mstateglfr 

I am convinced that most people do not understand wheels- from a theoretical or practical perspective. I have built wheels and I will fully admit that I dont totally understand all of the physics at play.
I can explain, in general, wheel strength. Get below the surface though and it gets less clear.

I am 100% sure most buyers expect a company to have spec'd the bike they buy to have wheels that will work because, you know, that should be the floor and not the ceiling when it comes to spending $2000(in this case) and buying a bike from a shop.


Wheels are also one of the last places a brand can cut corners without the buyer knowing. A moderately informed buyer can see the drivetrain components and thats typically what people start and end when they check a bike to compare to other bikes in a pricerange.
Wheels(and brakes) are just total unknowns due to hubs and rims being rebranded, so buyers(even informed ones) have a tough time figuring out if the components are quality or junk.
Good drivetrain to make buyers think they are getting a deal, then slap unknown quality wheels on which are cheaper and where the savings can be recouped. Genius!

Squeezebox

The "fact" that rims make no difference in the strength of a wheel. I guess spoke count doesn't count either.
Oh!! You must be presenting "alternative facts"
I'm not an engineer. I'm not claiming that I know the micro-details of wheel strength. Sounds like you don't ride low spoke wheels. So where does your detailed knowledge come from. Sure you have a right to an opinion. But claiming absolute knowledge???
I definately see mstatglf's opinion.
And we can get into the discussion about broken flanges with high spoke wheels, particularly 48*. There's really no simple answer.

cyccommute 

Never said that spoke count doesn't matter. In fact, I'm saying the exact opposite. Spoke count matters more than rim strength.

I'm not an "engineer" either but I am an educated man and trained observer. I also happen to be a highly experienced wheel builder with 30+ years of wheel building experience and, more importantly, 30+ years of wheel breaking experience. I've made something of a study of how to avoid breaking wheels and it all comes down to the spokes.

The reason that I say that rims provide little in terms of wheel strength has to do with the way in which the spoke interacts with the rim. The spoke nipple isn't a "nut" in that it doesn't attach to the rim. The nipple floats on the rim and with each revolution of the wheel, an individual spoke will go through a cycle of tensioning/detensioning/tensioning as the rim deforms and slides up the nipple (slightly). If you have enough of these cycles, the spoke elbow can fatigue and weaken like a paper clip that as been bent back and forth too much. The spoke can crack and fail at the head. When you build a wheel with fewer spokes, you are more of fewer spokes and are risking failure...as Trek is now seeing.

Consider what causes ultimate a wheel "death". You can wear through the braking surface of a rim and the wheel isn't dead. It's (mostly) trivial to lace in a new rim and keep riding with the caveat of the rim has to be of the same effective rim diameter. If you blip (minor dent) a rim due to impact, the rim can also be replaced. There is no damage short of a major impact that breaks the rim entirely that will kill a wheel and even that problem is due to spoke damage rather than anything else. But...

If you break a spoke, the wheel is suspect. If you break a couple of spokes, you are living on borrowed time. Break more than 3 and you should really consider replacing the spokes or the entire wheel. If you have an impact strong enough to break a rim, the spokes are damaged and the wheel is likely toast.
Basically, it's all about the spokes. Want strong wheels, build with strong spokes.

I'm a big guy and I ride all of my bikes hard. I don't ride on super wide nor super deep rims...with one exception but that's due to the color of the rim and what was available at the time. I don't ride super heavy rims even for hard core mountain biking. I buy rims based on the weight...or lack thereof...and I build the wheels around spokes that can handle the load.

And I doubt you'll find too many people who have experienced broken flanges of any kind. It's a very rare event. I volunteer at a bicycle co-op where we see every possible problem that you can see on a bicycle and more than a few that I didn't think you could possibly do to a bicycle. I've worked there for about 6 years now and I've seen maybe one broken flange. Outside of the co-op, I've only seen one other broken flange and it certainly wasn't on a 48 hole hub.

No, there isn't a simple answer. But there are answers and they usually require some experience and knowledge about the wheel to understand. I get it that you feel "attacked" because we are discussing something dear to you. But Trek has recalled these wheels because they are failing. The wheels are under-built for the task at hand and Trek is acknowledging that. Trek may have saved a little bit of money by under-building the wheels but they have lost money and, more importantly, their reputation by not paying attention to the details.

ColonelSanders

I'm wondering if the manufacturers are being penny wise, pound foolish.

Most of the hybrids of the world that cost under $800 come with 32 spoke wheels, so why do $2,000 bikes come with wheels that many riders would not want?

Surely it can't be the case that the people who buy $2,000 bikes are more into "bike fashion", than the noobs buying the hybrids.

ColonelSanders

Where and when does rim strength matter?

It is not unusual to see so called touring rims that are very heavy, but of course also allow for at least 36 spokes?

