gottago

I noticed that 6 spoke holes of the 28-spoke rear wheel had cracks. All on the drive-side - meaning 6/14 drive-side spoke holes were cracked (over 40%). The rim is a Bontrager TLR that came with my Trek Checkpoint ALR 5 with disc brakes. I had not adjusted the spoke tension since buying it and use the bike mainly for highway commuting.

From what I've read, spokes of disc brake wheels experience much more tension during braking than rim brakes. The rim is only 4 years old. To me, that seems like a short time for rims to be cracking. Would this be considered just normal wear&tear? What is the average mileage lifespan of disc-brake rims? I just assumed that they would last longer than rim-brake rims due to lack of wear. I hadn't considered spoke tension being transmitted from hub.
Thanks.

tFUnK

Those stock low end Bontrager wheels aren't great. I bought a used Trek bike and the rear already came with a replaced spoke. Then on a ride I broke another (only the second spoke I've ever broken in my 2+ decades of riding).

Not sure what else to say other than this is a good time for up upgrade to something nicer.

KerryIrons

4 years at 500 miles per year, or 4 years at 10,000 miles per year? It really does make a difference. That said, your wheel is well and truly done. The quality of the rim and how well the wheel was built are big factors, as well as your riding style. Some people "ride light" and rarely have wheel problems while others "ride heavy" and are constantly having issues. We can discern none of this from your post.

veganbikes

There are a lot of factors involved here but typically machine built wheels with lower spoke counts are a lot less durable but are cheaper to produce and save them money in the end which they pass on to you.

The wheel is finished and there really isn't a huge point in rebuilding it. However I would talk with a well regarded wheel builder and give them your info and what you need out of the wheel and they can build you something that will last longer. If you are riding off-road for a lot of miles and are a heavier rider they would probably suggest a wheel system to handle that however if you are on the road and a light rider they will probably suggest something different maybe a similar wheel but handbuilt and so it will last longer. When a wheel is built by the hands of someone who is well versed in wheel building it will come out generally ready to ride and not have to deal with de-tensioning and all of that as the wheel builder generally takes care of all of that.

Duragrouch

Disc rims have less spoke problems due to growth in diameter due to brake heat (I've popped spokes on 20" aluminum rim brake rims on long descents where braking was required), however disc hubs do pull on spokes hard too. Not sure which is worse.

On my old road bike, no discs, flat land so light braking, smooth roads. But I would wear out a set of rims via a crack at a spoke hole in three years with about 5000-7000 miles per year, 2 sets. Then I bought a set of double socketed rims to spread the load between inner and outer walls, so reducing the stresses by more than half. Each 10% reduction in stress roughly doubles fatigue life, assuming certain fatigue curves. So 50% reduction is 2^5 = 32X increase in fatigue life. That was decades ago and I've yet to wear out those rims. I was commuting in winter and wanted to use a cheaper set of freewheel rims, then one crack at a spoke hole. I took a 30 caliber boat-tail hollow-point match bullet, so solid copper base; I measure the depth between the inner and outer rim walls, then add the width of the flange I want, and measure up from the base of the bullet, and cut the tip off there with a hacksaw, then hold the bullet with pliers and heat with torch to melt out the lead. I drill the base to fit the spoke nipple. I use a plumbing flaring tool to flare the open end about 45 degrees, at where my measurement tells me will be the transition to the inner wall. I place it in the rim hole, install the spoke and nipple and tighten until just contact with the rim, no tension. Holding the rim, I use a punch and hammer to flatten the flare down to flat on the inner rim all the way around. Then I tensioned the spoke up and trued the wheel. I rode that rim for thousands of miles and still have that wheel as backup wheels. Socketed rims are bombproof. Adding a socket, even when there are cracks at the nipple exit, still holds, because the flare has SO much more area than the original nipple seat. Sockets add rim weight, that's the only downside. What's my name?

Iride01 

Did you ever have the wheels checked after you bought the bike? Spokes sometimes loosen up in random places. Especially wheels that were built on a production line whether by a machine or a person. If some were too loose, that might have put too much stress on the others.

Usually with any wheel I get, I take it to a shop with a decent wheel person and let them go over and check the spokes after I've put about 300 miles on them. Usually that one time is all they ever need. But you should always check periodically for loose spokes. My son tacoed a Bontrager rim on his Marlin 5. I had told him he needed to take it down for them to look at but he ignored me. It's what son's do. I would have done the same if my Dad had told me to have it checked.

