Ask the experts

[bagtagley]

If that is your second exploded wheel I would like to politely suggest USING A HIGHER PSI FER CHRISSAKES.

Haha. I’ve lowered my pressure a bit with the inserts, but am still around 28 in the rear. The 24h was blatant hackery, but the rim earlier in the season was really bizarre. First time I’ve killed a rim and not known it immediately.

[HAB]

Ouch. Is that a Virginia jab? [emoji16]

Haha, I meant to quote Andeh, who IIRC actually broke his on a curb.

[jm2e]

Local guy that's a part owner in a wheel / rim company is completely convinced that inserts put more stress on rims and cause them to break over time. His theory is that, while inserts minimize large impacts, they transfer stress from lots and lots of small impacts directly into the rim that fatigues it over time.

Or something like that. I'm skeptical, but who knows.

I'm completely convinced your local guy's theory is ridiculous. A wheel's job is to deal with stress. Maybe he's trying to make sense out of people coming in with crushed rims reporting that they're using inserts. Well, if they're like Andeh; 170lbs, riding pressure appropriate for a 130lbs rider, and using a lightweight version of the actual insert........ Then the affect of inserts on rims is more due to overconfidence in the insert.

[toast2266]

I'm completely convinced your local guy's theory is ridiculous. A wheel's job is to deal with stress. Maybe he's trying to make sense out of people coming in with crushed rims reporting that they're using inserts. Well, if they're like Andeh; 170lbs, riding pressure appropriate for a 130lbs rider, and using a lightweight version of the actual insert........ Then the affect of inserts on rims is more due to overconfidence in the insert.

I'm 90% agreed that it's ridiculous.

But for whatever it's worth, apparently his theory is based on their sponsored riders. Sponsored guys running inserts broke lots of rims. Same guys running without inserts didn't break any rims.

[rideit]

As said, their damn PSI was probably too low.

[ridinshockgun]

^ I'm guessing you don't ride in the wet very much?

[simple]

The spoke tension definitely changes with an insert. Same happens with tight tires.

With 24 spokes I doubt the overall wheel is strong enough with an insert, low psi, and sloppy rider. Just saying.

[rideit]

^ I'm guessing you don't ride in the wet very much?

I used to, but you can’t really ride in the wet here, too much clay. But I ride pretty low pressures. Just not rim bottoming pressures, usually, although it does happen. I am trying inserts this year...

[bagtagley]

I don't know many people that would consider 28-30 psi to be low, particularly with a DD casing and an insert. I can't argue with the sloppy part, and no doubt 24h wheels don't belong outside the XC realm, but it was a cheap experiment.

[simple]

Cool. People spend a grip on wheels but a nice wheel can be bought or built for pretty cheap. A takeoff set of DTSwiss wheels generally fits that bill

[plugboots]

almost fully completely unless you could figure out a way to anchor that spoke end with a washer or sft

Aquaseal. Eh?

[EWG]

I don't know many people that would consider 28-30 psi to be low, particularly with a DD casing and an insert. I can't argue with the sloppy part, and no doubt 24h wheels don't belong outside the XC realm, but it was a cheap experiment.

Should be nothing wrong with 28-30 psi in a 27.5/29" 2.4" wheel. You could check to see if your shock is bottoming out - that can add pressure. So can hitting knife edges with brakes locked, or bashing things while you are extending your weight upward from bent knees.

But one thing's for sure - that is not a product failure. You ripped that out of both ends. Like I said, nice damn work. I assume you didn't hit anything with the wheel sideways, and if so you actually pulled the spoke out of both ends (pull through spoke seat at hub, pull on rim enough to crack the inside in tension.) That's not JRA. You put the spoke under some serious tension.

The more I think about it the more I think you must've hit something sharp at enough of an angle that the wheel bent sideways. Is the crack only on one side of the rim? I'm betting it is. Let us know.

[bagtagley]

The crack is 90 degrees from the pulled spoke, not both ends of the same spoke. Looks like I hit at the crack - there's a nice flat spot there - flexing the wheel enough to pull the spoke.

[EWG]

The crack is 90 degrees from the pulled spoke, not both ends of the same spoke. Looks like I hit at the crack - there's a nice flat spot there - flexing the wheel enough to pull the spoke.

Ah, yup, you flexed it, that's for sure. Didn't realize it was opposite side but if so it makes sense.

Yeah, you might want to work on riding a little lighter if you've done it twice in one season.

