Gravity Zero

Discuss light weight issues concerning road bikes & parts.

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mrowkoob
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by mrowkoob

No no no this is not another crankset thread :wink:

Gravity Zero is an aussie company see here http://www.gravity-zero.com.au/
Apparantly according to the homepage the company has been around for 17 years so I guess Jeff at Zero Gravity and Gravity Zero can discuss who inspired which name.... I´ve never heard of them before though any aussies here who have?

They have a really interesting freehub , check it out.
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calogero_vizzini
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by calogero_vizzini

Albeit interesting, not a single product they produce is their own - The rims, hubs, spokes, disc wheels, etc.. are all generic.

footwerx
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by footwerx

you need to look a little closer at their website. Their rims are not generic. And neither are their hubs.

I was referring specifically to their 85mm rim. I guess the shallower rims are probably from Zipp/Gigantex etc.

Skillgannon
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by Skillgannon

The hub is manufactured by gravity zero - it has a different engagement mechanism (I forgot the term :|) instead of conventionay hubs having 3 or 4 offset pawls, so there is time to engagement, which supposeedly increases climbing ability and instant accelerations. I havent had a chance to try them by myself, but my friend had a set for a while on loan, and was drooling over them - he wasnt that impressed with the rims, and was planning to either swap out the rims for Zipp's or to try and see if carbonsports could do him a custom set of LW's. He couldnt believe how much faster it made him/made him feel

calogero_vizzini
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by calogero_vizzini

footwerx wrote:you need to look a little closer at their website. Their rims are not generic. And neither are their hubs.

I was referring specifically to their 85mm rim. I guess the shallower rims are probably from Zipp/Gigantex etc.

I am afraid you're incorrect - Their rims are all manufactured by Gigantex.

In particular, the 85mm Rim 'with sweeping side profiles' is part of their latest range. I suspect the reason for why you may not be aware of this product is because Gigantex are slow to update their Online Catalogues.

Another brand using this same rim is Pawson Reid Velo Limited trading as "Grammo-Bici" in New Zealand.



The description of the mechanism in the X-One Rear Hub is, might I add, somewhat vague and ambiguous. Another example of a Rear Hub with a freewheel mechanism without pawls is the DT Swiss Hugi 240 system, which operates on a "star ratchet" or "clutch plate" I believe...

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Knut
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by Knut

mrowkoob wrote:No no no this is not another crankset thread :wink:



Are you sure they're not going to release an überlight and extremely stiff crankset very soon? Actually I heard they're looking for testers, but maybe that's a secret... dammit! 8)

Actually they've been around for a while, Cyclingnews writes favorably about the wheels back in February.

http://www.cyclingnews.com/tech.php?id=tech/2006/reviews/gravity_zero

Tristan
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by Tristan

The hub design sounds like they are using a Sprag clutch: basically a sealed needle bearing that can rotate in one direction, but if load is applied to the opposite direction they bind on the outer race.

I'm confused how they attained a patent for this though, Sprag clutches have been used in racecars for decades and about 6 years ago while in Canada I saw a prototype hub using a Sprag bearing. The company who developed it was unable to obtain a patent. One problem this company encountered was the bearings were failing under load...basically for the size they wanted to use (physical contraints of the hub) the bearing could not support ~1000W geared down 22:34 (mountain bike application). Technology progresses though.....

Sprag bearings, sometimes called freewheel clutches, are used in industry to ensure one direction rotation (such as in pumps and fans.) Some washing machines even use them!
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calogero_vizzini
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by calogero_vizzini

Tristan wrote:The hub design sounds like they are using a Sprag clutch: basically a sealed needle bearing that can rotate in one direction, but if load is applied to the opposite direction they bind on the outer race.

I'm confused how they attained a patent for this though, Sprag clutches have been used in racecars for decades and about 6 years ago while in Canada I saw a prototype hub using a Sprag bearing. The company who developed it was unable to obtain a patent. One problem this company encountered was the bearings were failing under load...basically for the size they wanted to use (physical contraints of the hub) the bearing could not support ~1000W geared down 22:34 (mountain bike application). Technology progresses though.....

Sprag bearings, sometimes called freewheel clutches, are used in industry to ensure one direction rotation (such as in pumps and fans.) Some washing machines even use them!

Tristan, you're an absolute mine of information! But how would it be possible for this to engage quicker than either a star ratchet, clutch plate or pawl freewheel mechanism?

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by jeffr

calogero_vizzini wrote:Tristan, you're an absolute mine of information! But how would it be possible for this to engage quicker than either a star ratchet, clutch plate or pawl freewheel mechanism?


I'd guess the distance between the bearing and race is shorter than the distance between the pawl and the contact surface.

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by Tristan

calogero_vizzini wrote:Tristan, you're an absolute mine of information! But how would it be possible for this to engage quicker than either a star ratchet, clutch plate or pawl freewheel mechanism?


I must confess to not fully understanding how these bearings work, and a quick Google didn't do much. I'm a bit time-poor at the moment :-(

In most cases the roller bearings are held in a plastic housing. The plastic is shaped in a way that it allows the rollers to rotate in one direction, but if the rotation is reversed the plastic flexes outwards and the rollers contact the outer race, binding them.

Another (reasonably) common use is in 'ratchet' wrenches to tighten cutting tools into a CNC machine. Since the inside of the bearing is round it can tighten a round 'bolt' such as a rotary cutting tool, meaning no hex or wrench flats are needed.
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Tristan
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by Tristan

jeffr wrote:
calogero_vizzini wrote:Tristan, you're an absolute mine of information! But how would it be possible for this to engage quicker than either a star ratchet, clutch plate or pawl freewheel mechanism?


I'd guess the distance between the bearing and race is shorter than the distance between the pawl and the contact surface.


There are no pawls, it just relies on the flex of the housing, usually plastic.
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jeffr
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by jeffr

Tristan wrote:
jeffr wrote:I'd guess the distance between the bearing and race is shorter than the distance between the pawl and the contact surface.


There are no pawls, it just relies on the flex of the housing, usually plastic.


I was speaking of the competing design. It takes longer for the pawls to engage because it takes on average 1/6th the rotation of the wheel in a 3 pawl system to engage.

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by Tristan

jeffr wrote:I was speaking of the competing design. It takes longer for the pawls to engage because it takes on average 1/6th the rotation of the wheel in a 3 pawl system to engage.


Apologies!

In MTB circles they like to count engagement points per rev. King have 72, Hope about 24 and Shimano 16. Those numbers are all from memory and could be off. New XTR hubs use a different design and have more engagement points....smart money would gamble this crossing over to DA in the near future.
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calogero_vizzini
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by calogero_vizzini

Tristan wrote:In MTB circles they like to count engagement points per rev. King have 72, Hope about 24 and Shimano 16. Those numbers are all from memory and could be off. New XTR hubs use a different design and have more engagement points....smart money would gamble this crossing over to DA in the near future.

What is the measurement unit for revolutions in that context? Is it one full turn of the freehub?

Pardon my ignorance, but could that not be simply achieved by having more pawls (Like Tune Mag - 5 Pawls) or by having more teeth for the pawls to contact?

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divve
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by divve

In most cases faster engagement doesn't do anything for performance. Not even in regular MTB. Only in very tight and slow technical sections does a quick CK engagement offer a little advantage. It allows you to position your crank better after freewheeling or repeated "ratcheting back" in order to maintain balance and drive force.

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