Wheelbuilding / Wheel Building / Wheel build help

the retartadation rate in the toque part. Torque = moment of roation inertia x angluar aceleration. So it is in there. the higher the retardation rate the higer the torque applied

you can make it more complicated but the result still is disc brakes put more load on the the spokes than rim brakes do on average. The exact ammount will depend on a number of factors but it is wrong to assume they don't.

Not exactly. The loads are high due to the diamter the braking loads act over the hub flange. If you had a symmetrical disc brake hub the situation would be the same. the tension changes on the rotor side is not proportional to the static spoke tension. The tension changes will be dependant on the torque applied just like on a rim brake rear wheel with the exception that unless your chris hoy you cant apply disc brake torque when pedalling.

What are you aiming for with the wheel? Speed, strength or lightweight?
Current suggestions seems a bit all over the place tbh, as all those spokes negate the aero benefit of bladed spokes.
Since it’s a rear and disc, I would personally consider a deep carbon rim (50-60mm), fewer regular spokes and the 350hub.
But that’s just me :)

They might seem all over the place but I know what I don't want.
For example, low spoke counts are stupid for an ultra wheel, especially one under a 90kg rider.

What I do want is durability, serviceability and any speed benefits be they from lightweight or aero properties is a bonus.

I use CXRays in all my wheels, that's not really an aero thing, it's an 'I like CXRays' thing.

As for lots of spokes negating bladed spoke aero benefits, it's the opposite. I require 32h for durability so reducing the aero penalty by making them all bladed is no bad thing.

If you knew the trouble I've had with deep carbon rims and valve extenders you'd know why I'm not bothering with another one and staying shallow.

Wider rims are better because comfort during ultra races is more important than rear wheel aerodynamics and bigger volume tyres help in that regard.

I use a 350 now. Choosing a 240S instead of a 350 was simply me being a bit bling for a change. Typically I shoot for bang for buck within my specific parameters but sometimes I choose to splash out.

it is wrong to assume they don't

I'm not assuming they don't, I'm just countering the frequent assertion that there's magic involved in rim-braked wheels which somehow allows braking to occur without affecting the spokes, and that by contrast everything which happens to the spokes under disc-braking is the fault of the torque applied to the hub by the rotor.

What is certainly different is that brake loads from rim brakes are shared equally between the left and right sets of spokes, but disc brake loads bear more heavily on the rotor side. This makes me wonder whether the aero bike makers ought to consider two discs, as each could be smaller than a single disc, and halving the torque load on the rotor side would permit a lower spoke count.

Oh, keep digging sunshine.

What is certainly different is that brake loads from rim brakes are shared equally between the left and right sets of spokes, but disc brake loads bear more heavily on the rotor side. This makes me wonder whether the aero bike makers ought to consider two discs, as each could be smaller than a single disc, and halving the torque load on the rotor side would permit a lower spoke count.

This level of sophistication and reasoning is going to be seriously lost on @thecycleclinic given he can't even distinguish between the mechanical advantage in a braking system and the load applied to an individual spoke.

If you had a symmetrical disc brake hub the situation would be the same.

Not unless the hub shell was infinitely stiff.

retartadation rate in the toque

Is this something from Bake Off? I've never watched it, but it sounds like a rework of an open pie while wearing a chef's hat, so it could be.

Different story out here.

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Can I ask for some help please? I'm looking to build a set of road wheels with Miche primato sintesi hubs. Dimensions courtesy of The cycleclinic are as follows...
Front:

Flange PCD = 40mm
Centre of flange - centre of hub = 34mm
100mm OLD
Rear :
Flange PCD = 46mm
Centre DS flange - centre of hub = 16mm
Centre NDS flange - centre of hub = 38mm
130mm OLD

The rims I want to use are DT Swiss 411RR. My issue is that i want to use the asymmetric version of the rim on the rear. Can anyone help with spoke length calculation? I don't trust myself to get it right. The hubs are 28h and I want to do x2 front and rear. Thanks.
EDIT rim ERD is 601mm

If you use the DT Swiss spoke length calculator you can tell it you're using the 411RR Assymetric and it'll calculate the lengths. Assuming the hub dimensions are correct, and using 12mm nipples, it gives 288mm NDS and 286mm DS.

Alternatively, if you can find out what the offset is on the assymetric rims (I couldn't online) then you can just tweak the flange spacing figures. So if it's a 2mm offset, that would make the flange spacings 18mm and 36mm rather than 16mm and 38mm.

Usual caveats apply about making sure the hub dimensions you get off the net are correct.

Thanks Dan i'll measure up and confirm those figures

Isn't the force applied to a disc rotor greater than that applied to a rim?
If a wheel has to stop in say 1 turn, then that is roughly 2 metres long at the rim, but a lot less at the rotor, which means you need more friction at the rotor, hence more force...

Am I talking nonsense here?

the rim's turning faster though, right?

Does it matter?

The work is force x distance... if you have more distance at the rim, then you need less force to do the same work

Am I talking nonsense here?

No, you're quite right. In fact, if you want to bandy apparently impressive numbers based on an oversimplification, the total shear load on the rotor bolts is about 15 times that on the rim brake pad bolts. However, the question isn't "how big are the loads on the braking components?", it's "how big are the braking loads on the spokes?"

Harder to say... however, spokes tend to fatigue much quicker on a rear wheel, mostly because that's the driving wheel, where the acceleration "happens" and it happens at the hub, where typically spokes fail. Front wheel spoke failures are much rarer, suggesting deceleration at the rim has very minor effects.
I suspect in a disc braked wheel deceleration at the hub will have the same effect as acceleration, this time both front and rear... actually more front than rear. So, it is not unreasonable to think that all else being equal, disc braked wheels' spokes are bound to last less and therefore the wheel needs some "overbuilding" as well as benefits from a non radial lacing pattern.

spokes tend to fatigue much quicker on a rear wheel, mostly because that's the driving wheel, where the acceleration "happens" and it happens at the hub, where typically spokes fail. Front wheel spoke failures are much rarer, suggesting deceleration at the rim has very minor effects.

Fatigue is a function of both the number of cycles and the peak load. Drive side rear spokes get two load cycles for every revolution of the cranks, rotor side spokes get a load cycle from the braking torque once every time the brake is applied, a much smaller number in most cases.
While it would be a good idea to design drive side rears to operate under the fatigue limit for any sustainable torque input, there might be an argument for allowing total load under heavy braking to exceed the fatigue limit by a substantial margin since a fatigue life of 10⁵ cycles could easily represent more than 100,000km on a road bike

Glad to see you are still building wheels Ugo. The Ambrosio Nemesis you built for me a few years back are still going strong.
You inspired me to have a go myself.

I'm not really... every now and again I need to build a pair to remind myself how to do it LOL... a far cry from the hundreds I was building back in the days in London.

Nemesis are still the coolest rims... I had a pair and got rid of them when I decided to give up on tubulars...

36H X4 X2

Lovely

Why different lacing?

Looks like a 90s Campagnolo rim, what is it?