55

Frames designed for women do have that part - its called a top tube. Historically women wore skirts, so a lower frame in the middle made it easier to mount and dismount, and was less likely to accidentally show an ankle. This picture shows a modern "woman's frame" with the top tube paralleling the downtube, and attaching to the seat tube lower down. ...


36

Back in the day, women primarily wore dresses, and getting the dress over the top tube was difficult and awkward. So the women's bike was developed with a slanted or sloped top tube so women could step though with their dresses and ride without their dresses coming up. Although the top tube shouldn't be hitting you in that "embarrassing part" when you're ...


31

I think several of your assumptions are incorrect: no high speeds: rim dynamos spin quite fast, up to 10,000rpm, and that does require effort on the part of the designers. Typically the drive wheel on those will have a radius of about 1cm, or a circumference of 3 1/3rd cm and 30 revolutions per metre. At 10m/s (30kph) that means 300rps or 18000 rpm. This is ...


20

The short answer to your first question is "the power savings from using ceramic bearings compared to good steel bearings is almost zero." The short answer to your second question is "yes, it is possible to measure the difference but it's not easy." The longer answer, and the support for the shorter answers is below. First, however, it depends a little on ...


18

There does seem to be an upside down U-curve of spinniness on pedals with the horizontal axis being price and the vertical axle being how many rotations it makes when spun by hand. Cheap pedals are genuinely horrible. They just have a sleeve bearing, bushing, or single set of ball bearings. Tolerances are atrocious because they were made by drunken lemurs, ...


13

Anti-sieze is a corrosion preventer. It is not a lubricant. Generally, using it on threaded parts is acceptable, but using it on bearing races, bearings, pressfit installation points, seatposts, handlebar stems, etc... is not a good idea. There is no hard and fast rule, but if you think about the purpose of the "lubricant" on the specific part, you should ...


12

That looks like the compression ring for a threadless headset. Images by keithonearth on Wikimedia Commons, reproduced under Gnu free documentation license More information found at Sheldon Brown


11

I refurbish a lot of older bikes for re-sale. The first thing I do is to pop off the wheels and manually turn the axles to see if the bearings are suspect. If the axle turns roughly, has side-to-side play, or is hard to turn...They probably do. There should be "no more friction than supplied by the grease" when turned by hand. You cannot do this with ...


10

Firstly I disagree with the comment about high speed. The highest velocity bearings are plain: crankshaft bearings in a full size car engine are plain, whereas in a radio controlled model, ball bearings are used. Where velocity (rpm x diameter) is high the oil wedge effect tends to centre the shaft (hydrodynamic lubrication). This can be further enhanced if ...


9

I found a component diagram for these pedals here. Here's the main diagram: Looks like all the bearings are mounted onto the axle and secured with a bearing preload and lock nut at the outboard end. The axle and bearing assembly is then threaded into the pedal using the threads on part 2 - that's why the torque spec is printed on its shoulder. Obviously ...


9

It is indeed a compression ring, David D’s diagram is helpful to illustrate the following: What it does is transfer the force of the cap bolt to the inner face of the cartridge bearing. That then compresses the ball bearings inside properly, as they need to be, which is why the split ring is called a compression ring. The angled face must fit into the ...


8

There are several possible causes of noises you can get from your bottom bracket. Bad bottom-bracket bearings Bad pedal bearings Loose crank arms Loose bottom-bracket cartridge Loose chainrings Of these the loose crank arm (which may be silent or may be accompanied by a creak on each stroke) is probably the one needing the most immediate attention, since ...


8

Pick the bike up so the problem wheel is off the ground. Grasp the tire and push it back and forth (left/right relative to the frame). If you can get any perceptible motion then the bearings are loose and need adjustment. While the wheel is off the ground, spin it and watch the space between the rim and the brake block (assuming you don't have disk brakes)...


8

It sounds like your headset is not adjusted. Your stem cap is used to adjust this. Specifically, the more you tighten the stem cap, the tighter the bearings will get, and the less play you will feel. Here is a picture from Sheldon Brown's article on adjust headsets: My process for checking headset adjustment: Check the headset adjust: Grab the front ...


8

Probably never -- headsets can easily last the life of a bicycle for most people without needing an overhaul. If you ride in the wet, it is advisable to have a front fender, though (to reduce the likelihood of needing an overhaul even further).


