Skip to main content
84 votes
Accepted

What is the foam tube on the top of bmx frame for?

It's to ensure that young boys who ride BMX bikes will be able to have children when they grow up. Fine print: More accurately, it’s to assuage the worries of the parents that are buying the BMX for ...
RoboKaren's user avatar
  • 29.2k
81 votes

What is the difference between brake cables and derailleur cables?

Cables: The main difference that I am aware of is the diameter of the cable. Most brake cables are 1.5 or 1.6mm in diameter. Most shift cables are 1.1 or 1.2mm, galvanized shifter cables are 1.3mm. I'...
Nate W's user avatar
  • 9,272
59 votes

What is the foam tube on the top of bmx frame for?

It's to give the illusion of safety.
I Don't Know's user avatar
56 votes

Random piece of plastic

This appears to be a disc brake spacer (block). Such a spacer may be inserted in the disc brake caliper between the brake pads. When the wheels are removed, and hence the brake rotor, an inadvertent ...
gschenk's user avatar
  • 9,778
33 votes

Why is buying a bike as a whole cheaper than buying separate parts and building it?

Economics of scale. For instance, when a bike manufacturer buys thousands of groupsets directly from a component manufacturer, they get a significantly better per unit price than a retailer can. ...
zenbike's user avatar
  • 29.8k
24 votes

What is this device attached to the seat-tube?

It appears to be a clamp-on pump peg that got moved down out of the way either intentionally or from coming loose.
Nathan Knutson's user avatar
21 votes

Is it a good idea to buy second hand bike model that has been discontinued?

Generally it's absolutely fine to buy a relatively new bike, and not worry about component availability. Bicycles are not like cars that have specific components for each model, or at best some ...
Argenti Apparatus's user avatar
21 votes
Accepted

How maintenance-free can a commuter bike be?

The best is probably to look at the so called Dutch bikes - or the bikes offered by subscription services, that are usually designed to lower maintenance requirements and maximise utility - often at ...
Rеnаud's user avatar
  • 20.6k
18 votes

Why is buying a bike as a whole cheaper than buying separate parts and building it?

In addition to economies of scale, you also have to consider the difference in price sensitivity and leverage between a manufacturer and a consumer. If Shimano told Trek that they'd start paying ...
Ryan Cavanaugh's user avatar
18 votes
Accepted

What are the most basic parts of a bicycle which cannot be upgraded over a period of time?

Certain parts of a bicycle are more easily upgradeable than others, while other types of upgrades require special tools, much more money investments or are limited to whatever standards are used in ...
Grigory Rechistov's user avatar
18 votes
Accepted

What is this U shaped metallic piece with 2 holes?

Looks like a derailleur guard It mounts to the rear drop out on the derailleur side. It protects the derailleur from some impact damage. EDIT: 06/19/2021 The comments seem to be running strongly ...
David D's user avatar
  • 21.6k
18 votes

How maintenance-free can a commuter bike be?

The two ‘key’ things for a commuter bike to reduce maintenance are to use an internal gear hub, and to use a belt drive. An IGH has the distinct advantage of everything being encapsulated in a way ...
Austin Hemmelgarn's user avatar
17 votes
Accepted

What is this spring between the fork and the frame?

The purpose of such a steering damper is to stop the front wheel from turning when using a (two-leg) kickstand or while pushing the bike. Not much use otherwise.
linac's user avatar
  • 2,952
17 votes
Accepted

What are these tiny pieces of metal that came with my Giant TCR Advanced 2?

These are to protect your frame from the support bolt on Shimano front derailleurs (I don't know if SRAM have the same). You can see them on page page 7 of this manual.
alex's user avatar
  • 5,766
17 votes

Can a counterfeit Shimano chain be used on an authentic Shimano drivetrain?

You can normally use chains from other legitimate vendors, be it SRAM or KMC or something else. You do not need to use Shimano™® chains only. But no-one can tell you whether your chain is of ...
Vladimir F Героям слава's user avatar
16 votes
Accepted

Are Shimano 10 speeds going away?

