Front motor and aluminum forks

[jha07]

Hi, I'm new to this site and new to the world of electric bikes. I've been thinking about converting my bike to an ebike. I plan on getting a crystalyte 408 front hub motor, and using 43-48V. Still haven't decided yet.
One of my concerns is using a front motor with my aluminum forks. I've read that they should only be used on non supension steel forks and that cracks could form on aluminum forks.
My forks don't have a suspension, but they also don't seem overly strong. If I hold the front brake down and push the handlebars forward, I can see the forks flex. I assume this flex under braking is normal and acceptable. But would the additional stress of a front motor be too much?

 

[flecc]

Hello jha07, welcome to the forum. That flexing is a good thing in the sense that it's better to give a bit under stress than resist and snap.

However that Crystalite is very powerful so I'm a bit nervous about you fitting that. Why not have a chat with Mark at Team Hybrid about it, as they have plenty of experience on fitting this motor and also using for stunts with e-bikes, like hops, jumps etc, so they know all about the forces involved.
.

 

[frank9755]

It's a good idea to get advice from someone like Team Hybrid who would know a lot about this motor. You might also try the Canadian supplier www.ebikes.ca Homepage of the revolution who have a great web site and seem to be highly recommended by many, including UK customers

I would ask 'why do you want to fit it to the front wheel?' Bikes are designed to be pushed via the back wheel. Putting a motor in the front wheel of a bike not specially designed for it is bound to introduce all sorts of stresses and strains that increase the chances of failure. Unless there's a compelling reason, I'd put it in the back!

Frank

 

[flecc]

I'm with Frank on that, and the Team Hybrid stunt team use Crystalites in the back wheel, doing "stoppies" and crashing the back wheel down again, so they're tough enough for that.
.

 

[Jeremy]

The Crystalyte motors are very powerful, I have a 406 fitted to the front wheel of my recumbent and it managed to tear out the steel fork end the first time I fired it up!

The answer to the fork problem is to do two things. Firstly, make a torque arm. I cut mine out from a bit of 4mm stainless steel sheet. It has a slotted hole cut out that is a nice snug fit on the Crystalyte axle and fits inside the fork. It's anchored to the fork using an extended stainless steel bolt through the mudguard attachment. The second thing to do is make sure that the axle nuts are really tight. If they are not they will just spin the motor clean out of the forks the first time you fire it up (guess how I found that out......). Don't be tempted to apply the brakes with the wheel up in the air and powered, it will really try and rip the fork ends apart if you do.

I managed to repair my steel forks, by heating the ends and bending the opened out slots where the axle fits back into shape, without cracking things, luckily. This did mean stripping the forks out, fixing them and then repainting them, so is not recommended.

They work extremely well as front wheel drive, in fact in many ways front wheel drive can be a slight advantage. The only disadvantage I've found is that the wheel will tend to spin more readily on occasion, but given the power of these things I feel it might well do this on the back wheel as well! I would advise you to go for at most 36V to start with, with perhaps the 20A current limited controller. I opted to go for the 35A controller and 48V and it really is a bit of an animal.

Jeremy

 

[jha07]

The reason I prefer to have a front motor is because I really like my 9 speed cassette and don't want to change the gearing, especally on the top end. My cassette is 11-32, and the closest freewheel for hub motors i've found is a 7 speed 11-28. If I do that, I'd have to change my shifter to match. This would be more trouble, and makes the bike more difficult to change back to non electric. My 9 speed cassette would no longer be compatible with the 7 speed shifter.
With a front motor, my gearing is not affected. Plus I can swap the regular wheel back very easily.
I fired off a question to Team Hybrid just now about this.
I will also ask ebikes about it. I'm actually planning to buy from them and live very close to their store.

 

[Jeremy]

Provided that you fit a torque arm and keep the nuts tight the front motor will work fine. There are lot's of people running these motors at much higher power levels in front forks without any problems.

