BlazingPedals

I've had rims fail due to brake wear, but never that catastrophically. I caught it at the crack stage.

Ironfish653

Sounds like a pretty extreme use case. 75-80psi is crazy high for a 2" tire, and then you're adding up to ~45 kilo + Clyde ? Rim brakes, or not, that's way outside the design envelope for a 'regular' MTB wheel.
If that's the way you regularly ride, you need to look for something Cargo bike /E-bike rated, or accept that 'regular' rims aren't going to live very long under your conditions.

icemilkcoffee 

That seems to be a pretty high pressure for a 2" tire.

Sorcerer

This thread is significant. It makes me realize that we do need to convert our tandem to disc brakes of we ever go back to serious tandem riding.

Pretty much all of our bikes are disc braked now.

I ride and maintain a single speed rim brake mountain bike for the novelty. It's great yet inferior to it's disc brakes brethren.

I've seen 3 rim brake mountain bikes burst their walls on rides. They were explosive! It's possible to pack the tire with grass and use the inner tube to bandage the tire to the rim in order to ride out of the woods.

It's pretty straightforward to replace a rim by taping a new rim to the old wheel and transfer the spokes over to a new rim while sitting in front of the TV with a nice program and then dishing and tensioning the spokes with the wheel mounted on the bike frame.

Rim brakes are great. Some disc brakes are worse than rim brakes for sure.

At least ride a bike, right?

prj71

There is no joy in rim brakes. Disc brakes for the win.

indyfabz

I got lots of joy from my 10,000 miles of loaded touring during a 1.5 year period alone with rim brakes. That’s all there really was back then and what I use now. That there is now something better doesn’t diminish the experiences I had (and continue to have).

GamblerGORD53

The tire looks kind of fat for the rim too. My 38 mm SMP tires I like at about 66 psi. My 36 mm are 70/72, I used to go up to 76 psi.
SA Drum brake on the front for the WIN.

wolfchild

I've never worn out any of my rims yet...but people who claim to be getting 50 000 miles out of their rims with rim brakes are just full of ****.

Rolla

This x 100. If there's no joy in your riding, it ain't your brake's fault.

Koyote

Who has made that claim? Seriously, show me the post in which someone makes that claim.


This is the only post in the thread that is full of ****.

GhostRider62

I have a set of Flo 60 carbon wheels purchase in early 2016. I keep the track clean, use proper pads, and keep the pads clean. I would estimate 80% of my riding over that time is on these wheels. I ride a lot. I cannot detect any wear on them. I have a wicked ancient set of Zipp 404 with aluminum braking surface with a carbon aero portion. I have not worn them down to the wear marks but to be safe, I recently replaced them. I have a set of Flo 30 alu rimmed wheels that I rode pretty much exclusively in 2014-2015 and they are still fine. I still use them.

A common problem with carbon rims used with disc brakes is blowing out the side of the rim. The rim max pressure is much less on these. Google Zinn and Velonews, he has an article on it. Exceeding the rim spec is why OP blew out his rim.

ColonelSanders

Probably a few things contributed to the rim dying in addition to my higher than ideal tyre pressure.

ColonelSanders

50mm tyre and I think the rim had an internal width of 20 or 22 mm.

cyclezen

It's really great that you use the bike for so many varied purposes. But as noted by others, that 75-80 psi is way too high. Surprised that you didn;t blow the tire off, before blowing out the rim>
I did a quick look at the one 26" wheel I still have, with a 2.1 " Spec Tire - marked max of 65 psi. So I pumped it up to 65... (normally I ride my 2.1 front at 28 psi, for off-road) It was ROCK/Granite Hard ! Even 65 psi is serious crazy.
I immediately aired back down to 28...
Even with all the weight you mention, a pressure round 50 psi is gonna be hard enough for road riding your mtb wheel/tire.
I would look to getting a heavier duty wheel, rather than trying to lace up a new rim. Unless you've had some wheel building experience, building a rear wheel is more than just 'round' and straight - there's also the dish to get right. Add up a rim price and a complete spoke set and you're prolly close to a built wheel price.
DO try to get your pressures down considerably - that problem, on a front wheel, could be a injury disaster...
But do keep on using the bike for all the things you;re already doing !
Yuri

HTupolev

Rim brake tracks can absolutely wear rapidly if you're riding in an abrasive environment. It's a common problem for people who put in big miles in wet conditions in the PNW, for instance: the light rain never really cleans the roads, it just turns the regional dust into rim-eating fluid. However...

