Old freeride frame suitable for 1kw?

[hexadrome]

Hey guys, I'd like to hear your experiences regarding frame durability.

Currently I have this setup:

Noname 7005 alu frame. I use salvaged e-scooter parts, low-cost but ultimately unsuitable for my goals. Complete luck on the great battery-to-frame mounting, it is durable and unobtrusive.

The batteries are in parallel, together they got 36V and 31,8Ah according to the label. Never tested the capacity, but I'm very happy with them. I got a flat-ground no-pedal range of a little over 40km (25 miles).
I run a cheap generic 36v 500w controller. It does the job fine.
The motor is the issue. It hasn't got any label and I wasn't able to research any characteristics. Judging from size it should have 350 watts. I took the e-scooter wheel, cut off the tire and drilled and laced it as a hub. Axle spacing for the 8mm (0.3") steel single open-end torque plate was possible without problems.

So yeah, I knew going from 10" to 26" wheel diameter will make the motor have worse torque. But by how much? Also, it was using what I had or having no e-bike. Acceleration from standstill to top speed takes about half a minute, top speed is around 32km/h (20mph). Total cost was under 170 euro, I have a lot of bicycle parts laying around.

Controls are rudimentary. Water pipe clamps are very useful for mounting

I'm happy with what I built with next-to-nothing but the low-end torque is so horrible that I have to ride very foresighted in traffic because I know I have a hard time reacting to unforeseen situations. Build-wise, I feel that a 30 year old Marzocchi Bomber Z2 is not strong enough to take the bigger repeated braking loads. As a mechanic by trade, I know it is.

Still, this thing is not safe and capable enough. My requirements are better torque, so I will be upgrading to a 1kw motor. A top speed of 20-25mph (30-40km/h) is enough for me and while the current range is fine, the motor used doesn't allow for any type of sprocket attachment. A proper e-bike hub motor would make pedalling possible. Also I dislike the hardtail frame because the motor bearings get a lot of shock loads from bad roads. They have developed play in a year of riding. Not much but noticable.

Now the goal is to build a durable bike which can handle the higher loads reliably - preferably forever. I have this frame:

I like it very much and would be immensely sad if it would break. It's a '91 Giant Box One which they labeled as "Freeride Series". Enough of you guys are mountain bikers as well, we all know freeride in '91 wasn't what freeride is today or was during the 2010s. I don't want to ruin this old frame by over-stressing it. A lot of them broke on the seatstay joint, not this one.

Thus I conclude the welds to be of good quality.



What I'm worried about are three things:
- Are the dropouts structurally strong enough to cope with the heavy motor long-term? I plan on double clamping torque plates made from the same 8mm/0.3" steel. However, the unusual shape makes a prediction hard for me as I've not enough EV build experience.


- Would the swingarm pivot hold up well? It's a simple bushing made of some kind of plastic. I can refabricate the plastic sleeve when it wears, but is the construction itself beefy enough?
Also, is the damper mounting of suitable dimensions? It's M6 bolts, that would translate to a little less in diameter than 1/4" bolts.


And finally, is the headtube beefy enough to withstand the heavy Marzocchi DJ3 I will be using plus the higher braking stresses?


I read ES for a long time and saw that some of you guys build e-bikes from worse quality frames. But do they hold up long-term? This is 30-years-old 6061 T6 alu and it is precious to me. It must not break. I'd love to hear your opinions.

Also, look at that fit. It wants to happen

 

[E-HP]

They say, if you love the bike, don't convert it. Get a donor that you can do anything to, without a thought about undoing it. On the frame itself, the one thing I'd be concerned about it that when converting a full suspension bike using a rear hub motor, you can already expect to have to tuning challenges when adding that much unsprung weight to the mix. With the Giant's design, your body, or at least your legs, also are part of that unsprung weight, since the cranks are downstream of the pivot. If you only ride seated, then it would be like any other full suspension frame though, so depends on how you ride it. The frame is plenty strong for 1000W, probably triple that or more. You just need good torque arms and will probably need to file the dropouts a little deeper.

