KH29 55mm Rim Cracking

Anyone see this before? About half of the spoke holes are developing cracks. Some small, some large enough the spoke have moved. Seems to have started in last few weeks. This uni get very little trails, almost never does drops but does have over 16000km on road riding.



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Seems like overtightened spokes or loose spokes which caused too much stress riding tightened spokes

I’ve seen it before, but not on that specific rim.

I’d agree it’s likely due to incorrect spoke tension.

What attention/servicing has that wheel had over those 16000km?

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All new spokes at about half that distance.

Occasional re-truing which has probably caused some increasing tightening of some spokes.

Tyre replaced many times along with a couple of rim tapes.

Spokes are tight, but not super tight.

Don’t think I’ll be getting another KH 55mm rim. Only one in stock and that’s in the UK. After exchange rates and shipping it’s just way to expensive.

I’ve now installed a spare wheel, an old 47mm KH rim with hookworm. This rim has the large holes it, but the standard rim tape (as supplied with a KH) seems to buldge from the tube pressure, so there are now lots of blue bumps on my rim. Big blue pimples waiting to pop. Even though that tape is quite thick, this doesn’t seem safe. What tape is normally used with rims that have these holes ?

Normally used is exactly that, but they stretch over time. I’ve been using Shimano high pressure rim tape on a lot of rims recently, that should work very well.

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I have the same combo rim + tire setup on my new freewheel unicycle mounted with the Pipifax hub. It’s heavy stuff! :mechanical_leg: :mechanical_arm:

This rim with holes like the new KH rim are designed for off-road riding with low pressure. I wouldn’t advise using wide rims for road riding, maybe unless you use a 2.5" slick tire like you do. With narrower tires, there have been a lot of blowout problems.

Personally, I put one turn of 48mm gorilla tape (it’s not very pretty but it does the job), but I guess a 35mm tubeless tape should be enough to cover the holes.

For the cracked rim, I also assume it’s a spoke tension issue… but it’s surprising, I’ve only had problems with spokes breaking when I’ve rather heard that hubs are more sensitive to high tensions than rims. It seems to me that the limit for most rims is around 120-130 kgf while we often talk about 100 kgf for unicycle hubs (I often exceed this limit and I haven’t damaged my hubs yet).

One explanation is maybe that this rim has been designed for off-road riding and for unicycle. Especially since in theory the spoke tension should be less for off-road use than for road use.

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Good point, never thought about that. Even with the Hookworm at its lowest pressure of 35psi, that’s a lot more than an off road setup. I now prefer the wider off road tyres for just on road riding, such as the Duro Crux. Lots of rolling resistance sure, but rolls over anything also softer which means kinder to my old backside. If there was a 3.25" low pressure road tyre, I’d be interested.

Another good point. I thought spokes would break first but after that sort of distance I guess the rim just wore out.

Anyhow, I don’t think I’ll replace with another 55mm KH rim, and this old KH is not a suitable replacement. I may try a M41 rim, wider than the Nimbus and I get to pick the colour.

Really 16000 km and not 1600? That’s extremely much! That will be material fatigue, but you could benefit from the (very) low weight of the rim all the kilometers.

What is Kris @danger_uni opinion ?

I have only experienced this once, and that I think was due to my reckless method of learning to hop and jump on a 24" muni, rigid frame in the late 90’s, but I am much better at it now and have not had any problems since then. Read this and panicked (Ran out to the garage and checked them all.), but I’m OK now. Thanks for the reminder, sorry I can’t add anything about the problem but I was missing a few spokes and actually pulled spoke and nipple through. But I was destroying the rim just to learn out of frustration.

Yes really! Strava tells me so:
image

That would also explain the way my knees feel, they too are suffering from fatigue.

I’m not complaining about the rim failure, I think it has done well, just curious if this is common and how to avoid. Looks like spokes being tight is a factor.

Your distances are very impressive. Keep it up, very inspiring.