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Wheel misconceptions: Part 1 - Straight Pull vs J-bend wheels

Updated: Nov 15, 2023

The straight pull spoke vs J-bend spoke argument has been around for ages, with various opinions being discussed in angry cycling forums. I use the word “opinions” rather than facts as some of them are more speculation or theory.



KOM’s position:

KOM only make the straight pull Xeno hubs at the moment. However, we don’t want people to think we’re just backing it up because we have to. We have the choice to make either straight pull, J- bend or both types of hub. With extensive trials of both and seeing the advantages, we decided to make the Xeno straight pull only. For us, J-bend would be much quicker and cheaper to machine. However, we made the conscious decision to make the Xeno straight pull (even with the extra intricate machining our clever, tech filled, straight pull lugs require) because we want to make the best hubs possible, irrespective of price.


Advantages


Spoke replacement:

One of the potentially really big advantages of straight pull spokes is the ease of replacing them.

In contrast, spoke replacement on a j-bend wheel is difficult, as you need to remove the cassette (and usually the disc) to thread a spoke through the hub flange. Straight pull wheels differ. If a straight pull hub is optimised correctly then you can change a spoke without removing the cassette, disc and without having to reduce tension in the remaining spokes. Of course in the case of j-bend and straight pull, if your spoke nipple needs replacing then you have to replace your rim tape, removing and re-fitting your tyre either way, however if not, and your nipple doesn’t fall into the rim, then true trail-side spoke replacements become a reality.

Here is an example, with the Xeno hub, of changing any spoke with the wheel still on the bike. Video: Changing a spoke with the wheel on the bike

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Straight Pull hub laced ready to go: The spokes point in the right direction: straight to the holes in the rim.


Wheel lacing:

Lacing wheels is super easy with straight pull hubs that have been made correctly; put all the spokes in the hub then lace them to the rim hole they’re pointing at. For beginners or riders who want to give it a go, it’s “line up the hub correctly with the valve hole” and you’re set. We at KOM like to think of ourselves as experienced wheel builders, so lacing J-bend isn’t really a problem, however, as we build our own wheels, making the process easier and faster is always welcomed.



J Bend Hub Laced. More of a 'skill' to line the spokes up with the holes in the rim?


I personally think one of the big reasons some wheel builders are against straight pull hubs is that it de-skills wheel building. People who love the “art” of wheel building don’t like how a noob could throw together a straight pull hub with basically no experience – just my opinion.


Spoke strength:

People talk about the strength of the actual spokes, usually arguing that a straight pull spoke’s head, having not being bent, is stronger than a J-bend’s. True the J bend does add another possible weak point. However this makes pretty much no difference at all since the weak point of a spoke isn’t the head or J bend. With current spokes they nearly always break somewhere else first.


Straight Pull spoke load testing. Strong in Tension: These DT Competition 2.0mm -1.8mm double butted spokes failed at about 300kg after over 20mm plastic deformation.


Bedding in:

When J-bend spokes are laced and tensioned, they bed into the side of the flange hole. Wheel builders “pre-stress” a wheel so that this bedding in is largely complete when the wheel leaves. Unfortunately, a wheel builder can't do all of the potential bedding in, so the spokes may lose some tension out on the trail and require a re-true sooner than a straight pull. Straight pull are different as they pull straight from a specially drilled hub lug without the need to bend around corners. An almost infinitely small amount of bedding in is needed for straight pull hubs. The gains aren’t massive but they're there.


Twisting spokes:

This common argument is as follows: because of the way that straight pull spokes contact the hub concentrically down the spoke, they can turn. Therefore, if the friction of the nipple on the spoke is greater than that at the hub, the spoke will turn in the hub rather than tightening up. The friction of the spoke in the hub is the product of the spoke tension and co-efficient of friction, so the lower the tension, the more likely the spoke is to turn in the hub.

On our hub, the spokes only need to be held slightly with fingers when the spoke has no tension (rattling) however once the spoke has a bit of tension they don’t need to be held at all. (Using a special 'spoke pliers' or 'clamping spoke holder' tool makes holding the spoke even easier while the nipple is tightened. This tool is really good at preventing spoke wind up on J bend spokes as well.)

