De-fattening a folding Fatbike

[vklurk]

I have an older model RadMini that I rarely ride as I find the combination of fat tires and small wheels - particularly with Rad's default gearing - to be unpleasant to ride. Its in not-so-great condition and I'm not entirely sure what to do with it, but one plan I have come up with is to "skinnify" it, maybe using narrower wheels and a Grin torque sensing kit. Are there any issues with running normal sized rims on a fat hub? Would I be better off trying to get just a narrower "fat" rim (say, 60mm instead of the 80+ that come stock) and running the smallest tires I can on that, vs trying to go all the way to my preferred 2 to 2.5" tire size?

In general the Mini is sort of a strange beast: it folds, but is both heavy and fat, so the fold really doesn't actually do much. It's got a fun pair of integrated racks, so it could feel like a fun little hill climber with its small wheels and geared hub motor, but I can't stand the gearing or the handling. It's strange to me because I have a RadWagon from the same year - 2017 - and it's by far my favorite ever bicycle. 26" tires and a wider gear range do a lot. Plus, I seem to be the only person who actually prefers Rad's DD motor to geared motor.

I'm not sure how much weight the smaller wheels and a newer, better kit would really save me, and I'm open to other ideas. I'd sell it, but the condition is so poor I wouldn't be comfortable without selling it simply for parts, and at that point I'd need to basically just give it away.

 

[Papa]

Are there any issues with running normal sized rims on a fat hub?

Keep an eye on spoke-to-rim angles - I prefer no less than about 70 degrees (preferably 80>). Plug your rim and hub dimensions into Online Spoke Calculator to verify.


This chart might come in handy also....

 

[Nix Liou]

If you are planning on upgrading the motor kit, with a new controller, that's probably most of the value of the bike...

I doubt much would change by going to thinner tires except less impact absorption. It would be a little lighter and a little smaller but marginally on both.

If the battery still works, the battery + the new motor kit would let you DIY a bike to your tastes pretty easily.

I mean, for the cost of the Grin motor you could get a new ebike entirely

 

[docw009]

I was going to do that with my 20" Ecotric fat tire folder too. Bought the 60mm rims from Grin and new bafang fat tire motor from China. Built a new rear wheel and found it was too wide for my frame. Lost interest and gave the bike away. Don't miss it, I never did fold that bike.

I likely would have found the bike still too heavy. It did have steel rims, so the lighter 60mm would have improved pedal response. I don't think the narrow rim affects spoke angles, as long as both rims are 36 holes. Anyway, your project will cost a bit of money, more if you prefer to buy a pre-assembled rear wheel/motor from Grin. You'll also want a 11-34 freewheel, 52T front gear, better derailleur, full hydraulic disks,. maybe BMX bars to replace those wobbly steerers, and none of that loses weight. Better off putting that money into a new ebike.

Consider a carbon frame 20" e-folder. It will be like wearing sneakers afer a day of trudging around with ski boots. Wife and I have ridden over 6000 miles over 4 years on our alloy frame e-folders. Last two years have been on torque sense mid drive kits on full size bikes. Rode cadence ebikes for 8 years, I think T/S is really nice,

 

[amberwolf]

At a guess you're probably looking at a grand to replace all the stuff on there to do what you seem to be after. Myself, if I were going to spend that, I'd do it on a bike that is built the way I want it to be and does the job I want it to, and just needs a different assist / power system. I wouldn't start with a bike I didn't really like and try to make it less unlikeable.

That said:

Are there any issues with running normal sized rims on a fat hub? Would I be better off trying to get just a narrower "fat" rim (say, 60mm instead of the 80+ that come stock) and running the smallest tires I can on that, vs trying to go all the way to my preferred 2 to 2.5" tire size?

As long as the spoke angles come out ok it'll work either way. See Papa's post about that.

Plus, I seem to be the only person who actually prefers Rad's DD motor to geared motor.

What specifically do you prefer about it? That will help guide you to the stuff you'll want ot use or change on this bike to do the job you want it to do.

I'm not sure how much weight the smaller wheels and a newer, better kit would really save me, and I'm open to other ideas.

This one? 2017 Rad Power Bikes RadMini Review

If so, then

Total Weight:​

62.1 lbs (28.17 kg)

Battery Weight:​

7.8 lbs (3.54 kg)

Motor Weight:​

12 lbs (5.44 kg)

Rims:​

Double Walled Alloy, Black

Spokes:​

13 Gauge, Stainless Steel, Black

Tire Brand:​

Innova, 20" x 4"

Wheel Sizes:​

20 in (50.8cm)

So I'd guess that if you have 4" tires now they probably weigh 5 or 6 pounds each. I'd guesstimate that a decent 2.5" tire would be half that, maybe less, depends on each one's actual construction. So you might save say, 5lbs on tires.

But youll probably make the ride quality worse, as it doens't appear to have suspension other than the air in the tires. Be easier to pedal without power, though, and more efficient when powered. Depends on what you really want out of it.

