Archive | Hubs/rims

My PBP Bike: The Wheels

When I asked which part of my bike for last summer’s Paris-Brest-Paris our readers wanted to hear more about, the answer was: “Everything.” So I’m writing a series of posts about the parts of the bike. I’ve already talked about the frame and the centerpull brakes. Today let’s look at the wheels.

When thinking about the wheels for my new bike, I started with the tires I wanted to run, since everything follows from that. It was tempting to go with a really huge tire, like our 54 mm Rat Trap Pass. Our testing indicates that they don’t roll any slower, but there are other compromises when your tires get wider than about 44 mm. It’s harder to fit a rim brake around them. Fenders with good coverage start interfering with the chain. Really wide tires can be more sensitive to tire pressure, and their huge supple sidewalls tend to get deflected more on road cambers.

For a bike that gets ridden mostly on pavement, over huge distances and often at night, 42-44 mm-wide tires seem like the perfect compromise. From that followed that my new bike would have 650B wheels. Why not 700C? Continue Reading →

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New Parts from SON

SON has introduced a few useful products that have us quite excited. First, there is the 12 mm Thru-Axle Adapter.

You may know the dilemma: As the days get shorter, you really want to equip your bike with generator lights, but you don’t want to invest in a hub that soon may be obsolete. Your current fork has quick release dropouts – with or without a disc brake – but your next bike probably will have a thru-axle.

Enter the adapter: Simply slide it into your thru-axle hub, and you’ve effectively converted it to a quick release. You can use it even on a rim-brake bike. And when the time comes, simply remove the adapter and install the hub in a new fork with a 12 mm thru-axle. This ingenious widget works not only with generator hubs, but with all thru-axle front hubs.
Traditionally, SON lights have connected to their generator hubs with two simple flat spade connectors. These connectors have been trouble-free, and if they ever loosen, they can be fixed by the roadside.
However, some cyclists remove their wheels frequently and prefer a simpler, more elegant connection. SON’s new coaxial adapter (above) has been engineered to provide reliable service for decades of hard use under the toughest conditions. That means that we finally don’t have to worry about electrical connectors any more – in the past, they were the most failure-prone parts of a randonneur bike. The adapter (top) plugs onto the spade terminals of the hub, and then you connect the light with the neat coaxial connector (bottom).

SON’s Edelux lights are available with the coaxial connectors pre-installed. The adapter for the hubs is included, too, so it’s a plug-and-play solution. (And if you ever feel you’ll want the spade connectors instead, they are easy to install.)

The new coaxial connectors are such a breakthrough that you’ll want to use them wherever you need to make removable electrical connections on your bike. That is why we offer them separately, as males, females and complete sets.

The last new product is for everybody who wants to charge cell phones, GPS and other devices while riding. It’s a simple splitter box that you wire into the lighting circuit, anywhere between the generator hub and the headlight. Plug in the included coaxial connector, and you are ready to charge. You can use whichever charger you prefer (not included). After you solder your connections, the box gets covered with heat-shrink tubing. Just make sure that you wire the splitter box so the socket points downward. Otherwise, water can run down the wire and into the connector, which won’t be so good in the long run.
All these new products are available now. Click here for more information.

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New SON Generator Hubs!

We are excited to announce the latest SON generator hubs. The biggest news is the connector-less SL system for thru-axle hubs: Now you can remove your front wheel and its generator hub without having to disconnect any wires, even with a thru axle.

The system consists of three parts: The heart is the SONdelux 12 generator hub. The SONdelux is the lightest generator hub in Schmidt’s program, and it has the least resistance, so it was a natural choice for this application.  The flanges are spaced as far apart as possible while still leaving room for the disc rotor and caliper.
This hub has proven itself for many thousands of miles. What’s new is the lack of external connectors for the lighting wires. The current is transmitted via the axle (positive) and an insulated ring that is pressed onto the axle (negative). Like its counterpart with external connectors, the connector-less SL hub is available in black or silver.