As someone who has worked in a bike shop, I haven’t just experienced building new wheels, but also truing old, ridden ones. A common problem with truing used wheels is that the spoke nipples are seized or have increased turning resistance. If your nipples are very seized and you try to tighten them without holding the spoke near to the nipple, then even on our straight pull hubs the spokes will most likely turn. Wheel builders usually see this as a negative, while being unaware of (or forgetting about) the alternative.

I’ll give you an example. If you are an experienced wheel builder / bike mechanic, you probably will have gone through this: A customer has come in for a simple true and tension on a moderately used wheel. Spokes tightening well, everything going ok. You tighten a certain single spoke. Wait a second! That tension hasn’t gone up at all. You try again. Tension reduces. What…? Then the sinking feeling hits, the overwhelming dread and realisation that this spoke has begun to wind up. “Maybe it’ll come back?” you optimistically ask yourself as a tear rolls down your cheek. It won’t. “Do I have that spoke in stock?” You probably don’t. Ok maybe I overplayed that a bit, but it is bloody annoying. I hope your spoke distributor is quick because that spoke is now only suitable for the bin, and so is the wheel if you don’t replace it.

This is the case where I struggle to understand people’s frustrations for straight pull hubs. People see turning spokes when the nipple is seized as ALWAYS a bad thing. However, it is nowhere near as bad as the alternative.

Spokes are designed to have tension, and to stretch following Hookes law (have a spring constant and follow it). If you over tension a spoke it will begin plastic deformation rather than elastic. This is difficult to do accidentally as spokes can take a lot of tension before exceeding their elastic limit (in our testing up to 300kg).

In comparison, spokes are pretty poor in torsional or twisting strength, this is of course why wheel-builders practise turning a spoke as required then back an eighth of a turn or so. The problem is the following: with a bit of excess twisting force, the spoke will rotate at one end, too much more than the other, winding up your spoke and deforming it plastically, consequently ruining it.

I’ll repeat what I said earlier: once they’ve gone, they don’t come back. With this failure your spokes starts to get longer when you think you're winding more tension on and the wheel becomes impossible to true properly. If the spoke nipple is seized or very draggy, it needs to either be freed up or held near the nipple. Straight pull doesn’t solve the issue of seized nipples; however, it can prevent you from turning them into a bigger problem.




Disadvantages


Non-standard spokes:

Bike shops sometimes don’t stock straight pull spokes because various companies, such as Mavic, have made their own, custom designs, multiple times. So there are lots of different types out there. We build our hubs with Dt Swiss Competition double-butted spokes with a 2mm thread and 4mm head – much more of a standard. More bike shops will have these in stock, and they’re widely available, but we’d definitely recommend always having a few spare of your own.


Lacing pattern:

Some may see a possible disadvantage of straight pull hubs is that you can’t change the lacing pattern of the spokes. (E.g. you can’t change between 2 cross and 3 cross.) This is already pre-determined by the drilling of the spoke holes during hub manufacture. (The direction that the spokes point in is pre-set.) Our hub cross patterns are optimized to have as close to tangential crossing pattern as possible, which is mostly acknowledged to be the best way to do things. Tangential spokes also give better torsional wheel strength for braking and pedalling. Difference in spoke tension also makes less of a difference on bearing seat tolerances on hubs with closer to tangential spokes, due to the radial tension component transferred to the hub being far smaller.


Having reading through the last sentence and realising most riders don’t care, I have decided to wind up on this subject. Maybe we'll do a follow up on how the optimum number of spoke crosses is calculated as there is so little on the subject on line. (The calculations are pretty nerdy but the results are actually very clear cut.)


Lastly, I also prefer straight pull spokes because the hubs are lighter, stronger and look sick!


If you think we’ve missed something important, you’ve spotted a mistake, or would like to know our opinions on another matter, we’d love to hear from you! Please comment below!


Cheers for reading,

Leo.


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