Hi everyone, I’m building up a set of disc brake gravel wheels and was wondering about the number of spoke crossings that I should/can go for.
I have 28 spokes in the front and the rear so according to Jobst Brandt’s “The Bicycle Wheel” where he has the rule of thumb to divide the number of spokes by 9, I can go for 3 cross. I cross-checked the Roger Musson wheel building book and he essentially says the same thing except that he’s a bit contradictory in that he says that the number of crossings (as long as it’s not radial) does not matter while a paragraph later he says that more crossings are better for resisting torque. I get the mechanical argument that the more crosses, the more tangential the spokes, the better the torque resistance (at least on paper).
I’ve also plugged my numbers into Roger Musson’s spoke length calculator and 3 cross should be fine with 28 holes as it gives me a spoke (head) clearance of a little bit less than a millimeter.
It all seems good, I just wanted to double check before I commit to ordering my spokes to avoid getting the wrong length.
Theoretically 3x is preferable because of the brake torque. But in reality I personally wouldn’t care which it was. I typically default to 3x because I’ve always had good builds with it.
^ Only one side really has to be crossed - the other side could be radial; both Mavic and Shimano have made wheels like that. You might save the equivalent of one whole spoke length!!!
The rear might have the significantly more consistent load, but the front will have the significantly higher/more abrupt loading thanks to the braking forces. So if either needs 3x more than the other, it’s the front. Ultimately it will come down to rider weight, and riding style.
Personally, I run 3x on my 28 spoke gravel wheels.
Either will work - both have been done on the rear. Usually though the dished side is the crossed side, so the LHS (disc side) at the front, and the RHS (drive side) at the rear. With 2:1 spoking it pretty much has to be that way, but with equal spoke numbers on both sides it probably wouldn’t matter too much and any torque would just transfer via the hub shell to the crossed side. There’s no good reason I can see to make the disc side at the front radial tbough…
I would check out the ebikes.ca spoke calculator, it will tell you the angle the spokes exit the rim for various cross #’s. It will also give you the left/right tension balance. The Sapim Polyax and DT Pro Head nipples both uses rounded bottoms to better allow the nipple to align with the spoke. If you are using carbon rims, they may be pre-drilled for a certain lacing pattern, similar with straight pull hubs, they are designed around a predetermined lacing pattern. thick carbon rims that have the holes drilled straight down to the center of hub don’t allow the nipple to move as freely and for those I would opt for a lower number of crossings.
Cross 3 is a defacto standard, especially back in the day for 32h alloy rims, tub or clincher. For my gravel wheels used carbon rims built with Sapim aero spokes, alloy nipples x2 front, x2 LH/x3 RH rear. Zero issues over 4 years and counting.
Is there any spoke restriction by the hub? E.g. straight pull hubs may have the cross number predefined by way of the hole angle. Also, selfishly asking as I’m about to relace from carbon to steel spokes, how does nipple length factor into spoke length calculations?
This is a very good point. Straight pull with 28 spokes is likely sort of 2.5 cross, as the spoke heads may sit next to each other at the hub, sort of crossing, sort of not, with two crosses further along.
Are the hubs of the Stache straight pull? Quick check of photos of that bike online would suggest they are? If yes, things are a bit different re how you might count the number of crosses compared to j-bend (do you count the spokes sitting next to each other at the hub as a cross or not?), and you have essentially no choice in the spoke pattern.
Having seen someone snap multiple spokes at the j-bend (seemed like one per week at one point) on a 29er that had been built 2x, and the issue being resolved by rebuilding the wheels with new spokes and a 3x pattern, I prersonally wouldn’t risk 2x on a 28 spoke disc brake wheel with j-bend spokes - but then my routes/riding has a lot of steep stuff and lots of sudden/sharp braking.
Typically the spoke is calculated so it sits just flush with the bottom of the slot in your typical nipple. If you have long nipples for whatever reason it’s possible you’ll run out of thread on the spoke if you’re a bit long on the spoke length. Some rims require long nipples so I’d inquire with the rim mfg what lengths they recommend.
It’s good to remember the spoke charts are generally calculated for regular rims and hubs. Someone mentioned directionally drilled rims and you mentioned straight pull spokes. So be careful when you select lengths and build. This is one of my pet peeves, the last thing the bike industry needs is more non-standard stuff.
For my build, I’ll be using j-bend spokes so should be no issue there.
I’ll check with the manufacturer for directional drilling and see what they recommend. I’m working with rims from light bicycle and it’s my second set of theirs. The drilling is definitely directional although mainly in the drive side and non-drive side direction so that the spokes and nipples have an easier time pointing outwards.
Regarding the nipples, I’m using Sapim polyax so I should be good with the angle of the spokes exiting the rim. Using https://spokelength-project.com to compare the values for the angle of the spokes exiting the rim, I get 3.9 degrees for 2 cross and 4.6 degrees for 3 cross, so not a crazy difference and according to the information presented in the spokelength-project even the standard nipples can swivel 6 or 7 degrees while the polyax I’m using are closer to 9 degrees. So should be all good.
I’d say the two books, the Jobst Brand “The bicycle wheel” and the Roger Musson guide make a perfect combination for building wheels. The Jobst book covers more of the why while the Roger Musson guide is about the how. Together, you get a really complete picture.
The spokes on the Stache with 28° x2 are NOT srraight pull. Broken spokes IME have nothing to do with the lacing pattern, and everything to do with the quality of the build, and thus the skill of the builder. Some OEM wheels have been built disgracefully badly, to the point where we used to loosen all the spokes and rebuild them before sending them out.
Having said that, sometimes (in the distant past at least) really badly designed hub flanges and/or spoke heads could exacerbate matters, in which case a respoke or elimination of the dodgy parts was the answer. Once spokes start breaking one can safely assume they’re all fatigued and need replacement - unless they’re torn out via some traumatic event. Similarly, spokes gouged by chains might be okay, but if one breaks, chances are they all will.
Straight pull hubs seem to be primarily about making a fashion statement - “See how trick this is!” - or else about making parts proprietary and expensive. I’m not convinced there’s any practical advantage, and spares are definitely harder to source.
Definitely go for 2x. You don’t want the spokes to run completely tangential to the hub flange as that makes the spoke touch the flange further away from the spoke hole.
That increases the risk for flange failure in the future, and might lead to noises.
That’s a completely new one to me. I can see the spoke against flange rub/interference being a thing with 24 spokes 3x builds (which is why they should be 2x), but not seen those issues with 3x 28 builds. I don’t think I’ve ever seen a hub flange fail, ever, in any build style.
