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#1
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rim life.. questions...
Hi Wheel gurus,
my road bike is a '04 Trek 2100, which came with Bontrager Select Rims. Recently, when fixing a flat, i noticed there were cracks on the rear rim near the spoke holes. the rim surface looks like: =============================================== --o-- o --o-- o =============================================== 'o' is the spoke hole. and '--' is the crack and '==' is the braking surfaces. This wheel is a 24 spoke wheel and has paired spokes. The cracks are all on the drive side spokes only. And of the 12 total drive side spokes, 9 of them had cracks around them (on the rim). I have put on 10k miles on this wheel. About me: 6'3" ~190lbs. sometimes i like mash up over small hills, but usually spin up long grinding hills. i do not race, this is just a recreational/long distance riding bike. The LBS examined the wheel and said it was stress related cracks. At the LBS, I found a '05 Bontrager Select wheel for $120. I would have bought it, if i had my credit card with me. I decided to return later to buy it. During this time it got me thinking and few questions: why failure and why now: * at ~10k miles, i have 9 cracks on the rims (i wonder when was the first crack appeared - approx 1000 miles ago ?? probably) in that case if i were to get a new set of wheels, probably will last only 8k or 9k miles. * the rims has no eyelets is that a possible cause for this failure ? * from the time i bought this bike, only once a spoke came loose and got it fixed by the LBS and two or three times went out of true and got it trued by the LBS. Other than that nothing special was made to the Wheel. Also the rim is offset to accomodate the cassette - so the tension on the non-drive side wouldn't be as high - to cause this kind of failure. * paired-spokes is it helping or not helping or hurting the life of wheels. answers to the above concerns will help me choose one of the following options: * buy the '05 Bontrager Select wheel * get a rim and build up the wheel myself - i haven't examined the condition of the hub well to see what state it is in. In such a case, i would have to hunt for a 24h sturdy rim to start with. recently there has been lots of threads on wheels etc.. i am trying to catchup on those, but some of my concerns aren't addressed in those. please provide me your inputs so as to help me decide which way to go... thanks, ravi |
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#2
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rim life.. questions...
Ravi wrote:
Hi Wheel gurus, my road bike is a '04 Trek 2100, which came with Bontrager Select Rims. Recently, when fixing a flat, i noticed there were cracks on the rear rim near the spoke holes. the rim surface looks like: =============================================== --o-- o --o-- o =============================================== 'o' is the spoke hole. and '--' is the crack and '==' is the braking surfaces. This wheel is a 24 spoke wheel and has paired spokes. The cracks are all on the drive side spokes only. And of the 12 total drive side spokes, 9 of them had cracks around them (on the rim). I have put on 10k miles on this wheel. About me: 6'3" ~190lbs. sometimes i like mash up over small hills, but usually spin up long grinding hills. i do not race, this is just a recreational/long distance riding bike. The LBS examined the wheel and said it was stress related cracks. At the LBS, I found a '05 Bontrager Select wheel for $120. I would have bought it, if i had my credit card with me. I decided to return later to buy it. During this time it got me thinking and few questions: why failure and why now: * at ~10k miles, i have 9 cracks on the rims (i wonder when was the first crack appeared - approx 1000 miles ago ?? probably) in that case if i were to get a new set of wheels, probably will last only 8k or 9k miles. * the rims has no eyelets is that a possible cause for this failure ? * from the time i bought this bike, only once a spoke came loose and got it fixed by the LBS and two or three times went out of true and got it trued by the LBS. Other than that nothing special was made to the Wheel. Also the rim is offset to accomodate the cassette - so the tension on the non-drive side wouldn't be as high - to cause this kind of failure. * paired-spokes is it helping or not helping or hurting the life of wheels. answers to the above concerns will help me choose one of the following options: * buy the '05 Bontrager Select wheel * get a rim and build up the wheel myself - i haven't examined the condition of the hub well to see what state it is in. In such a case, i would have to hunt for a 24h sturdy rim to start with. recently there has been lots of threads on wheels etc.. i am trying to catchup on those, but some of my concerns aren't addressed in those. please provide me your inputs so as to help me decide which way to go... thanks, ravi rim cracks are usually either defective rims [not so common] or excess spoke tension. sounds like your lbs was over-tensioning if it had been trued multiple times. eyelets can be effective local stress mitigation, but even eyeletted rims crack if spoke tension is still too high. regarding repair/replacement, replacement is probably the way to go. i believe you can get rims to repair this wheel, but the economics may not make a lot of sense. standard rims are not usually available in paired spoking but you could try a 36h rim skipping every 3rd hole, but spoke length may be an issue, not to mention drilling offset. |
#3
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rim life.. questions...
