Low Speed DD in a suspension fork?

[Sunder]

Hi All,

I just wanted to ask an opinion. A friend of mine wants to do a cycling trip with me. I have two kids, and I was going to suggest that my wife carry one, and I carry one, but my wife isn't keen on riding with a kid (Had a few stacks in the past), and suggested I tow them both in a trailer.

Now, that's all fine and we bought a trailer, but I realised that the one I bought needs to be attached to the rear dropouts, which won't work with a rear hub motor. I have spare front hub lying around laced into a 26", but my only 26er is front suspension fork.

I know the general advice is to never put a motor in a front suspension fork, but my intention is to split my 12S pack into two 6S packs, and run the motor at less than 20kmh (Roughly 13mph). There will be no jumps, no kerbs, and hopefully few potholes.

This isn't intended to be a long term solution, but just for one holiday. Do you think this is an unreasonable risk of serious injury to me and the kids, or something that I could possibly take with a small chance of some grazed knees and inconvenience as the worst outcome?

 

[Samd]

There's a dearth of science available on this thread for free.

https://endless-sphere.com/forums/viewtopic.php?f=2&t=14195&hilit=front+fork+test+torque

 

[Sunder]

There's a dearth of science available on this thread for free.

https://endless-sphere.com/forums/viewtopic.php?f=2&t=14195&hilit=front+fork+test+torque

Thanks Sam. Looks like I have a lot of reading ahead of me.

I don't want to be a grammar Nazi, so please don't take offense at this, but dearth means "a lack of". I think you meant wealth.

 

[Samd]

You;re not doing irony today eh.

Semicolon intentional.
Fully sic.

 

[Chalo]

The thing to keep in mind is that low speed does not equal low torque. Axle torque is what breaks forks and dropouts. I say use a torque arm and be confident, rather than go without and doubt. If you use a well-fitted, well anchored torque arm, you'll have no problems.

 

[ScooterMan101]

The solution I will some day do for this is , to go to a machinist and have him make a 2 piece custom trailer hitch, that clamps to the inside and outside of the seat stays and go down to and clamp around the chain stays, and continue down to below the hub motor axle/wires , so that the hitch is now just in front of and below the axle .

like this burley one that uses the axle ,
https://www.rei.com/product/896409/burley-steel-hitch?cm_mmc=cse_PLA_GOOG-_-8964090001&CAWELAID=120217890001734605&lsft=cm_mmc:cse_PLA_GOOG

only longer so that it extends up around the chain and seat stays.

Hi All,

my wife isn't keen on riding with a kid (Had a few stacks in the past), and suggested I tow them both in a trailer.

Now, that's all fine and we bought a trailer, but I realised that the one I bought needs to be attached to the rear dropouts, which won't work with a rear hub motor.

 

[dogman dan]

Just do the install properly.

Start with two c washers, fill that QR cup. Then two good quality torque arms. The current version of front torque arms from Grin for example. They have extra reach to get around the beefier fork tubes than the common cheap TA type.

You will likely need to deepen the dropout at least 1 mm, to get a better fit. Not too much, so it won't affect later use of the original wheel.

Also, you may not get very good fork movement when powered up. The forks may bind some, and you will need to get off the throttle for the larger bumps, potholes, rr tracks, speed humps, etc.

8000 commuter miles on motors with suspension forks, and no mishaps ever. It can be done safe.

 

[Sunder]

Thanks for replying everyone. A consensus seems to be forming that if I do this right, the risk is tolerable. Good to know. I'll get a decent set of torque arms, make sure everything is sitting flat and get a torque wrench to make sure I do it up to at least 30-40nm.

ScooterMan - thanks for the idea, but having spent only $100 on the trailer, I think getting a custom made trailer hitch for it would seem a bit silly - it'd cost more than the trailer itself.

Thanks again everyone.

 

[LewTwo]

There are (possibly were) a bunch of comercial e-bikes that used low power hub motors in suspension forks. I do not think that they even use torque arms.
One brand that comes to mind is schwinn. Example: https://www.youtube.com/watch?v=dYSCtk4nKdM



http://www.ebay.com/itm/301954121389

 

[d8veh]

I've done a lot of front wheel builds with high torque motors. Generally, I think it's a bad idea to put a big DD motor in aluminium forks. It can be done, but there's always risk. My last one had two properly anchored torque arms, and was absolutely fine until I took the wheel off to fix a puncture and found that the fronts of the drop-outs were no longer attached. I would summarise by saying that it's best to avoid it if you can.

What about getting some steel forks as a temporary replacement? It doesn't take long to fit them.

Alternatively, can't you fabricate some adapters for the trailer fixing?

 

[dogman dan]

FWIW, that picture of the Schwinn has a squashed steel tube type , pogo stick, fork. Those steel drop outs don't really require a TA.

Sunder, if your bike is steel, you can weld some steel plate to the rear of it, and bolt on some studs to haul the trailer. Not huge expensive.

 

[LewTwo]

FWIW, that picture of the Schwinn has a squashed steel tube type , pogo stick, fork.

Pray tell what is a pogo stick fork ?

