58

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 ...


32

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 ...


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, ...


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

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 ...


10

Searching for "ndm rotational speed" finds that D and d are outer and inner diameters of the bearing. n is not the usual symbol for speed, but neither is the final unit "millimeters per minute divided by pi" an usual unit. And here we go: A slightly optimistic approximation for road bike speed would be 10 m/s (36 km/h, 22.5 mph) and wheel circumference 2 m....


9

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 ...


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

I would recommend doing two things: Reassemble the hub with the thickest grease you can find (within reason). It might slow you down a little, but it will help the bearings last as long as possible. Make a mark on the back side of the cone that corresponds to where the damage is. When you're putting the wheel on, rotate the axle so that the damaged side of ...


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

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 ...


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 ...


8

Some mechanic might have put a liberal amount of grease in the BB shell and also in the head-tube prior to assembly. Then copiously greased the seat-post as well. Grease has a tendency to migrate, especially in hot weather and move to the strangest places, the bike may have been stored upside down, head or tail-up. Think of it as a gift from whoever put it ...


8

I have sometimes made the mistake of not tightening the locknuts enough, causing the rotation of bearings to drag the cone, tightening it enough for the bearing to bind. The solution is to properly tighten the locknuts. I'v been also in the situation of not having the right tools to remove the freewheel, which makes it more difficult. What I've done to ...


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

Gasoline was used for many years as an inexpensive readily available solvent. There are a couple of real life issues with using gasoline for a solvent. It is very flammable thus a fire hazard. It is absorbed through the skin and it is toxic when inhaled in high concentrations. You have to find a way of disposing of the remaining dirty solvent. Pouring it on ...


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

The difference is in the lubricant. Ball bearings need to be lubricated with a sort of grease. This grease is in your wheel hubs and also in your pedal bearings. The grease is gooey. Gooeyness means that some very small amount of energy is consumed as the stuff moves around. You don't notice this energy loss on a wheel because wheels have a lot of ...


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

You stated that your frame is a Wilier Imperiale. I'm not certain what year this applies to, but it is very likely to have a proprietary bottom bracket standard known as the BB94 or BB93 standard. Per the Cyclingtips link: Wilier designed its BB94 (later re-named BB93) around Campagolo’s Ultra-Torque cranks. Seats for the bearings were moulded into the ...


7

You're going to need to replace the entire BB. The drive side cup is reverse threaded. (This isn't true of older bikes of certain nationality, but the nylon cable guide suggests yours is new enough for this not to be a concern.) To answer your questions: The squareness of the cups is very important for the BB to function. To get the cup out without ...


6

That looks fixable to me. What probably happened is the locknut was loose, and continued riding caused both cone and locknut to unscrew. It's a good job you've stopped riding that bike - riding on that hub now would cause significant damage. When a hub has a bit of play, the balls are free to move across parts of the cup and cone that aren't designed to ...


6

A bearing that is adjusted too tight can actually seize completely. This happened to me once. I overhauled my front hub and tightened the bearing cones too much. Result: a front wheel that plain stopped turning at some point. Too tight adjustment will exert more pressure on the cones and cups, and will probably wear out the bearings faster than too loose ...


6

Using gasoline as a solvent won't harm your bearings. It may dissolve some plastic components though. The drawbacks of using gasoline are mainly due to its properties other than as a solvent: it's volatility, flammability, and that it is toxic, as it will harm your skin if exposed to it for long periods of time, and that it requires careful disposal. ...


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