Rear wheel slippery/sliding after wreck

Jabotical

100 W
Joined
Jul 15, 2016
Messages
101
Location
Phoenix, Arizona
So a few months back I wrecked my steel-frame bike (based around a Trek 820) pretty hard.

1) I replaced the tacoed front wheel, but the bike felt like it rode kind of unstably afterward. I tried to convince myself it was in my head, but after several close calls the rear tire (with the DD hub motor in it) slipped on some loose dirt while riding fairly conservatively, and I crashed again (though not as badly). After that the fork was definitely bent (and it probably had been at least somewhat before), so I thought maybe that was the only issue.

2) I finally replaced the fork, and it definitely handles better now -- but it still feels less stable than I remember, and in particular the back wheel still seems unusually prone to slip sideways.

I really want to get back to commuting on my bike, but I don't want to be unsafe, and it really still doesn't feel quite right. I don't think it's just post-traumatic sensitivity.

Any thoughts on what might be going on? I can't see anything visibly wrong, but I've considered that maybe the rear dropouts aren't quite level any more? Or maybe the motor itself (1500W DD Leafmotor) has its axles slightly bent or something? Like I said, it doesn't look like either of these are a problem. And the wreck damage seemed mostly concentrated in the front. It would be very helpful if anyone has an idea whether it would be more likely I have to replace the frame, or whether I just need a new motor, or what. Or of course if there's anything I can look at that might tell me.

Many thanks!

[EDIT] And I should mention I have two sturdy torque arms on the rear dropouts.
 
Check the rear wheel for loose spokes or bent rim. Check the frame for signs of bending at the joints between the top tube and down tube and the head tube.

If you can't figure it out, take it to a bike shop for inspection. That's a cheap bike, never intended to go as fast as your motor makes it go, and it needs to be in tip top shape for what you're doing.
 
It sounds like possibly a cracked frame. Those can sometimes be tricky to spot if the frame isn't bent as well. the crack may close up and the frame looks normal, looking at it from a foot away. A crack on the seat stay near the dropout would be under compression and closed most of the time, but might allow the back wheel to twist under a side load, like you would have in a hard turn.

I'd take the back wheel off, scrub the frame clean around all the welds, and then give it a close inspection under a very bright light.
 
Chalo said:
Check the rear wheel for loose spokes or bent rim. Check the frame for signs of bending at the joints between the top tube and down tube and the head tube.
It didn't look like a bent rim, and I did feel for loose spokes, but I'll check again. Thanks for the tips on where specifically to check the frame! I'll definitely do that.

If you can't figure it out, take it to a bike shop for inspection.
I certainly thought about taking it to a bike shop. I like the one fine that sourced the fork for me and put a star nut in it. I gather that most bike shops aren't too keen on ebikes though, so I'd almost certainly have to revert it to a non-ebike form first, which I was hoping to avoid unless necessary just because detaching and reattaching everything is hours of work. Maybe I can find one somewhere that won't sneer at it.

That's a cheap bike, never intended to go as fast as your motor makes it go, and it needs to be in tip top shape for what you're doing.
Yes the 820 is certainly the entry-level Trek MTB model. Forgive my ignorance, but I'd thought that to a certain extent "cheap" bikes tend to be better ebike candidates, because higher-end ones tend to trade lightness for fragility, no? Isn't a steel framed one like this preferable to aluminum or carbon, for this purpose? What would be an example of a better choice for conversion, if money weren't an object?

Either way I agree it definitely needs to be in excellent shape to be putting the strains on it I'd like to. But even pedaling manually I can feel its instability.
 
DrunkSkunk said:
sounds like possibly a cracked frame. Those can sometimes be tricky to spot if the frame isn't bent as well. the crack may close up and the frame looks normal, looking at it from a foot away. A crack on the seat stay near the dropout would be under compression and closed most of the time, but might allow the back wheel to twist under a side load, like you would have in a hard turn.

I'd take the back wheel off, scrub the frame clean around all the welds, and then give it a close inspection under a very bright light.
Ooookay, that would make a lot of sense. I'll definitely do as you suggest. The feeling of slipping/instability often happens even when I'm not turning hard or even much at all, but it might be a back crack.

