Spoke aficionados assemble – 28, 32, Race, D-Light, CX-Ray ?

Speccing a 29er rear wheel for a trail bike (alu rim), I chose 32 Sapim Race spokes just to be sensible as a few grams won’t matter and I won’t have to worry about it. But I’ve since nerd sniped myself into thinking and making calculations about spokes anyway.

DT’s Spline wheels all run 28 apart from the DH rear one, so they seem to think that’s enough.

Is it better to have 28 stronger spokes or 32 lighter ones? I’d think the latter to spread out the load more evenly, and for better resilience after snapping a spoke. Back to DT, they put lighter spokes on carbon rim models presumably to offset the stiffer rim. Would it just be for supply chain and manufacturing process reasons that they use stronger rather than more spokes on the alu ones? It would (see below) be almost exactly the same weight and strength by my calculations.

Did some calculations of strength and weight for Sapim Race (2.0/1.8), D-Light (2.0/1.65), and CX-Ray bladed (0.9×2.2) spokes. Strength based on Sapim’s published N/mm2 figures multiplied by the cross section of however many of the respective type. I realise there’s more to it with lacing patterns etc. but these are some concrete numbers.

32 Race 182g, 1.0 relative strength
28 Race 159g, 0.88
32 D-Light 154g, 0.89
32 CX-Ray 136g, 1.49
28 D-Light 134g, 0.77
28 CX-Ray 119g, 1.30

There’s a 64g range there, and the lighter wheel is stronger (by this measure) although more expensive. That’s as much as the difference of the Deore/SLX/XT spec levels on Shimano cassettes, and more than the 45g difference between an XM481 and EX511 rim.

10% weaker wheel to save 25-30g, would you do it with fewer or lighter spokes?
30% stronger wheel and save 64g, any reason not to do it other than cost?

it’s a silly amount of weight IMO.

I would go on stiffness.

Agree with Al tbh, the variables are really pretty small while the price differences can be fairly large.

But, as far as 28 vs 32 goes, modern rims are mostly strong and stiff, 28h is absolutely fine for most and if it’s a matter of grams I’d still rather have those grams in the rim than in the spokes. A well built 28h wheel doesn’t suddenly go mad with a single broken spoke.

I don’t personally think the n/mm2 figures really tell you much of interest about the strength of a wheel, it always seems like a classic case of “we can’t measure much about this so we’re going to exaggerate the importance of the thing we can measure”.

Oh yeah and depending on use, I like the humble Laser. It’s literally just a CX-Ray with less forging, so yes it’s less strong but it’s cheap and it’s light, and they still build up really well. It’s my default choice for anything but a downhill rim and tbf I’ve never felt like for my use a cx-ray is any better.

Oh aye, after I’d been using Lasers for a few years Sapim put out a general range update which said they’re not approved for disc wheels, but stince i’d been using them already without issue I just kept doing it. The product guide still says they’re approved for mountain bike use. They’re directly comparable to a DT Revolution so I just don’t sweat it

I  build all my wheels with d lites – they are nice to build with and seem strong enough.

I have a 30mm wide 29er newmen wheel which is also dlite with 28h so they obviously thought it would be OK.

Disclaimer,  I am no wheel building expert, I just use wheel building as therapy to recover from work.

Poking around the pits at FT Bill suggests that plenty of the world’s fastest DH loons are running 28h, mostly on the front but quite a few on the rear as well.

Most of them were on DT Competitions.

CX-Ray’s give you stronger AND lighter, but at a cost which can be reduced by using 28 of them.

+1 for Lasers rather than CX Rays as Northwind says, for exactly the same reasons.

In the OP’s shoes I’d go for 32 Lasers, although in my case I go with 28 Lasers.

‘Stronger’ is an odd one where spokes is concerned. Since they’re all steel and the Young’s Modulus is the same, and they’ll all be tensioned to the 1000N or so that most rims support, the only real difference between these spokes is the change in length needed to support the dynamic load. Thinner spokes will compress more in use, but really since spokes stretch max around 1mm when building so can’t really compress more than that, and your suspension compresses 150mm, good luck noticing that. Hence I’m fine with more thinner spokes.

My preference is 32 sapim D-lights, I’ve had zero issues with them and you can get away with slightly too long spokes as the nips don’t bottom out on the shaft, I once build a wheel with CX-rays, never again, total pita as you need both hands to adjust every spoke to stop them twisting. Nothing wrong with lasers though, 30ish grams extra per wheel is nothing.

Aren’t the Lazer just as likely to twist as the cx-ray, you just can’t see it as easily.

Isn’t the trendy thing now to use 27 spokes now? 18DS and 9NDS. Slightly lighter and similar stiffness to a 36 spoke wheel.

I like to equalise the tension per square millimeter of the spoke section between drive and non drive side which usually means d-light on the non drive side and race on the drive side.

I would go on stiffness.