I see no reason to disagree with what you have said about the importance of spoke strength, but am curious about why various rim manufacturers offer rims of such varying weights and what that is all about?

Squeezebox

You clearly stated that rims have little or nothing to do with wheel strength. I think that is probably wrong. And spoke tension was not mentioned. Sure spoke count is important, but so are the rims. That's all I'm trying to say. The rim deforming and flexing is an assumption or at least an "alternative fact".
With all the testing that Trek says they do I'm very surprised they didn't catch this before. Maybe they did replace some wheels but finally did a full recall. My Giant momentum front wheel was replaced but not a big recall for example.
I've heard enough about broken 48* flanges that I probably would never consider it. Just saying.
There are a lot of MTBs and tandems, with what you would consider low spoke count, that hold up very well. Many people are satisfied. A few are not. And we haven't said anything about rim vs disc brakes.
Nobody seems to have the magic answer. There probably isn't one.

indyfabz

There are enough bikes out there that come with sufficient spoke counts to get the job done. And you can have your own wheels built. Personally, I don't see myself going with fewer than 36 in my lifetime for fully loaded touring. My first tour (across the U.S. west to east) featured serious wheel problems with 36. Not much is more of a buzz kill on tour than chronic wheel problems. I finally had to have the rear wheel replaced in Ohio. I couldn't wait around (I was with a group) and a 48 spoke rear wheel from a tandem was all the shop had to offer so I went with it. Early the next year cracks were found around the spoke holes of the front wheel shortly before I was leaving for a tour in Spain. Stayed with 36 spokes, but a much stronger rim. Everything went fine.

Squeezebox

There seems to be a lot of engineering that goes into rim strength. Rim width, rim height, single vs double walled, grommets or not, and I'm sure stuff I'm not aware of. So the engineers know about rim strength and appear to be working on it. I hope for future improvements.

cyccommute 

In my experience, rim strength doesn't matter not much of anywhere. There are limits, of course, but a wider, heavier rim doesn't make for a stronger wheel. It just makes for more rotating mass.

When I build wheels, I look at weight first. I almost never consider width nor do I even know, or consider, thickness of the extrusion. How thick the metal making up the walls of the rim might be the only place where the rim strength would matter but I doubt if anyone really considers it when wheel building. They look at how tall the rim is and/or how wide it is but not how thick the metal is. That would allow for higher tension without cracking the rim but I've never heard anyone talk about considering that aspect of rims.

Manufacturers offer rims of various widths, heights and weights because people want them. Many people...probably most as I'm definitely in the minority here...think that the rim is the key because it's the thing they see when they look at a bicycle wheel and they go off and buy the heaviest rim they can find because it's "strong". The same people will probably build the wheel with whatever spoke they find handy without considering what the spoke brings to the party.

Of course the whole system works together. Rims aren't absolutely unimportant but they are just less important then most people realize.

Based upon what? Do you build wheels? Have you any idea of the physics involved? Go build...and break...a few hundred wheels and get back to us on what you've found to keep them from breaking.

First, get off the damned "alternative fact" kick. It's a ad hominem that you are using simply to discount someone's argument without presenting a counter argument or evidence to back up your point. It's lazy and dishonest.

The rim deforming and flexing during use isn't an "alternative fact" anyway. It is a know and measurable phenomena. A bit of Googling will find you all kinds of discussions about it.

I didn't mention spoke tension because that's not germane to the discussion at hand. One can assume that the wheel will need to have spokes that are properly tensioned and that a spoke that is improperly tensioned is a problem but the rim has little to do with that aspect of wheel building as well. It's still the spoke that does the heavy lifting.

There is probably not a "test" that Trek could have run to "catch this". It's a longevity problem that seems to have taken 2 or 3 years of field use to raise its ugly head. Trek assumed that they can get away with fewer spokes and ignore years of experience that would tell them otherwise. After a few years of field use, they found that they made a wrong assumption. They probably never considered that their wheels would fail.

You want to make 48 hole hubs out to be these weak components and I just don't think the evidence is there to support your claim. Again, broken hub flanges of any kind aren't a major problem.

Yes, there are some low spoke count wheels out there that perform well but what is their use and who is riding them? A 140 lb rider can get away with them but a 200 lb touring cyclist with a 25 to 50 lb load would be wise to choose something else unless they really like replacing spokes. Trek's recall is evidence of the latter rather than the former.

As for "magic answers", no, there aren't any. But there are good solid answers based on good solid facts...actual true ones...and long experience. Choose low spoke count wheels because they are "sexy" (but not really lighter) or choose boring old high spoke count wheels built with good hubs, strong spokes and "meh?" rims. One will cause you all kinds of headaches and the other won't. Your choice. I know what I'll use and why.

