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Comment by prmoustache | Hacker News Reader

There is actually very little difference between a cyclocross bike and a lightweight gravel bike. Slightly lower BB, slightly longer wheelbase, sometimes slightly different headtube angle, flared handlebars. Actually the first gravel bikes were rebadged cx bikes. You can race cx with a gravel bike and race gravel with a cx bike. The rider makes most of the difference.

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So much bicycle acronyms and initialisms makes for a challenging read for the uninitiated (like myself)! I've researched the terminology and happily share in hopes you too will find it useful:

1. "lower BB" references a lower bottom-bracket, the part that holds the axle to which the cranks attach.

2. "CX", or cyclo-X is short for cyclocross, which is a style of bicycle race which takes place over varied terrain conditions such as pavement, wooded trails, grass, steep hills and obstacles requiring the rider to quickly dismount, carry the bike while navigating the obstruction and remount.

https://en.wikipedia.org/wiki/Cyclo-cross

https://en.wikipedia.org/wiki/Cyclo-cross_bicycle

The cyclocross bikes appear similar to road racing cycles, the major differences between them being frame geometry, and wider clearances for cx bikes to fit larger tires and generally still function after accumulating large amounts of mud and other debris.

edit: Thank you @jerrycrunch! I've incorporated your bb info.

Bottom bracket, the part that holds the axle to which the cranks attach.

Sorry for that. I am a hardcore cyclist, I don't always realize that people are not as accustomed to the terminology.

> You can race cx with a gravel bike and race gravel with a cx bike.

Sortof. The key defining difference is that a cyclocross bike meets the UCI rules for cyclocross, while a gravel bike doesn't. In a sense, the gravel bike trend is the result of consumers rejecting the UCI's definition of what an off-road-capable drop-bar bike should be.

A gravel bike is perfectly allowed by the UCI. You just have to mount CX tires (width 33mm) on it.

Geometry is actually probably the big difference - cyclocross bikes are designed for small repeatable courses often with tight turns and the need to carry the bike on your shoulder. A slightly lower or higher BB height would probably work well for either - it is the ratio of total height vs top tube (so height vs length of the frame) that really defines cross vs gravel. Cross bikes will be taller and shorter (length wise) to have shorter turning radiuses and slightly lower weight at the expense of long term rider comfort and stability at speed. Gravel bikes will be longer and have worse turning radiuses but slightly better stability at speed. You can see the same thing with cars. A shorter bike (just like a short wheelbase vehicle) will also have better approach angles relative to its height.

That being said depending on your leg length to upper body torso length you can of course size a cyclocross bike up or a gravel bike down and achieve sort of the same effect. In my opinion these types of geometry questions do not come up nearly enough in relation to the rider, however, as someone with a very long torso is going to be quite uncomfortable with a bike with a short top tube even if the "size" of the bike is correct for their leg length / height. And of course the opposite can also be true. Ideally we should be sizing and matching frame geometry to the persons geometry regardless of the intended use case of the bike.

And you can do fine in a road race with a gravel or cyclocross bike! Just gotta put appropriate tires on.

You have just proved you haven't rode a cyclocross bike. Since those bikes' center of mass is higher than the road bikes it is really "nervous" on high speeds for example long descents.

I won a criterium once on a cyclocross bike while waiting for my team supplied road race bike.

That so called nervousness is greatly overstated. I think this is a US thing actually.

But crit races are not like coming down from Stelvio kind of speed where nervousness counts. Crit races are exactly like cx races but on asphalt or at least where I'm in Europe ;)

I rode my cyclocross bike in the Swiss alps for months while waiting for my custom road bike. It was perfectly fine descending mountain passes.

As I said, that so called nervousness is overstated because people overthink it. BB height matter but for the most part we intuitively and inconsciously accounts for it and adapt. Also the difference is minute, from a 5 mm to 15mm. It is not like we switch from a road to a tall bike either. And guess what? A tall bike is pretty easily rideable, there are even people doing offroad on them.

A lot of people do not size their cross bike right - they ride a top tube length that is too short. Maybe this also helps with tight turning radius (which could be an advantage during a cross race).

not true - the "nervous" feel is because people also tend to ride cyclocross bikes that are shorter (top tube length). There is no reason a cyclocross bike cannot be designed with the higher bottom bracket AND a longer top tube - I never understood why the frames were designed like this in the first place (maybe for weight savings?)

edit: Realized it is for turning radius

I always raced CX bikes that had the same top tube length as my road bike but usually with a 1cm shorter stem for a slightly more upright position.

Cyclocross bikes also have higher bottom brackets

That is what I mentionned by "Slightly lower BB" for the gravel bike, just stated in the opposite direction.

It doesn't matter much anyway and CX bikes from US brands had already started lowering the BB of the CX bikes because US courses designers are usually less keen on putting off cambers section than euro courses designers.

Sorry somehow missed that.

The explanation I heard for the traditionally higher brackets is that it facilitates quicker turning. Is there truth to this or is this more of a marketing thing?

I think it is a mix of many parameters and the main one was that when cx was invented people were using toe clips with straps, albeit looser than on the road and they would hit the ground until the rider has put his foot inside when the bottom bracket was too low.

The rest is mostly the ability to pedal in the corners without clipping a wheel, which help maintain and feel grip, tradition and also to help on the many off camber sections the courses used to have.

I think quicker turning has never been the true reason imo.

Larger road frames are designed to accommodate longer cranks and their BB drop approaches that of traditional CX which is itself dropping to lower heights as fashion changes.

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