They're trying to sell you stuff. More expensive stuff (have you looked at 11 speed consumable (chain+cassette) prices vs 10 speed?). I would not bother upgrading. As groups go to higher and higher ...
Batman's user avatar
  • 46.2k
15 votes

Can a new chain significantly improve the riding experience? If yes - what else can?

The one substitution that will probably give you the most bang for your buck is better tires. High-quality tires roll with much less rolling resistance, have better grip, weigh less, and roll over ...
Adam Rice's user avatar
  • 30.1k
15 votes

What are the most basic parts of a bicycle which cannot be upgraded over a period of time?

Any and every part of a bicycle can be replaced, including the frame. (Many people would probably regard a different frame as a different bicycle though.) You ask whether there are components that '...
Argenti Apparatus's user avatar
15 votes
Accepted

What is this stamped metal piece that fell out of a new hydraulic shifter?

Providing the 7900 is the same, I’m sure it is but someone more qualified can chip in if it’s different. How did it fall out ? Shimano have a proper tool for removing them. Info from here Fawkes
Dan K's user avatar
  • 1,098
14 votes

Why are ball socket allen wrenches

The ball-end wrenches are really handy when there's an obstruction in front of the bolt, since they can be inserted at a slight angle. But since the contact area is smaller, you're slightly more ...
Mike Baranczak's user avatar
14 votes
Accepted

What is this device attached to the seat-tube?

Are you sure the upper part has not been sliding down such that we can really take a clue from the distance between the two parts? I suspect that the two parts of the fixture are meant to hold an air ...
Christian Lindig's user avatar
14 votes
Accepted

Can a counterfeit Shimano chain be used on an authentic Shimano drivetrain?

The main problem is quality, in terms of dimensions and variance. If you think its an 11 speed chain but someone has just repackaged some 10 speed chain, then there will be issues. Likewise, if it ...
Criggie's user avatar
  • 125k
14 votes
Accepted

How much faster would I go with a better road bike?

That's really hard to answer. Every year, bike makers come out with claims that this year's model is N% more aerodynamic than last year's, etc. Although they don't always give hard specs on CdA. Also, ...
Adam Rice's user avatar
  • 30.1k
13 votes
Accepted

Why do folding bikes usually have MTB components?

Great question! I think the market drives this -- not necessarily just the folding bike market, but the component market. Mountain bikes have been the predominant type of bicycle for the past ...
RoboKaren's user avatar
  • 29.2k
12 votes
Accepted

Why is there a koozie on this bike's chainstay?

That is a "chain stay protector" and it is installed in, let us say, a non-traditional way. Typically it would be a couple inches forward of where it is. As the name suggests, the purpose of the pad ...
JP May's user avatar
  • 340
12 votes
Accepted

What is the name of this small component inside Shimano Tourney STI

This part is officially called "cable hook" and "cable hook unit" in Shimano docs. See attached image (I won't link it because the PDF is not hosted by Shimano) and this document (page 7).
Klaster_1 Нет войне's user avatar
12 votes

What is a substitute inner tube for 27x2.125" tyres (in Prague)?

Tl;dr: use 700c or 29" 27x2.125" is very rare. 27x2⅛" would be more likely, and wouldn't quite be the same thing, but for tubes the answer would be the same. Generally though, 27"...
Chris H's user avatar
  • 59.7k
12 votes
Accepted

What is this part that came with my eggbeater pedals?

Without a picture it sounds like the grease port tool This picture was found in this article on rebuilding eggbeater pedals. The Crank Brothers Eggbeater pedals, however, require periodic ...
David D's user avatar
  • 21.6k
12 votes

Is it okay for my rear derailleur to be as "compressed" as this when in the lowest gear on the bike?

There's no issue with it looking like that while in small-small. It's very normal. The derailleur's total capacity number defines what large/large combination is supported while still allowing the ...
Nathan Knutson's user avatar
12 votes

How much faster would I go with a better road bike?

I maintain the bikes for an elite rider who funds his career by coaching while he finds a team. The main thing holding you back on a bike is aerodynamics. The faster you go, the more true this becomes....
Noise's user avatar
  • 14.2k

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