J
jim beam
Guest
Ben C wrote:
> On 2007-03-04, jim beam <[email protected]> wrote:
>> Ben C wrote:
>>> On 2007-03-03, [email protected] <[email protected]> wrote:
>>>> Ben C? writes:
>>> [...]
>>>>> I don't know about low spoke counts, and my own wheels are all 32 or
>>>>> 36 holes, but I have had cracked rims around the spoke holes on a
>>>>> drive-side rear with rather tight spokes. The rim didn't have
>>>>> eyelets and certainly not sockets. Whatever the reasons are for this
>>>>> design of rim, it is very plausible that lower spoke tensions will
>>>>> increase the fatigue life of such rims around the spoke holes.
>>>> You seem to be an apologist for the rim business. Fortunately I have
>>>> a stash of MA-2 rims that don't crack and allow as high a tension as
>>>> needed for the life of the wheel. I use motor oil.
>>> I'm getting quite envious of your stash.
>> don't. they're heavy, their eyelets rust, they're prone to
>> flat-spotting and their unmachined braking surfaces require you gamble
>> with less than 100% braking until your brake pads have worn to conformity.
>
> Certainly my CXP23 rims were very smooth braking from day one.
>
>>> I wondered if more recent Mavic
>>> rims might be lighter, and if there was therefore some tradeoff going on
>>> (you'd think leaving the sockets off would be lighter for one thing),
>>> but I have looked up the weights, and the MA-2 is 420g compared to 425g
>>> for the Open Pro. If the MA-2 is also stronger, it's not clear what
>>> progress has been made.
>> open pro is deeper for the same or less weight. that means it's more
>> rigid. and more rigid means better resistance to flat spotting.
>
> Does more rigid also mean that less spoke tension is required?
that, or lower spoke count.
> So
> there's a kind of tradeoff between the weight of sockets and putting
> more material on the rim itself-- stiffer rim in exchange for inferior
> spoke support, but because it's stiffer, you don't need such tight
> spokes. I expect there have also been changes in the flavour of
> aluminium used and manufacturing process.
for open pros, yes, there is supposed to be a change in flavor. exactly
what, i don't know, but hey...
>
> I think I've heard you saying high spoke tension has the effect of
> "borrowing" strength from the spokes to add to the rim.
other way around - you "borrow" compression from the rim to tension
spokes. spokes in tension can then support a compressive load. but the
more spoke tension you "borrow" from the rim, the closer the rim is to
cracking and buckling.
>
> A more rigid rim would spread the load over more spokes, so they will
> individually detension by less, therefore less pretension required.
yes, or you can use fewer spokes! i have some shimano r540 wheels with
only 16 spokes per wheel. big deep rim. spokes never touched since the
box opened. spoke tension, as measured with a park tensiometer, is
~1100N drive side rear.
> On 2007-03-04, jim beam <[email protected]> wrote:
>> Ben C wrote:
>>> On 2007-03-03, [email protected] <[email protected]> wrote:
>>>> Ben C? writes:
>>> [...]
>>>>> I don't know about low spoke counts, and my own wheels are all 32 or
>>>>> 36 holes, but I have had cracked rims around the spoke holes on a
>>>>> drive-side rear with rather tight spokes. The rim didn't have
>>>>> eyelets and certainly not sockets. Whatever the reasons are for this
>>>>> design of rim, it is very plausible that lower spoke tensions will
>>>>> increase the fatigue life of such rims around the spoke holes.
>>>> You seem to be an apologist for the rim business. Fortunately I have
>>>> a stash of MA-2 rims that don't crack and allow as high a tension as
>>>> needed for the life of the wheel. I use motor oil.
>>> I'm getting quite envious of your stash.
>> don't. they're heavy, their eyelets rust, they're prone to
>> flat-spotting and their unmachined braking surfaces require you gamble
>> with less than 100% braking until your brake pads have worn to conformity.
>
> Certainly my CXP23 rims were very smooth braking from day one.
>
>>> I wondered if more recent Mavic
>>> rims might be lighter, and if there was therefore some tradeoff going on
>>> (you'd think leaving the sockets off would be lighter for one thing),
>>> but I have looked up the weights, and the MA-2 is 420g compared to 425g
>>> for the Open Pro. If the MA-2 is also stronger, it's not clear what
>>> progress has been made.
>> open pro is deeper for the same or less weight. that means it's more
>> rigid. and more rigid means better resistance to flat spotting.
>
> Does more rigid also mean that less spoke tension is required?
that, or lower spoke count.
> So
> there's a kind of tradeoff between the weight of sockets and putting
> more material on the rim itself-- stiffer rim in exchange for inferior
> spoke support, but because it's stiffer, you don't need such tight
> spokes. I expect there have also been changes in the flavour of
> aluminium used and manufacturing process.
for open pros, yes, there is supposed to be a change in flavor. exactly
what, i don't know, but hey...
>
> I think I've heard you saying high spoke tension has the effect of
> "borrowing" strength from the spokes to add to the rim.
other way around - you "borrow" compression from the rim to tension
spokes. spokes in tension can then support a compressive load. but the
more spoke tension you "borrow" from the rim, the closer the rim is to
cracking and buckling.
>
> A more rigid rim would spread the load over more spokes, so they will
> individually detension by less, therefore less pretension required.
yes, or you can use fewer spokes! i have some shimano r540 wheels with
only 16 spokes per wheel. big deep rim. spokes never touched since the
box opened. spoke tension, as measured with a park tensiometer, is
~1100N drive side rear.
