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I recently saw a steel road bike in a road bike shop where the distance was well over 1cm. 99.9% of old road bikes had a very small distance (~5mm). At the time, they thought it was more aerodynamic. Is the distance still a quality feature from today's perspective?

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    Lack of clearance limits the range of tires that can be used. Additionally, lack of clearance prevents the use of fenders. But low clearance looks sexier, and that is a major design consideration for many bikes. Jun 14, 2023 at 12:56

4 Answers 4

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The distance will depend on the tyre width you choose for the stage on that day. Today's road bikes allow a wider range of tyre widths partially thanks to the adaption of disc brakes. For time trial bikes this is less of an issue and the manufacturer can count with one particular tyre size.

But the gap could indeed lead to some unnecessary wake behind the seat tube. Aero bikes today will often feature a cutout that will allow even smoother transition.

This picture is a gravel bike, so even bigger range of tyres considered and some mud clearance necessary, but still an aero one.

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A pure road racing bike may be much more extreme

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The seat tube acts as a sort of fairing (I could not remember the right English word when writing the initial version of the answer). True fairings are not allowed by the UCI competition rules, but can have a strong effect, especially on the front wheel, as shown, for example, by https://www.bikeradar.com/news/null-winds-technology-fairing/ or https://www.renehersecycles.com/aerodynamics-of-gravel-bikes/

Photos from Cervélo official bike photographs.

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This hasn't necessarily always been about aerodynamics, although it can be. There have been bikes with super-short chainstays for a long time; the most extreme example is the Rigi Bici Corta, which predated aero bikes, and used an un-aerodynamic split seat tube to tuck the rear wheel in more closely.

The reason for this is that a short wheelbase gives more responsive handling, and shorter chainstays should be less flexible, which is a benefit in racing.

To some extent, this is probably a consequence of the time the bike was built, when nearly all frames were made of steel tubes with standard dimensions. Today, racing bikes are often made of carbon fiber, and designers can put more carbon where they need it to compensate for longer chainstays. Also, fashions and philosophies in frame design change over time, and the focus on fast handling that was in the forefront back then is no longer emphasized as much. Bikes today are designed to balance comfort, stability, and responsiveness better.

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  • That's true, this has been a thing even a long time ago. Even in the 1970s or 1980s one can easily recognize an old Favorit (the only locally available - and with big difficulties - road bike brand) as a racing one (e.g. Favorit F1 Special) or a consumer one from the wheelbase length. Jun 14, 2023 at 15:03
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    Indeed, front wheel rising from the ground when riding steep uphills is "responsive". The bicycle responds to your pedaling by becoming a unicycle!
    – juhist
    Jun 14, 2023 at 19:39
  • @VladimirFГероямслава The Favorit frames that made it to Yugoslavia (rebranded to Rog) mostly have very long chain stays.
    – jayded-bee
    Jun 15, 2023 at 5:06
  • @jayded-bee No wonder, the racing ones mostly went to the west or to domestic organized racers and were very hard to obtain. An example: bike-forum.cz/foto/detail/47804-favorit-f1-special-1979 Still not extremely short, but too short for fenders. Jun 15, 2023 at 5:30
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In addition to Vladimirs answer:

Wider tires are more comfortable and better suited for rough surfaces. At the same time they can have less rolling resistance than slimmer tires. But slimmer tires have less air resistance at the same rim depth as wider tires.

The designer of the frame has to balance between aerodynamics and rolling resistance/comfort. What's best depends on the riding you as rider do. A quality frame will give you the best aerodynamics for a given tire width. But just tire clearance alone is not a quality feature of the frame.

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There is a reason and it's not for your benefit.

Bicycle manufacturers want to sell bikes. The more bikes they sell, the more profit they make.

A general-use bike would be an absolute disaster for them, since all cyclists would buy this general-use bike and not buy more bikes after that.

If a bicycle manufacturer makes the distance between seat tube and rear wheel very small, you can't ride your road bike on forest paths since dirt stuck on the tire will scrape away the paint from the seat tube. Thus, you need a gravel bike or a mountain bike. If the bicycle manufacturer made the distance large, you could ride road bike on a forest path and nobody would ever buy gravel bikes or mountain bikes.

Similarly, if a bicycle manufacturer makes the distance between seat tube and rear wheel very small, you can't fit wide tires. This limits the carrying capacity of the bike, meaning you need a touring bike should you travel long distances with heavy cargo.

Also, if a bicycle manufacturer makes the distance between seat tube and rear wheel very small, it's impossible to fit fenders. Thus, you need a commuter bike.

See? For a job one bike could do (a road bike), they sold four (road bike, gravel or mountain bike, touring bike, commuter bike).

Me myself, I only buy bikes which can fit wide tires WITH fenders and still have enough clearance that the wide tire won't scrape the fender when riding on forest paths. It's getting hard to find these kinds of bikes. My electric bike is irreplaceable, those models are no longer made (and it's not reasonable to build your own electric bike since mid-drive manufacturers have specifically made it hard to build your own to discourage "tuning" the bike which could bypass the 25 km/h speed limit). My non-electric bike I have built from parts.

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    This answer would be better without the hyperbole. Obviously with a MTB one can do things one wouldn't be able to do with a road bike with wider tires and vice versa. And a "one generalist" bike in between will obviously be a compromise about those functions. Jun 14, 2023 at 19:55
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    In fact manufacturers very often sell generalist bikes: the entry-level ones.
    – Rеnаud
    Jun 14, 2023 at 20:08
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    It's getting hard to find these kinds of bikes. uhhhh, it's never been easier to find this kind of bike.
    – Paul H
    Jun 14, 2023 at 20:15
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    Let me get this straight, you want a single frame to race on tarmac, do downhill, gravel/XC, tour, haul, and commute? The frame has to be wide and aero, you want fenders, and storage racks. I genuinely don't get it, these parameters can't coexist in one bicycle. I for one prefer owning 3 or 4 bikes that do their jobs well than one "jack of all trades, master of none" frankenbike.
    – jayded-bee
    Jun 15, 2023 at 5:13

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