Anyway, the braking forces in the front fork are very much greater than those that will be imposed by the motor. The hub motor won't accelerate a bike anywhere near as fast as even an average brake will slow one.

Jeremy

 

[jha07]

Hi Jeremy

Do you have any pictures of the torque arm you made? I don't think I fully understand what they look like from your description. Does the torque arm prevent the axle from being able to be pulled out the slot?
If so, would you need one also on the back wheel if a rear motor was used?

What is your top speed with your recumbent with that setup? I assume you have a 20" front wheel, right?

The Crystalyte motors are very powerful, I have a 406 fitted to the front wheel of my recumbent and it managed to tear out the steel fork end the first time I fired it up!

The answer to the fork problem is to do two things. Firstly, make a torque arm. I cut mine out from a bit of 4mm stainless steel sheet. It has a slotted hole cut out that is a nice snug fit on the Crystalyte axle and fits inside the fork. It's anchored to the fork using an extended stainless steel bolt through the mudguard attachment. The second thing to do is make sure that the axle nuts are really tight. If they are not they will just spin the motor clean out of the forks the first time you fire it up (guess how I found that out......). Don't be tempted to apply the brakes with the wheel up in the air and powered, it will really try and rip the fork ends apart if you do.

I managed to repair my steel forks, by heating the ends and bending the opened out slots where the axle fits back into shape, without cracking things, luckily. This did mean stripping the forks out, fixing them and then repainting them, so is not recommended.

They work extremely well as front wheel drive, in fact in many ways front wheel drive can be a slight advantage. The only disadvantage I've found is that the wheel will tend to spin more readily on occasion, but given the power of these things I feel it might well do this on the back wheel as well! I would advise you to go for at most 36V to start with, with perhaps the 20A current limited controller. I opted to go for the 35A controller and 48V and it really is a bit of an animal.

Jeremy

 

[Jeremy]

I can take a photo at the weekend, but perhaps this description will do the job.

The axle on the Crystalyte motor isn't like a conventional bike axle. It has big flats on either side, with a width of 10mm between them, which just fits the slot in most forks. On the side of the motor opposite where the wires come out, there is an extended lug, 10mm wide, that effectively fills the lower part of the fork dropout slot when the wheel is fitted. This is what gives the primary anti-twist location and is also what will tend to just tear open the fork dropout slot.

My torque arm has a slotted hole 10mm wide and long enough to slip over this extended lug part of the axle. It is rather like a big, unevenly shaped washer, with an extra hole for anti-rotation. The arm is quite small, about 2" wide by perhaps 1 1/2" high, and is shaped to fit in the space behind the fork when the axle is pushed fully home into the drop out slot.. The top corner of the plate has a hole drilled in it to take the extended mudguard bolt, which is what locates the thing in place.

On the wire exit side of the motor I just followed the fitting instructions that Justin at ebikes.ca provided; they are on his website.

If you still need a picture just ask and I will try and get one to you at the weekend.

I don't think they're so important at the back, as rear dropouts are usually much stronger.

I don't know the top speed - well over 30mph I'd guess. I haven't had the nerve to ride it full throttle to max speed yet - as I said before, it's a bit of an animal!

Jeremy

 

[flecc]

There's a similar torque arm on the eZee Torq, on the front wheel there, but which I remounted at the rear on my T bike:

.

 

[Jeremy]

Nice one, Flecc, that's very similar to the one I made up.

The only real difference is that it's better to fit the Crystalyte torque arm on the inside, as the extended anti-rotation lug on the axle is only on the inboard side (the axle reverts to a 12mm threaded section with two flats outboard of the drop out).

Jeremy

 

[jha07]

Thanks for the description Jeremy. And thanks for the pic Flecc. I think I understand now.
If your steel forks, without a torque arm, wasn't strong enough to keep the drop outs from tearing open, then I'm sure my aluminum fork won't do any better.
I may reconsider and go with a rear motor.

