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Titanium Hub?



 
 
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  #1  
Old January 11th 09, 12:53 AM posted to rec.sport.unicycling
hungry4uni
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Default Titanium Hub?


Hey everyone,

I have a question about the Ti hub. What is the weight difference
between it and the regular KH hub (08)?

Also, how much stronger is it? Is it worth it to get it if your not
breaking your normal hub?


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  #2  
Old January 11th 09, 01:07 AM posted to rec.sport.unicycling
Smilymarco
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Default Titanium Hub?


Saves about 180g-190g, dont know the exact amount sry.

I may be wrong, but i think i heard Kris saying that its as strong as
the normal hub.
If you have the money and want a lightweight and strong uni, then get
it!

Weightweenies FTW hahaha


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  #3  
Old January 11th 09, 01:56 AM posted to rec.sport.unicycling
Rowan
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Default Titanium Hub?


hungry4uni;1168406 wrote:
I have a question about the Ti hub. What is the weight difference
between it and the regular KH hub (08)?


According to Unicycle.co.uk

Kris Holm Titanium ISIS Hub Weight: 425g. Weighs 200g less than the
2008 KH ISIS hub with CrMo axle.

Kris Holm ISIS Moment Hub 2008 Weighs (including bolts and spacers):
644g

Nimbus ISIS Hub Weighs: 600g (635g including bolts and spacers)

Onza ISIS Hub Weighs: 600g (635g including bolts and spacers)

Kris Holm/Onza splined 36-hole hub- 2005 model Hub Weight: 680g (with
bearings & bolts)

Qu-Ax ISIS Hub (red) Weighs (including bolts, bearings and spacers):
815g

Suzue Unicycle cotterless hub Weight - 530 / 525g with bearings,
spacers & nuts.

According to Unicycle.co.nz

KH Moment Titanium Hub Weighs a miniscule 426g including bolts,
bearings and spacers!

KH Moment ISIS Hub Weight (including bolts and spacers): 644g

KH-Onza 36-hole hub- 2005 model Weight: 500 g (bare), 650 g (including
bearings, bolts and spacers)

According to Unicycle.com (USA)

Kris Holm Titanium Hub Weight: 1 lb w/hub bolts & spacers (453g)

Nimbus ISIS Hub (36-Hole) Weighs: 1.4 lbs (including bolts and spacers)
(635g)

Poznanter/Profile Hub Weight 2 pounds (907g)

It weighs less than a suzue (half a kilogram) and the old best hub
weighs nearly 1kg. It would be nice to have but with a price like that
not everyone can afford one.


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  #4  
Old January 11th 09, 03:26 AM posted to rec.sport.unicycling
gerblefranklin
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Default Titanium Hub?


For the record, titanium is weaker than steel, and unless there is
something funny about the heat-treatment process on the hubs, the ti hub
should be weaker than the steel hub (possibly by a significant
difference). Also, strong welds in titanium are much harder to do than
in steel (much less tolerant of contaminants), so the welded flanges
have a much bigger risk of breaking at the welds than the steel hubs do.
I believe Tony Melton already broke a hub in this fashion.


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  #5  
Old January 11th 09, 06:30 AM posted to rec.sport.unicycling
Rowan
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Default Titanium Hub?


gerblefranklin;1168445 wrote:
. I believe Tony Melton already broke a hub in this fashion.


Tony too?
You might be talking about 'Joe Dyson'
(http://www.unicycle.org.nz/bb/viewtopic.php?t=2172).
[image:
http://i7.photobucket.com/albums/y28.../IMG_1933.jpg]


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  #6  
Old January 11th 09, 10:23 PM posted to rec.sport.unicycling
agentQ
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Default Titanium Hub?


gerblefranklin;1168445 wrote:
For the record, titanium is weaker than steel, and unless there is
something funny about the heat-treatment process on the hubs, the ti hub
should be weaker than the steel hub (possibly by a significant
difference). Also, strong welds in titanium are much harder to do than
in steel (much less tolerant of contaminants), so the welded flanges
have a much bigger risk of breaking at the welds than the steel hubs do.
I believe Tony Melton already broke a hub in this fashion.