Found this https://bicyclewheel.info/wheel-simulator/, I don’t have all the right numbers to put into it but:

Stiffness:
32 1.8mm spokes – 4015 N/mm radial, 97.9 N/mm lateral, 2659 N/deg torsional
28 1.8mm spokes – 3599 N/mm radial, 85.1 N/mm lateral, 2447 N/deg torsional
32 1.6mm spokes – 3376 N/mm radial, 79.7 N/mm lateral, 2178 N/deg torsional
28 1.6mm spokes – 3026 N/mm radial, 69.4 N/mm lateral, 1999 N/deg torsional

Relative stiffness:
32 1.8mm spokes – 1.0 radial, 1.0 lateral, 1.0 N/deg torsional
28 1.8mm spokes – 0.9 radial, 0.87 lateral, 0.92 torsional
32 1.6mm spokes – 0.84 radial, 0.81 lateral, 0.82 torsional
28 1.6mm spokes – 0.75 radial, 0.71 lateral, 0.75 torsional

It makes a good case for fewer but stronger spokes.

the variables are really pretty small while the price differences can be fairly large

Yes for the CX-Ray, £50 per wheel! This is just for interest though.

A well built 28h wheel doesn’t suddenly go mad with a single broken spoke.

Agreed, but ancedotes do vary. There’s a spoke on each side every 13cm instead of 11cm, so double those if you break one.

I don’t personally think the n/mm2 figures really tell you much of interest about the strength of a wheel

Yes, I realised there’s more to it, and the calculator numbers above provide some of that.

Poking around the pits at FT Bill suggests that plenty of the world’s fastest DH loons are running 28h, mostly on the front but quite a few on the rear as well.

Most of them were on DT Competitions.

Interesting in terms of performance etc. but not longevity.

CX-Ray’s give you stronger AND lighter, but at a cost which can be reduced by using 28 of them.

Yes, they are 2 mm^2. So any reason other than cost for not going with them? The racers above aren’t using them, and the FR1500 DH are only available with Competitions.

Continuing the above numbers…

Stiffness:
32 2mm spokes – 4690 radial, 117.6 N/mm lateral, 3195 torsional
28 2mm spokes – 4203 radial, 102.1 N/mm lateral, 2945 torsional

Relative stiffness:
32 2mm spokes – 1.17 radial, 1.20 lateral, 1.20 torsional
28 2mm spokes – 1.05 radial, 1.04 lateral, 1.11 torsional

DOH, I meant race not laser, too late, can’t fix it now.

Thinner spokes will compress more in use, but really since spokes stretch max around 1mm when building so can’t really compress more than that, and your suspension compresses 150mm, good luck noticing that. Hence I’m fine with more thinner spokes.

There is also side loading to consider. If you look at slow motion high frame rate videos, wheels (even carbon ones) appear to displace centimetres out of plane during some manoeuvres. That will represent mm scale spoke stretch, and spoke stiffness may make a difference. I built my 27.5+ wheels with 32 DT Revs and Nextie Alligator carbon rims. I now think I would use a stiffer spoke as there does seem to be some wheel deformation. My 29″ trail wheels have 32 D lites and chunkier carbon rims, which is probably better.

Aren’t the Lazer just as likely to twist as the cx-ray, you just can’t see it as easily

I wondered this. Take a piece of paper, hold each end and try to twist it. Now roll it into a tube and try to twist it. Is that the answer, flattened section will twist more easily?

It makes a good case for fewer but stronger spokes.

To me those numbers are mostly showing that running 14% fewer spokes is stiffer than running 26% less spoke cross section area. For the most part stiffness is proportional to the total cross sectional area of the butted part of the spokes.
You want to think about the whole wheel though, not just the spokes. 28 heavier gauge spokes you’re going to have a higher target tension that 32 thinner gauge spokes, so how does that marry up with the rims max tension per spoke, does it have eyelets etc. Also a deep section stiffer rim is more suited to lower spoke count than a shallow sectioned one.

Aren’t the Lazer just as likely to twist as the cx-ray, you just can’t see it as easily

I wondered this. Take a piece of paper, hold each end and try to twist it. Now roll it into a tube and try to twist it. Is that the answer, flattened section will twist more easily?

Few random google results say a circular beam is better as resisting torsion than other shapes.

To me those numbers are mostly showing that running 14% fewer spokes is stiffer than running 26% less spoke cross section area. For the most part stiffness is proportional to the total cross sectional area of the butted part of the spokes.

28 spokes is 12.5% fewer than 32. Where does 26% come from? 1.6 gives 21% less cross section than 1.8, and 1.65 gives 16% less. Regardless, your point stands.

I wondered this. Take a piece of paper, hold each end and try to twist it. Now roll it into a tube and try to twist it. Is that the answer, flattened section will twist more easily?

