5 k miles check up.

[MarkJohnston]

Hi.

I've been riding for about 5 thousand miles on an aluminum frame. I'm wondering about the health of the drop outs because I run a 1000 watt motor. I also pedal a lot so I have an extra 250 - 500 watts coming though. I have a massive front chain ring and very small gearing in the back. Usually 55t/11t. I fly. 30 mph+

My question is can an aluminum frame handle all this without developing micro stress fracture? MSF scare the hell out of me, you can't see them with the naked eye. You need an x-ray machine.

I only use ONE torque arm. And it seems crappy. It needs to be welded instead of bolted at the arm point. Also is a tiny weak crappy hose clamp from the dollar store really going to keep the wheel in if the dropouts catastrophicly fail??

Well... I posted pictures... Let me know what you think. I know, I should just get a steel bike but it seems excessive and expensive. Look at it pics. Let me know

 

[99t4]

Good question.

From your photos ... the dropouts appear to be in surprisingly good shape given your usage case descriptions. However, you should not trust long-distance photo diagnosis for a clean bill of health. As you mention, x-ray inspection is in order if you have suspicions. Even then, be aware that it does not always catch all flaws. And it is expen$ive. Has it been crashed? Those last two photos of the RH side chain(?)stay-- are those just surface paint scratches or are they evidence of tubing buckling there near the dropout insert?

I only use ONE torque arm. And it seems crappy. It needs to be welded instead of bolted at the arm point. Also is a tiny weak crappy hose clamp from the dollar store really going to keep the wheel in if the dropouts catastrophicly fail??

Yep sure enough that looks like a cheap crappy TA. Why would you use a cheap crappy TA and expect that to keep up with your torture chamber treatment? And know that the hose clamp is not there to "keep the wheel in if the dropouts catastrophicly fail!" :lol: It is there to keep the TA from rotating with the axle. They seem to work pretty well for that task.

Given your weight, power, and riding style you should not settle for less than two high quality well designed, well executed TAs (Grin Tech has them, v.3 or v.4, made out of thick quality material, good machining tolerances, and they have slots for multiple hose clamps). Mounted in opposition to each other, to keep that axle from moving even a fraction in either direction. Maybe back them up with Nordlock washers or similar for peace of mind.

Also, inspect the area frequently, you are doing the smart thing.

IOW, use all the good tricks in the book to minimize your worries.

P.S.: Unless it is a pinchbolt clamping type of TA, the TA must be a really tight fit on the axle. What is known as an interference fit. Force fit. Almost needs to be hammered (at least tapped) into position. PIA to remove it. But anything less will allow eventual axle rotation, eventually rounding out the dropout slot.

 

[MarkJohnston]

No I scratched it . All scratches are my doing. NEVER had Been crashed hard. Yeah I thought the torque arm doubles as a way to keep your wheel in

Here the thing 99.

I contacted Chinese manufacturing (Voilamart) and they told me I don't need torque arms at all. It's so low low torque this motor. It's a cheap none geared hub motor.

I've been fine all this time. And those grin tech TA are EXPENSIVE! ALSO HOW THEY HECK DO I GET THOSE THINGS AROUND MY AXLE WIRING?

 

[MarkJohnston]

Also 99 good point about the weight of the rack over the drops. I guess that's why a bunch of guys use midtube packs. So all that weight hits the drops harder too. Damn.

But in the scenario the drops snap off completely like I have seen in some other members posts, what then keeps the wheel in place? The hose clamp ?


P.S. I don't think I get another single washer on here. Real estate is limited.

 

[LewTwo]

I contacted Chinese manufacturing (Voilamart) and they told me I don't need torque arms at all. It's so low low torque this motor. It's a cheap none geared hub motor.

From their WEB site: "Voilamart is the global online retailer"
They may even be a 'drop shipper' and likely never even seen a example of the products that they sale much less understand anything about the specifications (even if they got them translated correctly).

 

[99t4]

I've been fine all this time.

All right, so carry on.

 

[MarkJohnston]

The grin v3 looks great. I like how it mounts to an eyelet. Problem is that you still should put a tac instead of bolting the two pieces together. That way if the drops snap the wheel stays in

Also, Ive got to get the giant molex hall effect sensor though the middle of the arm. Not going to be easy

 

[E-HP]

Also, Ive got to get the giant molex hall effect sensor though the middle of the arm. Not going to be easy

You can use a small screwdriver to release the pins from the MOLEX connector. Just keep track of the wire positions so you can put it back together after you run the cable.

