Syncmaster

I'm trying to figure out the length of spokes I need for a road wheel build that I will give to a local builder to assemble. However, I don't know what length spokes I need. I asked one builder (who was originally going to build my wheels, but who has since vanished into thin air) what length I'd need, and he suggested 290mm for the front and 292mm/294mm for the rear.

However, now that I'm trying to calculate the lengths on my own, using the pro wheel builder spoke calculator, https://www.prowheelbuilder.com/spoke/index.php
I come up with 294mm/296mm for the rear and I don't know how to calculate the front since I don't have front hub dimensions....

The wheel I'm building consists of this:

28 spoke rear Kinlin XR-200 - 594mm ERD
24 spoke front Kinlin XR-200
https://www.bikehubstore.com/category-s/122.htm

Ultralight Front hub
https://www.bikehubstore.com/product-p/ulf66.htm

Superlight Rear hub
https://www.bikehubstore.com/SuperLight-211-p/sl211.htm



Sheldon Brown says, "The [spoke] length is not super-critical. Most spoke calculators give results to the tenth of a mm, but spokes are usually sold in 1 mm size increments (some brands only in 2 mm increments.) Generally, I round upward to the nearest available larger size."

SO I'm wondering, which length is right, or does it not really even matter if I'm a couple millimeters off? Will the builder be able to deal with this?

I've already bought the hubs and rims but I'd like to buy the spokes before I go to the builder. I would ask the builder but I don't know who it will be yet, or if they will be cool with me asking them to help me calculate the spoke length if I won't be buying the spokes from them. Not even sure if they'll have the spokes I'll need.

Any help would be greatly appreciated. Thanks

hybridbkrdr

I pushed some spokes hard enough to go through the other end of the nipple. So, if you have a double wall rim and they were longer, then I suppose one of the only factors would be if you have enough thread. In reality, I haven't built a wheel yet. But, I'm guessing a few people will jump in this thread.

DOS

As the hub graphic you posted shows, you can figure out the hub dimensions easily enough with a ruler. https://sheldonbrown.com/rinard/spocalc.htm.

You don't have to be super precise but 2mm difference seems a bit big (I try to stay within 1mm either way), so I suspect you are using different numbers for your hub and/or rim dimensions than did the original wheelbuilder. If you are sure about the ERD and the hub dimensions, I suggest run the numbers through a couple of calculators to to confirm numbers before buying the spokes. (the one on United Bicycle Institute site has never steered me wrong -- https://www.bikeschool.com/tools/spoke-length-calculator) .

Al1943

A good rule of thumb is to calculate the best you can and then round down at least a fraction of a mm. Just about the worst that can happen is to run out of threads because the spoke is too long. This is especially critical on the drive side rear where tensions are high and thin or double butted spokes can stretch.

mrrabbit 

Take the spoke with the actual threads that will be used - test with the actual nipple that will be used. Determine the minimal insertion allowed without showing threads - and determine the maximum insertion allowed before spoke dead ends.

Most 12mm nipples with box threaded spokes will be 1mm below screwdriver flat and exactly to top of head. That's about 2.5mm of targetted space that is aimed for. With .5mm reserved for overhead at the top in case of error - that leaves you with 2.0mm - 1mm below to 1mm above flat. Hence the +/- 1.0mm the DOS noted already....

Assuming 12mm nipple...use an ERD that aims for the flat - round down a 1/2 millimeter if necessary for the drive side of rear or disc side of fronts. You can get away with a .5mm round up if necessary for non-drive rear or non-disc front.

Having a spoke machine as I do makes things easier - spoke machines tend to add one more thread providing a little more overhead for the same nipple - thus 1mm more room for error at the top side.

=8-)

https://www.mrrabbit.net/wheelsbyflemingapplications.php

Have tools there you can use...

1. However you need to find out where that ERD is aiming and with what size nipple - check the source for that ERD you have.
2. You need to measure your hubs as noted already.

=8-)

mrrabbit 

Front Hub

d=29.7 (flange diameter)
c=33.5 (offset)

[I get 290.78 - .35 = @290.50mm using 14g elbows.] Use 290.00???

Rear Hub

d_left=38.4
d_right=49.3

c_left=31.75 (offset)
c_right=@17.00 (offset)


non-drive [I get 286.18 - .35= @285.75mm using 14g elbows] Use 286.00???
drive side [I get 281.80 - .35 = @281.50mm using 14g elbows] Use 281.00???


Calculate your spoke lengths....subtract .35mm from the result to account for the 2.7mm hole diameters.