 

[hexadrome]

Thank you for your input. I know about the characteristics of URT suspension designs but they coincidently suit my riding style well. Getting out of the saddle is for racers and people who can't shift properly :lol:
I don't expect the suspension tuning to be a big problem, I can switch to a coil shock if the little Manitou can't take high enough air pressures and tune with different springs.
You are right in that I'd be risk-free getting a donor. For me, cost is the limiting factor. Also I like how the Box One rides but I haven't ridden it much since I built the e-bike. It would kill two birds with one stone. The only thing I can't undo is breakage, as far as modifying the frame goes I can keep it completely original by
- mounting the batteries on pads of suitable thickness with cutouts for the cable stops and
- fabricating combined torque plate/dropout extensions if needed. One can achieve surprisingly complex shapes with patience and an angle grinder. I don't have the motor yet so this bridge will be crossed later.
Your answer makes me hopeful that durability is a non-issue. I'd love to hear more opinions.

 

[amberwolf]

So yeah, I knew going from 10" to 26" wheel diameter will make the motor have worse torque. But by how much?

It's proportional. Unloaded speed increases by the same ratio that torque decreases by. In this case, that's 10:26 for torque, and 26:10 for speed. So speed is 2.6x as high, and torque is 1/2.6th, or 0.385x as much (you could call it about 1/3 the torque of the smaller wheel, roughly).

If you like, you can use http://ebikes.ca/tools/simulator.html for seeing how the relationships between things work, and test ideas out before you build them, to see estimated performance.

I'm happy with what I built with next-to-nothing but the low-end torque is so horrible that I have to ride very foresighted in traffic because I know I have a hard time reacting to unforeseen situations.
<snip>
the motor used doesn't allow for any type of sprocket attachment.

If you had pedals for human input, and the right gears available to the human drivetrain, it would greatly increase your ability to overcome the motor's limitations.

You can add at least a single-speed sprocket to the motor by bolting the threaded flange off an old rear bike hub to the drive side cover of the motor. It's been done a few times successfully to turn front ebike hubmotors into rear ones, and will probably work with that motor too. I can dig up a link to the one I did if you need it.


Another option is to use the motor to drive a gear-shiftable drivetrain, eiher stokemonkey-style, or one of the other hubmotor-based middrive systems. (there are a number of useful threads around the forum about those, starting with Crossbreak's stuff from several years back).


A proper e-bike hub motor would make pedalling possible. Also I dislike the hardtail frame because the motor bearings get a lot of shock loads from bad roads. They have developed play in a year of riding. Not much but noticable.
Those can be replaced easily enough, if you like.

I like it very much and would be immensely sad if it would break.

If you love it as a bicycle, leave it that way. It will almost certainly never ride as an ebike like it did as a bicycle--the added stuff always changes it's behavior...rarely positively.

Get a frame that will do about what you want, or design and build one that does exactly what you need it to do.

You could, for instance, build a frame that is designed based on the frame you love, but satisfying the requirements of being an ebike, used the way you need to use it, under the conditions you'll be riding in.

- Are the dropouts structurally strong enough to cope with the heavy motor long-term? I plan on double clamping torque plates made from the same 8mm/0.3" steel.

If the plates are secured to the frame in a way that does not put rotational stress on the frame in places it would not have been designed to experience them, then it should be fine, if it was correctly designed and built originally. The longer the plates are where they mount to the frame, the less torque it will place on any particular part of the frame--for instance if it has long arms that parallel the stays for as much of their length as possible, and the metal is hard enough to transmit the axle torque thru the plates and arms without bending them, it will do less harm to the frame over time than if it is just a plate bolted to the original dropouts.

What exactly is necessary depends on the design and manufacture of the frame you're putting them on, and the amount of torque the system has to deal with.

The Torque Arm Picture Thread may help you with design ideas. There are also other threads about them, but that has more info / pics in one place.

- Would the swingarm pivot hold up well? It's a simple bushing made of some kind of plastic. I can refabricate the plastic sleeve when it wears, but is the construction itself beefy enough?

Use bearings instead of bushings and that will help with wear and play. If there is less play there will probably be less stress. Whether its' beefy enough depends on the stress it will see, and that depends on the ride conditions and riding style, as well as the weight the whole system must handle vs what it was designed for.

 

[hexadrome]

It's proportional. Unloaded speed increases by the same ratio that torque decreases by. In this case, that's 10:26 for torque, and 26:10 for speed. So speed is 2.6x as high, and torque is 1/2.6th, or 0.385x as much (you could call it about 1/3 the torque of the smaller wheel, roughly).

