Need advice - cracked rim at the eyelets

[Bendo]

Hi all

Hoping to get some input from the brains trust on this. Was cleaning my wheels this evening and came across what look like stress fractures, radiating from both sides of three eyelets on the rear wheel. It was getting dark so couldn't take a pic of the third, but two of them are below. The rim is a Synergy 650B off-centre. The wheel is only two years old, with about 5000km on it. It doesn't do a lot of off-road, it's on a randonneur, not an MTB. 90% of its use is urban commuting and touring on sealed roads. And I'm a pretty lightweight rider.





Obviously the rim needs to be replaced asap, but with shops closed over the holidays I was considering doing some three or four 20—50km rides on it in the meantime. Is that a dumb idea? How quickly will these cracks spread? Anyone have similar experience? With the same wheel? Must say it seems like a manufacturing (or wheel-building) issue, not a wear-and-tear one. b

[Redvee]

Personally I'd reduce the spoke tension on the spokes where the cracking has occured. You'll lose the trueness of the wheel but it will help you till the shops open again.

[TonyR]

Those cracks are quite common on some rims. I wouldn't worry too much about it. Do your rides and get them replaced when its convenient. The worst that usually happens is the nipple pulls through the rim which is not much worse than breaking a spoke.

[meic]

Obviously the rim needs to be replaced asap

Yes, of course it does.

but being the sort of person who doesnt take these dangers seriously enough, I have ridden rims with cracks like that until the rims wore out. They didnt grow any further or pull out.
In my case they were also being treated to a bad environment and the rims were totally full of white oxide.

[reohn2]

IMO if it's just the three spokes,I'd just ride it until the shops open again.
It's possible the cracks could have been there for 300km already without you knowing.
You could mark the end of the cracks with a felt tip pen to see if they worsen.

[Bendo]

Fantastic responses. Thanks everyone! I wasn't sure how much to worry. At least now I can do those rides.

Thanks again.
b

[Brucey]

If the rim has double eyelets, I'd not fret about it, and just get on and ride. If the rim doesn't have double eyelets, then I'd still ride it but I'd keep an eye on the crack length as suggested above.

If single-eyeletted and I thought I couldn't get another rim easily (weeks) then I might put a washer of some kind (perhaps a specially made piece?) under the nipple head to spread the load into the rim a little more.

cheers

[Mick F]

What caused it?

Over-tight spokes?

[mercalia]

hmm curious the valve hole is off centre? is that normal anyone?

[trieste]

The valve hole is centred, it's the spoke holes which are offset.

[Brucey]

hmm curious the valve hole is off centre? is that normal anyone?

For an asymmetric rim, yes.

BTW some folk may recall that I have a concern that asymmetric rear rims must (if the net spoke tension load does not pass through the rim section centroid) produce a net twisting load in the rim. I wonder if this is in any way related to the position of the cracks?

cheers

[andrew_s]

If the cracks get bad enough, the eyelets will start to pull through, with the result that the spokes lose tension and the rim goes out of true. In that case you won't be able to true the rim except on a temporary basis.
I build my own wheels, so I'd get a spare rim to be ready, then just keep riding until the rim gave problems, and do a rim transplant at that point.
Take a spoke key on your rides, for use if the rim gets sufficiently wobbly to hit the brake blocks.

[NATURAL ANKLING]

Hi,
Looks like a single wall rim with that offset of spoke hole, otherwise you would'nt get the nipple hole rivet in

[Brucey]

the synergy rim has this section in the front;



and this in an offset rear;



After a bit of digging about... AFAICT the rim has single eyelets rather than double eyelets.

There is a good description (except re the eyelets) of these rims here;

http://www.peterwhitecycles.com/velocity.asp

One advantage claimed for the offset rim is that they are less likely to crack because the spoke tensions are more balanced. Didn't work this time; I wonder what tension was used...?

cheers

[NATURAL ANKLING]

Hi,
Oh ......I did'nt realise it was an offset rim
I was writing after you had posted details of section I did'nt see that

Edited now I am confused I posted before the section details............

Edited again, offset rim sounds like a good idea, but is ayssemetric spoke tension really that bad anyway
Rims have been that way a long time with no problems.