Sort of, but this exaggerates the effect because a tube provides signicantly more torsional stiffness than a solid rod with the same sectional area.
A circular section is torsionally stiffer than an ellipse or rectangle with the same sectional area though.
A cx-ray has about half the torsional stiffness of a d-light, partly because it has only 75% of the sectional area and partly because of the different shape.

There is a nice wikipedia article on ‘torsion constant’

Oh yeah and depending on use, I like the humble Laser. It’s literally just a CX-Ray with less forging

Yes, they are 2 mm^2.

Ah, I’ve messed up my CX-Ray calculations in multiple ways. Lasers are 1.5 mm2 so CX-Rays must be the same, and presumably they aren’t perfectly rectangular in the 0.9×2.2 listed measurements which would give a cross section of 2mm (and make them heavier).

32 Race 182g, 1.0 relative strength
28 Race 159g, 0.88
32 D-Light 154g, 0.89
32 CX-Ray 136g, 1.49
28 D-Light 134g, 0.77
28 CX-Ray 119g, 1.30

Corrections:
32 CX-Ray 136g, 0.85
28 CX-Ray 119g, 0.75

So a CX-Ray is actually a bit weaker than a D-Light. But that’s just the tension aspect of a spoke, not stiffness of the wheel etc.

Stiffness:
32 2mm spokes – 4690 radial, 117.6 N/mm lateral, 3195 torsional
28 2mm spokes – 4203 radial, 102.1 N/mm lateral, 2945 torsional

Relative stiffness:
32 2mm spokes – 1.17 radial, 1.20 lateral, 1.20 torsional
28 2mm spokes – 1.05 radial, 1.04 lateral, 1.11 torsional

Corrections, although these are really numbers for the Laser. They don’t take into account that the CX-Ray is forged and a different shape.

32 1.5mm spokes – 3070 radial, 71.1 N/mm lateral, 1957 torsional
28 1.5mm spokes – 2752 radial, 62.1 N/mm lateral, 1794 torsional

Relative stiffness:
32 1.5mm spokes – 0.76 radial, 0.73 lateral, 0.74 torsional
28 1.5mm spokes – 0.69 radial, 0.63 lateral, 0.67 torsional

28 spokes is 12.5% fewer than 32. Where does 26% come from? 1.6 gives 21% less cross section than 1.8, and 1.65 gives 16% less. Regardless, your point stands

Yes I wrote it the wrong way round to how I calculated it going from 28 to 32 spokes is increasing by 14%.

I’d only use 28 spokes on carbon or very robust aluminium rims.  I tried it with Crests and it was a pain.

I’d happily use D-lights on anything.

On carbon rims, I’d happily use 2x over 3x.

Builder I use (DCR wheels) told me CX-Ray are super strong and compliant. DH approved. I have 32 in the rear.

From what I remember, a CX is a flattened, (and thus forged) D-light spoke.  It will have higher tensile strength, higher out of plane bending strength and lower torsional strength. This leads to a slightly more forgiving wheel, which can be quite important for carbon.   All-in, a d-light will build into a stiffer wheel for a marginal weight and aero penalty.

Aesthetically, I think a low spoke count (<28) looks great on a gravel or road bike, but the super thin d-lights almost seem to disappear on MTBs as they’re so much smaller than the wheels, frame, tyres, etc that you tend to not notice them until you look really closely.  Same with DT Revs.

Builder I use (DCR wheels) told me CX-Ray are super strong and compliant. DH approved. I have 32 in the rear.

They have a good page about spokes. It mentions a cheaper CX-Delta spoke which is flat rather than aero, however there is little mention of this online.

From what I remember, a CX is a flattened, (and thus forged) D-light spoke. It will have higher tensile strength, higher out of plane bending strength and lower torsional strength. This leads to a slightly more forgiving wheel, which can be quite important for carbon. All-in, a d-light will build into a stiffer wheel for a marginal weight and aero penalty.

It’s a Laser. I’m not sure whether (or how) the bending and twisting strength of a spoke carries over to the radial, lateral, and torsional stiffness of a wheel. I thought spokes only stretch and relax.

This isn’t scientific, at all, but I built up some road wheels with some very twisty round j spokes, some daft skinny thing I’d got cheap. They were twistier to build with than cx-rays, I ended up paint marking them so I could track it as it was a pain in the arse and final adjustment was just really annoying… In the end I just thought, why not see what happens with the other one? So I built the second wheel without really thinking about twist, and it was all over the place but after a few hundred miles they’d largely untwisted themselves. That resulted in a wee bit of tension wandering but I’m pretty sure it was the nipples turning in the rim so it was basically like a quarter or half turn here or there, not really any different from what you might expect from an adequate factory build.

It’d have still looked crap if they were bladed of course but it worked out just fine, it made me think about how twisted/untwisted my round spokes might be on average, I’d not be at all surprised if there’s a whole bunch of minor twists in there that I just don’t know about and that aren’t causing any issues.