Tourist in MSN

I am an engineer. And I worked as a bike mechanic before I went to engineer school.

I completely agree when it comes to the types of wheels that us bike touring folks use.

There are those odd low spoke count racing wheels that none of us would ever consider putting on a touring bike but I am sure you were not talking about those either. Those rims may have been designed to compensate for a low spoke count, but they were clearly not designed to haul a load of camping gear.

In the 60s and 70s a lot of cheap bikes had steel chrome plated rims that were amazingly flexible. It was the 36 spokes on those wheels (some rear wheels were 40 spoke) that gave them the strength they needed. A few front wheels had 32, but I do not recall ever seeing anything less. A few bikes had 32 front and 40 rear, they put the spokes where they were needed.

It was rare to find true "high pressure" clincher tires back then that took more than 55 or 70 psi, in part because the tires could blow off the rims if you ran the pressures that we often put in our tires today. (Plus hooked rims also play a part in that.) It was not uncommon to find people riding bikes with tubular tires back then because they wanted to have higher pressure tires than you could get with clinchers. Now you will only find a tubular tire at the races because high pressure clinchers are commonplace.

I really think that part of the reason for "rim strength" today is the amount of pressure in the tire, the two beads on that tire at high pressure are trying to split the rim apart. Thorn (the maker of two of my bikes) has actually published pressure ratings for different tire widths based on rim failure and they have commented that many tire manufacturers have tire ratings that exceed rim strength. The photo is of a Mavic A719 sticker on one of my wheels listing pressures for two tire sizes. I do not recall seeing stickers like that on other rims, which to some degree surprises me. I bought those A719 rims in 2004, I am not sure if they still put stickers like that on rims today. And I have some 28mm tires that have a higher pressure rating than that rim has for that tire width.

So, my point is that yes rim strength is important, but it is important because it has to hold a high pressure tire on it without splitting. I fully agree that a really strong wheel for touring needs lots of spokes. Rohloff used to say that you only needed 32 spokes, but when I built up my Rohloff bike I bought the 36 spoke version because I wanted lots of spokes to carry a heavy load on my expedition bike.

fietsbob

Yea , R'off had people using their hubs on more than single MTBs,
so they developed the 36 hole for the tandem riders, and also created a backing ring, that could go on the flanges to hold the edges together should the spoke try to pull thru the flanges..

My 04 Koga WTR came with a 3 cross lacing of a 32 spoke hub,
3 cross in a 36 hole is easier to do. Have to get the 1st spoke in the pattern right,
so it clears the casing left side separation bolts, [8 on the 32, 9 on the 36.]


...

Doug64

Heck, it seems that sometimes less can be more. I'm not sure this is really a very practical wheel; it was on a Dutch touring bike.

Squeezebox

With only 3 spokes, makes me wonder how the rim is designed.
So obviously there's a lot more to wheels than just spoke count.
And do keep in mind the 720 is for credit card touring, maybe bikepacking. the low gear is 34-32. It's not an expedition bicycle.

HTupolev

Wheels made from a small number of rigid spokes locked to the rim are usually used for aero, a notable use case being track racing. They're generally much heavier than classical many-spoked wheels; 5-spoke tubular front wheels that cost $700 often weigh as much as a basic $50 clincher front wheel. But you also won't find mountainous ascents inside of a velodrome.

I'm not sure what the deal is with the wheel Doug64 posted.

cyccommute 

I would agree that 36 will get the job done in most cases. If you use triple butted spokes, the wheel will be as strong as at least a 40 and maybe a 48.

I will say that your problem with cracked rims on the 48 spoke wheel could be due to either spokes that were too loose or spokes that were too tight. Both will result in similar rim failure. If the spokes are too loose, the rim flexes too much and cracks. If the spokes are too tight, the spoke puts too much upward pressure on the spoke hole and the rim also cracks. After cracking, it's hard to tell which case caused the problem.

cyccommute 

You are comparing cheese to chalk. The wheel in Doug64's picture is a wheel and it is on a bike but there the similarities end. The three "spokes" are in compression like a car or wagon wheel rather than tension like a wire spoked bicycle wheel. The wheel carries weight differently and responds to impacts differently. Whether that is good or bad depends on what the rider wants. The strength to weight ratio is very different as well. In all likelihood, that wheel weighs a lot more than most wire spoke wheels. Carbon wheels like that one weight more than most wire wheels.

That design also offer unique challenges if the wheel ever need truing.

But it didn't have to be a credit card touring bike if it had been designed for touring rather than for something else. Since Trek is recalling the wheels, Trek is admitting that they made a mistake on this one.

Rayven01

Just to clear up some misconceptions, Trek is not replacing 24H wheels with higher spoke count wheels. They are replacing 24H wheels with different 24H wheels.