=8-)

Syncmaster

Hmmm with this calculator, I'm getting 291.9 and 292.6 for the rear hub... I don't think I'm doing this right.

All this is very confusing for me for some reason..... Given that rear hub diagram I posted at the top of the thread, for 28 spokes in a 3 cross pattern, can anyone help me out and figure out what length I'd need for both sides of the rear hub?

I may just have to bring the hub and rim to the shop and see if they'll be generous enough to help me calculate it. I may just buy my spokes there if they do and they have the spokes I want....

mrrabbit 

I assumed 2X for both front and rear...that's why my rear measurements are different.


non-drive = 294.03 - .35 = @ 293.50
drive = 291.99 - .35 = @ 291.50

You could probably get away with 294.00 and 291.00 using 12mm standard profile nipples.

=8-)

Jeff Wills

Back when I started building wheels, we'd lace rear wheels with the same length on the left and right sides. One the wheel was built, dished, trued and tensioned, some of the right side spokes might be poking out the back side of the nipple. We'd grind those off with a skinny grinder.

IMO: you can get away with a lot when building wheels. Rabbit's +- 1.0mm is ideal, but most standard parts will let you get away with +- 2mm. Personally: don't overthink this. It's a bicycle, not rocket surgery.

mrrabbit 

With 10mm nipples which were pretty much standard back then...yes...

But with today's 12mm and 14mm...and box threaded spokes...it's more no.

...add to that today's hubs with extreme asymmetrical offsets........

=8-)

urbanknight

Get as close as possible with the calculator, because the real life of it has variance, and the closer you are, the less risk of that variance being too far from the size you buy.

I rarely recommend 3x for 28 spokes. 2x is plenty tangential, and 3x risks the heads rubbing the neighbor spokes. Also, for some reason, most calculators (at least the 3 I use regularly) seem to come up a tad short on 28 spoke patterns. I always round up for 28, and down for everything else.

Syncmaster

Thank you guys for your help.

I'm understanding much more about how to calculate spoke length. I really appreciate it. I think my original builder's calculations were pretty close at 294mm and 292mm for the rear and 290mm for the front.

I think I'll stick to this and pass along the supplies to the wheel assembler at the shop....

Thank you all for your valuable input! I really appreciate it. Maybe next time I'll be building the wheel myself.....

Syncmaster

Hmmm well the first wheel builder I spoke to recommended that I do 3x in the rear and 2x in the front. These rims are really light weight and have rider weight restrictions. I was under the impression that a 3 cross rear would be stronger overall? Or am I not understanding this correctly?

Would there be any disadvantages to going to 2x instead of 3x in the rear?

mikezs

Less torsional strength, so you're more likely to snap a spoke if you wind up some massive torsion through torque going up a hill.

2x does look a lot cooler though...

urbanknight

Not quite. The goal is to have the spokes close to tangential, meaning that they leave the hub at almost a 90 degree angle from radial. This allows the spoke to be pulled along its length instead of yanked sideways. You could hang over 1000 lb from a spoke, but put put a 1 lb load on it sideways and it will bend. Now, the number of spokes, the hub flange diameter, and the effective rim diameter all determine how many crosses will make it close to tangential. A 36 or 40 spoke wheel will usually like 4x, a 32 spoke wheel will like 23x, a 24 or 28 spoke wheel will like 2x, and 20 or less likes 1x. Going less than those recommendations will make for a slightly weaker wheel, but going over will run the risk of the spoke getting rubbed by the neighbor spoke's head, potentially causing it to break.

fwiw my wheels are Kinlin XR-200 rims, 28 spokes laced radially front and 2x rear on American Classic hubs. Looking at them makes it obvious that 3x would be a mistake. I weigh 180lb and have no problems with them whatsoever.

FastJake

IME, you can usually get away with +-2mm. Any more than that and either the spokes will not reach or you'll thread them all the way through and run out of threads. Neither of these is fun, and it's best to get it right the first time.

If you're having someone build the wheels for you let them determine the spoke length. That way if they screw up they can't blame you, they'll have to fix it. If you were building the wheels my advice would be different.

urbanknight

Considering this, if your spokes are too short, you can get 2mm longer nipples. If they're too long, you need new spokes. Also, if you do a mock up build with only light tension and without using any gunk on the spokes, some shops (such as wheelbuilder.com) will exchange them for the right size.

Drew Eckhardt 

You can use 2mm longer brass nipples. Alloy nipples like the original poster needs (for the lightest practical wheels - otherwise he'd be using deeper rims for aerodynamics and durability) won't hold up if the spokes don't make it above the seat.

Or more threads rolled on.