I'd guess that the rim weight difference is negligible.


As far as chanigng out the motor: The motor that's on there is probably capable of more than it's being used at, but like any geared hubmotor it's limited by the multiple layers of thermal transfer (vs basically just one for DD hubs), so if you need it to work in it's low efficiency range more of the time it'l have a harder time shedding that heat than a DD, but it will be lighter for the same torque output vs most DDs

The controller / display set on it is probably pretty inexpensive and not very high current, so if you also replace the battery with one capable of supplying hte power, you could swap out to a VESC or Phaserunner / BR (or one of the Lishui's that supports open source firmware and torque sensiing), and "wake up" the existing motor if you simply need more torque out of it, or be able to sufficiently power a DD to give similar torque.

The battery has probably been affected enough by aging alone that it is unliekly to perfrom well at anything beyond it's orignal desing demand and it probably doesn't even really do well with that, being nearly a decade old at this point.





Other info that might be useful:

Motor Brand:​

Bafang

Motor Type:​

Rear-Mounted Geared Hub

Motor Nominal Output:​

750 watts

Motor Torque:​

80 Newton meters

Battery Brand:​

Panasonic

Battery Voltage:​

48 volts

Battery Amp Hours:​

11.6 ah

Battery Watt Hours:​

556.8 wh

Battery Chemistry:​

Lithium Nickel Cobalt Aluminum

​

 

[Nix Liou]

Battery Brand:​

Panasonic

Battery Voltage:​

48 volts

Battery Amp Hours:​

11.6 ah

Battery Watt Hours:​

556.8 wh

Battery Chemistry:​

Lithium Nickel Cobalt Aluminum

Results from a 2021 study on calendar aging of Panasonic NCA 21700 cells.

If just left above 50% charge for most of those 8 years since 2017, it could almost be EoL already just from sitting there.

 

[vklurk]

If you are planning on upgrading the motor kit, with a new controller, that's probably most of the value of the bike...

I doubt much would change by going to thinner tires except less impact absorption. It would be a little lighter and a little smaller but marginally on both.

If the battery still works, the battery + the new motor kit would let you DIY a bike to your tastes pretty easily.

I mean, for the cost of the Grin motor you could get a new ebike entirely

Oh, definitely the value of the bike. Grin sells an adaptor to use the Baserunner with the existing motor, which is the only reason I'm considering it. I could replace the controller and display with a Baserunner + CA, and add a torque sensor if I wanted, which is very appealing to me.

At a guess you're probably looking at a grand to replace all the stuff on there to do what you seem to be after. Myself, if I were going to spend that, I'd do it on a bike that is built the way I want it to be and does the job I want it to, and just needs a different assist / power system. I wouldn't start with a bike I didn't really like and try to make it less unlikeable.

This has the ring of truth to it.

What specifically do you prefer about it? That will help guide you to the stuff you'll want ot use or change on this bike to do the job you want it to do.

Oh, I find it very quiet and I like the regen braking quite a bit. I live in a hilly area and it's nice to have what is effectively a drag brake. The complaint most people seem to have is that it isn't strong enough, but on Cookie Policy - my wagon - I find it plenty strong for what I want, which is a bicycle that helps, not a moped.

This one? 2017 Rad Power Bikes RadMini Review
View attachment 380496

That's the one!

As far as chanigng out the motor: The motor that's on there is probably capable of more than it's being used at, but like any geared hubmotor it's limited by the multiple layers of thermal transfer (vs basically just one for DD hubs), so if you need it to work in it's low efficiency range more of the time it'l have a harder time shedding that heat than a DD, but it will be lighter for the same torque output vs most DDs

The controller / display set on it is probably pretty inexpensive and not very high current, so if you also replace the battery with one capable of supplying hte power, you could swap out to a VESC or Phaserunner / BR (or one of the Lishui's that supports open source firmware and torque sensiing), and "wake up" the existing motor if you simply need more torque out of it, or be able to sufficiently power a DD to give similar torque.

Yeah, this is sort of what I was thinking about: making a device with a bit less rolling resistance, and adding a more powerful controller and display. I am getting the sense that the other issues might make this a non-starter.

The battery has probably been affected enough by aging alone that it is unliekly to perfrom well at anything beyond it's orignal desing demand and it probably doesn't even really do well with that, being nearly a decade old at this point.

Results from a 2021 study on calendar aging of Panasonic NCA 21700 cells.

If just left above 50% charge for most of those 8 years since 2017, it could almost be EoL already just from sitting there.

Hrm, it charges fine and I've had no issues riding it, though I admit it was probably drained for a good while. I confess I'm now a bit paranoid about battery safety after reading this. I've never had the slightest issue with it, but should I consider recycling it?

 

[neptronix]

A 22 inch wheel would be a good way to de-fatbike something with 20" wheels.