If you like, you can use http://ebikes.ca/tools/simulator.html for seeing how the relationships between things work, and test ideas out before you build them, to see estimated performance.

It was my first build. I haven't wrapped my head around the theoretical side of things enough yet, so I found myself unable to use the simulator properly. I also had no baseline. I did get the same numbers but without any clue as to what that would translate to in real life. I know what to expect from a given size of motor a bit better now.

You can add at least a single-speed sprocket to the motor by bolting the threaded flange off an old rear bike hub to the drive side cover of the motor. It's been done a few times successfully to turn front ebike hubmotors into rear ones, and will probably work with that motor too. I can dig up a link to the one I did if you need it.

I have thought about it. But my intuition told me it wouldn't be worthwile. The motor is cheaply made and the hub shell is really soft cast alu. I had very little resistance drilling the spoke holes. I didn't trust a reasonable sized (6-8mm/ 1/4-3/8") 6-bolt pattern to properly hold the freehub under load so I didn't try that route.

If you love it as a bicycle, leave it that way. It will almost certainly never ride as an ebike like it did as a bicycle--the added stuff always changes it's behavior...rarely positively.

Get a frame that will do about what you want, or design and build one that does exactly what you need it to do.

You could, for instance, build a frame that is designed based on the frame you love, but satisfying the requirements of being an ebike, used the way you need to use it, under the conditions you'll be riding in.

Well, thinking hard about it I love the boxy looks and the full suspension. It's flat here, so for trail riding I sold my big FS bike in favor of a hardtail. Too much travel made the trails too smooth and not exciting.
I do love the Box One for city transportation, it has enough travel to eat up road bumps and curbs. That could be said about any decent FS bike however, so it's more of a case of I love it because it's mine. Hmmm.

The longer the plates are where they mount to the frame, the less torque it will place on any particular part of the frame--for instance if it has long arms that parallel the stays for as much of their length as possible, and the metal is hard enough to transmit the axle torque thru the plates and arms without bending them, it will do less harm to the frame over time than if it is just a plate bolted to the original dropouts.

What exactly is necessary depends on the design and manufacture of the frame you're putting them on, and the amount of torque the system has to deal with.

Good point. But longer arms will weigh more and thus put more load on the damper. E-HP said to keep an eye on that. It seems the most sensible solution is to use just torque plates and file the dropouts. Nobody will ever see them anyway.

Use bearings instead of bushings and that will help with wear and play. If there is less play there will probably be less stress. Whether its' beefy enough depends on the stress it will see, and that depends on the ride conditions and riding style, as well as the weight the whole system must handle vs what it was designed for.

But a bushing transmits the load over a wider area compared to a ball bearing, no? And you need a bit of play anyway for the pivot to work.
Judging by the 25kg weight of the current setup and my 90kgs, I expect the total system weight will be approximately 120kgs/240pounds. Riding style is civil, ride conditions are the usual city traffic, potholes and curbs.

I have the impression I may be worrying too much. Thanks for your replies so far.

 

[Deleted member 82754 (removed by user request)]

for what its worth, my first build was on a trek fuel 95 full suspension. it was my first mountain bike and it was buried in the shed for years after i hurt my back. at some point in it's life, all the suspension bushings had been replaced. i added a bbs02 from Luna. after about 1200 mi, there was a noticeable "flex" in the frame when using the throttle. the local franchise store said the bushings are no longer available.
i have since moved it to my wife's trek 3700 and have a bbshd for myself on a hardtail i am using as a "utility" bike.

 

[amberwolf]

But a bushing transmits the load over a wider area compared to a ball bearing, no? And you need a bit of play anyway for the pivot to work.

The play I refer to is not pivot movement, it's the wiggle that you don't want--the non-circumferential movement around the pivot center. Getting rid of that play is good; the pivot does not need that. It only needs to rotate about it's center. (if it needs that play to operate, there is something wrong with the design or the manufacture, such that things aren't concentric or straight, etc...).

 

[99t4]

If I am understanding correctly, most of your concerns are that the bike frame and its suspension components may not hold up under a conversion featuring a higher power rear hub.