On Sun, 28 Aug 2005 11:07:23 -0700, Ravi
wrote: Hi Wheel gurus, my road bike is a '04 Trek 2100, which came with Bontrager Select Rims. Recently, when fixing a flat, i noticed there were cracks on the rear rim near the spoke holes. the rim surface looks like: =============================================== --o-- o --o-- o =============================================== 'o' is the spoke hole. and '--' is the crack and '==' is the braking surfaces. This wheel is a 24 spoke wheel and has paired spokes. The cracks are all on the drive side spokes only. And of the 12 total drive side spokes, 9 of them had cracks around them (on the rim). I have put on 10k miles on this wheel. [snip] Dear Ravi, The spoke tension on the drive side was too high. Cracks like these are not uncommon when wheels are built to the highest tension that they can stand without immediately deforming, a value that can be higher than the rim manufacturer expects and recommends. Either get a sturdier rim or reduce the tension. Carl Fogel |
#4
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rim life.. questions...
On 28-Aug-2005, wrote: Dear Ravi, The spoke tension on the drive side was too high. Cracks like these are not uncommon when wheels are built to the highest tension that they can stand without immediately deforming, a value that can be higher than the rim manufacturer expects and recommends. Either get a sturdier rim or reduce the tension. So Carl, did you perform experiments and analysis to support your argument, or did you decide to take jim beam's side just to rankle Jobst Brandt? -- Sniper Anon ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#5
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rim life.. questions...
On Sun, 28 Aug 2005 19:07:52 GMT, "Sniper Anon"
wrote: On 28-Aug-2005, wrote: Dear Ravi, The spoke tension on the drive side was too high. Cracks like these are not uncommon when wheels are built to the highest tension that they can stand without immediately deforming, a value that can be higher than the rim manufacturer expects and recommends. Either get a sturdier rim or reduce the tension. So Carl, did you perform experiments and analysis to support your argument, or did you decide to take jim beam's side just to rankle Jobst Brandt? Dear Snip, Er, what other explanation besides the spoke tension being too high for the rim do you offer when the rim cracks around the base of 9 out of 12 of the higher-tension drive-side spokes after a few thousand miles? It's not as if this is a new complaint on this newsgroup. Jobst's approach of increasing the tension until the wheel deforms and then backing off was developed with sturdy 36-spoke rims back in the 1980's. When applied to flimsier, lower-count modern rims, this practice can lead to cracks around the spoke holes. To produce the same overall drive-side tension of 18*T that will cause local yielding with only 12 spokes instead 18, each spoke has to be tightened to 1.5*T. Hmmm . . . a 50% increase in tension, cracks appear around the spoke holes in a few thousand miles, and someone starts a thread to ask what to do. This is why Jim Beam keeps suggesting that wheel-builders should use a tensiometer and tension the spokes to the rim manufacturer's recommendation. Carl Fogel |
#6
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rim life.. questions...
