merlinextraligh

From Rolf's own website:

How do Paired Spokes allow Rolf Prima to build stronger wheels?
A: Rolf Prima wheels get their strength, stiffness and stability through the use of high spoke tensions. By pairing the spokes at the rim, we can build each wheel with a higher and more targeted spoke tension than a traditionally laced wheel.

For us that has lead to multiple cracked rims and hubs. We still have the wheels but IIRC both rims and the front hub have been replaced due to cracking, pull throughs.

If you look through threads over the years on this forum, we're not the only team to have had problems with ROLFs related to failures caused by the high spoke tension design.

Here's an example: https://www.bikeforums.net/tandem-cy...-wheelset.html

The newer carbon fiber ones may be better, but the hubs and rims still have to be built to withstand higher tensions.

Carbonfiberboy 

Yeah, but weird. There's no discernable reason for it, other than that they used too few spokes for their chosen rim section (see below). And no reason for them to pull through the rim other than piss-poor engineering. I think that's all BS, which doesn't mean that the wheels were not POS. They're blaming their engineering failure on a design element, which is probably better than the other way 'round. IIRC my single 20H DS rears are at 90 kgf.

Looking at it from the other direction, I think it's possible to use higher spoke tensions with paired spokes because you're not distorting the rim laterally, but just because you can is not a reason to do so. OTOH, if you want to use the absolutely fewest spokes possible, then of course you go paired and high tension, but you have to engineer for that.

diabloridr

Engineering 101: Light, Strong, Cheap. Pick any two (or sometimes one...)

Rolf has been my preferred wheel for all our bikes since they were licensed to Bontrager.

Looking at wheels for single bikes, I replaced Bontrager's several times due to both rim and hub failures. As the user base experience broadened, the design matured and I have not had any failures on later generation Rolf stuff.

The population of tandem wheels is much smaller, and I expect it took longer for the design to mature. I replaced both rims and hubs on our aluminum rimmed tandem wheels early on, but the later rim and hub designs did not fail in our use.

Our Machiatto has been running the carbon fiber Rolfs trouble free for over 3 years now, but to be fair our mileage and riding style has tempered as our team age increased.

torger

I've finally got all parts and ready to build the wheels (or actually I've had them for some time, but I got involved in other stuff so I haven't had time to build wheels). Having no rim bed nipple holes in combination with J-bend spokes proved to be a bit of a challenge (as when you have laced some spokes and the hub starts to get fixed, you can't slide the spoke back to guide it into the nipple, one need to bend it increasing the risk of shooting the nipple back into the rim having to guide back out again with the sewing thread/magnet drill). Lacing the wheel takes forever. Still snow outside where I live though so no hurry yet...

torger

So the back wheel is now laced. It was no easy task. Sewing thread, magnet, lots of electric tape and patience finally did it. I used morgan blue aquaproof grease as spoke prep, I did not want something that would stiffen fast, as it took me a couple of hours just lacing this thing. I will also monitor and service these wheels periodically so a thread locker is unnecessary anyway.

Not yet tensioned. I need to measure the stiffness of the spoke type (pillar wing 23) first so I can get in the proper tensioning range. Due to the 36 -> 24 lacing (not recommended) half of the spokes needed to be a couple of mm shorter and may need a few percent less tension. I'll see if it becomes a problem. I think it will work out fine though. The reason I'm using a 36 hole hub is simply because that was what I could get hold of with 145mm width at a (somewhat) reasonable price here in Europe.


24 spokes on 36 hole hub. Due to 2.5 degree offset between flanges half of the spokes need to be 2mm shorter.


laced, but not tensioned yet


24 spokes on 36 hole hub. Darker spokes are shorter to compensate for the 2.5 degree flange offset.

torger

Tensioned and trued! Theoretically, due to the special 36->24 lacing, half of the spokes would need couple of percent higher tension so I was a bit worried that would cause me problems when truing, but I trued it just as any other wheel and it worked out fine and the spoke tension ended up as even as on any other wheel. Still winter and a couple of months before I can try them outside, and I need to make the front wheel too.


Tensioned and trued!

LV2TNDM

"more targeted spoke tension"

Unadulterated marketing bull****!

What does that even mean? Nothing, that's what! Do they put crosshairs on the spokes? Shoot them during development and testing?

The tension wheel's strength characteristics are well known. All Rolf and others have done is utilize reinforced, extra-stiff rims with bolstered nipple seats to ensure their wheels can tolerate higher tensions.

But does that make them better? Debatable. But as some have experienced, rim failure is an issue. Servicing them is definitely a pain. Repair on the road? Difficult at best. And what IS the objective utilizing this design? Hard to say weight savings, as the heaver rim material offsets the weight savings in lower spoke count - and the weight penalty is in the WORST spot, the outer radius of the wheel. Perhaps reduced wheel drag. But on a tandem, you already have a significant advantage aerodynamically, so the small savings by utilizing 8 fewer spokes per wheel has got to be inconsequential. Rim profile is probably the biggest factor affecting wheel drag anyway (Hambini has a great YouTube video explaining aerodynamic drag as it relates to rim profile).

On a tandem, durability is key. It translates to fewer problems, and more importantly, higher safety.

I just don't think trading safety for marketing BS is a worthwhile trade-off.

LV2TNDM

Nice wheels! Fun build!

I'm not sure you're reaching the correct conclusion. Why should some spokes on the same hub flange require more or less tension than others? Given your build, I see clearly why you need to utilize shorter spokes to achieve consistent, or even, nipple thread engagement. But this should not affect tension. Pretty much all wheels end up with variation in effective spoke length due to the spokes emanating from different sides of the hub flange, which changes their effective length. These spokes do not need different tension values (and one could actually argue they DO because they actually have different dish or leverage angle, which would influence their needed tension. But again, such a small difference in angle means no real difference in tension on the wheel). In other words, the lengths may differ, but the tensions should not. Even tension is what you want to achieve on each side (DS, NDS). [Ha, I just realized that the "DS, NDS" designation can mean two different things: drive side, or disk side. Opposite meaning, but consistent.]

Anyway, even tension from each spoke hole is your goal; spoke length is irrelevant. However, spoke ANGLE is not. Tangential versus radial will affect tensions, I understand (not sure though, to be honest). But your slight angle difference due to spoke offset shouldn't really matter. Too small a difference to end up affecting measurable spoke tensions.

At least that's my take on it. I'd be curious to hear arguments to the contrary, if there are any.

torger

Thanks :-). Actually the small difference in spoke tension is due to different spoke angle you mention. It's indeed very small, but the shorter spokes are a little bit less tangential than the longer which one can see in the CAD drawing. I have tucked away the calculations so I don't have them fresh now, but I think the difference was in the range 3% or so. I'm not a very experienced wheel builder, but as far as I understand variations from other aspects in a wheel build can be larger than that, and surely the precision of my consumer spoke tension meter wouldn't pick it up anyway. So it's probably okay. If the wheels will be proper stiff or feel like noodles for us with only 24 spokes we'll see when summer comes here. I don't actually know, so it's a bit of a gamble. The Pillar Wing 23 is a rather stiff aero spoke though and we are not a heavy team, so I hope it will feel alright.

This will be the "going fast on nice roads"-wheels. I'm also re-building the original 36 spoke 700c wheels the tandem came with to 650B gravel wheels which will be the new "default" wheels, as we do quite a lot of gravel.

torger

Haven't had that much time to ride, but here's the finished wheels mounted on the bike. So far pleased with the performance and they feel stiff enough.


Tandem with new aero wheels