In my experience, the addition of the e-bike components do not appreciably impact the stresses beyond what a good bike can handle. Yes the added weight from batteries strapped to the frame, and the added weight from the rear hub do likely add stresses to those areas but take into account what conditions the bike was designed for-- rugged offroad riding with high impact and shock a given. What is the mfr. weight limit? Will you exceed that full up?

Riding on the smooth as you envision will reduce the stresses quite a bit. Likely the bike will see less stresses (even with the conversion) than it was designed for.

From your comments, you understand the potential problem areas. Inspect them often and replace worn components. If you see startings of frame cracks, they can be repaired. See forum member Dogdipstick's recent photo essay on his alu. FS frame rework.

The longer the plates are where they mount to the frame, the less torque it will place on any particular part of the frame--for instance if it has long arms that parallel the stays for as much of their length as possible, and the metal is hard enough to transmit the axle torque thru the plates and arms without bending them, it will do less harm to the frame over time than if it is just a plate bolted to the original dropouts.

What exactly is necessary depends on the design and manufacture of the frame you're putting them on, and the amount of torque the system has to deal with.

Good point. But longer arms will weigh more and thus put more load on the damper. E-HP said to keep an eye on that. It seems the most sensible solution is to use just torque plates and file the dropouts. Nobody will ever see them anyway.

You may have misunderstood AW's explanation. He was describing a TA with a long extended moment arm. (Think of an old style coaster brake arm-- now extended longer almost to the BB. The stress at the chainstay there is much less because of the long moment arm.)

 

[E-HP]

I think two of the "TorqArm_V2" from Grin would work, flipped over, and anchoring to the fender/rack eyelet. On the brake side, anchoring to the rear caliper bolt is an option. You'd need one washer between the chainstay and torque arm to line up the anchoring arm.

 

[hexadrome]

What is the mfr. weight limit? Will you exceed that full up?

It's pretty much impossible to find that information. Even so, it looks like I worried too much.

You may have misunderstood AW's explanation. He was describing a TA with a long extended moment arm.

This is how I understood the explanation as well. If I were to fabricate such a TA, I'd overbuild it. It'd lie flat upon the chainstay, be double hose clamped and at least half the stays length. And then I'd build another for the drive side. I have a selection of 8mm mild steel here, I weighed two suitable pieces. It'd add at least one kilogram and be totally unnecessary.
Seeing how E-HP recommended the much smaller TorqArm_V2 which is made from thinner 6,35mm steel (but of a harder alloy), I'll be fine adapting the design in 8mm mild steel for my frame specifically.

The play I refer to is not pivot movement, it's the wiggle that you don't want--the non-circumferential movement around the pivot center. Getting rid of that play is good; the pivot does not need that. It only needs to rotate about it's center. (if it needs that play to operate, there is something wrong with the design or the manufacture, such that things aren't concentric or straight, etc...).

That is how I read you as well. And the bushing design of the frame is in my understanding even better than bearings since the bushing is wider than two ball bearing races. Wear will be worse, I know. Also, I still don't get why manufacturers use regular ball bearings instead of roller bearings in frame suspension elements. But maybe I'm clueless and there is no difference given the design is proper.

Guys, thanks so much for all the advice. I've studied the forum, finally understood how the electrical interdependencies behave and modelled a lot with the ebikes.ca simulator.
I am very ashamed of myself, turns out all the time I've been completely abusing the poor scooter motor. It wants 60V/40A and to run at 60km/h speeds. I've been starving it with the weak 15A controller and only 36V. I was always running it in overheat mode, especially on acceleration from a stop. It took the abuse well but now I know better. And I know exactly what I want, so that makes it easier.

I'll be pairing a Bafang G040 (48V 500W) with a Kelly KLS4812S controller at 36V. I'll pedal hard during acceleration to be at my preferred cruising speed of 30km/h fast. The motor should run efficiently at a speed range of 30-39km/h which is perfect. I've simulated with a comparable motor and controller and I should get upwards of 70km range motor-only. Currently I only got 40km from 31,8Ah. Oh the inefficiency! I have maltreated the scooter motor enough, parts are on the way and a build thread shall follow.

Edit: bunch of electrical questions removed, wrong forum.

 

[E-HP]

Seeing how E-HP recommended the much smaller TorqArm_V2 which is made from thinner 6,35mm steel (but of a harder alloy), I'll be fine adapting the design in 8mm mild steel for my frame specifically.