...you probably shouldn't do this. Think about how much surface area the pressure is acting over, the amount of force that the air is putting on the tire. In this sense, putting 80PSI into a 2" clincher is a little bit like putting 160PSI into a 25mm clincher.

Even without wheel structural integrity as a concern, that's a huge amount of pressure in a 2" tire unless we're talking about something like optimizing a 400+lb bike+rider for smooth pavement.

chaadster

Is there a possibility that this was not even a rim brake compatible rim? The EX721 is an old model which may have existed in a couple of iterations, and it’s not clear to me if all or any were rim brake.

It would explain the unusual nature of this failure.

GhostRider62

Mavic EX721 is spec'd for 2.3-3.0" tires, not 2 inch tires.

I also understand the max pressure of the rim (tire rating is not relevant) is 54 psi.....not 80 psi or whatever OP used to blow the rim up.

Koyote

Okay in other words, the thread title should actually be “The joy of overinflation.“

GhostRider62

OP thinks there are other factors. Like what?

He grossly over pressured the rim, used too narrow a tire, and probably scored the rim with pads worn to the bone or imbedded stones. How's that.

63rickert

I called overpressure as a possibility back at post #12.

A 50mm tire holds four times the volume of air that a 25mm tire does. Inflating to 80psi is equivalent to inflating a 25mm tire to 320psi. It is impressive that the rim or tire was able to survive or function at all.

Tire pressure is a matter of faith and belief. It has never been possible to get riders to inflate rationally.

What happened in this case was the rim sidewall bulged under 80psi. It did that the first time 80psi was used. The high spot of the misshapen rim wore down, failure followed.

OP also complained about marginal braking performance. Of course. The rim sidewall was not in the normal position. With 80psi the tire tread could not develop normal braking traction. This is why there are complaints of poor performance from rim brakes. In any half normal situation rim brakes have more power than can be used. In any half normal circumstance the bike owner has sabotaged good performance from rim brakes.

OP has not told us how much he weighs beyond “Clyde”. He does carry loads that require a cycle truck. The Surly Troll he rides is close enough. He needs 2.4 tires or greater. He is likely one of the cases where disc brakes make sense. To get the discs to work he will need to display more common sense than has appeared thus far. Nearly all of the disc brakes I see are performing very poorly. No amount of engineering overcomes user error.

ColonelSanders

I actually said I was pleasantly surprised by how well the XT rim brakes worked.

I am currently reducing.

But my weight was over 400lbs for the first year I was riding the bike and I am down to 330lbs at the moment, with further reductions scheduled.

My LBS has replaced my wheel(with a different rim, spokes and hub combo) and I will be very mindful of not inflating the wheel to the previous levels which I now realise were too high.

Whilst I suspect my new wheel should do fine with it not being pumped up as high, me being lighter and I am going to stop using my basket on my rear rack and use my Burley Travoy instead, this new wheel will have a much easier life.

I have also replaced my original Shimano rim brake pads with some Koolstop black and salmon on the front and Jagwire pads on the rear, but it isn't like the Shimano pads were responsible for what happened, so no real difference there I suppose.

As the LBS mentioned that they thought my front tyre showed signs of some damage, I have ordered the below wheels of which I had their 29 inch brother on my Merida Big Nine hardtail, and they are indeed strong as an ox, and should be even stronger in 26 inch form.

Sun Rhyno Lite 40 spoke 26" Mountain Bike Commuter Wheelset

Front and Rear Wheel Included
MACHINED SIDEWALLS
Sun Ryhno Lite 40 Hole Rims
Strong enough for an ox!

79pmooney

Ah, the learning curve! (I'm laughing but not at you. I've been doing this a long time and I'm still learning.)

rydabent

IMO there is no joy in rim brakes, when in the end they scab up and destroy high priced carbon fiber rims. Or any rim for that matter.

rsbob 

Having had road and mountain bikes with both rim and disc brakes (and still currently do) there is no comparison between the stopping power of discs, especially in wet conditions.

Just my experiential opinion, I could be wrong. (Credit to Dennis Miller on that abused phrase)