If I do discover a crack, does it make the most sense to buck up and get a new frame? Or would it be reasonable to try to get it welded? (I have no experience/equipment doing that myself, but presumably I could find someone?)
 
If you bought in the myth that a cheap frame does make a better ebike, forget that stupid idea right now. Steel frames are easier to mod and that's all. Good cro-mo steel frames are rare and expansive today, they are making a better ebike than a cheap steel one of course. A big alu frame is best for stiffness, difficult to mod and a tad harder to build, but they don't flex or bend unless you crash hard enough to scrap the whole bike anyway. They are also lighter, and that is a neat advantage for performance or efficiency.

Your frame is crooked, or even cracked and crooked. Pretty difficult to make it straigh and sound, but possible if you value it enough.
 
The Trek 800 is the entry level model. I have one of these with a 500W motor, and its chro-moly frame seems fine to me. Damn good bike, if ridden at bike speeds (under 16 mph). I put on a new and better front wheel because the original was warped, but I didn't know how to true wheels then, Today, I could make the original straight. Pedal bearings were squonking so I did new pedals. I kept the eccentric crank. Also added a suspension fork, for a softer ride and disk brake capability.
 
Jabotical said:
If I do discover a crack, does it make the most sense to buck up and get a new frame? Or would it be reasonable to try to get it welded? (I have no experience/equipment doing that myself, but presumably I could find someone?)


While it could be welded, the cost of hiring a welder would probably be more than the value of the bike. Trek 800 series frames are cheap used.

It's a good bike for a first conversion. The 800 series are ideal for a generic starting point. Not for high powered rides, though.
 
MadRhino said:
If you bought in the myth that a cheap frame does make a better ebike, forget that stupid idea right now. Steel frames are easier to mod and that's all. Good cro-mo steel frames are rare and expansive today, they are making a better ebike than a cheap steel one of course. A big alu frame is best for stiffness, difficult to mod and a tad harder to build, but they don't flex or bend unless you crash hard enough to scrap the whole bike anyway. They are also lighter, and that is a neat advantage for performance or efficiency.
Interesting. I hadn't heard that perspective before. The Trek 820 is supposed to be made from cro-mo steel, but I wouldn't be surprised if it's subpar in some ways. I will keep your advice about aluminum frames in mind -- I can certainly attest first hand that having a steel frame doesn't make it impervious, and lighter is without a doubt advantageous!

Your frame is crooked, or even cracked and crooked. Pretty difficult to make it straigh and sound, but possible if you value it enough.
I appreciate the insight. The other two above you pretty much seem to agree that I have a cracked/crooked frame. Yeah unless it were a trivial operation to repair a crack (which it doesn't sound like it is), I have no special love for this frame. Mainly I just hoped to avoid the hassle of transferring everything over to a new frame. But I'm sure it will build character.
 
docw009 said:
The Trek 800 is the entry level model. I have one of these with a 500W motor, and its chro-moly frame seems fine to me. Damn good bike, if ridden at bike speeds (under 16 mph). I put on a new and better front wheel because the original was warped, but I didn't know how to true wheels then, Today, I could make the original straight. Pedal bearings were squonking so I did new pedals. I kept the eccentric crank. Also added a suspension fork, for a softer ride and disk brake capability.
Yeah I really, really enjoyed riding mine until I crashed it hard. It was really a great bike. If only I hadn't gotten careless, that fateful day... Admittedly, I tended to ride it more in the 20-30 mph range (hence the severity of damage when I wrecked).
 
Drunkskunk said:
While it could be welded, the cost of hiring a welder would probably be more than the value of the bike. Trek 800 series frames are cheap used.
Yeah, that's kind of what I figured. I wouldn't even have considered it except I really like how I have it rigged up, and hoped to avoid the hassle of transferring everything.

It's a good bike for a first conversion. The 800 series are ideal for a generic starting point. Not for high powered rides, though.
I'll say! It seemed to work wonderfully for my purposes, and I could hardly have been more pleased. Until I smashed it up at least. Out of curiosity, what's an example of a bike that you think would be a good basis for a "high powered" ride?
 
MadRhino said:
Steel frames are easier to mod and that's all. Good cro-mo steel frames are rare and expansive today, they are making a better ebike than a cheap steel one of course.