It's more about a tight fit than anything else. Mine are subject to 7kW every time I ride my bike. They've also been subject to thousands of miles of regen. You can overbuild it, but it won't make it more effective, than something less stout but with a good fit.

 

[hexadrome]

I agree. I would've gone for an interference fit and tried handfiling for >0.2mm tolerance for the overbuild TAs.

Mine are subject to 7kW every time I ride my bike. They've also been subject to thousands of miles of regen.

7kW with regen? I'm impressed, I've already decided that regen would stress the frame too much. Now I'll reconsider.

Ideally it will be possible to respacer the motor axle so that the TAs can go inside the dropouts. If so, I'll try my best at handfiling a shrink fit. Else I'll go for a 'hammer-tight' fit. It will be a total hassle removing the rear wheel, but I only will need to do that to change rotors and tyres since I plan on running Schwalbe Marathons tubeless.

I'll get BB7s for the brakes. I thought I could go Shimano mechanical but the BB7 has bigger pads, therefore more stopping power. E-HP, I see you run them as well with what looks to be 203mm rotors. Is your frame rated for those by the manufacturer or did you just install the biggest one that fit? I'm pretty sure my frame is only officially rated for a max rotor size of 160mm as it was common on those frames at the time, but I've only ever seen ripped off IS2000 brake mounts on front forks. I'd like a 203mm rotor for bigger thermal mass. What do you think?

 

[E-HP]

I'll get BB7s for the brakes. I thought I could go Shimano mechanical but the BB7 has bigger pads, therefore more stopping power. E-HP, I see you run them as well with what looks to be 203mm rotors. Is your frame rated for those by the manufacturer or did you just install the biggest one that fit? I'm pretty sure my frame is only officially rated for a max rotor size of 160mm as it was common on those frames at the time, but I've only ever seen ripped off IS2000 brake mounts on front forks. I'd like a 203mm rotor for bigger thermal mass. What do you think?

The BB7s were great. I ran them for a couple of years, but am using cheap four piston knockoff hydraulics now. I had a 180mm rotor out back for a while, but changed it out to 203 when I swapped out the calipers. It's an old school hard tail downhill frame, so the chain and seat stays have plenty of clearance, and it's plenty strong using Easton RAD tubes. It's still somewhat coveted a decade an a half later. The large rotors are nice, and the stopping power increased and lever effort decreased when I put them on. I don't really get any fading, although now that I'm not using regen, it seems the pads only last a couple of months.

 

[hexadrome]

It's an old school hard tail downhill frame

Oh no. Oh no no no. Just as I was so sure on the Box One because of the suspension. But guess who also got an old school hard tail downhill frame!


Mine has combined DJ/DH geometry and as you can see, it is currently built as a hybrid. I have considered using it as a donor. It is stable at the speeds I'd be riding. I'm unsure about the short wheelbase under motor acceleration however. I wouldn't want a wheelie machine.

Also I don't have tooling to change motor bearings. Would that be a concern using a hardtail frame? Sure, my current bearings have developed play. They weren't of that high a quality to begin with. I could invest in tooling, but from what I read disassembly and reassembly of the rotor without tilting is a bit of a hairy operation. I'd rather not risk damage at all.

So now I'm undecided between the two. What would you guys suggest is the more suitable one for the build?

 

[amberwolf]

Also, I still don't get why manufacturers use regular ball bearings instead of roller bearings in frame suspension elements. But maybe I'm clueless and there is no difference given the design is proper.

Cost, weight, possibly even "designer didn't think of it" (but usually "management vetoed it") .

I don't see roller bearings used as often as I would expect to in things. And sometimes a design will use rollers and then change to ball for apparent cost reasons. One example is the "U-boats" used in retail warehousing/stocking/merchandising applications.
https://m.media-amazon.com/images/I/41aWqNMb89L.jpg

The large weight-bearing center wheels in those
https://www.nationwidecartparts.com/HD_STOCK_CART_WHEEL.html
https://www.nationwidecartparts.com/thumbnail.asp?file=assets/images/8x2a.jpg&maxx=300&maxy=0

used to come with good roller bearings, and have grease nipples to lubricate them with. Nowadays, the replacement wheels (because the "tires" are easy to damage with virtually any debris on the floor, and once damaged they tend to just tear apart from the weight on the wheels pressing the damage points apart) we get where I work use typical "sealed" ball bearings and have no lubrication nipples. The bearings still outlast the "tires" (which you can't replace as they are cast onto the wheels), so it doesnt' really matter, but if they had good tires....