The hub mates to a special dropout. By the way, the machining traces that form the funky pattern in the photos can be removed by your framebuilder. Above you see the outside, which looks like a standard stainless steel dropout for 12 mm thru-axles (12 x 1.5 mm thread).

It gets more interesting on the inside, where one dropout has a recess…

… into which an insulated contact plate fits. As you install the hub, the axle connects to the dropout for the positive contact, while the insulated ring on the hub mates to the dropout’s contact plate, which is insulated as well. A wire goes inside the fork leg from the contact plate through to the lights. That way, you provide a path for the current to flow from the hub to the light without any exposed wires that can get snagged or break from repeated flexing during installation and removal of the front wheel.
We have a small number of contact plates and dropouts in stock, with more to come once production catches up with demand. And of course, the connector-less SL system has been available for non-disc hubs all along, and we have those components in stock, too.

That isn’t all the generator hub news! Many modern rear hubs are black, and we are now offering SON hubs and lights in black to match. We’ve worked with Schmidt Maschinenbau to make our favorite hub, the SONdelux Wide-Body, in black, too. The black hub is available in the standard and connector-less SL versions, with 32 holes. This is a one-time production run, so quantities are limited. If there is sufficient demand, Schmidt will make more for us, and in other spoke counts, too.

We also have the SONdelux Centerlock Disc for quick release forks in black…

… and the Edelux II headlight for hanging mounting. (We’ve been stocking the ‘standing’ Edelux II in black all along.) Now you can choose between silver and black components when equipping your bike with the best and most reliable generator lighting.
All these products are in stock now. For more information or to order, click here for hubs and here for lights.

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Making Strong and Durable Wheels

When building a bike, one important decision concerns the wheels. How do you get the best performance and still make your wheels strong enough to withstand 20,000+ miles of riding on rough roads without needing service?
By now, most cyclists know that spokes don’t break from overloading, but from fatigue as the spoke is loaded and unloaded when the wheel rotates. The wheel flattens at the bottom, which unloads the spoke at 6 o’clock. With each wheel revolution, every spoke passes through that spot, where it is slightly detensioned, and then tensioned again. Over time, that causes the spoke to fatigue.
To get the maximum life out of your spokes, you want the detensioning to be as small as possible. That is what double-butted spokes (above) are for: They are thinner in the middle, so they can stretch more, which means that they don’t detension as much as a thicker spoke would. Yet the ends, where spokes fail if they break, are thick and thus will last a long time. It may seem counterintuitive at first, but the thinner mid-sections make double-butted spokes more durable than thicker straight-gauge spokes.
Wheels tend to go out of true when you hit a bump and a spoke detensions so much that it goes slack. As the spoke is tensioned again, the nipple unwinds a bit. Now the spoke has less tension, so it will go slack more often, allowing the nipple to unwind more and more… For more information about the basics of wheel building, I recommend the late Jobst Brandt’s excellent book The Bicycle Wheel.
Now, let’s look at the specifics of building a strong wheel.
How many spokes do you need? For many years, 36 spokes was the standard (above), then it became 32 as modern spokes became stronger. On my René Herse (top photo), I use a 28-spoke front wheel. I built the wheel six years ago and never touched it again. If the rim hadn’t cracked (different story!), I am sure it would still be going strong today.
We can use fewer spokes, because the wider tires we ride today transmit far fewer shocks to the rim. Imagine hitting the bump above with a 23 mm tire: Even if you don’t bottom out, your tire is so hard that much of the impact will be transmitted to the rim. The big, soft tire not only transmits less shock to the rider, but also to the rim.
With smaller 650B or 26″ rims, the spoke bracing angle is greater, which makes the wheel stronger as well. That means that 28 spokes are plenty, even for rough roads.
However, the SON Delux hub I usually ride on my Herse has very narrow flanges, which results in a smaller spoke bracing angle, negating the benefits of the smaller 650B rims. For the Oregon Outback 363-mile gravel race, I put on a wheel with an old SON20 generator hub that has wider flanges (above). When you negotiate rough terrain, your wheel can slip while it’s pointing sideways, then suddenly catch and regain traction. If the wheel is not strong enough, it can collapse into a potato-chip shape, and your ride is over.
We wanted a wider spoke bracing angle, so we asked Schmidt Maschinenbau for the Wide-Body Delux hubs, which have the widest flange spacing possible and thus build into the strongest wheels. Compass now offers these hubs in 28 holes, in addition to the 32h and 36h that have been available for a few years. If I had a Wide-Body hub on my bike, I would have been perfectly happy with 28 spokes for the Oregon Outback.
shimano_disc_blogThere are cases when a front wheel with more than 28 spokes makes sense. With disc brakes, your flanges are more narrowly spaced to make room for the rotor – that is why there is no Wide-Body Disc hub – and the entire force of braking is transmitted by the spokes. In this situation, a 28-spoke wheel usually is OK, but 32 spokes gives you an additional margin of safety. The same applies for 700C wheels (larger-diameter rims result a smaller spoke bracing angle), or for very heavy bike/rider combinations. For tandems, I’d go with 36 spokes.
Compass offers the excellent SON Delux Wide-Body hubs with 28, 32 and 36 holes, so you can choose the spoke count that is right for you. We also offer the Delux for disc brakes with 32 holes, both in quick release and thru axle versions (above).
What about the rear wheel? Here, too, the answer is: “It depends.” If you have a strong rim, then 28 spokes may be enough. When HED send us test wheels with their Belgium rims a few years ago, they used 28 spokes front and rear, and they held up fine even when we rode them on mountain bike trails. One reason is that the rear wheel never sees significant side loads.
However, the rear wheel has a much narrower spoke bracing angle to make room for the freewheel/cassette. That is why British builders often used rear wheels with 4 or 8 more spokes than the front. I did the same on my René Herse, which has 36 spokes on the rear. Most wind tunnel studies indicate that the rear wheel is in such turbulent air that its aerodynamics don’t matter much, and the little extra weight isn’t a big deal, either.