It'd be a lot smarter to get rims, measure actual ERD, and then order the right length spokes.

Although Kinlin claimed a 577mm ERD for my XR-300s I measured a round 579.5mm, round 578mm, and ovoid 578 x 579.5 example. If you were aiming for the slot at 577mm the big one could be an issue with alloy nipples.

Drew Eckhardt 

DT spokes have 9mm of thread, DT 12mm nipples 8mm of thread to the end of the nipple, and the slot is 1mm deep. At 2mm long you run out of thread even if the rim is exactly at its stated ERD and you were spot on estimating spoke stretch.

+1.

urbanknight

That's true. I hadn't considered that since I'm a big advocate of brass nipples. My XR-200 wheels weigh in at 1375 grams, and dropping it down to 1350 (less than 2% savings) at the cost of durability wasn't something I was interested in.


Also true, but if you can exchange them for free instead of paying another 20 cents per spoke...


My suggestion was assuming that was already done. It still doesn't always come out just right. It's rare, but even with me measuring every rim and running 3 different calculators just to check for errors or inconsistencies, about one of every hundred wheels comes up wrong (assuming all unique builds, of course).


My XR-200 rims were similar. I don't recall the measurement off the top of my head, but I believe they were both a little larger than advertised, although fairly round. Even with me taking those measurements, the spokes came up about 2mm too short.

ultraman6970

+-2 mm wont make any difference for the builder and pretty much the guy gave u a size because he knows what will fit the built. Sometimes u go by instinct sometimes u go for the formulas.

If the builder guessed wrong well, is his fault. But if you get spokes 2 mm longer it wont make too much of a difference IMO. As long the spoke is 2 mm inside of the rim (to play safe with the nipples) the size is ok. Some guys like them exact but even in the stores they dont carry everything, some stores carry even numbers, other ones uneven numbers in the spokes (sizes) so u have to figure it out with that they have in stock.

Talk with the guy and ask him about your calculations.

Drew Eckhardt 

DT spokes 2mm too long from an exact measurement will bottom before you get to full tension.

A DT spoke has 9mm of thread. A standard DT 12mm nipple has 8mm of thread to its end with a 1mm deep nipple slot. That means that spokes run out of threads once they're 2mm past the nipple slot.

Most of the calculators are just a convenient way to do the trigonometry and return the distance between hub hole and ERD which is typically measured at the slot. Thin spokes like DT Revolutions, DT Aerolites, Sapim CX-Rays stretch nearly a full millimeter. The rim also shrinks under tension. So a spoke "2mm too long" runs out of thread about 1mm of where it needs to at full tension.

Spokes 2mm less than either traditional length (slot or nipple top) won't make it through the head and are likely to result in broken alloy nipples.

Syncmaster

Thank you everyone, for the comments and suggestions.

Urban Knight, I feel much better knowing you have the same rims as I will have. I was nervous about durability for my weight, but it seems like I'll be okay.

I am in fact going for a very light wheelset on a budget, but I"m not opposed to using Brass Nipples.

From what I've been reading, it seems like it's actually not the best idea to round up? Should you round down? Or rather, it'd be easier to fix the mistake of the lengths are slightly off if they're a bit shorter rather than longer.

My plan now is to go to the shop tomorrow when I have the rims and hubs and talk to the wheel builder personally and show him my measurements. If they have the supplies I need, I'd be happy to buy them from the LBS (unless they're ridiculously over priced....), if not, I'll buy what I need and return with everything for them to help me out.

Hopefully they're accommodating. I haven't been to them before but they're recommended as being good wheel builders here in NYC.

Thanks again everyone

urbanknight

If you saw the conversation between Drew and me, don't trust published ERDs. As suggested above, have the builder suggest the spoke length. That way, it's his problem if they come out wrong, plus if he is a reputable builder, he'll likely have the right spokes right there to swap out.

If you're not against brass nipples, I feel they are the best choice and they only add about 20-30 grams for the set. Of course, this is because I'm the builder, and the biggest thing I hate about aluminum nipples is working with them. When you get near tension, they are too easy to round out and they sometimes bind (although cheap brass ones do as well). But the concern for the rider is that even slight rounding reduces the strength of the hold on the threads, and aluminum nipples commonly snap at the heads of let go of the spoke. That being said, I've never had an aluminum nipple break on me, but I also only ran them when I was a total weight weenie and weighed only 130 lb myself.

mrrabbit 

Nipple are exactly that - nipples. They are not spoke and not intended to act as such.

If the spokes are too short - more than a mm below the flat - using longer nipples only hides the problem and likely will result in the nipple snapping where the barrel meets the rim.

=8-)