Front wheel fork dropouts shear off

[lozgreen]

Hello,

Sorry for only joining to ask a question - I do feel guilty.

I've been enjoying a 500w front wheel hub motor electric bike conversion for about 2 months - using it commute. On Thursday, I was just about to set off home from work, I twisted the throttle and my wheel shot off, but I stayed where I was. Unfortunately, the front prongs on my fork drop outs had sheared straight off.

I feel slightly stupid, being a structural engineer, that it never occured to me that from front fork is not really designed to carry drive through from the wheel to the rest of the bike - and is subjected to lots of torque and lots of fatigue stresses.

The fork was a fairly good on (Rockshox) and was aluminium. I've since read on the net that I shouldn't use aluminium or suspension forks with front wheel hub motor - and I quite annoyed that I received no warning at all from the seller (I bought the kit off Ebay) .

My real question is what should I do. I'm thinking I'll go for non-suspension steel forks, good idea? I've read on US forums that you can (and should) use things called 'torque arms' - does anyone know if these can be sourced in the UK. If not, the Heath Robinson solution seems to be using two spanner and steel tie.

I'd really appreciate any advice.

Regards

Laurence

 

[flecc]

The Torq 1 used alloy rigid forks with one of the most powerful legal motors Laurence, but they did have thivk dropouts and a tiny torque arm on one side to prevent spindle twist.

I'd say rigid steel forks should be ok, but you'd need to fabricate your own anti-torque arms as at least two members have already done. For double security, if you have a reliable local welder, you could get narrow blades welded onto the front and rear of the lowest part of each fork leg to strengthen that lower six inches or so. That would also give a handy place to relay torque stresses to.
.

 

[Tiberius]

Welcome Laurence,

Sorry about your problem - I don't think you are the first it has happened to, though. You do need to check whether you have stripped the wires out of the hub motor in the process.

There is no fundamental reason not to use suspension forks. The reason people caution against them is that you can't spread them apart to take the extra width of the hub motor. Equally, there is no fundamental argument against aluminium, but its softer than steel. Sometimes you can get away without extra torque devices with steel forks, but I wouldn't try it with aluminium.

As for torque arms or torque plates, they have been discussed a few times here. Start by having a read through this thread http://www.pedelecs.co.uk/forum/electric-bicycles/2268-mounting-hub-motor-torque-arm-man-thats-hard-work.html.

Nick