 

[E-HP]

Oh no. Oh no no no. Just as I was so sure on the Box One because of the suspension. But guess who also got an old school hard tail downhill frame!
another_option.jpg

Mine has combined DJ/DH geometry and as you can see, it is currently built as a hybrid. I have considered using it as a donor. It is stable at the speeds I'd be riding. I'm unsure about the short wheelbase under motor acceleration however. I wouldn't want a wheelie machine.

Awe come on man, I was looking forward to the full suspension build, which might inspire me to finally convert mine. But yes, my wheelbase is also short and it is prone to wheelies.

 

[amberwolf]

Regarding BB7's, I use a single BB7 MTN caliper with 203mm rotor on the SB Cruiser trike, and my only limitation to how quick I can stop from my 20MPH max is the limited contact patch size and grip of the front 26" CST City tire--it's easy enough to lockup the wheel, but that isn't helpful to control direction during braking. I get a bit better braking with lower tire pressure, down between 30-40PSI...but I usually keep it up nearer 50 because handling is better.

I don't have any suspension, so braking pushes the whole trike (and me and cargo) weight that's forward of the rear wheels onto that.... It does heat the rotor up quite a bit though (been blue tinged for some time now).

(someday I'll get around to modifying the rear frame to allow installing the rear wheel brakes too)

 

[amberwolf]

I'm unsure about the short wheelbase under motor acceleration however. I wouldn't want a wheelie machine.

Put the battery weight up at the front as far forward as you can (like on an extension from the toptube, over the front wheel) and it will help with that, and should still handle fine otherwise.

 

[hexadrome]

Awe come on man, I was looking forward to the full suspension build, which might inspire me to finally convert mine. But yes, my wheelbase is also short and it is prone to wheelies.

Your wheelbase is much longer than mine. And it's still prone to wheelies. I see.

Put the battery weight up at the front as far forward as you can (like on an extension from the toptube, over the front wheel) and it will help with that, and should still handle fine otherwise.

It will help, but by how much?

No, this is not the right frame, I'll be using the Box One still. But have a look at that bottom bracket height guys... This is the perfect starting point for a BB motor conversion

 

[amberwolf]

Put the battery weight up at the front as far forward as you can (like on an extension from the toptube, over the front wheel) and it will help with that, and should still handle fine otherwise.

It will help, but by how much?

Depends on the weight and where it is. If you know the torque produced by the motor, you can find the formulas for torque on a lever length and mass, and figure out how much mass has to be how far forward to counter it, in addition to the existing mass of the bike and you.

 

[hexadrome]

I forgot rhetorical questions don't work well on the internet. I think a future Bafang BB build for the Spank is most suited to solve that wheelie problem without needing calculations beforehand. I was under the impression that the Bafang BBSHD is a 48V only system. And since I already got the 36V batteries I'd figured I stay on that system voltage. That assumption is wrong as I know now, but even then the initial investment and the cost of operation (chain/cassette wear) is much higher with the BB motors, so I didn't want to follow that route for a cheap/cost-effective utility build.

 

[99t4]

Also I don't have tooling to change motor bearings. Would that be a concern using a hardtail frame? Sure, my current bearings have developed play. They weren't of that high a quality to begin with. I could invest in tooling, but from what I read disassembly and reassembly of the rotor without tilting is a bit of a hairy operation. I'd rather not risk damage at all.

Sure looks to me like you are starting to overworry again. Lots and lots of us run or have run hardtails thousands of miles without bearing problems. Not saying it can't happen, but the probability is pretty low. If an axle bearing does fail, it's more often an issue of either poor quality, defective, water or debris, or extreme abuse.

Both of those bikes appear to be of high quality, far better than many examples here on ES. Either would make a good candidate.

If there are any guarantees, its this: When you "finish" your build :wink: , you will want to either rework it, or start another one, to incorporate lessons learned, or better ideas that you have generated along the way.