 

[MarkJohnston]

The pins release? They're designed to clip in?

 

[MarkJohnston]

Also depending on how aluminum is designed it CAN be good. Case in point the JANDD expedition touring rack vs the TUBUS stainless steel rack.

The JANDD rack uses reinforcement in the rack, i. E. Aluminum rod cores inside the rack struts. That way if it cracks the struts still have support. I cracked a cheap aluminum rack with solid core rods inside the struts and this bontrager one is going to go soon. Same thing, it will never fail catastrophicly it has that solid rod running thru.

I talked to Dave the owner of the company directly. He told me that stainless steel is brittle and can snap. He said that people have snapped TUBUS racks. He told me they make their aluminum racks so well you can SIT ON THEM.

I'M wondering the same thing about bikes. Can aluminum be superior to a cheap steel bike? I mean they did a wonderful job on this frame looks like. All the welds look amazing. I got it from bikesdirect.com motebecane for $300 the whole bike. But steel bikes run double that at least. And it's just better at absorbing road buzz

Also no bike is truly all aluminum or all steel. Aluminum is 6061 and steel is chromoly. These are alloys, so neither is truly just plain old aluminum or steel.

 

[E-HP]

The pins release? They're designed to clip in?

Look at the pins bottom edge, where the arrows are pointing, and you'll see the metal clip that holds the pin from backing out of the housing. You can use a small screwdriver to press up on the clip, so that pin will slide out when you pull the wire. There's probably better terminology, which is why it's easier to use your picture.

 

[MarkJohnston]

Thanks for clarification. Now let's hope nothing snaps and I don't botch it. I have have just the screw driver

 

[E-HP]

These are alloys, so neither is truly just plain old aluminum or steel.

Technically steel is an alloy.

 

[E-HP]

Thanks for clarification. Now let's hope nothing snaps and I don't botch it. I have have just the screw driver

It's a matter of pulling lightly on the wire, while pressing up on the clip. But, take a pic so you remember the wiring order!!

 

[MarkJohnston]

Oh you are right. Yeah that just pops in and out super easy. Very nice. Ok. Now I guess I don't have an excuse anymore

 

[MarkJohnston]

Yeah it's gotta be something like 2000 watts when I'm pedaling full burst on this thing. I'm pretty strong and with the high gearing I can really pedal hard especially with the throttle full blast.

Also I don't know if you can guys can see but the dereilleur hanger IS steel and if you look at the pics you can see that. Not sure if that ends up strengthening the drops or not. 1st pic have a look thanks.

I'm gonna buy ONE torque arm from grin and ONLY ONE. How the heck do I get a PRESS FIT though? You said it needs to barely slide on.

What does " mounted in opposition to each other" mean?

P.S. yeah I've hit some BIG potholes HARD at 30mph. Can't always avoid them.

 

[DogDipstick]

Can aluminum be superior to a cheap steel bike?

P.S. yeah I've hit some BIG potholes HARD at 30mph. Can't always avoid them.

Oh yeah. I have a high end frame. Its aluminum, and much better than any steel frame I have found. World class suspension is typically not found on steel bikes. The aluminum is very very strong (> 60,ooopsi tensile strength , nearing steel). Only thing I dont like is that if flexxes around turns. Fleeexxxy.

I got an aluminum frame with 4000w contin and 8000w peaks, I impact it, have hit curbs at 30mph+, rain grates, ect. I jump. I beat it up. I donut. i climb hills. I linelock rolling. On pavement, a hundred times, on a row. I destroyed tyeh back yard more than once. I impact the dropouts as hard as I can. I hit shit forward so hard I have burnt my tire onto my box, that hangs under the downtube. It has been fine. Build it good, not loose or banging around, you will be fine. My bearings are going out on the brake side too.. Whole hub shifts, is rubbing the rear caliper if I hit it hard enough, from the flex Ithink, or the bad bearing.. IDK which. Aluminum dust from the caliper covers the rear brake. Lol.

Your dropouts should be fine. I also only use one tork arm, on the left, pointing forward. Six inches long. INSIDE teh dropout, not ont he outside .