Ravi toravir writes:
My road bike is a '04 Trek 2100, which came with Bontrager Select Rims. Recently, when fixing a flat, I noticed there were cracks on the rear rim near the spoke holes. the rim surface looks like: =============================================== --o-- o --o-- o =============================================== 'o' is the spoke hole. and '--' is the crack and '==' is the braking surfaces. This wheel is a 24 spoke wheel and has paired spokes. The cracks are all on the drive side spokes only. And of the 12 total drive side spokes, 9 of them had cracks around them (on the rim). I have put on 10k miles on this wheel. About me: 6'3" ~190lbs. sometimes I like mash up over small hills, but usually spin up long grinding hills. I do not race, this is just a recreational/long distance riding bike. The LBS examined the wheel and said it was stress related cracks. That's self evident. What else causes metals to crack in service. At the LBS, I found a '05 Bontrager Select wheel for $120. I would have bought it, if I had my credit card with me. I decided to return later to buy it. During this time it got me thinking and few questions: why failure and why now: * at ~10k miles, I have 9 cracks on the rims (I wonder when was the first crack appeared - approx 1000 miles ago ?? probably) in that case if I were to get a new set of wheels, probably will last only 8k or 9k miles. * The rims has no eyelets is that a possible cause for this failure ? * from the time I bought this bike, only once a spoke came loose and got it fixed by the LBS and two or three times went out of true and got it trued by the LBS. Other than that nothing special was made to the Wheel. Also the rim is offset to accomodate the cassette - so the tension on the non-drive side wouldn't be as high - to cause this kind of failure. * paired-spokes is it helping or not helping or hurting the life of wheels. There are several effects coming together that cause these failures. One is too few spokes another is no steel sockets or eyelets, another is hard anodizing together with excess tension caused by using too few spokes. In addition, to accommodate 10-speed gear clusters, rear hubs have gotten narrower to reduce offset (and the required difference in tension from left to right). Just the same rear wheels, carry at least 2/3 the load with the right side spokes. No wonder the rims develop fatigue cracks. Before the equipment fad got rolling in the present mode, low spoke count wheels were used for special events like time trials. Then professional teams, sponsored by component manufacturers, began using them on a regular bases, to hell with the expense of frequent replacement. So here we are with no market for reliable and durable wheels, most riders being convinced that if Lance Armstrong does it, it must be what I need. I am at a loss to suggest what rims you should get but with the hubs and spokes you have, there is no alternative to shelling out yet more for the same. Paired spoking, patented by Lovelace in 1890, had no benefits then and has none now. For recreational bicycling (oops, that's not PC, we are all on training rides for our next competition) 36-spoke wheels are still the reasonable compromise between rim weight and number of spokes. With low spoke count, one spoke failure will make the wheel unridable but to make up for that, the spoke cannot be replaced in the field because such wheels require special fixturing to be tensioned and trued. I suppose the cell phone has absolved people of touring with tools and equipment to be self sufficient, so wheels will probably continue to be as fragile and excessively expensive as most currently are. It was not long ago that a rider was assured of finding a replacement rim at most any bicycle shop in the USA or overseas, the standard being the 36-spoke Mavic MA-2 and other rims that had the same effective dimensions. I recall rolling into a shop in Italy where we bought a new MA-2 rim to replace a severely dinged one and no one thought it was unusual to expect to find one. Most every bicycle shop had these on the overhead rack. Jobst Brandt |
#7
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rim life.. questions...
Carl Fogel writes:
The spoke tension on the drive side was too high. Cracks like these are not uncommon when wheels are built to the highest tension that they can stand without immediately deforming, a value that can be higher than the rim manufacturer expects and recommends. Either get a sturdier rim or reduce the tension. So Carl, did you perform experiments and analysis to support your argument, or did you decide to take jim beam's side just to rankle Jobst Brandt? Er, what other explanation besides the spoke tension being too high for the rim do you offer when the rim cracks around the base of 9 out of 12 of the higher-tension drive-side spokes after a few thousand miles? It's not as if this is a new complaint on this newsgroup. Jobst's approach of increasing the tension until the wheel deforms and then backing off was developed with sturdy 36-spoke rims back in the 1980's. When applied to flimsier, lower-count modern rims, this practice can lead to cracks around the spoke holes. Ah yes, "modern" rims. How much e have progressed To produce the same overall drive-side tension of 18*T that will cause local yielding with only 12 spokes instead 18, each spoke has to be tightened to 1.5*T. Hmmm... a 50% increase in tension, cracks appear around the spoke holes in a few thousand miles, and someone starts a thread to ask what to do. This is why Jim Beam keeps suggesting that wheel-builders should use a tensiometer and tension the spokes to the rim manufacturer's recommendation. That makes little difference. What comes from that is the need for Loctite on the spoke threads because spokes are now so loose (to not crack rims) that they slacken in use. It is not unusual to hear spoke rattle over rougher pavement and that is what unscrews spoke nipples. At first it was machine built wheels, ones that machines could not true if made tight as they should be, that introduced thread locking compounds. Now that we have them, wheels have taken the next step, that of requiring loose spokes to prevent rims failure and thereby making thread-lock a necessity. Thread-lock has become the norm in lieu of reasonably tight wheels because so many have so few spokes. Jobst Brandt |
#9
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rim life.. questions...