Welcome to BF!

gottago

The spoke tension is fine all around and the wheel holds true but it looks like cracking rims is considered “normal” after 4 years (only the last 2 were dedicated commuting at around 240km/wk on paved surface. It’s a Bontrager TLR rim but no model given - so I’m assuming low-end stock wheels with Trek Checkpoint ALR 5 bikes. I still say it’s a design flaw since all 6 spoke hole cracks are on the drive side of the rear wheel.

Iride01 

I don't consider rims cracking around the spoke holes after 4 years normal for a alloy rim. I've got alloy rims from the late seventies that don't have cracks. And none of my newer alloy rims do either. In fact I don't think I've ever had cracks around the spoke hole of any rim. Even the remaining Bontrager rim on my son's Marlin is in fine condition. And it is the rear which bears most of the weight and the differing tensions from drive side to non drive side spokes. And it's 8 yo.

If anything it's high end rims that will suffer the most from spoke tension not being correct. Low end stuff is heavier and more durable.

gottago

Were they rim brake rims or disc brake? Mine is disc brake.
So now I’m forking out over $350 for a new 32 spoke disc brake wheel (not sure what brand rim though). I asked the store to inquire about a warranty replacement from Trek/Bontrager but it doesn’t look promising.

Iride01 

Virtually all of them were rim brake. My current bike is disc brake and coincidentally is four years old. I guess I'll have to wait and see. So far no cracks.

Duragrouch

Spokes on drive side are higher tension than non-drive side, to compensate for the lower lateral angle for the wheel dish on derailleur gearing. It makes complete sense that drive side cracked first. That doesn't mean it did not crack prematurely due to some other issue.

pdlamb

Well-built wheels don't have cracked spoke holes unless they've been abused. As-built stock wheels are built on a machine, and the spokes won't be overtensioned unless somebody at the factory was angry and/or hung over. That leaves bad rims. My guess, they weren't checked for proper annealing and hardening on receipt, and the poorly tempered aluminum cracked under a much lower load than they should have. Might be a design flaw, if the rims weren't specified correctly, but I'd still bet on poor quality control in manufacturing.

Of course, since mass produced bikes are bought in thousands, that may have been "normal" for one year's production. It still should have been caught and corrected after a year. If you've got the receipt for the bike, you might want to file a warranty claim.

dedhed

Check with the dealer where you bought the bike. I know a couple people who had cracked Bontrager wheels replaced under warranty. Worst they can say is No.

Duragrouch

I've had cracks at spoke holes, that's the primary failure mode, on road bike wheels on smooth roads. But 35 miles a day, 8 months of the year, for 3 years, that's a lot of miles. Wore out the factory set and a new set, each 3 years. Aluminum has no "fatigue limit". Steel does; Below a certain stress level, you can stress steel forever in fatigue and it won't break. Aluminum has no such limit, eventually it will fail by fatigue with enough stress cycles. But, put double sockets at the spoke holes to spread the load between both inner and outer walls, and a very wide surface area on the outer, and stress levels due to the spokes are slashed immensely. That's the LAST set of wheels I put on that bike, and it's now retired in favor of a townie, but I have little doubt that had I been riding that bike all these years since, those rims will still outlive me, though in this much more hilly environment, the sidewalls would eventually succumb to rim brake wear, my townie wheels are almost at that point after 10 years.

The Chemist

I had a rim fail with spoke hole cracking after only around 18 months / 15000km. It was a 24 spoke disk brake wheel. Wasn't particularly happy with the cracking, but it wasn't a super expensive wheel and it had seen quite a bit of use. Replaced it with a 28 spoke rim and hopefully that one will last a little bit longer.

georges1

I knew a friend of mine who had pair of Bontrager Aeolus on his madone which cracked after he went into pot holes when racing , he got a factory replacement from Trek because they were under warranty. Another friend had a Trek Singletrack 970 fitted with Bontrager Corvair rims, he later changed those after 10 years because they need to be trued too often and they didn't have the qualities of the mavic sup, ub control and cd (ceramic braking coating). He later bought a pair of Mavic XM719 rims that he had assembled with hope hubs and since 10 years he never had to true them despite his very agressive riding style.Maybe the quality of Bontrager rims is not that stellar. On my two Trek MTBs I have Mavic D521 rims laced to Hope RS4 hubs, they are some of the best wheels I have ever had.

