What are the chances of this motor ripping out a fork?

General Discussion about electric bicycles.
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OneWayTraffic   100 W

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What are the chances of this motor ripping out a fork?

Post by OneWayTraffic » Nov 16 2008 8:12am

http://www.evshop.co.kr/item.php?it_id=449

http://translate.google.co.nz/translate ... n&ie=UTF-8

(for those that don't like reading Korean.)

Being in Korea, I have until recently been unable to easily get a decent ebike conversion going, so I've sat on the sidelines dreaming.

However I saw this kit recently along with some Crystalyte kits (second link on the left) on a website in Korea and I'm ready to take the plunge.

Some things to note: they are all front wheel kits as far as I can tell, and I'd rather go that route anyway.

Second: I've no intention of riding on the roads here; that would be even more suicidal than doing so in the States and a lot more so than back in NZ. There's a cycle path along a river that I can take to work some days (18km (11miles) each way and flatish.) The path is shared with other cyclists and the occasional pedestrian or rollerblader and when I'm not on that path it's quite permissable to ride on the footpaths. Therefore I doubt I'd need more than 250W, which is almost all I can take back to NZ with me later anyway. 20 mph is as fast as I can safely go in most areas I'll be riding in, and in other areas, it'll be a bit slower than that. I'm not a big guy, but I'll sometimes be carrying a kid on the back for a total rider weight of 95kg or so.

Third: I have a bike, though it's a very cheap and crappy Chinese made MTB lookalike that I picked up used for $50. I doubt that it's worth $100 new if you get the picture. 21 speeds, heavy steel frame, front forks are welded steel one piece (dropouts not quick release type). It's strong enough, but the components are crap and I'm not at all sure if the brakes would handle the extra stress.

If I upgrade my bike, would I need to worry about suspension forks? Or should I just retrofit my current bike and replace the gears and brakes as and when I need to? Any upgrade would be a Samchuly or similar I guess. Think $250-$300 range. The wife wouldn't release a lot more money than that right now.

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dogman dan   100 GW

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Re: What are the chances of this motor ripping out a fork?

Post by dogman dan » Nov 16 2008 8:35am

Go for it. The cheap mtb will work fine, if not better as an ebike than some expensive bikes. All steel can be a plus for an ebike. As long as it has v brakes they should work fine with the motor. If side pull brakes, then most likely they need upgrade, or find the next up grade of cheap bike that has v brakes. The motor looks good to me, as long as you don't expect too much speed. 24v is pretty inadequate on direct drive motors, but if slower riding is what you want, with a geared motor, it is very efficient so the battery will go a long way. I wouldn't sweat the gears, once you have a motor, you will use them a lot less, and tend to just pick one gear and stay in it, or maybe just use the top couple gears.

If you upgrade to a real good bike, the suspension forks can be a problem, since they will be aluminum alloy. I have found that the cheapest possible suspension forks are still steel, and can work great with a front motor. Just check forks with a magnet when shopping. These forks are easy to identify once you see one. They look like a steel tube was pinched shut at the end, to form the dropout. I have 1700 miles on a fork like that now with no problems other than they are not very long travel. They are more than adequate for what you describe though, or a good bike can just have a set of steel non suspension forks installed on it, possibly the ones from the bike you have.

OneWayTraffic   100 W

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Re: What are the chances of this motor ripping out a fork?

Post by OneWayTraffic » Nov 16 2008 4:17pm

Thanks!

How exactly does a hub motor destroy suspension forks anyway? I would imagine that they should be built to take abuse sufficient for any sub 500w hubmotor what with being designed for off roading and all that.

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Re: What are the chances of this motor ripping out a fork?

Post by Duracutter » Nov 17 2008 12:03am

OneWayTraffic wrote:Thanks!

How exactly does a hub motor destroy suspension forks anyway? I would imagine that they should be built to take abuse sufficient for any sub 500w hubmotor what with being designed for off roading and all that.
The torque it produces will destroy forks. That said, if you don't accelerate fast and watch the way you use the throttle, the front forks are strong enough.

I myself ride a crystallite 5303 front hub with 84volts with aluminum "front forks" :shock: . It has plenty of power but I always watch the acceleration where most of the torque happens.

Also, I got a specialized bike that has me sitting more upright, so the front wheel will slip a bit, thus saving the forks from too much torque...

:mrgreen:

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dogman dan   100 GW

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Re: What are the chances of this motor ripping out a fork?

Post by dogman dan » Nov 17 2008 6:53pm

Mostly, motors destroy forks when the bolts get loose, or a bad fitting washer bends some, allowing the axle to spin. No bike has a fork designed for this. If you get a really low wattage motor, usually 24v, then it tends to happen less. The problem with suspension forks is that many of them are aluminum alloy, and when it does fail, it happens suddenly, and then you get to see the emergency room. Steel forks failing let the axle spin, but the wheel stays on the bike in most cases.

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Re: What are the chances of this motor ripping out a fork?

Post by OneWayTraffic » Nov 17 2008 7:16pm

So it sounds like a good fit of axle to dropout is more important than nearly anything else. I don't think this will happen to me, but given I'm sole support for a family of four (no health coverage for days off-I freelance) I'd like the chances to be as close to zero as practically possible.

So a 250w geared hub motor, a good steel (preferred chromoly) fork, a damn tight fit, regular checks and care with the throttle=0%

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Re: What are the chances of this motor ripping out a fork?

Post by Doctorbass » Nov 17 2008 10:28pm

The real best way is to analyze the number you get with this equation:


Motor max power input(kW) x (2 x pi(Wheel diameter in inch/2)) x % of regen use over the time 1=0% 1.1=10% x Beta x the toughness you drive your bike (0-10)

Beta is:
0.25= for double steel torque arms installed and welded axel to frame
1= for double steel torque arms installed
2= for one steel torque arm installed
10= no torque arm installed on steel dropout
30=no torque arm installed on alluminium dropout
100= same as 30 but with loose nut on one side
200=same than 100 but both loose nuts ! :shock:



In my case my score is : 6104 :twisted:

Doc
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dogman dan   100 GW

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Re: What are the chances of this motor ripping out a fork?

Post by dogman dan » Nov 18 2008 7:33am

That should do ya. Basicly with a steel fork, you are very unlikely to go to the emergency room. Unless you do something really stupid like I did, and get a waterbottle stuck in the front wheel! :shock: Just look for forks that have big flat dropouts, usually the kind you see on cheaper bikes. The expensive ones have a small cup in the fork dropouts made to fit the quick release that can cause fit problems. The main thing is that the washers don't span any air space, since that will later squash down, and then the nut will be loose. The washer on a hub motor is usually pretty big, so sometimes it is bigger than any cup shapes made to fit smaller nuts and washers. Be carefull not to overtighten either, since then a stripped nut can get loose too. Danged if you do and danged if you don't. Get em pretty tight, but not with a 2 foot wrench.

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