Carbon gravel wheels for a heavy rider

[JoninSweden]

If you get an i30 XC rim there may well be problems with tyres blowing off at your weight. Bear in mind these are intended for ~55+mm tyres at <30PSI. If you instead use 42mm tyres at much higher pressure they might not stay on, whereas the i25mm rims are intended to take tyres from ~29mm (current ETRTO lower limit) upwards, so should tolerate much more before blowing off.

Thanks for that - every day a school day!

I'm going around in circles here, spoilt for choice but unsure of priorities. And with Black Friday looming, I'd be mad to order anything before then.

Given that there is so much in the way of short burst acceleration in gravel racing, would prioritising weight be more sensible than aero? How much of an affect does aero have when knobbly gravel tyres are factored in?

Obviously, in a gravel race, you're likely to spent a lot more time in the wind than on the road, and the speeds are still fairly high (I expect I'll be around 33kph average, if I hope to qualify for the worlds). But if shaving several hundred grams off the spun mass has a bigger positive effect....

But then you're back to durability, and being a veritable lump, I ought to prioritise strength and durability.

This is a question with (I feel) a great many right answers, depending on your perspective.

And for perspective, this is me with my 2XL Canyon Grail

[JoninSweden]

9 Velo - does anyone have any thoughts?

https://www.9velo.com/products/gravel-g ... tsId=10032

They seem to be impeccably reviewed, sub 1400g at 45mm and have no rider weight limit. With a 10% discount code from one of the Youtube reviews, they come in at $800 delivered.

Maybe cheaper still for Black Friday.

[ND4SPD]

https://www.dtswiss.com/en/wheels/wheels-road/gravel

[Mr.Gib]

Great photo, never seen a 2XL Canyon look so small.

As for wheels, let me put it this way, your best chance at avoiding regret of your purchase is to prioritize durability. It is unfair that you are almost a different species than most cyclists, but none of us cyclist would be happy playing rugby against you.

As for aero vs weight, that discussion is almost a waste of time in the gravel realm. Aero for the body and bike yes, but the tires you choose will almost certainly render wheel depth irrelevant. Light weight is nice but of course not at the expense of durability.

Lycka till!

[JoninSweden]

Great photo, never seen a 2XL Canyon look so small.

As for wheels, let me put it this way, your best chance at avoiding regret of your purchase is to prioritize durability. It is unfair that you are almost a different species than most cyclists, but none of us cyclist would be happy playing rugby against you.

As for aero vs weight, that discussion is almost a waste of time in the gravel realm. Aero for the body and bike yes, but the tires you choose will almost certainly render wheel depth irrelevant. Light weight is nice but of course not at the expense of durability.

Lycka till!

Haha! Thank you for the encouragement!

It's funny, but my regular training partner since May is another 'genetic aberration' (as a good friend used to call me) - another 2m chap, used to play professional basketball. My sense of what's normal is really skewed.

But you can't help the sports you love and I love cycling.

I totally agree on the durability front. That's why the 9Velo wheels really appeal as there aren't many brands that have no weight limit at my price point.

[pdlpsher1]

+1 on what Mr. Gib said. You could choose a mid-depth wheel (40mm+) as a compromise. A deeper rim is vertically stiffer, and that stiffness will allow more spokes to share the workload.

I have a local cyclist friend who's 6'5". He breaks frames and components (a Giant frame and a Shimano crank). He's also an ex-cat 2 racer so lots of power output for his body frame. Crazy.

Below is the best book ever written on the subject of wheels.

[Mr.Gib]

@pdlpsher1, that's fabulous stuff from the Jobst book.

My complaint about all these 24 spoke wheels built with CXray is that there is too much lateral movement of the rim under load. When descending and cornering agressively, I find this sort of wheel flex interferes with the predictable tracking of the bike. On a road that is a bit rough or has some ripples in the surface, it's a fight to put the tires exactly where you want them. The most extreme case I can think of is having an older Zipp 303 (20 spoke?) literally collapse momentarily against the brake pad and fork leg in a compression during a high speed curve. Suddenly there's tire rub and some braking forces I wasn't expecting. Those were shite wheels and modern stuff is better but still far from perfect.

