Aluminium and Front Hubs

[nabidana]

Hello - I've ordered a XiongDa 2-speed motor, I've ordered a strong rim (Ryde Sputnik) and strong spokes and I have a bike firm in Dublin in principle happy to take a trade-in on my Cube Hyde Race bike (with which I will be sorry to part, sort of). I've decided to get the new big 15Ah battery from Woosh, because I suspect they will be quicker to help me out than a factory in China (Although I will solicit other options).

So I now have to get myself a bike to build my new wheel and motor into - the Irish bike market being relatively immobile (Giant, Specialised and Merida, mostly), I am hit with a number of extremely undesirable bikes with steel rigid forks, or much nicer units for reasonable prices with aluminium forks.

So I'm confused. The XiongDa puts out good torque, obviously - but tell me, in your view, if all else was equal (hub fitted between the dropouts, prepared to use a Torque Arm etc), is there anything specifically militating against aluminium forks? Is there a basic cardinal rule saying they're not compatible with a 250w motor of this sort? Also, by extension, is front suspension now ruled out? Decathlon have some inexpensive, nice looking bikes.

I treat your words as gospel, chaps and chapesses. I have no desire to faceplant nor be scraped from underneath the wheel arches of an 18-wheeler. Save my life.

 

[Alan Quay]

I ran a 350 watt (ish) front drive motor in a Suntour XCT suspension fork, for over 1000 miles, without any torque arms.

I'm a big chap, but I did not have a problem.

If I were to do it again, I'd use a torque arm for peace of mind.

 

[Deleted member 4366]

Suspension forks are not possible with a front Xiongda because it's too wide. Get a rear one instead.

 

[jackhandy]

If you go for the battery from Woosh, it might be as well to tell them zackly what you are using it with/for, so they can confirm the warranty will be valid.

 

[nabidana]

Parts for a front one ordered. Happy enough to dump suspension if necessary - haven't found a need for it before, but before I had been using carbon forks, which were lovely. The things we trade down to trade up...

 

[drsolly]

Suspension forks are not possible with a front Xiongda because it's too wide. Get a rear one instead.

My XiongDa is fitted in a front suspension fork. But I had to use a car jack to widen them by about an inch. These are steel forks, I wouldn't do that with aluminium.

 

[Deleted member 4366]

You wouldn't physically be able to do that with aluminium forks. Even with steel forks, you'll limit their ability to slide because the legs won't be parallel, but the bridge, crown and axle are fixed lengths. The only way they can slide would be if the bridge could stretch or the legs could bow. In practice, cheap steel suspension forks have a bit of free-play in the bushes, which will allow some kinking of the legs.

I can see that it's possible to for the motor, but surely the suspension can't work very well.

Please don't anybody try this with proper air forks.

 

[nabidana]

Thank goodness, I wasn't hallucinating. I've been following drsolly with extreme interest, since his timescales and processes seem very close to those I'd like to follow myself. I haven't seen photos of drsolly's bike so I was reading between the lines of his (excellent) blog.

So - realistically, what I have been gathering is as follows -

I can use a DECENT aluminium rigid fork as long as I use a torque arm - and Americans seem to think that's only necessary for big powerful motors. I'm taking the view that the XiongDa probably outputs a reasonable torque - and therefore it'd be better if I used an arm to offset the spreading force active on the dropout, I should be golden.

Alternatively, if I can, I should get a steel fork, but still use the torque arm because I may as well do everything I can to mitigate potential risks.

I shouldn't try to use a suspension fork because I can't rely on the XiongDa fitting and I shouldn't bugger about with a suspension fork.

 

[Deleted member 4366]

Steel forks will be better because the drop-outs don't suffer metal fatigue like aluminium ones. Whether you need a torque arm on a steel fork depends on the thickness of the drop-out. For 5mm or thicker, I wouldn't bother, but 3mm or below I definitely would. A badly anchored torque arm is as good as useless, so get a fork with a disc mount to fix the tie-bar to.

If you want to use a disc brake, you'll probably need a rotor of at least 180mm.