Since my Crossrip 3 also has 24H wheels that look nearly identical to the 720 wheels, I took my bike in to the local dealer and they contacted Trek for me about the recall. Trek stated the 720 wheels are being replaced because they were made in a new factory that so far had only made wheels for that bike. The spokes in that factory were not created to spec and were the cause of the frequent breakage. The replacement wheels are identical except they have black spokes (originals were silver) of the same gauge but from a different factory.

Just to be clear I'm not disputing the fact that higher spoke counts usually means a stronger wheel, but in this case the fact that 24H wheels are too weak in general is not the reason for the recall.

saddlesores

what about low-flange 48 spoke hubs? can too many spoke holes reduce the
amount of metal between the spokes?

also possibility of poor lacing pattern, with spokes running over heads
of adjacent spokes.

indyfabz

Maybe I wasn't clear. The cracked rear rim was 36h. I had it replaced with a 48h rim.

Squeezebox

cyccocommute -- I was just saying that the 3 solid spoked wheels must be very different than wire spoked wheels, particularly in the rim cross section between the spokes.
I don't understand what you are trying to say about the credit card bicycle, it was designed that way, for a particular style of riding. Please clarify your comment.
Saddle sores -- about 48 holed hubs. IIRC Phil Wood would only sell 48* high flange hubs. I don't know about anyone else. but my knowledge on the subject is ancient.

DropBarFan

Trek pays little attention to the touring market but even so one wonders what they were thinking with 24-spoke touring wheels. Cutting spokes is an easy but pointless way to save weight. Ironically I like the Trek recreation bike I inherited: light alu frame with suspension fork/seatpost. I'd like to see drop-bar touring bikes with suspension: comfortable ride & would allow lighter wheels & higher-pressure tires.

cyccommute 

You are getting bogged down in details. What you've said is important to consider in terms of design (manufacturer) and build (consumer) considerations. But it's not something to be overly concerned about. I'm not saying that hub flanges can't break but I am saying that it's a rare occurrence. It's rare still in 48 hold hubs because those are rare in themselves.

Yes, a solid spoked wheel is different from wire spoked wheel. One works in compression, which makes it very strong but also very heavy, while the other works in tension which makes it less strong but extremely light. Wire spoke wheels are strong enough...or can be made strong enough...for the task at hand but also light enough to have less of an impact on low power vehicles like bicycles.

"Rim cross section between the spokes" is meaningless.

Trek designed the bike for touring. Once out the shops doors, Trek has no control over how it is used. However the implication from how they have set up the bike is that it can be used for carrying some kind of touring load. They should have spec'd it for that application if they are going to sell it for that application. By putting on race wheels, they aren't building it for the task that they are selling it for. The recall of the wheels...something I've not seen before..clearly shows that they didn't specify the proper equipment for the bicycle.

Bottom line is that the bike was poorly designed and Trek is paying for what they saved now. A recall for a bad in-house design costs more then just the cost of the replacement part. It costs a lot of good will and, possibly, future sales.

cyccommute 

Sorry but it was a bit confusing. That said, it doesn't change what I said about rim cracking. I would suspect that wheels with fewer spokes are more susceptible to cracking because each section of the rim has to carry more load.

Squeezebox

But Trek did design the 720 well. It's for CC touring. A change of clothes in 1 fork bag. Rain gear in the other, not much else. no tent etc. Rayven explained it well, his cross bicycle has 24* wheels, and holds up okay. A properly setup 24* wheel should be good enough for an "adventure" bicycle. Trek had a problem with the factory that made the 720 wheels. They are saying other 24* wheels are okay. A cross bicycle will put much more stress on a wheel than CC touring. The big boys race Paris Roubais on 20* wheels. Light spoke wheels can be done properly, for certain situations, the Katy for another example. If you just don't know or want to use 24*, use 36* as a fall back. The way you say "touring bicycle" it sounds like you expect the 720 to handle medium to heavy loads on rough roads. That's just not the case. If Trek fixes the wheel build problem the 720 should be a good bicycle for it's particular niche. My 20/24* road wheels have been fine as another low spoke example.

Tourist in MSN

Look for a mountain bike with a short top tube and suspension fork and convert it.

My expedition bike was designed so that it could take a suspension fork or use the solid fork that was sold with it. I have put a suspension fork on it and have used it on some mountain bike trails. But for touring I put the solid fork on the bike.

For one thing a front rack should be mounted so that the weight is unsprung. Tubus made such a rack years ago, but no longer sell it. Other front racks that are mounted on suspension forks put the weight on the bottom part of the fork so that the suspension no longer works the way it should.

On the first bike in the photo, that bike has the Tubus rack that they no longer make. The owner of that rack had it repaired a few times, but is unable to replace it so she keeps getting it repaired.

The second photo, the bike owner told me that he locked out his suspension.

Also, consider that suspension forks are not that light.