Spoke lengths

[brad890]

Ok before some of the hubbers tell me to use the search function I have, and have been browsing the web for the last few days.

 

I was wondering if people who have built wheels or do build wheels could maybe help make a nice thread explaining how to choose spoke length correctly, as I'm take a shot at building a wheel myself.

 

I see John normally has all the answers, and if there is a thread with regards to what I'm asking please point me in the right direction and I will have this one deleted.

 

Questions.

 

1. when building a wheel from scratch, one uses one of the many spoke calculators on the net and you get the lengths of the spokes you need.

 

A. are there any factors one needs to compensate for with these values, in one of the previous threads I see JB said you must compensate for spokes lengthening/ stretching? I think it was DT swiss spokes that were being spoken about.

 

B. what tolerances can one accept in terms of length, I see on some websites they say you can get away with spokes being 1-2mm shorter then required?

 

 

2. say you want to upgrade hubs on your wheels, but keep the rims, and yes I know different hubs brands etc have different dimensions thus need different spoke lengths, but bare with me

 

A. If just changing the hubs and keeping everything else, what tolerance could one accept with regards to spoke length, say you've got 263mm spokes but need 264mm would that work? or if a spoke calculator spits out 263mm for the old wheel dimensions and 264mm for the new wheel can you get away with it?

 

B. Is it a bad idea to re-use spokes? especially in older wheels where spokes have developed a slight notch where they cross over? will this affect the ability to true the new wheel as the spokes might not cross exactly at the same point on the new wheel?

[Johan Bornman]

Eish! This is a big one.

 

Question 1: You have to figure out how the spoke calculator calculates the result. DT Swiss' calculator for instance, asks you what type of spoke you're using, which tells me that it already compensates for stretch. I notice that if you put in DT Revolution (thin)in and do the same calculation with DT Champion (thicker), you get two different lengths.

 

The best is to use a calculator that doesn't try and do any thinking for you. That way you remain in charge of the process and can make the intelligent decisions required to bring two disparate entiries togeter - the right length and what is available to me at the time.

 

If you use a calculator that calculates the geometric length, then you would round down by up to 2mm for normal spokes and up to 3mm for Revolution/Laser spokes. The latter are thinner and stretch more. An ideal calculator is Damon Rinard's SpokeCalc.xls. It is sophisticated but leaves the decisions to you.

 

Tolerances? You always use a spoke that's shorter than the geometric lenght - Always!. The reason for this is that spokes can stretch but not shrink. Not even in the wash on hot cycle.

 

 

Question 2: I can't answer the first section specifically since I don't know how much the first builder rounded down by, if indeed he had. If he rounded by the absolute maximum, then the 1mm could be the difference between seeing thread exposed or not. It isn't really serious but every good wheelbuilder will do that only under exceptional circumstances.

 

Re-using spokes. It would be bad practice in a professional shop but since you're building your own wheels, who you gonna blame? When re-using spokes, try and re-use them in the position they came out of. By this I mean you need to distinguish between left and right and in each of those bundles, between inbound and outbound. They will have different bends at the head and rebending them for the opposite position would introduce accellerated metal fatige. In other words, tomorrow's problem.

 

Calculating spoke length is a mathematical problem. The solution lies in the formula for a Line in Space.

 

Imagine a box with its lid open. Inside the box you're holding a stick of unknown length. However, you know the angle of the stick viz a vie all dimensions. You also know how far the stick's ends are from the edges of the box. With this data, you can calculate the stick's length.

 

On a bicycle wheel you have the same problems. The stick (spoke) is inside a "box" with known dimensions. You know how far the spoke is from the (radial) centre of the hub axle (Spoke Pitch Diameter or spoke hole diameter, which is the circle of the spoke holes). You also know have far it is from the lateral centre of the axle (hub flange width measured from the axle centre to the centre of the flange.

Futher you know how big your error in measuring is at the spoke hole - it is the difference between the spoke thickness and spoke hole diameter (usually 0.5mm).

Nog verder: You know the inside diameter of the box (rim). This is the ERD or Effective Rim Diameter. You cannot measure this with a measuring tape since the points are somewhere inside the rim.

 

Just to complicate things, you have to figure out the angle of the spoke in the box. Here the number of spokes and their number of crossings give you a figure.

 

Chuck all of this into the formula and you have the geometric length. Now you have to apply some IQ to the length to get the optimum spoke length.

[brad890]

Thank you Johan.

 

A nice precise answer as always, explaining everything nicely.

[shaper]

There are a lot of spoke calculators on the net that you can use. Have found this one pretty easy to give you the geometric lengths as Johan has stated.

 

http://www.prowheelbuilder.com/spokelengthcalculator/

[Tuxstir]

i played around in V.B and created my own spoke calculator

you more than welcome to give it a try

just let me know what you think of it

 

https://docs.google.com/open?id=0B3Ks1yhnxIPGYnI2Y3Jwc29HV1U

[brad890]

i played around in V.B and created my own spoke calculator

you more than welcome to give it a try

just let me know what you think of it

 

https://docs.google....YnI2Y3Jwc29HV1U

 

Thanks I'll give it a shot and see what values it spits out for me

 

There are a lot of spoke calculators on the net that you can use. Have found this one pretty easy to give you the geometric lengths as Johan has stated.

