J
jim beam
Guest
David wrote:
> Jim,
>
>
>>hmmmm, you do not cite which page, and you didn't bother to context the
>>link to the 90% statement. it may have been clear to you, but not to
>>me. and having quickly scanned the site, i /still/ don't see a 90%
>>statement.
>>
>
>
> Read the part where the rim will ovalize under a 200lbs load with
> loosely tightened spokes. Any stiff rim, including the A719 or the
> T520, T519 will ovalize or go out of true when built poor or tensioned
> incorrectly. Therefore, the stiffness of the rim has nothing to do
> with the final stiffness of the wheel, hence the 90% figure. The 90%
> figure is just what I think, but seemed to concur with another master
> builder in town who he seemed to agree with me.
ok, 3 things:
1. by definition, rims distort [ovalize] under load, /regardless/ of how
many spokes support it. if it didn't, there would be no load. the
extent of ovalization under load is a function of rim thickness, not
spoke tension.
2. going out of true is a function of localized plastic deformation,
which is precisely why "stress releiving" the wheel is so important.
it's got nothing to do with ovalization under load.
3. the stiffness of the rim is fundamentally important to the stiffness
of the wheel.
to paraphrase; "er, i reckon it's 90% and my buddy reckons that's about
right". just doesn't cut it david. sorry.
> Spokes take all the
> stress (compression and torque) and therefore, they all have a fatique
> lifespan which (depending on the spokes you use) sometimes can be
> shorter than the rims they hold, if ridden in very dry and sunny
> weather all year round.
spokes don't experience torque, just tension [not compression] in the
main span and bending at the elbow.
>
>
>>besides, do you really think a low-pro lightweight racing rim is just as
>>stiff as a heavy duty touring rim?
>>
>
>
> You are comparing apples and oranges here..
no, i'm comparing rims to rims. that's valid.
> Light weight low spoke
> count wheels carry less spokes, tensioned much higher than normal
> wheels and the rims are designed stiffer to compensate for that, while
> still maintaining light weight status.
tension has nothing to do with weight. and it doesn't have much to do
with count either.
> Therefore, it has less (or
> lesser) meat area (braking) than say a T520 or a A719.
you mean thickness, not area. it's the rim thickness that decreases
with wear, not the rim area.
> If both are
> ridden in foul winter weather with constant braking and pads are
> contaminated with sand and grit, the pro lightweight rims will be
> killed sooner than touring rims. When the braking area of the rims
> have less than 1mm thickness on both sides
thickness, not area.
>, you are looking at
> structural integrity being compromised really soon -- rims will break.
> The A719 will break later, because it's got a lot of meat area. And
> yes, I replaced my T520s twice a year and that is using Koolstop black
> pads!
>
> David.
> Jim,
>
>
>>hmmmm, you do not cite which page, and you didn't bother to context the
>>link to the 90% statement. it may have been clear to you, but not to
>>me. and having quickly scanned the site, i /still/ don't see a 90%
>>statement.
>>
>
>
> Read the part where the rim will ovalize under a 200lbs load with
> loosely tightened spokes. Any stiff rim, including the A719 or the
> T520, T519 will ovalize or go out of true when built poor or tensioned
> incorrectly. Therefore, the stiffness of the rim has nothing to do
> with the final stiffness of the wheel, hence the 90% figure. The 90%
> figure is just what I think, but seemed to concur with another master
> builder in town who he seemed to agree with me.
ok, 3 things:
1. by definition, rims distort [ovalize] under load, /regardless/ of how
many spokes support it. if it didn't, there would be no load. the
extent of ovalization under load is a function of rim thickness, not
spoke tension.
2. going out of true is a function of localized plastic deformation,
which is precisely why "stress releiving" the wheel is so important.
it's got nothing to do with ovalization under load.
3. the stiffness of the rim is fundamentally important to the stiffness
of the wheel.
to paraphrase; "er, i reckon it's 90% and my buddy reckons that's about
right". just doesn't cut it david. sorry.
> Spokes take all the
> stress (compression and torque) and therefore, they all have a fatique
> lifespan which (depending on the spokes you use) sometimes can be
> shorter than the rims they hold, if ridden in very dry and sunny
> weather all year round.
spokes don't experience torque, just tension [not compression] in the
main span and bending at the elbow.
>
>
>>besides, do you really think a low-pro lightweight racing rim is just as
>>stiff as a heavy duty touring rim?
>>
>
>
> You are comparing apples and oranges here..
no, i'm comparing rims to rims. that's valid.
> Light weight low spoke
> count wheels carry less spokes, tensioned much higher than normal
> wheels and the rims are designed stiffer to compensate for that, while
> still maintaining light weight status.
tension has nothing to do with weight. and it doesn't have much to do
with count either.
> Therefore, it has less (or
> lesser) meat area (braking) than say a T520 or a A719.
you mean thickness, not area. it's the rim thickness that decreases
with wear, not the rim area.
> If both are
> ridden in foul winter weather with constant braking and pads are
> contaminated with sand and grit, the pro lightweight rims will be
> killed sooner than touring rims. When the braking area of the rims
> have less than 1mm thickness on both sides
thickness, not area.
>, you are looking at
> structural integrity being compromised really soon -- rims will break.
> The A719 will break later, because it's got a lot of meat area. And
> yes, I replaced my T520s twice a year and that is using Koolstop black
> pads!
>
> David.
