out of round paired spoke wheel
 

I have a new bike with Bontrager SSR paired spoke wheels (20 front, 24 rear). The spokes on the rear got very loose after the first ride, the LBS has retensioned it and the wheel is ok but slightly out of round. I doubt that it's enough to cause any problem but it's enough to bug me especially on a new bike.
Two questions:

1. how far out of round does an otherwise true and well-tensioned wheel have to be before it's worth the trouble of messing with it?

2. I have done simple lateral truing on traditional wheels but have never touched a paired spoke wheel before. Should I be afraid to give this a try?

If you can't feel it while rolling fast, and it's not enough to put your brakes off the braking surface, then you're ok -- as far as the roundness goes.

FWIW: a "well tensioned" paired spoke wheel is an oxymoron. Consistent tension is key to long wheel life, and paired spoking has inconsistent tension by nature.

I mean, of course, that the spokes all have similar and adequate tension, not that tension is constant along the entire rim. Do your traditional wheels have consistent tension between the spokes? :)

I would not have gone out of my way to buy a paired spoke wheelset, it just came with the bike I wanted. However it does seem to me that there is some advantage to having the left and right spokes pulling on essentially the same part of the rim. Not saying this is better than traditional spoke patterns overall, what with the small number of spokes and large gaps between pairs. But I don't think the design is all bad with no good.

Make the LBS fix it, it's not like it's going to get better over the life of the bike, and the longer you run it the more weird brake wear you put on it.

No offense to the OP, who seems to know what he's doing, but I wish Trek would make people sign a waiver that says something like "I realize that these wheels are an annoying, futzy design that doesn't really benefit entry- and mid-level riders that much, and totally sucks for clydesdales. I accept that trek only really puts them on stuff because they look cool and sell a lot of bikes." I see so many people having probelms with these rigs it's not even funny, and so many of them just won't accept that it's not better for them just because it's "what the pros use."

Sort-of touche' :)

Paired: clusters of even tension.
Conventional: as even tension as possible with a finite number of spokes

:roflmao:

It's an interesting design invented in the 1890s. Generally, it's probably pretty fast in a race, but nothing I'd want to train on. Bontrager makes some tandem wheels that seem to hold up really well, but not that many people put 10,000 miles on a tandem in a year, so it's tough to compare with a racer's training schedule.

I'd go back to the shop and make them true it again. According to the manual here:http://www.bontrager.com/assets/File...ile325_970.pdf Bontrager wheels are trued to +/- .4 mm. If you can feel some bounce when you ride, you are definitely out of spec.

em

In that case Bontrager does not practice what they preach. My wife's 5200 Trek with Bontrager Race Lites were way out of true and had uneven tension when they were brand new out of the box. The front wheel has a 1mm lateral bow in one spot.

Al

From Trek: wheels are considered true within the thickness of a credit card.

As for Al1943's case, blame for out of true new wheels falls on the dealer you bought the bike from, not Trek. No matter what bike it is, I true the wheels out of the box (as any LBS should do on any bike), even on a $5,000 Cannondale Six13. If the wheel is out of true when you get the bike, someone at the shop dropped the ball.

So the manufacturer is not responsible for quality control? I didn't know that. I always assumed that when you build something you build it right.

Al

I can't feel a bounce when I ride the bike, but the out of roundness is more like 1 or 1.5 mm than 0.4 mm.

I did take it back to the shop because after riding about 5 miles the creaking sound came back. The LBS said they would loosen all of the spokes and then tighten them all up again and make it nice and true. Hopefully I will have no more twisted spokes and it will stay true and silent for more than a few miles!

I agree that the LBS should check the wheels more carefully than mine did before selling the bike. However, it seems to me that this wheel was not built to what could be considered a reasonable standard.

My son's bike came with a rim that was out-of-round, don't remember the wheel brand, the bike was Specialized. There was no way to make it round by adjusting the spokes. The LBS and Specialized agreed and replaced the wheel. Sometimes trying to round out a wheel can lead to uneven spoke tension that can be problematical down the road.
Park makes a tensiometer available for about $55, a good investment.

Al

Is there any reason to think they are faster?
 