PoorInRichfield

OP... what do you weight? Wheels do have rider weight limits, not sure if that applies in your case. If you're on the heavier end of the scale, you may consider looking for wheels with higher spoke counts.

If your weight isn't an issue, it sounds like your wheel is/was defective. In 35+ years of cycling, I've only had one wheel fail at the spoke and it was a high tension Rolf Vector wheel, which was probably a bad design to begin with.

Flip Flop Rider

if you ride enough I'm guessing you will see this

Fissile

Thank you. You don't know now many times I've tried to explain this to the Lance Wannabes. Wheels with half the spokes taken out that cost 5 times what a 36 spoke 3X wheel costs are for SUCKERS. The only exception being people WHO ARE ACTUALLY RACING.

mpetry912 

Agreed. Same discussion with riders who insist that their wheels are tensioned to 140KgF. Why ? Because they saw it in a GCN video on YouTube.

If you want to run equipment that is super light and stressed to the limit, guess what, it ain't going to stand up to years of abuse. Expect some failures.

/markp

veganbikes

I mentioned nothing about Lance nor was it relevant to the conversation in any sense of it. A wheel doesn't need 36h to be strong, it is about all the parts and who or what is putting it together. I would rather have a handbuilt 28h wheel built by someone who knows what they are doing and is using the right parts and tensions to make a strong wheel then a cheap machine built 36h wheel with more random stuff that may not work as well together.

Also a 36h wheel can be expensive having fewer or more spokes doesn't always equate anything to price however yes you can have lower spoke count wheels that can get quite expensive but typically the rims are carbon and they are handbuilt with high end hubs and spokes that are designed as a system but I could easily build a 36h wheel that is similarly expensive with higher end hubs and really strong rims and say a DT Swiss Alpine III spoke or maybe even still using Sapim CX-Rays.

I am not disagreeing with myself. A machine built lower spoke count wheel tends to be less durable and in some cases having more spokes can make a wheel durable. However that is not what makes a wheel durable it is how the wheel is constructed and with what parts you are using. Having say a light duty rim with a ton of spokes at high tension from a machine will not make a strong wheel despite having 36 spokes. A wheel is a system and all the components need to be similar and selected for purpose to work correctly.

Duragrouch

Fatigue failure is a function of the magnitude of fluctuation in stresses, in addition to the peak stress loads. Worse would be fully-reversing loads, not the case here as slender spokes will not support compression loads. And, number of stress cycles, which equates to the distance the wheel has rolled. But reduce the stresses, and the fatigue limit gets pushed way to the right on the graph.

I'll accept a lower-spoke wheel if the rim then is thicker and stronger at the spoke holes, I think I have seen this on some rims, so it's not a pure extrusion but is formed or machined to be thinner between the spoke holes.

Otherwise, double eyelet/socket rims are the magic bullet for rim durability, if you don't mind the extra rim weight.

I think on a thread about either an old Lemond or Armstrong race bike, a closeup of the rim showed the spokes exiting, not at the center, but on each side, with a hole halfway between inner and outer diameter, and I immediately thought, that's a great design, because a) the spoke hole area is loaded more in shear than bending normal to the surface, and b) with the rim overall in bending, that halfway point is near the neutral axis in bending, a really good place to attach something. Also, the spokes crossed laterally, from rim right to hub left, and vice-versa, which increases the lateral spoke angle to improve lateral stability and improves truing I think.

terrymorse 

Or use a rim material that's more resistant to fatigue than aluminum. Say, carbon fiber.

georges1

Not really , carbon fiber rims on mountain bikes won't support bad treatment or extreme jumps, not without the reason the Mavic Deemax wheels , the Mavic D521 , D321, XC 717, XM 719, XM 819, X 823disc rims are the most after sought rims now commanding premiums on the second hand market. Mavic rims with SUP, CD and UB control are more advantageous and more solidly built than any Sun or Velocity or Bontrager rim . For road bikes that is another story, it depends where the carbon wheel is manufactured and if the quality control is stringent and thorough, I won't buy wheels made in China or Taiwan for quality and security reasons. I stopped to buy Mavic Cosmic Carbone wheels after the year when they outsourced the production in Romania. I have a pair of Zipp 404 and two pairs of Zipp 60s that were built in the US.

terrymorse 

Yes, really. Quality carbon rim will outlast aluminum rim.