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#10
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rim life.. questions...
On Sun, 28 Aug 2005 20:29:01 GMT,
wrote: Ravi toravir writes: My road bike is a '04 Trek 2100, which came with Bontrager Select Rims. Recently, when fixing a flat, I noticed there were cracks on the rear rim near the spoke holes. the rim surface looks like: =============================================== --o-- o --o-- o =============================================== 'o' is the spoke hole. and '--' is the crack and '==' is the braking surfaces. This wheel is a 24 spoke wheel and has paired spokes. The cracks are all on the drive side spokes only. And of the 12 total drive side spokes, 9 of them had cracks around them (on the rim). I have put on 10k miles on this wheel. About me: 6'3" ~190lbs. sometimes I like mash up over small hills, but usually spin up long grinding hills. I do not race, this is just a recreational/long distance riding bike. The LBS examined the wheel and said it was stress related cracks. That's self evident. What else causes metals to crack in service. At the LBS, I found a '05 Bontrager Select wheel for $120. I would have bought it, if I had my credit card with me. I decided to return later to buy it. During this time it got me thinking and few questions: why failure and why now: * at ~10k miles, I have 9 cracks on the rims (I wonder when was the first crack appeared - approx 1000 miles ago ?? probably) in that case if I were to get a new set of wheels, probably will last only 8k or 9k miles. * The rims has no eyelets is that a possible cause for this failure ? * from the time I bought this bike, only once a spoke came loose and got it fixed by the LBS and two or three times went out of true and got it trued by the LBS. Other than that nothing special was made to the Wheel. Also the rim is offset to accomodate the cassette - so the tension on the non-drive side wouldn't be as high - to cause this kind of failure. * paired-spokes is it helping or not helping or hurting the life of wheels. There are several effects coming together that cause these failures. One is too few spokes another is no steel sockets or eyelets, another is hard anodizing together with excess tension caused by using too few spokes. In addition, to accommodate 10-speed gear clusters, rear hubs have gotten narrower to reduce offset (and the required difference in tension from left to right). Just the same rear wheels, carry at least 2/3 the load with the right side spokes. No wonder the rims develop fatigue cracks. Before the equipment fad got rolling in the present mode, low spoke count wheels were used for special events like time trials. Then professional teams, sponsored by component manufacturers, began using them on a regular bases, to hell with the expense of frequent replacement. So here we are with no market for reliable and durable wheels, most riders being convinced that if Lance Armstrong does it, it must be what I need. I am at a loss to suggest what rims you should get but with the hubs and spokes you have, there is no alternative to shelling out yet more for the same. Paired spoking, patented by Lovelace in 1890, had no benefits then and has none now. For recreational bicycling (oops, that's not PC, we are all on training rides for our next competition) 36-spoke wheels are still the reasonable compromise between rim weight and number of spokes. With low spoke count, one spoke failure will make the wheel unridable but to make up for that, the spoke cannot be replaced in the field because such wheels require special fixturing to be tensioned and trued. I suppose the cell phone has absolved people of touring with tools and equipment to be self sufficient, so wheels will probably continue to be as fragile and excessively expensive as most currently are. It was not long ago that a rider was assured of finding a replacement rim at most any bicycle shop in the USA or overseas, the standard being the 36-spoke Mavic MA-2 and other rims that had the same effective dimensions. I recall rolling into a shop in Italy where we bought a new MA-2 rim to replace a severely dinged one and no one thought it was unusual to expect to find one. Most every bicycle shop had these on the overhead rack. Jobst Brandt Dear Mr. Peabody, Posts asking if the MA-2 had been discontinued first appeared in 1996. By 1999, some people were even hoarding them: http://groups.google.com/group/rec.b...7?dmode=source It's hard to buy rims that haven't been made in this century. http://www.timetravelreviews.com/tv_...ndsherman.html Sherman |
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