SpasticSprocket

I have a 27 X 1/4" 36 hole rim, and I wanted to know how long a spoke I needed, I have a busted spoke and I figured I might as well order in a bunch in case it happens again. Thank you in advance for your advice.

Airburst

It depends on the size of the hub - measure one of your existing spokes.

SpasticSprocket

Alright I can try that. I thought the hub would probably affect the length I need.

Andrew R Stewart 

Spokes are usually measured from the elbow's inside to the end of the threading. A spoke ruler has a hole the elbow will sit in and the point along the scale that the threaded end stops at is the spoke length. this means that for most accurate measurements a good/unbroken spoke should be removed from the wheel, made sure it's straight and then measured. A very good approximation can be done with a good spoke still in the wheel. Elbow inside edge to rim's inside edge and add a couple of MMs to account for the slight bowing of the spoke, the rim's thickness and a little bit of the nipple's head. It's not uncommon for a newbie to miss judge the length doing this and the resulting spoke length might be a bit short as to not fully thread into the nipple (or too long and stick out beyond the nipple's head). BTW the spoke lengths are different on either side of rear wheels, the gear cluster side usually have a length a couple mms less then the LH side does and front wheels won't be the same as rear wheel length wise. When doubt remove a good spoke, from the same side and wheel, and directly measure. If you've never replaced spokes and/or trued wheels before you might pick up a used, tossed out, wheel to practice on. lastly the rear wheel's gear cluster usually needs to be removed, a special tool purchase. If you came into the shop I worked at we'd offer to remove the cluster and measure a spoke for a small labor fee. The cluster's reinstalling won't need any tools if it's a freewheel design. Andy.

Bill Kapaun

Rim diameter (where the spoke nipple beds aka ERD) varies between different brands & models.
Rear DS is typically about 1-2MM shorter than rear NDS, depending on the dish of the wheel. More cogs, usually more dish.
Flange diameter varies from different hubs.
Number of crosses affect the length.
Sometimes, the rear NDS spokes will match the front spokes.

Best to pull off a good spoke and measure. You might actually check how deep the spoke is threaded in the nipple in case the factory length is off a MM.

And as has been said in these forums-
ONE spoke breaking is bad luck. TWO spokes breaking is a trend. You may have reached the end of the life of your spokes, in which case, it may be a better idea to go ahead and replace all of them. Possibly the rim too, depending on the condition of the brake track or you want to get something better than steel rims etc.

Telling us WHAT rims & hubs you have might allow us to give more precise advice.

Ex Pres 

302mm

Bill Kapaun

I actually built a PAIR of 27" wheels a few weeks ago.
302MM was ONE of the 3 different lengths I used.

JohnDThompson 

Spoke length is a function of rim diameter, hub diameter, number of spokes, and how many times (if any) they cross other spokes between the hub and the rim:



Source: Sutherland's 4th Edition

Needless to say, these days most people use a spreadsheet or on-line calculator:

https://www.google.com/search?q=spok...hrome&ie=UTF-8

hueyhoolihan

^^

square roots?, exponents? AND trig? geesh.

cny-bikeman

That is to be expected when dealing with straight spokes connecting a circular hub to a circular rim at compound angles. That's how we did it before computers, online calcuators and spreadsheets. But there's no need for going through all of that now. At the worst you need to measure the ERD and the hub dimensions and plug the results into a spoke length calculator. In the OP's case I don't see the need to even measure. Take it to a shop and buy a few spokes.

SpasticSprocket

Woah, a lot of stuff involved in buying a set of spokes.. I think I'll probably take the advice of bringing it into a shop.

Bill Kapaun

I looked up one of the 27" rim charts provided with a spoke length calculator.
ERD varied from 609-622mm.
That in itself means the spoke length could vary by 13/2mm just from possibly different rims. Add in the possible variance between different hub flange diameters and the number of crosses and......

IF you have the actual spoke in hand, you have the best reference.

robow

I was told that there would be no math on this website.....................(Chevy Chase)

mrrabbit 

Most 27" wheels built using low flanges hubs w/ 36 hole drillings are going to be in the ballpark of:

301-302mm front
299-300mm non-drive rear
297-298mm drive side rear

But you really need to measure the old spokes - especiailly with single wall rims in order to make certain you don't get poke-through that threatens the underside of the tube.

=8-)

cny-bikeman

I would not recommend buying a set of spokes, or even more than a few and then replacing them as they break. Once you break a couple then more are sure to go, and they have a habit of not doing so when you are rolling into your driveway. If you start to break them you will either need to rebuild or get a replacement wheel, depending on budget, quality of what's on there already, and any preferance or need you have for type, width, etc.

SpasticSprocket

Yeah I put some thought into it and I'm thinking of going with a new wheel entirely, I just wish I could find a Wolber Super Champion Model 58. I can't even find a wheelset of those let alone a single rear wheel.