Next, let’s talk about rims: Most rims today are stiff and strong. If rims crack, it’s usually caused by poor design or sub-standard materials. Once you’ve eliminated those problems, what you want from your rims is a good fit of the tires. With classic rims, it needs to be good enough to seat the tire automatically as you inflate it. And the tire shouldn’t come off even if you have a sudden blowout on the front. With tubeless-ready rims, the fit needs to be even more precise, so the tire seals easily and doesn’t blow off the rim despite lacking a tube that reinforces the joint between tire and rim.
Compass offers two rims:

  • The brand-new Pacenti Brevet rim combines classic appearance with tubeless-ready construction. Compass has them in stock in 28 and 32 holes.
  • The HED Belgium Plus is a modern, lightweight, wide semi-aero rim. It is tubeless-compatible, with a tire fit that is consistently excellent. A few of us have been riding them for a few years now (above Theo’s bike), with zero need for truing and easy tire mounting. Black anodized and available in 28 and 32 holes for rim brakes, and in 32 holes for disc brakes.

For each of these rim/hub combinations, we now offer spoke packages with the highest-quality, double-butted, superlight Sapim Laser spokes (2.0 – 1.5 – 2.0 mm) and aluminum nipples. That makes it easy to build a generator hub wheel that is perfect for your intended use: Just select your hub and your rim, and then order the spoke package that goes with this combination. (We also offer the spokes individually.)
Click here for more information about Compass wheel goods.

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Mounting Tires on Rims with Deep Wells

Sometimes we get a call or an e-mail from a frustrated customer: “I have a brand-new set of your tires, and both wobble when I mount them on my rims.” In most cases, it is not the tires’ fault. Usually the problem stems from the difficulty of mounting tires on poorly designed rims. However, there are some tricks for mounting tires on these rims.
Above, you see a correctly mounted tire. Most tires made today have a line molded into the sidewall (arrows). This line must be visible all around the tire, and parallel to the rim edge. The line not only helps seat the tire, it also serves as a visual indicator that the tire is concentric with the rim. (Usually, the line is a little higher above the rim, but always parallel to the rim edge.)

