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65 votes
Accepted

How is this damaged aluminium frame likely to fail?

How is this damaged aluminium frame likely to fail? Sorry. It's not going to fail, it has failed. It's no longer ridable. The head tube is near vertical making the steering very unstable and the ...
Argenti Apparatus's user avatar
65 votes
Accepted

What is the purpose of the top tube on bicycles?

Same basic purpose as the roof on a unibody car. To prevent the back end of the bike folding towards the front end when vertical forces like your brother are applied to the cranks or seat. Very ...
Warren Burton's user avatar
61 votes
Accepted

Can I glue this crack as a temporary solution?

No. The consequences of fork failure are likely to be severe and painful. This may only be a secondary fork crown but it's still structural. The fact that it's such a wide crack means something is ...
Chris H's user avatar
  • 59.6k
60 votes
Accepted

Why do men's bicycles have a top tube while women's bicycles don't?

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 ...
Criggie's user avatar
  • 125k
60 votes
Accepted

Front tire and downtube are extremely close

Your fork is installed backwards. Loosen the stem, rotate the fork 180°, retighten the stem. You'll probably need to adjust the front brake's cable too. Some details that show the fork is installed ...
Adam Rice's user avatar
  • 30.1k
47 votes

Can I glue this crack as a temporary solution?

NO!! That's not a "crack" – it's broken in two! You need a new fork. Your current fork has completely failed. Any attempt to repair it will create a massive weak spot which will just break ...
David Richerby's user avatar
39 votes

Why do men's bicycles have a top tube while women's bicycles don't?

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 ...
lulubelle's user avatar
  • 714
35 votes

Can road bumps excite frame eigen frequencies?

A resonant frequency encountered on a road surface would be for the whole bike system, i.e. frame, wheels, rider etc. The rider is effectively attached to the frame via elements with spring, damping ...
Argenti Apparatus's user avatar
30 votes
Accepted

Is it worth buying a high end light bike (8.5 kg) from 80' vs recent mid range bike (10kg)

Although I support keeping older bikes in circulation in general, this particular bike comes with some caveats. One of my riding buddies had a very similar bike. The Vitus 979 is a bonded aluminum ...
Adam Rice's user avatar
  • 30.1k
30 votes
Accepted

How to choose a bike for a very tall and heavy person?

At 480lb/220kg: You need good custom handbuilt wheels from day one on any bike you get, regardless of genre or usage, and it has to be from someone who knows what they're doing. Rims exist that can ...
Nathan Knutson's user avatar
29 votes

Frame failure sudden death?

If an aluminium frame has to be bent back into alignment, it's trashed. Aluminium cannot be deformed without causing weakness in the material. If the bicycle repair shop literally hit the seat stays ...
Argenti Apparatus's user avatar
25 votes

Is it safe to ride an aluminium bike with a big top tube dent?

My opinion, which is very much my own, is that this is safe to ride home and may provide some level of “emergency use” where no other bike is available and you need to get around for a short while, ...
Noise's user avatar
  • 14.1k
25 votes
Accepted

Which frame material is the most sustainable?

The process of manufacturing Carbon Fiber Reinforced Plastic (CFRP) parts—what we call "carbon" bikes—stands apart from the rest as extremely undesirable for the environment. Some bike ...
Therac's user avatar
  • 820
24 votes
Accepted

Why are all road bike frames now squashed parallelograms?

Sloping top tubes started with mountain bikes, and were brought over to road bikes by Giant, following a design from Mike Burrows. Partly because a perpendicular joint between the seat tube and top ...
Adam Rice's user avatar
  • 30.1k
24 votes
Accepted

Did my frame just break?

I think its just the hanger that has broken. They're not cheap, but they cost less than a new frame. Keep the old bits and reassemble them, and then compare with https://wheelsmfg.com/derailleur-...
Criggie's user avatar
  • 125k
24 votes

Why Did Old Soviet City Bikes Have Longer Frames in General

A soviet bicycle is designed to carry very heavy loads on the rear (like two large containers of milk one each side). Hence the rear wheel and the pannier are moved backwards, giving more weight of ...
nightrider's user avatar
  • 7,849
23 votes
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What is this frame feature for?

Its a chain hanger. Purpose is to hold the chain when you take the wheel off. The idea is to support the chain and stop it falling through itself, making a tight loop and shortening the life of ...
Criggie's user avatar
  • 125k
23 votes
Accepted

Is it correct that the bottom bracket shell thread does not go all the way around?

Are you referring to the absence of material at the chainstay openings in the bottom-bracket shell? This is absolutely normal. This is what a BB shell looks like before being built into a bike: ...
Adam Rice's user avatar
  • 30.1k
22 votes
Accepted

Is it worth buying carbon fiber road bike for short commutes?

Comfort isn't really an issue for a 30-minute ride, as long as the bike fits. Also, for any given price point, an aluminium bike will have better components than a carbon bike, so will probably be ...
David Richerby's user avatar
22 votes

Making bigger steel frame smaller

It isn’t possible to resize a bike like this. You would be talking about removing each individual tube, cutting it down to size, and then rejoining them. We would be talking about all the tubes, not ...
Weiwen Ng's user avatar
  • 32.3k
20 votes

Is it safe to ride an aluminium bike with a big top tube dent?

I’m not an engineer. With that caveat, I think this frame is likely to fail. It may depend on how thick the tubing is, and if you see little cracks anywhere on the tube, I would stop immediately. ...
Weiwen Ng's user avatar
  • 32.3k
20 votes

Do carbon MTB frames crack easily?

First of all, carbon is stronger than aluminium. It's mechanically on par with steel, while being much lighter. That's why it's the go-to material in aerospace and race cars, and it's also why it is ...
leftaroundabout's user avatar
19 votes

Banged frame: Is it still safe to use?

Unfortunately I think that level of damage with a big dent and buckled top tube will make the bike dangerous to ride. There's a chance that when a big bump or pothole is hit the top tube will fold ...
Argenti Apparatus's user avatar
19 votes

Is it worth buying a high end light bike (8.5 kg) from 80' vs recent mid range bike (10kg)

Depends what is your goal, but personally, I'd go for the modern one. Maybe for this budget, you can find something second hand with Shimano 105, that would be also an option. The reasons are: weight ...
Rеnаud's user avatar
  • 20.6k
18 votes

How is this damaged aluminium frame likely to fail?

Oh, that frame is done. It’s not worth saving a few hundred bucks now and spending thousands in the hospital later. Make sure to check over the rest of the bike, especially the fork. It might have ...
MaplePanda's user avatar
  • 15.6k
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

Rear wheels are dished. Why not "dish" the frame instead?

A reason I would see is related to the cranks: a dished frame would require to have a chainring further from the center of the bike, which can be a problem from ergonomic and structural points of view....
Rеnаud's user avatar
  • 20.6k
18 votes

What is the purpose of the top tube on bicycles?

I don't have an engineering background, but I believe the top tube makes the bike stiffer laterally and torsionally (i.e. resisting twisting movements). You could build a bike without a top tube. Many ...
Weiwen Ng's user avatar
  • 32.3k
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

Bike with a hi-ten steel frame for getting around the city?

I have 4 bikes, and the one I keep for just riding around a city is high-ten steel. Yes, they're heavy, and normally cheap, but they can be tough and practical. What's more important is that it works ...
Chris H's user avatar
  • 59.6k

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