Mine are much more hacked than yours. I do use a steel arm that has been case hardened. It does not bend at all. It is just an old steel dropout welded to a washer with a wrench as a arm. Securely anchored. The anchor is important. I have even crashed and ripped the derailer off, bent the Alu frame.. Hub stayed where it was supposed to. Ripped it off more than once.

Typical hub motor only needs to make some ~30-50 nM wheel tork to get that human/bike combo rolling ( starting tractive effort).... and that is usually the max a vehicle sees..... The STE or the CTE. Design for that and you should be fine. My hub motor has 110nM. Max before it can put out no more. 2x what is necessary to move a human to speed.. but I do get there REALLY fast.

 

[Mclewis1]

Great pics, it's nice to see these as they can be very educational to other folks.
I can't add to the discussion about the torque arms but I do have a suggestion since you are interested in maintaining that aluminum frame. There is some minor damage around the openings and I'd gently sand that surface area smooth and also remove some of the anodizing/paint to create a smooth uniform surface that will a) be easier to monitor for any new issues and b) will remove any sharp points in the damaged area which should help prevent cracks from propagating.

I would not work too hard at the sanding as you don't want to remove too much material, you're just trying to create a visually uniform area.

I'd then try to be careful when dropping the motor in, and bolting on the torque arms and axle nuts to keep any additional marking to a minimum. This should all help you during the next checkups when monitoring the dropouts as it should then be more obvious if there's any substantial changes.

 

[99t4]

Yeah it's gotta be something like 2000 watts when I'm pedaling full burst on this thing. I'm pretty strong and with the high gearing I can really pedal hard especially with the throttle full blast.

Your high (I think you mentioned 750W? 1000W? in the other post) human pedaling contribution won't cause much damage potential to the dropouts. Do the elite athletes Tour de France cyclists (they might be stronger than you?) suffer dropout failures from their strong pedaling?

I've hit some BIG potholes HARD at 30mph. Can't always avoid them.

We have to separate out two failure modes here that you are confusing into one:

1. Hubmotor axle spinout, which chews up and rounds out the dropout slots. Worse with hi power motors, heavy loads, strong regenerative braking forces. Really, it is caused by flawed hubmotor design-- Too-strong repetitive forces concentrated along the too-small surface area fit along the axle flat/dropout slot. This is what a good TA can protect against.

2. Dropout damage from overstressing the frame. Large jumps, potholes, gnarly crashes, heavy loads, etc. Common TAs not designed to help here. TA might help keep wheel located during a catastrophic dropout failure but I wouldn't count on it 100%.

Also I don't know if you can guys can see but the dereilleur hanger IS steel and if you look at the pics you can see that. Not sure if that ends up strengthening the drops or not.

Derailler hangers usually softer steel so they bend on impact instead of snapping so easily.

I'm gonna buy ONE torque arm from grin and ONLY ONE. How the heck do I get a PRESS FIT though? You said it needs to barely slide on.

If the TA fit is even the tiniest bit sloppy-- if it can rock back and forth even a little bit when fitted to the axle-- it's not much help because it allows the axle to rock back and forth which will eventually chew out both the TA and the dropout.
DIY TA makers cut the hole slightly small, and incrementally file out the flats until it will just barely slide onto the axle with some help from hammer taps.

What does " mounted in opposition to each other" mean?

Important if you use strong regenerative braking. Hubmotor acceleration wants to rock the axle backwards rotation; regen rocks the axle forwards rotation. That constant back and forth rocking can accelerate the tearing out the dropout. To compensate you can tension the TAs when final clamping so one is tensioning the axle in one direction, and clamp the other so it tensions the axle in the opposite direction. Axle will have a hard time rotating in either direction!

Actually, looking again at your photos here, I see no evidence of axle spinout caused dropout damage. Do you see any from your in-person inspection? Evidently, your stated motor torque forces are not as high as you thought, or your current TA is doing its job, or you have been able to tighten the axle nuts tight enough to control it, or some combination of all.

Just out of curiosity-- how much volts and amps are you feeding the 1000W hubmotor?

 

[MarkJohnston]

54.6 volts 20 amps. I have an aux battery in the other bag. Same thing.

 

[99t4]

So what is the motor drawing? 960W at max?

 

[MarkJohnston]

1200 watts peak. Actually. The cheap torque arm does have a pretty tight fit on there now that you mention it.