| Author |
Message |
TE Cheah
Guest
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 Posted:
Mon Dec 06, 2004 10:37 am Post subject:
Re: Inaccurate wheel balancing - has any1 here experienced t |
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| All
| that matters when balancing is that the computer doing the balancing has to know
| the RPM during the spin. What that RPM is doesn't matter.
I disagree ; wheels are hard solids so their shapes cannot change when
wheels are spun fast, but radial tyres @1.8 to 2.3 kg/cm² pressure are not
: when spun 4x as fast as 4 rps, centrifugal force will push tyres outward,
then any heavy spot of a tyre will be slightly further from axis of rotation
& need more counter weight than @ 4 rps. Your microprocessor cannot
predict how flexible ( varies with brand, model, size ) tyres' walls will be.
Even when tyres ( like my spare tyre @4.2 kg/cm² pressure ) are hard
solids, higher speed can produce bigger vibration which are more
detectable than small vibration @ low speed.
Why can't manufacturers offer 3 or 4 different speeds ( e.g. 5,10,15,20
rps ), so tyre shops can charge more for a higher speed ?
If I cannot find faster machines, I'd find German machines ; their
autobahns have no speed limit, so their machines likely need to satisfy
faster drivers there.
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Mike Behnke
Guest
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| Posted:
Mon Dec 06, 2004 10:50 pm Post subject:
Re: Inaccurate wheel balancing - has any1 here experiemced t |
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You may have lost a balancing weight, but doubtful you'd notice 5g. 5
ounces, yes.
TE Cheah wrote:
| Quote: | My 4ws accord's steering has been often fine since '93, but has been
wobbling @ >100 kph since 8-04 after I replaced 2 front tyres with 2
Michelin green model of 205/65R15, no wobble @ <100 kph. I
suspected 1 shop's balancing was inaccurate, so got another shop with
a newer machine to re balance 1 tyre : this newer machine found a 5g
shortage on the outer rim of the 6½ x 15" JRD alloy wheel, just 200
km after the 1st shop's older machine reported this wheel as balanced
& OK. I never found a 205/65R15 to be 5g out of balance after such a
little wear, so I think the 1st shop ( located far from highway )'s
machine was not accurate enough.
I suspect shops near highway are more likely to have accurate
machines ; customers who drive on highway @once after wheel
balancing will know @once whether balancing is accurate.
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Rick Brandt
Guest
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| Posted:
Tue Dec 07, 2004 5:21 am Post subject:
Re: Inaccurate wheel balancing - has any1 here experienced t |
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"TE Cheah" <no@spam.biz> wrote in message news:41b3f1ca_2@news.tm.net.my...
| Quote: | | All
| that matters when balancing is that the computer doing the balancing has to
know
| the RPM during the spin. What that RPM is doesn't matter.
I disagree ; wheels are hard solids so their shapes cannot change when
wheels are spun fast, but radial tyres @1.8 to 2.3 kg/cm² pressure are not
: when spun 4x as fast as 4 rps, centrifugal force will push tyres outward,
then any heavy spot of a tyre will be slightly further from axis of rotation
& need more counter weight than @ 4 rps. Your microprocessor cannot
predict how flexible ( varies with brand, model, size ) tyres' walls will be.
Even when tyres ( like my spare tyre @4.2 kg/cm² pressure ) are hard
solids, higher speed can produce bigger vibration which are more
detectable than small vibration @ low speed.
Why can't manufacturers offer 3 or 4 different speeds ( e.g. 5,10,15,20
rps ), so tyre shops can charge more for a higher speed ?
If I cannot find faster machines, I'd find German machines ; their
autobahns have no speed limit, so their machines likely need to satisfy
faster drivers there.
|
I can't imagine a modern tire, particularly the newer lower profiles changing
diameter at high speed enough to affect the balance of the tire/wheel assembly.
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Juhan Leemet
Guest
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| Posted:
Tue Dec 07, 2004 10:25 pm Post subject:
Re: Inaccurate wheel balancing - has any1 here experienced t |
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On Mon, 06 Dec 2004 18:21:02 -0600, Rick Brandt wrote:
| Quote: | "TE Cheah" <no@spam.biz> wrote in message news:41b3f1ca_2@news.tm.net.my...
| All
| that matters when balancing is that the computer doing the balancing has to
know
| the RPM during the spin. What that RPM is doesn't matter.
I disagree ; wheels are hard solids so their shapes cannot change when
wheels are spun fast, but radial tyres @1.8 to 2.3 kg/cm² pressure are not
: when spun 4x as fast as 4 rps, centrifugal force will push tyres outward,
then any heavy spot of a tyre will be slightly further from axis of rotation
& need more counter weight than @ 4 rps. Your microprocessor cannot
predict how flexible ( varies with brand, model, size ) tyres' walls will be.
Even when tyres ( like my spare tyre @4.2 kg/cm² pressure ) are hard
solids, higher speed can produce bigger vibration which are more
detectable than small vibration @ low speed.
Why can't manufacturers offer 3 or 4 different speeds ( e.g. 5,10,15,20
rps ), so tyre shops can charge more for a higher speed ?
If I cannot find faster machines, I'd find German machines ; their
autobahns have no speed limit, so their machines likely need to satisfy
faster drivers there.
I can't imagine a modern tire, particularly the newer lower profiles changing
diameter at high speed enough to affect the balance of the tire/wheel assembly.
|
I recall seeing some film showing the changes in shape of a tire at speed.
The outer surface of the tire had a kind of scalloped shape, definitely
NOT a smooth, round circle. It looked like there were some kind of surface
waves rippling along the outer surface. If there is that kind of
distortion in the shape of the tire, then any arguments about grams of
weight here or there are likely moot. I suspect the balance of a tire
rolling along the ground may not be that precise? Best approximation kind
of thing? OTOH, I do not recall what kind (radial?) of tire in the film.
--
Juhan Leemet
Logicognosis, Inc. |
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MasterBlaster
Guest
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| Posted:
Wed Dec 08, 2004 5:42 pm Post subject:
Re: Inaccurate wheel balancing - has any1 here experienced t |
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"Juhan Leemet" wrote
| Quote: | I can't imagine a modern tire, particularly the newer lower profiles changing
diameter at high speed enough to affect the balance of the tire/wheel assembly.
I recall seeing some film showing the changes in shape of a tire at speed.
The outer surface of the tire had a kind of scalloped shape, definitely
NOT a smooth, round circle. It looked like there were some kind of surface
waves rippling along the outer surface.
|
Yep, considering that at 60-mph (car speed) each part of that flexy rubber tire
has to go from 0 (on the road surface) to 120 (top of tire) and back to 0, about
13 times per second. All that centrifugal force is going to do strange things!
| Quote: | If there is that kind of
distortion in the shape of the tire, then any arguments about grams of
weight here or there are likely moot. I suspect the balance of a tire
rolling along the ground may not be that precise? Best approximation kind
of thing? OTOH, I do not recall what kind (radial?) of tire in the film.
|
And of course, wheels aren't perfectly round, neither are tires, and most
tires will have slightly stiffer sections where the belts are overlapped during
manufacturing. Not only will the stiffer parts not flex the same when they hit
the ground, they won't stretch away from center as much at that 120mph
"top of the circle" either, both of which can cause vibrations or seemingly
(as the thread is named)... "Inaccurate wheel balancing". |
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