I don't know if the cause of this kind of flex is flimsy spokes or the hub geometry or both, but I do know that wheels with stiff spokes don't do this, even when there are relatively few of them. As for Thor sized riders like the OP, surely flex of this sort would be relatively greater and accelerate metal fatigue. Spokes and nipples would be in peril.

And also for the OP - whatever wheels you do end up with, brass nipples are the smart play. Alloy is asking for trouble, particularely for any wheels that see damp conditions.

[pdlpsher1]

I agree with Mr. Gib that the OP would benefit from at least 28 spokes if the spokes are the lightweight variaty (CX-Ray). He could get away with 24 but the spokes would need to be something in the 5.5-6g. variaty like the CX-Sprint. The problem with pre-built wheelsets is that they mostly use CX-Ray type spokes and only come in a 24 hole drilling. If he were to choose a custom build from LightBicycle or Farsport, then I'd recommend CX-Sprint equivalent spokes on a 28 hole hub.

My rim brake Campy Boras come with 18H front and 21H rear hubs. But the spokes are the CX-Sprint equivalent and spokes on rim brake wheels don't need to transfer braking forces. Since disk brake wheels need the spokes to transmit torque from the braking forces (a much stronger force than even Olympian track sprinters could generate), 28 CX-Sprint is a much safer bet for the OP.

[pdlpsher1]

9 Velo - does anyone have any thoughts?

https://www.9velo.com/products/gravel-g ... tsId=10032

24 CX-Ray spokes is much weaker than your curent G 1800 Spline's Aero Comp spokes. You're downgrading, not upgrading.

Your G 1800 Splines tick all of the boxes for your riding. It's got DT Swiss rachet hubs. Heavy duty butted aero spokes. Is it really worth the expense trying to save a tiny bit of weight? If you're purely going for the looks of deeper carbon wheels, be prepared to spend a decent amount of money as good hubs aren't exactly cheap. One other alternative is to recycle your current hubs and build them with good quality carbon rims and spokes.

Strong, light, cheap. Pick two.

[satanas]

In practice, I think what counts for lateral stiffness of wheels are the rim (deeper and/or wider and/or heavier will be stiffer, all else being equal), and the total spoke tension. I doubt changing the spoke gauge will do much if whatever spokes are used are built to the same tension, i.e., 120kgf. More spokes will allow more total tension in the wheel, and thus stiffness (and strength), while the shorter spans of rim between the spokes will have less chance of flexing too. As for hubs, there's not much variation in flange placement so stiffness will be similar - unless the wheels are using 2:1 spoking, G3 or some other unusual pattern.

The easiest way to increase wheel durability is to use more spokes, assuming the rim is stiff enough, and the tyre is wide enough.

[pdlpsher1]

Spoke gauge makes a big difference, because the thicker the spoke the less tension changes (hence deflection) when the spoke is loaded. A 6g spoke will deflect 33% less than a 4.5g spoke. If you have two wheels, one with 24H and 6g spokes, one with 32H with 4.5g spokes, both would deflect equally laternally when cornering (total spoke weight is 144g on both). But yes, having more spokes would produce a more reliable wheel as each spoke would take up 33% less load. But in terms of lateral deflection what really matters is the total spoke weight, not just the quantity of spokes.

[satanas]

^ The limiting factor on spoke tension is the rim strength, and many rim makers (LB, Nextie, Stans, etc) often specify the maximum tension permissible; typically it's somewhere between 110 & 130kgf. If the spokes are built to that maximum tension then I can't see how the force per unit area matters, just the total force between the hub flange and rim. Having said that, thinner spokes will be more elastic and less likely to lose all tension, so should if anything be more reliable, albeit more likely to windup annoyingly during building; this is more easily controlled with aero spokes.

