Dished Wheel

[EigerSA]

For about the 4th time in as many months, my rear wheel has "un-dished" (not sure of the correct terminology there) itself so that every power stroke has the wheel rubbing on the chain-stay. I've taken the bike to two lbs, with the same results from both, the wheel stays straight and true for a while and then invariably on a beautiful biking day, "ping" and the wheel's out again.

 

I'm not taking this wheel back to the bike shop, it's cost me about R2000,00 so far for them to constantly true it, so no more, I'm going to do this myself. But want I want to know is whether it could be a fault of the rim itself, and not the wheel building process? Oh and the last time it happened the lbs re-built the wheel with new stainless steel spokes. Any advice?

 

[spano]

where are you from??

 

 

 

anywhere near Gauteng? contact Johan Bornman

[EigerSA]

              Unfortunately I'm in Durban...

 

 

[Wyatt Earp]

I simply cannot understand how a wheel can "un-dish"

[Wyatt Earp]

Forgot to add, I love your signature, Death Cab for Cutie.

[EigerSA]

Last time I heard a 'ping' and the wheel was out, checked it there and then and found a broken spoke. After it came back from lbs, thought everything was fine till this morning. Heard another 'ping' and straight away the tire started rubbing on the chain-stay, only this time I can't find any broken spokes.

[EigerSA]

 

Forgot to add' date=' I love your signature, Death Cab for Cutie.[/quote']

 

Nice one... everyone else has had to ask me what it's from!

 

 

[Wyatt Earp]

It's from their Plans album, I have the vinyl record.

 

Your wheel problem, is it on a roadbike ?

 

Sounds to me like you need the wheel re-built by a good wheel builder using proper butted spokes.Summit Cycles2009-09-26 01:56:06

[EigerSA]

sorry should have said so... it's mtb. And I didn't hit anything or crash or anything, I was out the seat climbing a short but hard little hill...

[Wyatt Earp]

Do you know what spokes were used ?Summit Cycles2009-09-26 01:57:46

[EigerSA]

Ummm... not sure, they were supposed to have re-built the wheel... I just had a look at the invoice but it doesn't say what spokes, but they cost about R9 each?

[Wyatt Earp]

I know you don't really want to hear this, but I will get that wheel to a shop that has a good and understanding wheel builder, let him asses everything and get him to re-build with butted spokes, make sure he has a dishing tool, ask him to show it to you, this would give you some indication that the dude "might" take his wheel building quite serious (but not always )

 

I fear that your wheel might not have been re-built to the proper criteria.

[EigerSA]

You're probably right... thanks anyway 

[Johan Bornman]

You are describing a very strange phenomenum. For a wheel to "undish", each nipple on say, the left side, would have to be turned loose by a given number of turns and each spoke on the right side, tightened by a given number of turns.  At the very least, one of the sides has to undergo the mysterious exact tightening or loosening thoughout all the spokes. The wheel would then be perfectly true, but off-centre in the bike.

 

This is highly unlikely to happen by itself. About as likely as winning the Lotto.

 

I think you're experiencing one or two spokes that are unscrewing and the wheel then develops a wobble and touches the chainstay.

 

From the clues that you give us ("ping" and occasional broken spokes), I think the wheelbuilder has allowed some residual twist in the spokes. Your weight (or a bump) onloads the bottom spokes and they can untwist themselves into a neutral position. The problem with this is that the nipple stays put and the spoke turns in the thread. It causes a characteristic ping sound and immediately presents as a wheel with a wobble.

 

It takes a skilled wheelbuilder to eliminate residual twist, especially on double-butted spokes (and even more so with extra-thin Revolution spokes) which have little resistance to torsion. Resistance to torsion decreases by the square of spoke diameter - so double butted spokes, even though they're only 0.3mm thinner, twist exponentially easier.

 

It takes a very skilled wheelbuilder to build a 28 spoke wheel with Revolutions on both sides of the back wheel. It is such hard work that it would be fair to charge double for that type of build.

 

You say you are not sure if your spokes are double-butted or not - it is not really important in this instance, but it is easy to find out if they are straight or butted.

 

The butt refers to a thicker end piece on the spoke. If both the thread- and the elbow-side are thicker than the shaft of the spoke it is double butted. It is difficult to see, since the transition is smooth, but pinch the spoke at the nipple end with your thumb and forefinger and run it down towards the crossing. You'll feel a reduction in thickness.

 

On DT Swiss spokes the reduction is about 60mm from either end and on Sapim it is only 10mm from either end. Once you've felt it, you'll probably be able to visually identify it too, now that you know what you're looking for.

 

 

As for the breaking spokes. They're your cue to find a new wheelbuilder. Spokes should not routinely break.