dabrucru

i would like to put an xt hub dynamo on my existing rim. do i need to change the spokes or i can use the ones i have?

thanks

david

rhm

That depends on the relative sizes of the hub flanges. If the new hub and the old hub have the same dimensions, then the spokes should fit. Frankly, this is not likely. In most cases a dynamo hub has larger flanges than a non-dynamo hub, so you will need shorter spokes.

There are a lot of spoke calculator programs; some of them are discussed here: https://bikefat.com/5-best-spoke-length-calculators/

2_i 

It may be possible to rethread the shortened spokes.

rhm

True, good point.

52telecaster

if you need to buy spokes after figuring the proper length on a spoke calculator there is a thread in the vintage forum about the best and cheapest places to get your spokes.

btw, you'll love having a dynamo. they are awesome.

noglider 

Cutting and rethreading spokes is probably not economical, and it's certainly not quick.

fixedweasel

Also, if you have to cut a bit on a double butted spoke, you will lose the purpose/function of the spoke. I can't afford a Phil but I have a Hozan and it works quite well on the straight gauge spokes I have to occasionally replace on the old(er) time rollers.

sweeks

Hub dynamos are great, as noted by others. However, you almost certainly will need new spokes; they're not that expensive and a whole lot less hassle than trying to cut and re-thread them. (BTW, the threads on spokes are *rolled*, not cut with a die.)
Why not build yourself a wheel with the dynohub and keep the original as a spare?
Steve

ThermionicScott 

My money is on needing new spokes. Steve has a good point -- if your existing rim is nothing special, why bother taking the old wheel apart at all? Just build up a new wheel out of new parts.

zacster

I know for us here in the states it is easy enough to get spokes, but this guy lives in Malta. It may be expensive to get new spokes and new rim, but I would definitely go new myself here in the US.

Boye

No, not really. Rosebikes.de would be my go-to shop for rims, spokes and dynamos here in the EU, and they deliver to Malta. They also provide prebuilt wheels.

dabrucru

hi guys thanks for all your input. at the present i use a bottle dynamo, it does the work great but sometimes i feel the drag. as for shopping parts i buy frequently from rose bikes and bike 24.

fietsbob

I never lose power because my bottle dynamo hydroplanes on a wet tire, with a hub dynamo.

you can get a built wheel with a Shimano dyno hub in it for pretty low cost .. wholesalers ship them to your LBS

for less than retail for the parts to build them..

Dan Burkhart 

Not necessarily. I shorten db spokes all the time.

fixedweasel

Dan, I've been doing it a long time. It depends on how much you need to shorten. It could go either way depending if you are going from a short flange front to a huge flange dynamo or large to large. In any case, if it were my choice and I had access, I would use new spokes unless it was in a pinch or it was on a true beater. Not worth any other way methinks.

Archwhorides 

One of the beauties of cycling is that every project leads to another project. If I had back all of those hours spent tinkering with my commuter rig, I would have been a more productive and much less happy man.

fietsbob

even a 14 -15 -14 DB could be shortened, past the outer butt. , I have a 15 ga straight spoke, wheel set .. thinner is not a handicap..

and the 15 ga spoke nip just has a smaller threaded hole, , so perhaps a wee bit stronger than the ones with a 14ga hole...?



....

fixedweasel

The whole idea behind a double butted is to try as much as possible to have equal length straight gauge between the thinner butted center portion. Because of this, there is an equal tension placed on the straight gauge portion which directly leads to the thinner portion/middle of the spoke to flex as close at/to the center as possible. Can you cut the end of a double butted spoke to fit? Of course you can. Will it work? Yes, of course. Wheels overall are an absolutely wonderful design/work of art. They are built to be terribly strong and are a Physics dream to rotation under torque. But as soon as you start pulling away to much distance from the end of the spoke, you begin to lose your center of relieving stress from the center of the butt. Yes, it will still work, but if you have to cut too much, just save the integrity of the design and get the proper length spoke.

ThermionicScott 

I think you're imagining a lot more going on than really is. If it were important at all to have exactly equal lengths of thicker sections on each side of the thinner center, I'd think more of the spokes I'd purchased over the years would have had them.

The main reason to have the elbow and threaded sections thicker than the center is because they are slightly weakened by the forming and the threading. (Looking at it the other way, a straight-gauge spoke is stronger in the center than it needs to be, compared to the ends.) The thick section between the elbow and center section is probably just due to manufacturing, and any remaining thicker section between the center and the threaded end is so that you don't have to swage every spoke length a different amount.

Abe_Froman

Right. Butting spokes just removes unneeded material, which serves 2 purposes. It lightens them, but also creates more built in ability for the spokes to elongate when under tension, which increases fatigue life.

fixedweasel

Therm, ah, no. That is not correct. Straight gauge spokes are weaker than double butted spokes in practice and theory. It's not that the flange and spoke end are "thicker" as you say for strength. It's that the butt or thinner section of the middle of the spoke takes up the tension that would normally would be put on the threads/nipple and angled flange. This is why you will see a straight gauge spoke fail more often than double butted. The fatigue of the spoke does not take place in the center of the spoke. It is always transferred to the elbow and threads/nipples. This is where you normally see spokes fail. Straight gauge put more/transfer fatigue on/onto those two areas. Period. Double butted pull some of that fatigue off the same two areas. This is just a fact.
I was giving an optimal as far as length on both sides of the butt. Yes it can be off some but you cannot cut down the straight gauge portion of the end of the spoke too much because you begin to lose the whole purpose of a double butted spoke. If you're going to do that, then just replace with a straight gauge spoke.

fietsbob

Definitions : Actually 'Butting' * is the thickening, the side effect is it allows thinning of the center,

or top in the case of seat tubes the upper portion..



the thinner center of the spoke reduces, the tensile strength,

but in weakening it, allows additional elasticity to be transferring stresses to the middle, relieving some from the ends..

but you can make up your own definitions.. they may be inaccurate, but you can use them ..

* Think of the 'flying buttresses' in the great cathedrals .. like Cologne..






///

fixedweasel

Quite so, in my haste to post I described the butt as the middle when indeed the butts are on the end.* Albeit in both of our writings, the facts cross** and remain true with butted spokes and the principles of.





*hence.............double..............butted
**no matter what word(age) we use***
***and thanks for the jab

ThermionicScott 

Never said that straight-gauge spokes were stronger than double-butted, and the footnotes are getting tedious.

fixedweasel

No worries. Asterisks* aren't for everyone. But they were only used to inform the proper differences between straight gauge and double butted spokes. There is no "imagining" or "probably". There is evidence based fact on why spokes are specifically designed the way they are. Was only attempting to shed light to that. We are all here to learn. No matter how old we are, how experienced, or how long we've been on a particular Forum.




*as used above/below