For the hypothetical wheels mentioned above, the unsupported distance between the spokes will be significantly larger with 24 rather the 32 spokes - the rim would flex more between adjacent spokes. The total spoke tension could only be the same if the fewer spokes were at higher tension. In practice this is why modern wheels can have fewer spokes - stronger rims allow the maximum tension per spoke to be greater, and deeper, stiffer rims limit unwanted flex. However, using thicker spokes does not allow more tension - per spoke - as this is limited by rim strength - if there's too much tension the rim will crack at the spoke hole sooner or later. (Many classic alu rims failed this way too, and using thinner spokes on lighter rims was pretty much standard practice as a result.)

Wheels are tensioned structures, more analogous to concete beams with tensioning cables than to stone pillars, so the deflection for a given load doesn't depend entirely on the cross section or shape. With wheels I doubt the difference in (lateral) section modulus with different spokes has much effect on stiffness compared with the number and placement of the spokes, and the rim design. The strain on different thickness spokes will vary with their cross sectional area, but shouldn't affect strength unless the elastic limit of the spoke's material is exceeded.

[pdlpsher1]

Wheels are tensioned structures, more analogous to concete beams with tensioning cables than to stone pillars, so the deflection for a given load doesn't depend entirely on the cross section or shape.

Have you not used a spoke tension gauge before? The gauge's reading is affected by the cross section thickness of the spoke. You can have two spokes with the same tension, say 120kgf, as measured on a spoke tension calibration jig (i.e. measured via a crane scale). The thicker spoke will deflect a lot less than the thin spoke when using a spoke tension gauge. Therefore the spoke tension gauge needs to be 'calibrated' for a specific spoke gauge/type. Wheel strength and durability can be affected by spoke number and placement. But the discussion on spoke thickness was originated from the topic of the wheel's lateral deflection, not wheel strength or durability. In the context of a wheel's lateral stiffness, spoke cross section is key to increase it. Spoke tension alone won't do anything to laternal stiffness of a wheel, as long as the spoke tension doesn't go completely slack (0kgf). You could tension a wheel's spokes to 25kgf and that wheel will have identical laternal stiffness as another wheel with spokes tensioned to 120kgf (assuming the spokes never goes slack). If you have a wheel built with 6g spokes and a tension of 25kgf, this wheel will be laterally stiffer than a wheel built with 4.5g spokes tensioned to 120kgf.

[satanas]

Tensiometers measure spoke tension by attempting to bend the spokes laterally, so yes the thickness left to right will affect how much the spoke bends, and hence different calibrations for different shaped spokes. In a built wheel though the spokes are loaded in tension when riding, not bending, so I really don't see how this matters - the loads on the spokes are axial, not lateral.

[pdlpsher1]

Tensiometers measure spoke tension by attempting to bend the spokes laterally, so yes the thickness left to right will affect how much the spoke bends, and hence different calibrations for different shaped spokes. In a built wheel though the spokes are loaded in tension when riding, not bending, so I really don't see how this matters - the loads on the spokes are axial, not lateral.

OMG. Steel is a material that is isotropic in modulus of elasticity. If it's harder to bend a spoke laternally, it's equally harder to bend it longitudinally. When you ride a bike each spoke is experiencing changes in tension due to the changes in load placed on the spoke. The amount of the tension change is affected by the spoke's cross section area, not the amount of tension on the spoke. Tension changes is the result of the spoke changing in physical length. A wheel might appear to be a rigid structure. But with each revolution of the wheel, each spoke's length goes from short to long, then back to short. The spoke tension change is very dynamic, based on the revolution of the wheel, the torque from the rider and braking forces, and from cornering forces. Imagine each spoke is made of a rubber band. A thicker rubber band will be harder to stretch than a thin rubber band, even when the two are tensioned equally. A steel spoke's length change is microscopic, but it doesn't take a lot of movement to cause the wheel to deflect laterally by a few millimeters.

I have already posted this above but I'll say it again. You could tension a wheel's spokes to 25kgf and that wheel will have identical laternal stiffness as another wheel with spokes tensioned to 120kgf (assuming the spokes never go slack). If you have a wheel built with 6g spokes and a tension of 25kgf, this wheel will be laterally stiffer than a wheel built with 4.5g spokes tensioned to 120kgf.