 

[giguana]

don't get carbon ones anyway, I heard this guy on an expensive bike was going downhill and he fell on his head at 50 miles an hour because the fork cracked, and his eye fell out-fortunately his friend got aid fast enough...well so much for carbon forks.

 

[jha07]

I got a reply from Team Hybrid. They don't recommend using a front motor on aluminum forks, only steel. So I think I'm going to go with a rear motor. But I still think it would be good to have a torque arm on the rear.
Jeremy, was it hard to make yours? I would imagine making that slotted hole would be difficult without a milling machine.
Does anyone know if they sell torque arms?

 

[Jeremy]

As it happens I have a small vertical milling machine, but I actually made my torque arm with nothing more complex than a drill, hacksaw and a couple of files. It took about ten minutes to make, most of which was spent repeatedly trial fitting it to the fork/motor axle to make sure it was a snug fit.

The material was a scrap of 4mm thick 316 stainless steel that I had in the junk box, I think it was an offcut from making new chainplates for a yacht I rebuilt years ago. To cut the slotted hole I simply drilled two 8mm holes close together, then filed the slot out to 10mm wide by approximately 20mm long.

Jeremy

 

[giguana]

Jeremy, was it hard to make yours? I would imagine making that slotted hole would be difficult without a milling machine.
Does anyone know if they sell torque arms?

easyest way is to find a cheap flat spanner that fixes on to the bolt and is attached alongside the fork, else 2 bolts on either side should be pretty strong.

 

[jha07]

I went down to Renaissance Bikes, or Ebikes as they are known online.
I was planning to get a rear motor, but thought I'd ask them about using a front motor with aluminum forks. He told me that it was fine and that fork failures are very rare. The few cases he's seen were because the nuts on the axles weren't installed on a flat surface. Most forks designed for quick release wheels have a raised outter lip around the axle. If you tighten the nut on this lip, the washer behind the nut won't be able to sit flat. He said that if you file down this lip, you shouldn't have any problems. I suggested putting a smaller washer instead. Small enough to fit inside this lip so it can sit flush. He figured that would work as well.
So in the end I went with a front motor. Hope it won't give me trouble down the road.

One thing I noticed when I installed the motor yesterday was that the motor wasn't sitting parallel with the fork arms. I could see it was tilted. The top of the tire was about 5-10mm closer to one side of the fork arm.
I look more closely and found that one side of the axle, on the side without the wires, there was a 1mm step where the fork would sit on the axle. On the other side, this step wasn't there. The fork just sat on the threaded part of the axle. I guess 1mm isn't much, but it gets amplified through the length of the wheel and would account for a tilt of 5mm.
Has anyone else experience this with crystalyte motors? I wonder if I got a defect or if there are all like that.

 

[Jeremy]

Have you made sure that the wires are coming out at the bottom of the axle?

The Crystalyte axle is not symmetrical and has a lug to better engage with the lower part of the drop out on the non-wire side, if the motor is in upside down then it's possible that this lug might be the reason for the offset your seeing.

I went with a small washer to even out the drop out faces too. I found that I needed to file the washer out to get it to fit, as you need one with a 10mm hole, which then needs to be slotted to fit over the 12mm axle with 10mm wide flats. It was pretty easy to do.

As Justin says, make sure the nuts are really tight!

Jeremy

 

[jha07]

Yup, the wires are pointing downwards. I emailed Ebikes about it and Justin said that it could be bad machining. I'm going to file that step down.
I was thinking about using a filed open 10mm washer as well to give me a flat mounting surface.

Jeremy, do you know what the nuts should be torqued to?

 

[Jeremy]

I'm afraid I don't, but I'm just about to call Justin, so I'll ask him and post back on here.

I just tightened mine "very tight" by hand, about as tight as I could get with a fairly short ring spanner!

Jeremy

Edited to add:

I haven't been able to get hold of Justin on the phone, maybe the store is shut today. I did find the link Zev sent me to the Crystalyte installation instructions though, which may help. Here it is: www.ebikes.ca Installation Guide