Titanium - Can it handle the TORQUE?!

[Mr. Danelectric]

I have a BlackSheep Titanium 29er fork and a Crystalyte 5304 front Hub, on 700c. I was wondering how ti compares to aluminum and steel. I know the general concensus is that aluminum is inferior and you will round out your drop-outs.

My ti fork is more dampening than steel. The drop-outs on this fork are insane. Check the picture.View attachment 1

You think I'd have to worry about the extreme torque of my motor rounding these drop-outs out? I could also use torque arm(s). It's 72 volts of 5304, keep in mind...

Is rounding out the fork's drop-outs the only thing to worry about, or is the strength / rigidtry / material thickness of the actual fork tubes also important when it comes to "torque"? This fork is meant for a 29er MTB, so it's pretty beefy, and meant to handle abuse, but it's also meant to take up a lot of road impurities with it's "elastic" fork tubes. I don't know how to explain it, it's like it's "springy". If you hit it, like a tuning fork, it will vibrate a lot more than an aluminum one.

Another thing - does anybody know if you can fit a disc to a 5304 FRONT? (I know you can in the rear, cause there's a lot more room...)

 

[recumpence]

I use titanium extensively in my RC helicopter mainshafts. Ti is much stronger than aluminum for sure. If it is grade 5 Ti (6AL4V), it should hold up just fine. The problem is, if you do round out the slots, Ti is almost impossible to get welded. Very few people weld Titanium.

Matt

 

[Drunkskunk]

i would use torque arms, as Ti is softer than steel, and might round out, but I think they should hold up. It realy depends on how beefy they are, but a DH fork is usualy plenty beefy

 

[dogman dan]

I think a lot of the aluminum fork faillures also had some kind of issue with loose nuts, bad washer fit allowing nuts to loosen, or bad washer fit causing the washers to put spreading pressure on the dropouts. Be real fussy about the washers and the fit, and of course a tourqe arm will at the very least keep the thing attached if it breaks suddenly on you. The fit of the washers on the dropouts is in my opinion a bigger issue than the torque of the motor. On a normal bike, when you hit the brakes hard, does it not load up the forks with a ton of force? But that wheel fits, and the ebike motor is often a sort of fits kinda thing. Once the dropouts spread , or washers bend, the loose nut is all it takes to ruin a fork, motor wires, and maybe controller.

 

[Mr. Danelectric]

On a normal bike, when you hit the brakes hard, does it not load up the forks with a ton of force?

That is the most brilliant thing I've heard in a very long time! Why didn't I ever think of that?!?!?

After visualizing the amount of force on a fork with my 200 lb body flying down a hill and SLAMMING on the brakes, I realize that NO motor could possibly ever come close to exerting that kind of force!

Now, I agree that most failures have to do with the nuts coming loose.

Wait a second, braking wouldn't put the force on the drop-outs so much, as to where the V-Brake bosses are, if applicable, or the hub, where the rotor bolts on...

My X5 motor is 24.5 lbs, and puts all that torque at it's axle and the drop-outs.

It does answer my question as to whether the fork blades themselves could handle the power. Since it handles the stress of heavy braking, it can handle heavy acceleration.

These drop-outs are pretty beefy, but it's a risk, considering these forks aren't cheap. I think it would handle it, but I'm reconsidering. The point of ti is usually the weight savings, which is pointless on such a beast of an electric bicycle. With that hub on that fork, I think it would lose all the benefits of being made of titanium. It would look cool though.

 

[dogman dan]

Brilliant.... uh no. But I do see things where others may only look. Just noticed a few things while having the usuall noob problems with forks and hub spin on my first build. On some thread or other Justin sorta agreed with me that most fork failures happen when somehow the nut gets loose and the axle spins. Once the axles spin in the dropouts, few forks and even some torqe arms cant handle the forces involved then. That prying force can bend the best steel dropouts pretty easy, and most aluminum ones crack. If that doesn't happen, sometimes a groove just gets machined into the axle. One thing for sure, once the nuts get loose on an x5 , or even lesser motors, damage will happen to something for sure. If that force is what people refer to when they talk about torque, no dropout is ever designed for that on a bicycle. If the nut loosens and torque is applied bye bye. Bikes are designed for the leverage forces applied when braking so the pulling of the motor forward on the dropouts is no more than the pushing back on the dropouts when you brake hard. Dropouts that bend did that for other reasons, washer fit, or just slippage on a loose nut.

Tight nuts are crucial, and if you can tighten them more after a very short test ride, alarm bells should start ringing about the fit of the washers. Same thing if the axle wants to creep out of the dropouts as you tighten the nuts. Usually that means a dropout is spreading as the nut is tightened. Unfortunately you can easily overtighten and strip out the threads too, I wish they sent out a thicker nut that engaged a few more threads. Since half the thread is gone on the flats, it leaves less thread holding more force.