Above are three 700C rims, which all have the same outer diameter. However, the cross sections show that they are very different on the inside. Rim 1 is a proven design. Rim 2 has a shallower well (the place where the tire mounts). Rim 3 has a very deep well. Tires seat differently on each of these rims.

When you mount a tire, the tire beads need to go over the rim’s hook (above; the foam is used to hold the tire in shape). Tire beads are what holds the tire on the rim. They don’t stretch much – otherwise, the tire would just blow off the rim when you inflate it. The well of the rim has a curved bed. When you mount the tire, the tire beads drop into the center of the rim’s well bed. This provides enough slack to get the last bit of tire bead over the rim’s hook on the opposite side. As you inflate the tire, the beads slide up the rim’s curved well bed until they seat tightly underneath the rim’s hooks.
The photo above shows Rim 1. The tire’s beads fit perfectly onto the well bed and underneath the hook. The tire will seat concentrically by itself as you inflate it. The bead seat diameter is 622 mm, as industry standards specify (ETRTO). This is how rims should work.

Rim 2 has a shallower well. The bead seat diameter is 624 mm, which makes the well bed higher than the standard 622mm. To seat correctly, the tire has to stretch by 2 mm in diameter. This translates into 6.5 mm (1/4″) along the tire’s inner circumference, which is a lot of stretch for a tire bead. Often, the beads don’t stretch enough, and don’t quite reach the rim walls (arrow). Then the tire will wobble on the rim. Putting talc (baby powder) on the tire bead may help it slide into position. A very thin and slippery rim tape also can be helpful.
The high well bed also makes the tire difficult to remove: It is difficult to insert a tire lever underneath the tire bead, because it is stretched so tight onto the rim.

Rim 3 has a very deep well. The tire is not supported by the well bed at all (arrows). The tire has to float. When you inflate this tire, it cannot just slide into position on the well bed. You will have to manipulate the tire until it is seated correctly.
Unfortunately, several common rims for wider tires, including the Velocity Synergy, several Velo-Orange models, and the no-longer-available Grand Bois, have overly deep wells. This makes mounting tires difficult. The sole advantage is that the tires come off the rim easily.
On their 650B rims, Synergy tried to “fix” the problem of poorly seating tires by increasing the overall rim diameter. In my experience, this has made things worse, because now the hook is in the wrong place. There is nothing to locate the tire: The well still is too deep, so the tire cannot sit on the well bed. And the hook is too high, so the tire cannot sit underneath the hook.
If you have rims with wells that are too deep on your bike, there are some tricks for mounting tires on them. There even is a “fix” that can overcome the problem of the overly deep wells to a large degree.

On all rims, even well-designed ones, tires often don’t seat well at the valve. The tube is reinforced here, making it stiffer, and it sometimes gets caught under the tire bead. Above, you see how the molded-in line moves away from the rim at the valve. (Often, this is more pronounced.) Not only will this cause the tire to wobble, but if the tube is trapped under the beat, it can chafe until you get a flat tire.

With the tube barely inflated (~5 psi), push the valve stem inward as far as you can. This usually frees the part of the inner tube that is trapped.

Harder to fix is the problem shown above: The line that is molded into the tire sidewall disappears into the rim (arrow). This often happens on rims where the wells are too deep, such as the Synergy Velocity shown here. (The Grand Bois rims we used to sell unfortunately were not much better.) It also can happen if the well is too shallow, and the tire bead does not contact the rim sidewall.

Push the tire to get it into the right place. Inflate it to about 15 psi, and use both hands to push it away from you, until the molded line appears. Go around the tire on both sides until the molded line is visible everywhere and parallel to the rim edge. This takes patience. It can be frustrating, and it’s the last thing you want to do when you have a flat on the road, and all your friends are waiting for you to get back on the road.

