iantag wrote:I'm a heavy rider ~120kg and build my own wheels ( DT competition and/or Alpine III's). I generally don't break spokes but recently while riding one of the GVBR's I had about 3 drive side "pulling" spokes lose their heads. ( of the 6 spokes I've broken over 30-years all have been rear drive pulling spokes) As luck would have it I carried extra spokes and simply replaced the offending one - and for good measure the immediate neighbors. The bike mechanics on the ride (both Kiwi's) both swore that brass spoke washers under the head would have prevented the breakage. This was news to me so I did some research to discover that the use of spoke washers (at the hub) is up there with religion and politics as a way of generating emotive responses. The pro argument goes like this: 14 gauge spokes measure 2.0mm and most hubs have 2.35 mm holes. Hence with each revolution their is the possibility of some movement & therefore repetitive stress. Alpine III's are 13g or 2.3mm and besides being thicker at the hub - better "fill" the hole resulting in less chance for movement. Brass washers deform under tension and "fill" into the hole creating a snug fit ( you can get different sized washers for 14g and 13g spokes). Anyway - long story - I've now built my latest sets of wheels with washers - which means I've bought into the "pro" side. I also (now) use a tension meter - as I think while true - some of my past wheels had non-uniform tension - which only makes matters worse. So I guess I'm a spoke washer believer ( for now). (I've also built with O/C rims - but that's another story)
I am not sure if it is quite as contentious as religion and politics! However what I am about to say is!
You may be surprised how many bike shops/mechanics just don't build enough wheels to have seen this issue (and the need for spoke washers) or the outcomes of not using them (when they should have been used). As a result, they just lace the wheel up, tension it and hand it over to the customer. I know that I didn't even know of the existance of spoke washers in my first few years building wheels (back in the last century .... now I feel old) - and I would have built a couple of hundred wheels in that time.
I always use spoke washers in two different circumstances, and potentially in a third (the last one).
1. The hub flange is very thin compared to the length of the J-bend of the spoke - in which case the J-bend is not fully supported at its "bend", and pulls out of the hub hole and is bent straighter/stretched as the wheel is tensioned. This will result in early failure of the bend.
2. The holes are drilled >0.2mm larger than the spoke guage, in which case the J-bend straightens within the hub flange as the wheel is tensioned. This will result in early failure of the spoke head (most usually).
3. Reuse of hubs with very worn/grooved flanges and/or hole elongation. Washers may be used to get a nice tight fit, often after some filing/cleanup of the hub is done.
fixie wrote:Also, hub manufacturers do not all use the same dimension for the thickness of the flange on the hub where the spokes insert. Sometimes with a wide bend spoke and a thin flange the space between the line of the spoke and the flange is significant and this introduces a real bending strain into the J bend part of the spoke which can contribute to spoke failure. To reduce or eliminate this, the cheap practical method is to put a spacing washer under the head. This will ensure that the spoke tension to the flange is as direct as possible and that the spoke at the bend is as much in a shear stress rather than a bending stress as possible.
Eloquently said. A common issue with some of the ultralight hubs being produced these days in Taiwan. Not an issue if addressed when the wheel is built.
Most high quality maufacturers (think White Industries, Project 321, DT Swiss, Shimano, Campag) have nice thick flanges.
fixie wrote:If you have ever tried to lace a wheel with an old steel hub or a Sturmey Archer three speed with a steel shell you will realise how thin a hub flange can be and how large a gap there will be if you do not use a spoke washer under the head. Often you can get away with it because with steel rims, they are so stiff, the spoke tension variation on rotation is minimised and even a poorly built wheel will survive, but with modern alloy rims of variable section and construction you will not.
On a similar vein, the radial stiffness of quality carbon rims means that terribly uneven spoke tension can be hidden for quite some time. I have seen the highest quality carbon from the US and Taiwan, built with appalling and uneven tensions, but still quite rideable. They will present reliability problems over time - often pulling spokes at the rim.
That said, I have also seen some beautifully built factory carbon wheelsets. On a well constructed carbon rim, one can achieve impressively even spoke tensions.