8

It's the most common kind of threadless headset. External cups, caged bearings. It uses a 5/32x20 retainer (bearing size x count), which again is the most common type and available online and at most shops for cheap. If you want you can also use loose 5/32" balls, which is more of a hassle but slightly better for headset longevity because you get more ...


8

Anywhere there is a cone, there is also a "race" that the bearings sit in. The cone holds the bearings in place against the race. The picture you have posted shows the very definition of "pitted cone". As the wheel turns there will be increased friction when the bearings contact the pit. It will get larger and eventually the bearing will freeze in the pit. ...


8

Put the 3/16" bearings back in, even if you have to buy some fresh ones. Your quarter-inch bearings are not sitting in the bearing raceway right which is causing the too tight/loose problem. They will never sit right, and if you do ride on them the bearings will run on the wrong parts of the cup and cone races. This will lead to early failure of the cup ...


7

It's not unusual for an asymmetric shaft (on some rear wheels or solid-crank bottom brackets, eg) to have different numbers of balls in one side vs the other. But it's a little unusual for a standard front hub. And if there's intentionally a difference then there would be a small but visible difference in the size of the races as well. Likely the hub was ...


7

I don't have the source at hand, but from what I've read, converting your wheel bearings to ceramic will net you something like a 1 W savings at racing speeds, thanks to reduced mechanical losses. A ceramic bottom bracket would result in less improvement. Considering the rider is putting out 200+ W at racing speed, the savings are clearly minor. Additional ...


7

The common Shimano Dynamo hubs don't actually use sealed cartridge bearings, see the DH-3N71 and DH-3D72 techdocs. Shimano dynohubs do use good seals, however, and should hopefully be maintenance-free for many thousands of miles. Alistair Spence has a good exploded view of an Alfine DH-S500, which is very similar to the DH-3D71. He also links there to a ...


7

I've also never seen a bearing ball fail like that. In Jahaziel's answer to this question: When do bearings need to be replaced? he notes that in Honduras where he lives they sometimes could only get cheap Chinese bearings that "used to 'peel off' like an onion". Perhaps you got some of those? See also the response of "Mike" in this thread [1], who had ...


7

With a trapped axle like that you use a hammer, ideally a soft face one or I use a bit of wood as a pad. Hold the block against the axle, tap the block with a hammer. Holding the wheel in your hand rather than blocking it against a solid surface also reduces the impact. You will still probably damage the bearings, so preferably don't do this until you have ...


7

First, not all full suspension bikes use bearing for all pivot points, and some bikes don't use them for any. They use bushings instead. That said, assuming you have bearings at all points on your bike: There are 2 types of bearings damage which require replacement in a suspension system. The first, bearing play, means lateral movement inside the bearing ...


7

Can you clarify if you mean a cup and cone housing, to change from loose bearings to bearings in a metal retaining cage? Like this: ANSWER 1 These can totally be used instead of loose bearings. There are fewer balls to carry the weight, and over time the cage may break down and get chewed up. OR do you mean cartridge bearings with ABEC ratings like this:...


7

My father worked at Fafnir Bearings for 35 years and even though it ceased to exist as an independent company about 50 years ago, the trademark is still active. In the post World War 2 era, Japan rebuilt its bearing industry using Imperial standards. Bearings are a strategic technology in a manufacturing society and any rational government will promote ...


7

I haven't done this one in particular, but here are some things that may be applicable: The spacer between the two bearings may be a tubular spacer that with the axle out is simply held in place by friction. If so, with some persuasion you can nudge to one side, allowing you to hit the outer bearing with a punch from the inside out. The inner bearing may be ...


7

Bearings are of standardised dimensions. In your case 6902 is 15 x 28 x 7 (inner diameter x outer diameter x width) and 6903 is 17 x 30 x 7 (which you probably got from Google). Thus, dimension-wise, as long as you stick to the original dimensions, you're good to go. In other words, you can safely replace these bearings with others of the same size (6902 ...


6

It depends on the kind of bearing, but I can offer a little hint. The easy ones are the open bearing, the kind that comprises a race, a cone, bearing balls (or rollers) and (optional in many cases) a ball/roller cage or retainer. These are common in non sealed hubs, non sealed headsets and non sealed bottom bracket. For these types of bearing, proper ...


Only top voted, non community-wiki answers of a minimum length are eligible