To address the problem of the overly deep wells, you can add two layers of rim tape (or handlebar tape, which is the correct width for 23 mm-wide rims). This raises the bottom of the well. Now the tire should seat correctly without as much manipulation.
Do not ride a poorly seated tire! The tire could come off the rim and cause a crash.
Of course, it would be nice to have correctly designed rims, where the tires seat automatically as you inflate the tubes.
Update 3/19/2014: Grand Bois has redesigned their rims with a shallower well, so they fit the tires properly. The new rims are in stock.

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Rim Weight

At Compass Bicycles, we are not obsessive gram counters, but none of us want to carry extra weight on our bikes. A few grams here and there add up quickly to a couple of pounds, and that can make a difference not only in how the bike performs, but also how it feels when you ride it.
There are some components where you cannot save weight without undue compromises, and rims are a very good example. A well-designed clincher rim weighs about 450-500 g (650B) and 480-530 g (700C). To reduce this weight further, you only can remove material in four ways:

  • Thinner sidewalls. Example: 1.3 mm instead of 1.6 mm. Savings: 30 g.* The rim sidewall abrades as you brake. You need at least 0.7 mm of sidewall thickness to keep the tire from exploding. With the thinner sidewalls, your rim can lose only 0.6 mm until it is worn out, instead of 0.9 mm. That means your rim will last only 2/3 as long.
  • Narrower rim: Example: 20 mm instead of 23 mm. Savings: 24 g. On the down side, the rim no longer supports wide tires well.
  • Thinner rim “floor” (the side facing the hub): Example: 0.9 mm instead of 1.0 mm. Savings: 11.4 g. Now there is less material to counter the stresses imparted by the spokes, and the rim is more likely to crack.
  • Bottom of the well (the side facing the tire): Most rims already have the bare minimum here, so there are no further savings possible.
  • Rim shape: A more triangular shape can save material over a traditional box section, but the brake tracks are much shallower. You will have to adjust your brake pads frequently as they wear, otherwise they will cut into the tire (with sidepull and centerpull brakes) or dive under the rim (with cantilevers).

None of these weight saving options are very appealing. In the end, a good rim has a certain weight, and there is little you can do about it.
If you really must have a lighter rim, just ride it, and it will get lighter every time you brake. Of the two rims shown above, one is 70 grams lighter. Both rims started out from the same extrusion (Mavic MA-2/MA-40). The rim on the left is brand-new. The rim on the right has been used for a few years. The abrasion of the brake pads has removed 0.7 mm from each sidewall. The rim has lost 70 g of weight, but it is close to the limit where it becomes unsafe to use.
Even if you are willing to compromise durability and tire support to save weight, all the potential savings add up to only 65 g per rim. If you use a disc-only rim, you save another 30-40 g, but the separate brake disc weighs more than you save on the rim. (And using “disc-only” rims with rim brakes is a bad idea for obvious reasons: the brake tracks are worn out from the onset.)
Here are a few better ideas to reduce the weight of your wheels:

  • Folding tires: A Kevlar bead saves about 70 g per tire. Such a tire performs the same as one with a wire bead.
  • Superlight Tubes. On a 650B x 42 mm tire, using a superlight tube saves about 45 g. The down side is that you’ll have to inflate your tires every couple of weeks, as the air leaks out of the thinner tube more quickly.

Together, the weight savings from lighter tires and tubes are more than you’ll ever get by using a “pre-worn” rim. Light weight components have their place, but they should not come with undue compromises.
* The circumference of a 650B rim is 183 cm, the sidewall is about 1 cm tall. The aluminum removed by making the sidewall 0.03 cm thinner is 183 x 1 x 0.03 = 5.49 cm3. There are two sidewalls, so you remove 9.98 cm3. Aluminum has a specific density of 2.7 g/cm3, so the savings are 9.98 x 2.7 = 29.6 g.

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