I'm not totally convinced that torque arms will prevent dropout damage if the nuts loosen, but I am totally convinced that if the dropouts break, they will go a long way to prevent jaw , head, and collarbone damage!

 

[John in CR]

Yes it's exactly the twisting torque that's the issue, though on the front you have the additional issue of leveraged forces on the headset and connection at the top of the fork tubes. Sure braking forces are similar to the later, though in the opposite direction, so to a large extent they are addressed in the original design. The twisting forces at the axle, however, are not an issue at all in any normal bicycle, so no consideration is given in the design because it isn't necessary.

While I agree that the friction related to the nut bears some of the load, it seems wholly inadequate to me. Think of the little bit of force needed to loosen (or tighten a bit more) the axle nut with a wrench that is in this case 14.5" long (the radius of his wheel). Don't you think that amount of force is commonplace between the tire and the ground with an electric bike, and that's the leverage of the forces involved at the axle.

IMHO, no bicycle designed for pedal use, regardless of the material used for construction, has sufficiently strong dropouts for an X5. There is no reason for them to be designed that way, so why would they be? All my bikes are steel, and instead of torque arms I add at least 1/4" of steel to thicken each dropout. For the one motor I have with comparable power to an X5, I added 1/2" to each side for piece of mind. I only count on the threads and nut to hold the wheel on, just like a normal bike.

I'm sure your titanium dropouts are stronger than aluminum and won't snap as easily as aluminum ones do, but do yourself a favor and add torque arms. Just imagine how bad an accident could be if your front wheel suddenly fall off. It's already happened to people.

 

[Mr. Danelectric]

Wow, some really great replies. This place is awesome.

 

[trappermike]

I worked with titanium cosiderably in making custom engine parts for racing. It is extremely strong(Grade 5 is stronger than most steels),the raw material is not that expensive. Machinists hate it,it is hard on cutting tools.
Looking at the photos of your drop-outs they look stronger than anything I have seen yet! The I-beam construction of the dropout and the large flare above should make them very tough.
I always use good quality hardened washers under the axle nuts.(Such as "Fedaloy",they're very inexpensive)
Where did you get them,are they a "motorcycle-type" fork with triple trees?

 

[Mr. Danelectric]

Looking at the photos of your drop-outs they look stronger than anything I have seen yet! The I-beam construction of the dropout and the large flare above should make them very tough.
Where did you get them,are they a "motorcycle-type" fork with triple trees?

No, not at all. They are pretty regular looking straight blade unicrown forks. (Regular looking, except for those work-of-art dropouts) They are made by BlackSheep. http://www.blacksheepbikes.com/ I wish I would have gotten both disc and canti option, so I could use if for anything, but mine's only disc. So I have no idea how to put brakes on a front x5 Crystalyte, I should contact the company and see if they'll add some brake bosses for a minimal charge.

Here are some pics of it from their site:




I don't know what they're for, I guess they're a boutique fork or something. I got it cause it really dampens the ride, especially on a 29er, and it's so LIGHT!

 

[John in CR]

I wish I had roads smooth enough to go suspensionless, because that cantilever type would be just the ticket with a reinforced headtube. I'll have to borrow on that concept for a composite frame I'm planning. I thought I'd have to go with a store bought front end, but not so. I can use the general idea of a triangle anchored both above and below the headset for strength and still do a springer fork for a suspension ride.

John

 

[dogman dan]

Holy crap! If that ti fork is $475 to replace I'd be looking at rear hubs.

 

[Mr. Danelectric]

That's exactly what I did! REALLY rear! As rear as you can get!

Last night, I chopped my HG 1000 (Currie Electric Scooter) in half, and welded it to my BOB trailer. The ONLY modification to my actual bicycle itself, is the addition of the throttle (which I extended 6 FEET!). When the trailer is disconnected, my bicycle is as nimble and light as can be. I've got two awesome disc brakes now, and my bike doesn't look "electrified" at all (cause it isn't, 'cept for the throttle)

It feels a lot different being "pushed" along, than it does to be "pulled" by the front hub motor. I like it. The original HG 1000 center stand works perfectly to hold the entire rig upright.

No worry about stressing my fork now... I even have trailer brakes now, if I want... I'll post a thread about it soon, with better pics, but for now - here's a teaser pic that I shot on it's first test ride... (Already I've ditched the flag and the seat, and I added some saddle bags on the Trailer's (HG 1000's) rear rack) It's now a serious Sport Utility Bike!

 

[dogman dan]

That'll work, till you sell the front motor and get a rear.

 

[Mathurin]

facepalm.jpg

How on earth can a bike company selling at such a price frock up so badly at taking pictures? That's the kinda stuff I'd expect to see in a box store catalogue.