Thank you. Was about to say something along these lines.


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  #7  
Old January 12th 09, 03:50 AM posted to rec.sport.unicycling
skrobo
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Default Titanium Hub?


how is titanium weaker than steel?

everything i've ever heard says that titanium is far stronger than
steel by weight/strength ratios
unless titanium is far less dense...but that makes no sense, i want to
see some background to what you're saying. show me where you are getting
this from.


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  #8  
Old January 12th 09, 04:35 AM posted to rec.sport.unicycling
saskatchewanian
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Default Titanium Hub?


I wish I had my old text books handy with all the properties of common
metals and alloys but I seem to remember carbon steel and titanium
having similar strength but titanium weighing about 60% as much as the
steels.


A google search could probably verify this.


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  #9  
Old January 12th 09, 04:41 AM posted to rec.sport.unicycling
pedrotejada
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Default Titanium Hub?


skrobo;1169130 wrote:
how is titanium weaker than steel?

everything i've ever heard says that titanium is far stronger than
steel by weight/strength ratios
unless titanium is far less dense...but that makes no sense, i want to
see some background to what you're saying. show me where you are getting
this from.




If weight doesn't matter Ti is stronger, but on bikes and unicycles,
weight matters and Titanium is used to save weight.

Is impossible to say if it's strong or not. Depends of the weld quality
and design.

Ti is lighter cause it's strong than ALUMINIUM and you can use really
thin walls. But if the walls are to thin it may breaks, like any other
materials brakes. Also Ti is really rigid and don't flex!


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  #10  
Old January 12th 09, 05:29 AM posted to rec.sport.unicycling
gerblefranklin
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Default Titanium Hub?


The amount of misinformation in the cycling/RC anything/Motosports
communities is ridiculous. Any thread like this is a fine example.

pedrotejada,
Titanium is NOT rigid. It has a significantly lower modulous of
elasticity than steel ( http://tinyurl.com/8qxp49 ), making it far
flexier. I seem to remember talking to Kris about this issue when
discussing whether titanium muni frames are worth the trouble. Also,
since the design of the steel and titanium hubs is essentially
identical, we can compare strength and make reasonable predictions. But
you are right to say good design work should account for material choice
therein.

Skorbro, your post makes it sound like you've never picked up a big
chunk of titanium while expecting it to be steel. It is a dramatic
experience to notice how light it is. And my source for the density and
strengths of materials is _Machinery's_Handbook,_27th_Edition_. Go buy
yourself a copy if you don't believe me.

The density of titanium is, according to my copy of
_Machinery's_Handbook,_27th_Edition_, 0.163 lb/in^3, while steel is 0.25
lb/in^3. So titanium is about 35% less dense.

In a situation where strength is the ultimate issue, and the dimensions
of the part are fixed (we can't make bigger ISIS splines), what matters
are the strength to volume ratios. 6Al-4V titanium, the alloy which I
believe Kris uses in the hubs, has a (0.5% ?) yield strength ranging
from 120-160 ksi, depending on heat treatment. While 4130/4140 steel,
depending on heat treat, has a 0.2% yield strength of 100-155 ksi. 4130
steel can be made much harder than 6Al-4V titanium. So if the titanium
hub is fabricated perfectly, it can be of comparable strength to the
steel hub, but it is unlikely to ever exceed the steel hub's strength. I
am ignoring spline hardness, by the way, since I assume no rider is
regularly changing cranks.

Now, factor in the issues with the difficulty of welding titanium, and
quality control thereof, and the titanium hub's strength is an issue.
Hence the fact that a much smaller sample of riders has already broken a
titanium hub, while I, at least, have never seen a broken steel hub. If
the titanium hub were machined from solid (prohibitively expensive), I
would have more faith in its durability.

You would not be wrong to argue that the softer titanium hub builds a
stronger wheel by conforming to the spokes better, but I don't think
that's where a hub will be failing.

I hope this clears things up. And the answer to the original question
is, the titanium hub is ONLY worth getting if you aren't breaking the
steel hub. If you are, you should either switch to profile, or get a
custom built hub/crankset with a larger splined interface.

P.S. Rowan, you are right. I did mean Joe Dyson.


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