But you don't have suspension and you have small diameter wheels. Your tire is your suspension in this case.

Because you sit significantly forward of the rear wheel on this bike, adding a front suspension fork means that the front wheel can help with suspending the rider. A 20" fatbike fork intended for 20 x 3.5" should fit a 22 x 2.5" wheel

The end result may look funny but i think it could maintain the comfort level and increase efficiency substantially ( expect some minor boost to acceleration )

 

[Nix Liou]

Oh, definitely the value of the bike. Grin sells an adaptor to use the Baserunner with the existing motor, which is the only reason I'm considering it. I could replace the controller and display with a Baserunner + CA, and add a torque sensor if I wanted, which is very appealing to me.


This has the ring of truth to it.

Oh, I find it very quiet and I like the regen braking quite a bit. I live in a hilly area and it's nice to have what is effectively a drag brake. The complaint most people seem to have is that it isn't strong enough, but on Cookie Policy - my wagon - I find it plenty strong for what I want, which is a bicycle that helps, not a moped.

That's the one!

Yeah, this is sort of what I was thinking about: making a device with a bit less rolling resistance, and adding a more powerful controller and display. I am getting the sense that the other issues might make this a non-starter.


Hrm, it charges fine and I've had no issues riding it, though I admit it was probably drained for a good while. I confess I'm now a bit paranoid about battery safety after reading this. I've never had the slightest issue with it, but should I consider recycling it?

A discharge battery tester like an Atorch 150 or 300w tester is relatively cheap, and can be used to determine the remaining capacity. Beyond that if the pack seems to perform fine, it is probably fine. Well built batteries from reputable companies tend to fail softly and just stop charging or similar due to proper protection circuits. Not a huge worry.

 

[vklurk]

A discharge battery tester like an Atorch 150 or 300w tester is relatively cheap, and can be used to determine the remaining capacity. Beyond that if the pack seems to perform fine, it is probably fine. Well built batteries from reputable companies tend to fail softly and just stop charging or similar due to proper protection circuits. Not a huge worry.

Thank you!

Pardon if this is a weird question - and off my own topic, lol - but I noticed in your sig you had experience with ToSeven kits. I am curious, do any of their displays provide information about how much torque or wattage the human rider is putting in, vs the motor? I know some of the OSF stuff for Tongsheng can do that, but I have heard not great things about their reliability.

 

[Nix Liou]

Thank you!

Pardon if this is a weird question - and off my own topic, lol - but I noticed in your sig you had experience with ToSeven kits. I am curious, do any of their displays provide information about how much torque or wattage the human rider is putting in, vs the motor? I know some of the OSF stuff for Tongsheng can do that, but I have heard not great things about their reliability.

Perhaps similar issues with ToSeven in regards to reliability- at least with the older models which had much more open firmware.
I don't think any of the screen options give you a wattage for the torque sensor, but there's a variety of options, each with some differences in the data you can extract... It will tell you pedal cadence, and torque sensor voltage though.
Maybe one day there will be OSF for the Toseven motors...

 

[vklurk]

Perhaps similar issues with ToSeven in regards to reliability- at least with the older models which had much more open firmware.
I don't think any of the screen options give you a wattage for the torque sensor, but there's a variety of options, each with some differences in the data you can extract... It will tell you pedal cadence, and torque sensor voltage though.
Maybe one day there will be OSF for the Toseven motors...

Thank you! That's too bad. I find it interesting that there's been so much concentration of OSF around the TongSheng kits, to the exclusion of all the other mid-drives on the market. One reason I've been leaning towards Grin stuff for this tentative Mini rebuild project - beyond that I might be able to keep my motor and only have to upgrade the controller and display - is that their technology, on the computer side, seems much more stable and mature while still being open. CYC seems more convenient, of course, but as the world of slick apps goes, more locked down.

 

[Nix Liou]

Thank you! That's too bad. I find it interesting that there's been so much concentration of OSF around the TongSheng kits, to the exclusion of all the other mid-drives on the market. One reason I've been leaning towards Grin stuff for this tentative Mini rebuild project - beyond that I might be able to keep my motor and only have to upgrade the controller and display - is that their technology, on the computer side, seems much more stable and mature while still being open. CYC seems more convenient, of course, but as the world of slick apps goes, more locked down.

You can also get a hub and a vesc controller and have tons of options and adjustability, for a fraction of the cost. The CYC stuff is based off of VESC iirc.

 

[vklurk]

You can also get a hub and a vesc controller and have tons of options and adjustability, for a fraction of the cost. The CYC stuff is based off of VESC iirc.

Eh, if I was to go somewhere other than Grin, it would be for a mid-drive. Again, my priorities are to get a torque sensing setup, preferably one that gives me lots of information, which the CA will. I suspect going for any other hub motor kit would involve a great deal of work beyond the outer edge of my current competency, just to get a system that wouldn't be as polished.