solution by converting a beefy mid-2000s Downhill FS bike. Long-travel full suspension and 2.35" tires really smooth out the ride and promote comfort, surefootedness, and safety at the speeds I prefer to cruise at (19-22 mph when road conditions and traffic permits). It's all a tradeoff and I had to give up a sturdy rear rack and its large load carrying utility.

What tire size are you running? Higher volume tires in themselves offer a notable suspension effect.

 

[vmcroller]

If you're talking about spreading a front suspension fork to force fit a hubmotor axle's wider O.L.D. (Over-Lock-nut Distance)-- Not a good idea. Picture the telescopic sliders having to now slide in unison when not in plane with each other. You can get away with this to a certain extent with steel non-suspension forks.

I hear you about riding on poorly maintained rough irregular road surfaces. For me, I finally found a good solution by converting a beefy mid-2000s Downhill FS bike. Long-travel full suspension and 2.35" tires really smooth out the ride and promote comfort, surefootedness, and safety at the speeds I prefer to cruise at (19-22 mph when road conditions and traffic permits). It's all a tradeoff and I had to give up a sturdy rear rack and its large load carrying utility.

What tire size are you running? Higher volume tires in themselves offer a notable suspension effect.

Yeah, was originally hoping there'd be just enough play in the sliders that I could get away with forcing them a hair out of parallel/resting state configuration. Figured it was kind of a long shot, but initially wanted to try. Now realize this is definitely not going to work .

Currently riding 700c x 35mm tires. So much going on with the bike that I keep them around 80ish psi, which is pretty close to maxing out. I had them down at like 50ish previously, but got a pinch flat and was told that was probably too low for my setup. I think I've heard of people getting away with 38mm (maybe? would have to look), but the front brake is already rubbing a bit (which is what first prompted my interest in a fork replacement!)

 

[nicobie]

Don't think I fully grasped how much my suspension fork idea would have been playing with fire.

Then you need to thank Chalo and the others that did not want you to kill yourself.

 

[99t4]

Currently riding 700c x 35mm tires. So much going on with the bike that I keep them around 80ish psi, which is pretty close to maxing out. I had them down at like 50ish previously, but got a pinch flat and was told that was probably too low for my setup. I think I've heard of people getting away with 38mm (maybe? would have to look), but the front brake is already rubbing a bit (which is what first prompted my interest in a fork replacement!)

OK so since you are desiring more "suspension" but as you are locked in to using a front hubmotor, you probably should not pursue a telescoping front suspension fork because of front dropout breakage risk. (Note: there was an innovative front TA design a few years ago here on ES that also firmly secured the axle to the forks even in the event of dropout failure. Some time spent searching should unearth it. That design would require some dedicated DIY fabricating on your part.)

You may gain some substantial suspension by upgrading to high-volume tires. This mostly depends on the space between the front forks where the tire itself passes, distance between the rim and bottom of the fork crown, and also at the rear at the space between the chainstays (and possibly seatstays) and distance between the rim and BB. Measure these clearances to see how large of a tire you can run. Generally the more air volume in the tire the more "suspension" it provides. For example, the Schwalbe Crazy Bob 26x2.35 that I run are designed for 30-35 psi, plenty of cushioning. Never had a problem with snakebite pinch flats, not even close.

Hard to tell from photos at the Priority website but that style bike is usually limited in how big a tire you can fit. Not really designed for higher speed comfort on rough roads. For that you may need to trade for something more appropriate for that.

I can't think of what a rubbing brake has to do with tire width. Can you clarify?

 

[vmcroller]

Then you need to thank Chalo and the others that did not want you to kill yourself.

Ohhhhh, yeah, folks may have missed them. I've condensed them here:

"Haha thanks, the candor here in this message is noticed & appreciated."

"Thanks for the idea."

"Anyways, eminently grateful for the mass of follow-on messages that have opened my eyes a bit"

"Very grateful for the many thoughtful and kind explanations."

"Yeahhhh, appreciate the perspective here."

"Thanks for the explanation plus examples."

"Riding_on, glennb, and E-HP, thanks for the genuine responses. The stuff you've each shared is both illuminating and somewhat alarming."

"Your points about thickness are helpful."
___________

Seems odd that these don't show up for you? If you're having difficulty accessing these comments, I suppose that's likely a back end IT issue. I'd reach out to AWS or whoever hosts this site.

 

[AGS]

Maybe a suspension stem is the answer to your problems. Not as good a suspension forks but will help a bit. And also maybe a suspension seat post to go with it.

 

[2old]

This probably would be difficult to locate, but Cannondale had a headshock (the shock was located in the headtube of the bike) which had rigid fork tubes. I had one many years ago and it functioned adequately. I see one on Craigslist every so often, but don't know whether rebuild kits are available.

 

[A-DamW]

@vmcroller , I just did a quick did a quick search, found a couple of examples of mid drives on your model of bike.
Might be an option, I will leave it to you to read up on the links below.
2019 Priority Bicycles PRIORITY CONTINUUM ONYX

https://www.reddit.com/r/ebikes/comments/xt4hiy

Edit, I just read up on the two links above, and while it may introduce some challenges like belt alignment, the overall benefit may
outweigh trying to go with a front hub.
I am willing to say with some confidence that that you could probably solve the belt alignment.
Plus, you can run any fork that suites you.

 

[richj8990]

Unfortunately I suspect you’re probably in a minority doing it safely. There’s sure to be an army of kids bolting motors into suspension forks that never publicise their failures. Once one kid has one done it, all his mates will want the same. And because the first installation didn’t (immediately) fail, they’ll take this single instance as proof of the validity, without understanding the material properties and forces involved. Or maybe I underestimate the average teenager and their proclivity to research these subjects.

The 'army of kids' are now riding cheap rear hub motors all over the place that their mommy and daddy bought for them. I rarely see any front hub motors, in fact I cannot remember ever seeing one besides my own. Maybe once or twice a long time ago. I think you guys are by definition looking at things from a DIY perspective and therefore the rest of the outside world 'should' be looking at it that way. There are rear hub complete bikes now selling for under $500, and more powerful ones for around $1500, so there is no point in a kid buying a conversion kit and battery, they just ask for the whole bike as a present.

It looks like the Grin ready to roll front hub drives are the usual 600-1200W. The 500-1000W front hub motor I have was my first ever conversion and I had zero problems in 5000 miles with two different (and cheap) aluminum forks. Nothing cracked, nothing failed. Worst thing that happens is the tire can slip offroad because the traction is not as good as a rear hub drive. Don't assume everyone wants to put a 3000W front hub drive on. Again, just because on this site a lot of people are looking for a lot of power doesn't mean you should extrapolate that to the outside world. If someone does do a 3000W front hub drive, then yes, you can warn them, and plus the torque steer on something like that is going to be horrible even with rigid forks. It would be the equivalent of putting 1000 horsepower in a front wheel drive car. No bueno, regardless of the suspension setup.

One last piece of advice: if a kid wants to do something stupid, no one can talk them out of it. If you try, they will simply do more stupid stuff out of rebelliousness. Just sit back and realize that some people are out to win the Darwin Award.