Why would they be appropriate for the high-performance athlete? All things being equal, what advantage could they give? More aerodynamic? When the members of the spoke pairs are not in the same plane?

Just wondering.

Klister

I never said that, but there is NO manufacturer that ships a perfectly true wheel (except Cannondale and Burley on occasion). Its understood when you assemble a bike that truing the wheels is part of the process. If the LBS didn't catch an out of true wheel, I would question their compentency. Every bike that leaves our store is checked over as it is being built by the mechanic building it (every wheel goes in a truing stand, no matter what), then checked by a 2nd mechanic when its done being built, and then checked over again when it is bought and delivered. This is the way its worked at any bike shop I have worked at, and if you miss and out of true wheel, blame falls on the shop. Just because a wheel arrives out of true doesn't mean it isn't built right, a lot can happen during shipping/packaging, etc.

The advantage of fewer spokes is that the wheel is more aerodynamic. When you reduce the number of spokes in a conventional wheel, the rim can bend laterally between the spokes, because of the greater tension in each spoke and because of the longer span between spokes. To resist that bending, you need to use a heavier rim. With a paired spoke wheel, the lateral bending moment between spokes is minimized, allowing the use of a lighter rim.

em

A wheel is well tensioned when all the spokes have reasonably equal tension. A paired spoke wheel can be as well tensioned as any other wheel. The rim is held in compression, not tension, and that compression is more or less equal everywere on the rim for all spoking paterns. The lateral bending moments vary along the rim for all spoking paterns, but they are smaller for paired spoke wheels. That's why paired spokes are superior for low spoke count, lightweight wheels.

em

Wow, you drank the punch, huh? :rolleyes:

There's a tradeoff between dealing with the lateral bending of the rim and dealing with long sections of the rim being unsupported. The only way to deal with either is to make a stronger rim. As it turns out, the minimal lateral bending of an even spoke spacing is much easier to deal with than the longitudinal weakness with paired spoking. This is evidenced by the failure numbers we see in the Rolf threads. Granted, many cyclists are forced to ride Rolfs because they are spec'd on so many bikes, so that will raise the numbers.

Another consideration is that paired spoking is actually LESS aerodynamic than even spoking due to the eggbeater effect of having one spoke travel straight through the turbulence of the leading spoke. The old Rolf Vector Comps were more aerodynamic (wind tunnel tests) than the "better" Rolf Vector Pros, because there was more distance between the pairs.

Lightweight doesn't require low spoke counts either. The lightest aluminum clinchers made are American Classic Sprint 350s, and they are pretty conventional with 28/32 spoke counts. Rolfs gain weight by making a heavier rim to compensate for the high-fashion spoke pattern. Weight is overrated anyway, but that's another argument.

But hey, Rolfs look great, so everyone should wear a pair! :D

You read a lot into what I wrote. Of course wheel building involves various trade offs, and I only described some of the solutions to the problems caused by using fewer spokes. I never said low spoke count wheels were necessarily lighter, or that paired spoke wheels were more aero than an equivalent spoke count conventional wheel.
A wheel is supported by compression in the rim. If all you had to deal with was the vertical load, you could build a wheel with 3 spokes. as long as you suffiient tension on each spoke, there would be no need to use a heavier or stronger rimn. It would be laterally unstable, and susceptible to pothole damage, but it would easily support you weight. There is no "tradeoff between dealing with the lateral bending of the rim and dealing with long sections of the rim being unsupported." Increasing the spoke count satisfies both requirements. The true trade off is between low spoke counts and lightweight rims. A paired spoke patern changes the trade off a little, allowing adequate lateral stability with a slightly lighter rim (for the same spoke count), at the expense of a wheel that is somewhat more easily damaged by road hazards. Whether the average rider (or even racers) needs a paired spoke wheel or any low spoke count wheel is another issue.
Theres's no doubt that low spoke count wheels are less robust than high count wheels, but this thread started with a story about a Bontrager wheel that was delivered out of spec. Maybe those failures have more to do with quality control than with the fundamental design. So far, I've had pretty good experience with my Rolfs.

em

Actually, in a lab, all you'd need to support the vertical load is one spoke. But we don't ride in labs.