Like for like, I'd use a 7 pound steel frame over a 4.5 pound chromoly frame every time, for an e-bike. The extra weight buys back the strength lost by using a cheaper material, but it also adds stiffness and lowers peak stresses (where cracks precipitate). And it adds dent resistance and the opportunity to weld stuff on without inviting subsequent failures.

I like chromoly and I use it when I can, but light chromoly is not as applicable to e-bikes as heavy steel. Heavy chromoly is, of course, even better.
 
Very confusing thread for me.

Feels slippery,, to me that screams your tires are worn out, poor choice, you corner too hard for that tire, the road sucks, etc etc.

But if you said the frame feels rubbery, you see it flex as you pedal hard, and such like observations, that's more like you'd expect from a cracked frame. Or one that has been flexed enough to soften up and bend too easy. Often there will also be high speed wobble, at slower speed than before. The bike wags its rear end like a dogs tail.

Bent frame, I'd expect you to say I fall to the left, or the right more, or it won't track right anymore. Can you ride no hands on this bike at all? If not, its time for a replacement. Mis alignment of front and rear wheels screws up your handling quite a bit.

If you don't care about weight, and plan to ride pretty much under 20 mph, its hard to beat 7 speed beach cruisers, including the mild steel ones. But an equally good choice without the weight, are good alu ones, like the electra townie. But you said high powered ride, so it does sound like you corner fast. Which brings my thinking back to tires as at least part of your problem.

Any kind of performance riding does call for much better bike frames, quite possibly full suspension. But NOT cheapo shocks. The bike shaped object full suspension bikes will feel more or less ok at first, but the thin frame tubes will soften up, and soon the bike will be wagging its tail.
 
Have you moved more weight to a rear rack such as battery and/or controller? And is that secured tightly? Poor handling and feeling "wobbly" at the back can be because the center of gravity is moved too far rearwards and upwards.
 
Check your wheel alignment with a plank of wood or string to see if the front is off-set from the rear:

alignment_chass.gif
 
I'm still thinking the bike is so easy to flex now, and possibly flexing more because of weight on a rear rack, that it tweaks out of line both ways on every corner.

Straight when parked, but the tails wagging on that bike. If its bad, you can see easily it every pedal stroke when you pedal hard.
 
Odd description bordering on vague about slipping. Take the rear wheel off the ground and give it full throttle to see if your motor & frame are making vibrational harmonics aka shaking. If it's shaking violently, it's the motor/wheel. :idea:

Are your dropouts horizontal aka track, semi vertical, or are they through axle?
 
dogman dan said:
Very confusing thread for me.
Feels slippery,, to me that screams your tires are worn out, poor choice, you corner too hard for that tire, the road sucks, etc etc.
Yes, sorry the description is a little vague. It's because I've been having a hard time characterizing what's going on. The back tire is nearly new with no signs of being worn out, and this "slippery" effect happens even when not cornering, even on good road surfaces sometimes. Though it is especially guaranteed to hit on bad road surfaces, I'd say.

But if you said the frame feels rubbery, you see it flex as you pedal hard, and such like observations, that's more like you'd expect from a cracked frame. Or one that has been flexed enough to soften up and bend too easy. Often there will also be high speed wobble, at slower speed than before. The bike wags its rear end like a dogs tail.
Perhaps I don't have a good enough sense of my bike to have noticed the frame itself feeling rubbery -- or maybe that's really the sensation I'm experiencing, without realizing it.

Bent frame, I'd expect you to say I fall to the left, or the right more, or it won't track right anymore. Can you ride no hands on this bike at all? If not, its time for a replacement. Mis alignment of front and rear wheels screws up your handling quite a bit.
Yeah it does seem like the bike wants to go to the left, and it seems like I find myself sitting on it with some bias to compensate. I'd say riding it with no hands would be immediately disastrous. The feeling of stability I remember is simply gone. I bet those front and rear wheels are mis-aligned. Yeah I'm rapidly reaching the conclusion I should just get another one.