[Andeh]

I'm completely convinced your local guy's theory is ridiculous. A wheel's job is to deal with stress. Maybe he's trying to make sense out of people coming in with crushed rims reporting that they're using inserts. Well, if they're like Andeh; 170lbs, riding pressure appropriate for a 130lbs rider, and using a lightweight version of the actual insert........ Then the affect of inserts on rims is more due to overconfidence in the insert.

There's almost no rocks on our local trails. It's all hardpack and dust. I literally haven't flatted in like 6 years. 20-25 psi is totally normal around here. I don't know of anyone running more, even the local HS schralpers.

[detrusor]

Local guy that's a part owner in a wheel / rim company is completely convinced that inserts put more stress on rims and cause them to break over time. His theory is that, while inserts minimize large impacts, they transfer stress from lots and lots of small impacts directly into the rim that fatigues it over time.

Or something like that. I'm skeptical, but who knows.

The old school (like late 70’s early 80’s) inserts and tubeless tires were kryptonite to spokes. I have always thought this would be shown to be the case with modern cushcore type inserts in either he spoke or rim.


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[rideit]

Do you mean tubular tires?

[EWG]

Do you mean tubular tires?

Yes, I'm confused by this one also.

[jm2e]

Seems like whether the question is about tubular or Cushcore, it'd be worth checking spoke tensions after mounting the tires. Regardless of tire on/off, if your spoke tensions are out of balance then you're going to have problems with your wheel. I'd think this would be the case in any very tight tire-wheel pairing as well. Pluck the spokes, use a tension meter or get that thing back on the truing stand if you're worried.

[carlh]

Related question.both my mtbs have well wised aluminum rear wheels. I have been truing them with the goal of semi even tension at the expense of trueness both radial and lateral. Any downside here?

[EWG]

Related question.both my mtbs have well wised aluminum rear wheels. I have been truing them with the goal of semi even tension at the expense of trueness both radial and lateral. Any downside here?

I always build and rebuild to true, not to even tension. My theory is that out of true but even tension is more likely to fail than true with uneven tension. The arguments for and against this are long and epic and more than I want to go into. However, on my side of the argument the theory is that when you stress the wheel vertically (riding it, hitting things etc) spoke tension somewhat evens out and starting in the strongest configuration (true) is the best way to go. For this to work you need minimum tension on all spokes though. Nothing really loose.

However I will admit the difference is minimal and as long as even tension does not take you more than a few mm out of true you should be fine.

[Dumbest Known Time]

Looking at building up a bike with an XT groupset. Heard all the noise about the smooth shifting which is what I'm after. Do all the chain related bits need to be hyperglide+ specific to get the full effect? Specifically, can any old narrow-wide chainring work just as well? Or is it worth tracking down a HG+ specific ring?

[carlh]

The only time either if these wheels was in a few mm of true was before riding them. On my fs (stock e13 novatec) I have a ~10mm radial flat spot and similar amount of lateral at this point the wheel just needs to be replaced but I figure I can keep riding it until it won’t hold a tire anymore. The hard tail (first gen arc27 to king) is round but similar 5-10mm lateral and unlikely to true out. I figure I will keep tightening it until it gets much worse then rebuild. The rocks around here are wheel killers so I don’t want to trash something new just to have it true for a couple rides. I think I might need stronger rims.

[jm2e]

Looking at building up a bike with an XT groupset. Heard all the noise about the smooth shifting which is what I'm after. Do all the chain related bits need to be hyperglide+ specific to get the full effect? Specifically, can any old narrow-wide chainring work just as well? Or is it worth tracking down a HG+ specific ring?

I’m thinking it’s purely academic. If you come back here in a month bitching about how the XT drivetrain ain’t all it’s cracked up to be, but you stuck a bastard ring in there .......... you won’t have much of a valid position. That said, if we never hear from you again, perhaps we can infer that 3rd party rings actually work okay sometimes.

I can say the when I switched to a budget Eagle drivetrain, it was quieter and had less backpedal bullshit after I pulled the MRP oval ring and stuck on a SRAM round ring. Which, at the end of the day, tells you very little.


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[jm2e]

I always build and rebuild to true, not to even tension. My theory is that out of true but even tension is more likely to fail than true with uneven tension. The arguments for and against this are long and epic and more than I want to go into.

I think it would be a blast to charge down that rabbit hole .......... in a totally different thread. I’m of the opposite school, that an out of true wheel with balanced tension is superior. But really, if we’re putting that much effort into the one, we’re probably getting close on the other.
Would love to hear an actual engineers perspective ........... in a different thread.



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