 

http://www.prowheelb...ngthcalculator/

 

 

thanks have actually tried that one and quite a few others , wasn't quite sure if I needed to compensate for those values when buying spokes

[brad890]

Have any of you guys tried Spocalc? I got it off the Sheldonbrown website, Looks pretty good, had to put my own info into the calculator as the didn't have novatec hubs and the DT rims I have in their mini-database

 

seems I dont have permission to load .xls files, but here is the link

 

http://sheldonbrown....ard/spocalc.htm

 

and just to confim that I understand JB correctly,

 

If the calculator says I need 266.4mm spokes I should buy 264-265mm spokes because of the stretching? as I'm going to try go spoke hunting in town tomorrow.

[Minion]

Have any of you guys tried Spocalc? I got it off the Sheldonbrown website, Looks pretty good, had to put my own info into the calculator as the didn't have novatec hubs and the DT rims I have in their mini-database

That's the one I use. I wrote a slightly updated version for JB to improve the automation and add some error checking. If he's OK with it, I'll upload it here (it's got a whole lot of measurements he's taken personally which is why I won't upload without his say-so).

[brad890]

That's the one I use. I wrote a slightly updated version for JB to improve the automation and add some error checking. If he's OK with it, I'll upload it here (it's got a whole lot of measurements he's taken personally which is why I won't upload without his say-so).

 

That would be cool,

 

I'm guessing you improved the macro's? I see they dont work so nicely with the microsoft office 2007 I've got

[Tuxstir]

That's the one I use. I wrote a slightly updated version for JB to improve the automation and add some error checking. If he's OK with it, I'll upload it here (it's got a whole lot of measurements he's taken personally which is why I won't upload without his say-so).

 

i'm assuming you kept it to the excel format?

if you(and JB) are willing to share can i use it to update my VB version?

its a function i want to add into it, and i have no problem sharing in return,

[Minion]

I'm guessing you improved the macro's? I see they dont work so nicely with the microsoft office 2007 I've got

Yip. Added a couple of confirmation dialogs and improved the range handling in Excel. The basic functionality is the same.

 

i'm assuming you kept it to the excel format?

if you(and JB) are willing to share can i use it to update my VB version?

its a function i want to add into it, and i have no problem sharing in return,

The original spreadsheet is Damian Rinard's Spokecalc.xls and I just improved the VBA code. I've got no problem sharing the macro code and I'm pretty sure JB won't mind sharing his measurements, but I won't make that call on his behalf.

[Johan Bornman]

Have any of you guys tried Spocalc? I got it off the Sheldonbrown website, Looks pretty good, had to put my own info into the calculator as the didn't have novatec hubs and the DT rims I have in their mini-database

 

seems I dont have permission to load .xls files, but here is the link

 

http://sheldonbrown....ard/spocalc.htm

 

and just to confim that I understand JB correctly,

 

If the calculator says I need 266.4mm spokes I should buy 264-265mm spokes because of the stretching? as I'm going to try go spoke hunting in town tomorrow.

Your rounding down is correct if you use double-butted spokes. If you use 2mm straight-gauge, you may want to round down to 265 only, since they don't stretch much. However, you should NEVER build with such rubbish spokes.

 

@Edman. I have no problem with you uploading that version.May I suggest you first sort the new additions in all the databases in alphabetical order. I know where they are but a newcomer may find it strange to have no order.

 

Once I see yours again with the data 12 months old, I'll upload the new rims and hubs I've since added and people can just add it themselves.

 

Just an aside for those of you wanting to play with your own spoke lengths. NEVER trust a rim manufacturer's ERD measurements. Companies like NoTubes don't have a clue how to measure it and print mistakes on their rim stickers. Always measure it yourself. I've taken the issue up with NoTubes but they're American. When they see an African criticising them they clam up and refuse to communitate. Bunch of poepols they are. I've had this with Raceface, NoTubes, Enve and one or two others that now elude me.

[brad890]

Your rounding down is correct if you use double-butted spokes. If you use 2mm straight-gauge, you may want to round down to 265 only, since they don't stretch much. However, you should NEVER build with such rubbish spokes.

 

 

thank you for all the help Johan, I really appreciate it.

 

do you by some chance sell individual black spokes or sets? Just in case I cant find any in Pretoria?

[Johan Bornman]

thank you for all the help Johan, I really appreciate it.

 

do you by some chance sell individual black spokes or sets? Just in case I cant find any in Pretoria?

Yup. Cut to exact lengh.

[brad890]

I'm guessing I can contact you via your website's "contact us" link if I need to get hold of you and order? or if now how do I go about ordering from you?

[Johan Bornman]

I'm guessing I can contact you via your website's "contact us" link if I need to get hold of you and order? or if now how do I go about ordering from you?

johanatyellowsaddledotceeodotzeda