I don't know for sure how to explain this, but unsupported length of rim (the space between the spokes) is radially weaker. Even though the spokes are pulling on the rim, they prevent it from bending radially inward when you hit bumps. If you have a bigger space without spokes, it is more vulnerable to bumps. You will see that paired spoke wheels with flat spots frequently have them between spoke pairs.

To look at it a different way, since you agree that more spokes will make a stronger wheel, then why is that so? Why would more spokes make a wheel stronger? Why not just use stronger spokes? When a rim bends in radially, that is accompanied by a slight outward adjecent bend on each side. If there are spokes there to resist the outward bend, then the rim can better resist deformation.

My assertion is that paired spoke wheels are less robust than evenly spaced patterns with the same spoke count on the same rim. They're also less aerodynamic.

No, the minimum number of spokes for strength in the vertical plane is 3. A 2 spoke wheel might support some weight, but the spokes would need to be as strong compression as in tension, and it would be impossible to compress the rim enough for optimum weight bearing. A flexible rim with 1 spoke would collapse immediately under any load.
In 4 posts, this is the third serious misunderstanding of the structure of spoked wheels.
That assertion can only be proven with reliable data. I have an open mind on that, but so far, my anecdotal evidence is that my paired spoke wheels are as reliable or more reliable than most of my conventional wheels. My best guess is that the total spoke tension is more important than the spoke patern, and the theory is that a paired spoke wheel can brought to a higher tension without distorting the rim laterally. That implies that paired spokes would be stronger, but as you pointed out, it's all about trade offs. The larger span between spokes might make them a little more susceptible to pot hole damage, even if they are stronger otherwise.

em

You didn't say anything about strength in a plane. You said "vertical load," and a single spoke will support a vertical load like this:
http://img393.imageshack.us/img393/3650/onespoke3lw.jpg

This wheel won't roll or take any force other than vertical. But in the vertical direction, it's just fine, and it works in your stated case .

I know, but you're learning. You'll probably have it figured out soon ;)

Here's some aero data on wheels (see "Vendor Data" at the bottom). Notice that Rolf has a surprisingly high coefficient of drag -- even compared to direct market competition (Mavic Cosmic):
http://www.bsn.com/Cycling/WheelAerodynamics.html

It's really tough to say what's more reliable from the evidence you and I have available. My point is that even if they were as reliable, why bother if they're less aero?

Of course, I've already argued that the spoke pattern makes the wheel weaker and less aero...

$850 is a lot of cash to spend on benefits that may not even exist. If the features (strength and aerodynamics) do exist, then why isn't Rolf flooding the cycling world with their test data? All they post on their site is comparative rim weight and rim depth. No durability test numbers. No wind tunnel test numbers.

They're still wheels. They roll. They mostly hold the bike of the ground. They're light. So, they do work, but I don't see how they're so expensive with nothing setting them apart other than looks.

I picked the bike up today. The wheel is now perfectly true and round to my eye, and the spokes are nicely tensioned. Hopefully it will stay that way! If it goes out again the shop said they will get me a new wheel. Thanks for the information everybody.

But I don't think anybody answered this question -- how much harder is it to true a paired spoke wheel compared to the usual kind?

Wheels get tougher to true with either low spoke counts or high tension. Paired spoke wheels feature both, so they are harder.

I've trued a couple on friends' Vigors before ride departures, and found that the claimed "high tension" wasn't high enough to make truing difficult, but I didn't have my tensiometer with me. They've always been easy enough for me to true them pretty quickly on the roadside like that. Both times the wheels had a loose non-drive spoke on the rear wheel. This is an easy fix to make on any wheel, so my experience may not apply to general truing.

If I had a typical paired spoke wheel, like a Bontrager Race Lite, to compare to a conventional 32h 3x wheel, and if both rims were built with close tollerances near perfect, then I could true them in about the same time, maybe a bit faster on the paired spoke wheel. But after both wheels had been ridden 1000 miles I would expect the conventional wheel to true better and faster because there are more spokes with smaller gaps between spokes. The problem with the paired spoke wheels is the large gaps between spokes where you have no control over lateral flex or bending.

Al