If you don't care about weight, and plan to ride pretty much under 20 mph, its hard to beat 7 speed beach cruisers, including the mild steel ones. But an equally good choice without the weight, are good alu ones, like the electra townie. But you said high powered ride, so it does sound like you corner fast. Which brings my thinking back to tires as at least part of your problem.
I've considered the electra townie! They seem like a nice chill ride. I do kind of enjoy being able to go up to 30 mph on it though, to make my commute more manageable. I know that's not necessarily "high powered" compared to some on here, but I do appreciate the prompt acceleration I get from the 1500w motor @ 14s6p battery.

Any kind of performance riding does call for much better bike frames, quite possibly full suspension. But NOT cheapo shocks. The bike shaped object full suspension bikes will feel more or less ok at first, but the thin frame tubes will soften up, and soon the bike will be wagging its tail.
Okay thanks, that is good advice!
 
SlowCo said:
Have you moved more weight to a rear rack such as battery and/or controller? And is that secured tightly? Poor handling and feeling "wobbly" at the back can be because the center of gravity is moved too far rearwards and upwards.
I'd considered that, but I hadn't changed anything at all other than wrecking and subsequently replacing the front wheel and fork. I did have to bend my cargo rack back a little, but it seems about where it should be. The battery is center mounted.
 
d8veh said:
Check your wheel alignment with a plank of wood or string to see if the front is off-set from the rear:
alignment_chass.gif
Oh!! That's brilliant! I will definitely try that! I would love to find conclusive evidence to back up my sensation of horrible instability, to confirm it's not in my head (I'm pretty sure it's not) and justify a replacement (that I'm pretty sure I need).
 
dogman dan said:
I'm still thinking the bike is so easy to flex now, and possibly flexing more because of weight on a rear rack, that it tweaks out of line both ways on every corner.
Straight when parked, but the tails wagging on that bike. If its bad, you can see easily it every pedal stroke when you pedal hard.
I can try taking off the rear rack to see if it makes any difference (I usually keep a few pounds worth of tools and things in there). My impression is that it won't, but it would be another data point. I responded to your earlier comment to say that the instability isn't limited to cornering, by any stretch. But maybe I can see it bend, I can give that a look.
 
melodious said:
Odd description bordering on vague about slipping. Take the rear wheel off the ground and give it full throttle to see if your motor & frame are making vibrational harmonics aka shaking. If it's shaking violently, it's the motor/wheel. :idea:
Yeah, sorry about that. Part of my problem is that it's been hard to characterize even to myself precisely what's going on, other than that the ride feels unstable, and the rear wheel seems to slip to the side sometimes as part of that instability. Perhaps I'm wrong to focus on the slippage though, since it makes it sound like I don't have good traction or something, which is certainly not the main culprit.
Oh okay, that's the first anyone has suggested that particular test. It would definitely be worth knowing if it's the motor/wheel instead of the frame (and I still haven't found any definite cracks in the frame, but I have yet to take the wheel off entirely to get a better look)

Are your dropouts horizontal aka track, semi vertical, or are they through axle?
They're semi-vertical, it looks like? Either that or vertical. I didn't know about the distinctions until I looked at pictures just now, but they definitely have an opening on the bottom that the axle is pushed up through.
 
Do a faster torque check on all hardware on the bike, and an inspection of all the welded frame areas.

Last time the bicycle I rode felt like it's tail was loose it had only finger tight axle bolts...
 
If you've got a couple boards you can stand on that you can strap the rear chainstays to, then you could use a couple cargo straps to secure those stays to the boards, stand on the boards, and grab the seat, then wiggle the bike back and forth, observing all the joints in the frame in turn as you do it. You can grab the stem or headtube and try them, too.

Anything you can strap the frame to would be useful for this test.

I'd do the test in sunlight to make it easier to see details.

You shouldn't be able to wiggle the frame to any significant extent, if it's normally a stiff frame.


it doesn't test the wheels (axles, bearings, hubs, spokes, rims, tires, etc) but it'll show you frame problems.


If the frame tests ok, then you can remount hte rear wheel, and flip the frame upside down, strap the frame down again, and begin wiggling the rear wheel. If there's any wiggle there, you can then see exactly where it is happening at as you do it.
 
Betcha you cant ride it no hands. That means the wheels are out of line. Maybe you just bent it.
 
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