 

[spinningmagnets]

Pogo stick fork: no proper dampening, just two coil springs inside a tube-in-tube, found in low end Walmart China BSO's

Sam...there's a *plethora of science... (sips beer, and then sniffs condescending like a right proper c**t)

 

[Zarkon]

I have two Schwinn Tailwinds (his and hers) with the front hub motor. Its equipped with the Suntour Nex 4610 front fork and magnets fall right off it. The dropouts are 7/16" wide and is listed as an alloy as in not steel. Also, this bike was never sold in Walmart ($3200 retail back in 2008 - NOS still available today). Been running fine without any torque arms.

Interesting topic since I wonder how powerful a hub motor I can put on it. Can any other Tailwind riders chime in? Thanks for the link to the other thread on dropout experiments.

 

[LewTwo]

I have two Schwinn Tailwinds (his and hers) with the front hub motor. Its equipped with the Suntour Nex 4610 front fork and magnets fall right off it. The dropouts are 7/16" wide and is listed as an alloy as in not steel. Also, this bike was never sold in Walmart ($3200 retail back in 2008 - NOS still available today). Been running fine without any torque arms.

Interesting topic since I wonder how powerful a hub motor I can put on it. Can any other Tailwind riders chime in? Thanks for the link to the other thread on dropout experiments.

Drat ... now you have gone and revived my interest in those ebay adds.
I also note that it has a Shimano Nexus 8-Speed IGH which is worth about half the cost of the bike.
How much does that little beasty weigh ? and what max width tires will it mount?
Better yet, I do not suppose that you could be encouraged to do a full review of the tailwinds and post it (hint, hint, hint, hint)?

 

[Zarkon]

Drat ... now you have gone and revived my interest in those ebay adds.
I also note that it has a Shimano Nexus 8-Speed IGH which is worth about half the cost of the bike.
How much does that little beasty weigh ? and what max width tires will it mount?
Better yet, I do not suppose that you could be encouraged to do a full review of the tailwinds and post it (hint, hint, hint, hint)?

It weighs 58lbs but you can easily shave off a little weight by removing the rear rack and moving the controller and a modern battery to the triangle. The bike rides really well and the best part is that it comes with a Lithium Titanate battery that is easily revived - credit to Syonyk here https://syonyk.blogspot.com/2015/07/bypassing-schwinn-tailwind-battery.html
he also did a review here https://syonyk.blogspot.com/2015/09/schwinn-tailwind-review-in-2015.html

I am much more fond of it than he is - the advantage of a 30 minute quick charge battery is that one can charge immediately before use (20 mins is the typical charging time for me since it still has juice left in it before the charge). No need to keep the battery in a high state of charge at all. Also, no hills in Houston so this bike could work really well for you. An absolute bargain at only $300 (note: I have no ties to the seller at all).

For longer trips I am putting together two alternate batteries - one 16Ahr HK lipo based and the other with 18650 cells with phase change thermal jackets (ie Texas summer batteries - no sense subjecting nice battery packs to 100+ F ambient temperatures). Once I have some data to share on that I will post it up in a new thread.

Not sure what the max tire size is but it looks to have lots of room for bigger rubber.

 

[LewTwo]

Thank you for the links Zarkon

 

[dogman dan]

Thanks for the correction on the fork. Better fork than I thought then, likely does have some oil damping in there. Also looks a lot like they have a flatter dropout there too, like they are made for the larger washer on the axle. That larger dropout made them look like the pinched steel tube kind.

 

[Gregor]

Zarcon, is the original Schwinn battery a 7s (x3.7v) battery?

 

[motomech]

Hi All,

I just wanted to ask an opinion. A friend of mine wants to do a cycling trip with me. I have two kids, and I was going to suggest that my wife carry one, and I carry one, but my wife isn't keen on riding with a kid (Had a few stacks in the past), and suggested I tow them both in a trailer.

Now, that's all fine and we bought a trailer, but I realised that the one I bought needs to be attached to the rear dropouts, which won't work with a rear hub motor. I have spare front hub lying around laced into a 26", but my only 26er is front suspension fork.

I know the general advice is to never put a motor in a front suspension fork, but my intention is to split my 12S pack into two 6S packs, and run the motor at less than 20kmh (Roughly 13mph). There will be no jumps, no kerbs, and hopefully few potholes.

This isn't intended to be a long term solution, but just for one holiday. Do you think this is an unreasonable risk of serious injury to me and the kids, or something that I could possibly take with a small chance of some grazed knees and inconvenience as the worst outcome?

....but my intention is to split my 12S pack into two 6S packs....

You would have to use a 24V controller w/ a LVC of 21V, slightly low for 6S(cell value of 3.5V).
A more useful Voltage would be 9S, which when used w/ a 36 V controller, also gives a LVC of 3,5V/cell.

 

[Sunder]

You would have to use a 24V controller w/ a LVC of 21V, slightly low for 6S(cell value of 3.5V).
A more useful Voltage would be 9S, which when used w/ a 36 V controller, also gives a LVC of 3,5V/cell.

Thanks Motomech, but I have a fully programmable controller, with customisable LVC. It can do up to 40A continuous and 80A peak at any voltage up to 100V.

Should be enough for my purposes.

 

[Zarkon]

Zarcon, is the original Schwinn battery a 7s (x3.7v) battery?

The original Schwinn Battery for the Tailwind is the rather unusual Toshiba SCiB Lithium Titanate 10s with each cell having a nominal voltage of 2.4V (pack voltage of 24v nominal). As far as I know this is the only ebike with this battery chemistry https://en.wikipedia.org/wiki/Lithium%E2%80%93titanate_battery