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I live in a city but also like to go into a cross-country areas as well.

I've also noticed that there are rare models of road-bikes that offer an option to install wide tires:

Oh, and you can fit a 34mm tire in there.

https://www.cervelo.com/en-US/bikes/caledonia

Is this really practical to have such a bike? What other models offer such an option? Is this a good idea to buy a "normal" road bike and then buy a third-party fork that allows for wider tires? Should I watch out for some anomalies in geometry when installing non-standard fork in such a case?

List of models of road bikes that allow wider tires that I've found so far:

  1. Cervelo Caledonia - up to 34mm.
  2. Trek Domane - up to 38mm.
  3. Giant Defy - up to 38mm.
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    If you want the option to go really wide you could also look into gravel bikes which would also give you lots of clearance for mud and stones.
    – Michael
    Apr 8 at 6:26
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    I looked seriously at the Trek Domane before getting a really good deal on a nearly new Canondale Topstone with two wheelsets for road and gravel. I'm very pleased with it. Comfort is up there with my steel tourer, but it's 5kg lighter and noticeably faster
    – Chris H
    Apr 8 at 7:47
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    Also went in the same direction than @ChrisH recently: on the market for an endurance road bike, ended up with a gravel with double chainrings and two wheelsets instead. The additional versatility (not only the one allowed by wider tires and sturdier frame, but also related to mounting points) won over the additional weight. A more comfortable frame/tires is also notably faster when the road surface is getting rough (I live a country known for its cobblestones).
    – Rеnаud
    Apr 8 at 9:34

3 Answers 3

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For long days in the saddle, on rough paved roads, 32-35mm tyres provide a significant comfort benefit over the likes of 25mm, when run at an appropriate pressure. Riding in the dark also benefits from some shock absorbing in your tyres, as it's harder to dodge all the rough bits in time.

I find the biggest benefit to my wrists rather than anywhere else, and can't imagine buying a road bike that couldn't take 32mm tyres (most likely with mudguards as well.

There's a slight weight penalty, but very little aerodynamic penalty (choice of rims is more important) and the rolling resistance of wider, softer, tyres can easily be less than that of very thin hard tyres on realistic surfaces. So even if speed is your thing, this sort of width can be good.

Endurance road bikes often offer such tyre clearances (but I run a gravel bike with 32mm road tyres for my long rides in summer, 35mm with a little grip in winter, or even my gravel wheelset when the roads get filthy).

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    To put this view in context, my idea of a long day ride is anything from 9 hours to 24 hours, including stops but not many of those. But I commute on similar tyres on my tourer
    – Chris H
    Apr 7 at 16:53
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Yes, it's extremely practical.

There are in general two reasons to favor wide tires at lower pressures.

One is riding on soft sand roads. On such roads, a narrow high pressure tire can squirm a bit, not travel straight, making the bike hard to control. Whereas, a lower pressure wide tire rides on the sand surface comfortably. This especially happens in areas with snow when the snow melts and the sand roads are wet, making the road softer than when dry.

A second reason is punctures. If you have a 32mm tire, you probably pump it to 6 bar, letting it fall slightly below 5 bar before repumping. Slightly below 5 bar is easily doable with many mini pumps with wide barrel diameter, enabling you to ride home and pump them to full 6 bar with a floor pump.

However, if you have 23mm tires, you probably pump them to nearly 8.5 bar. Try to do that with a mini pump with wide barrel diameter, you'll quickly see that the hand force needed for pumping becomes unacceptable, making your hands really tired. Try to do that with a mini pump with narrow barrel diameter, the number of strokes needed increases to such a huge number that you lack patience to do them all.

I think most 23mm tire users have a CO2 pump and a number of CO2 cartridges with them. However, they are single use. A lightweight and small patch kit has 6 patches. Try to carry 6 CO2 canisters and you'll see you never match the capacity of a patch kit with CO2. However, a mini pump allows unlimited number of tire fill-ups, but is not feasible on 23mm tires. With 32mm tires, it's perfectly feasible.

I switched from 28mm tires to 32mm tires precisely because I found that it's hard with my Quickex Quicker Pro mini pump to fill a 28mm tire to an acceptable pressure, but 32mm tires have a lower acceptable pressure.

I personally recommend to buy only bikes that allow wide tires. One reason is 32mm tires for summer (generally the widest width at which high pressure slick tires are still available), but another reason is that in areas with snow, you can run studded tires. However, some types of slush require a ~120mm fatbike and nothing fitting on a regular bike is safe.

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    23 mm is virtually non-existent now except for bikes older than at least 10 years. The choice is 25-28 or 32-34. Even older rim brake bikes without wider dual pivot calipers use 25, better ones 28. Disc brakes allow more. Pumping larger tyres to lower pressures also takes time because it is simply so much volume that has to be pumped in and with pumps capable delivering high pressures it takes many pump strokes, especially for MTB tyres if one uses a pump that can also pump a road bike. Apr 8 at 8:47
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    Your example pressures are a bit on the high side (though I recall you are heavier, so you are probably used to higher pressures). I (66kg) would be perfectly fine and happy riding a 32mm tyre at 4bar. I can get up to ~6 bar with a Lezyne Road Drive pump which is enough for me even with 23mm tyres. As for studded tyres: Unfortunately the narrowest ones are ~35mm wide (or even wider on modern rims) so you’d need enough clearance for that (plus snow). A typical road bike frame with 32mm clearance won’t cut it.
    – Michael
    Apr 9 at 8:48
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The benefits of wider tires has been discussed in the other answers if you want stay within the rated limits, so I won't develop it.

There are some points in the question that suggest that you may want to go beyond these values, for which it might be good to develop a bit: "going to cross country areas" and "swapping forks", but first I'll need to diverge a bit on two trends on the bike market.

On the road side of the market, endurance bikes are going wider to be more at ease on "light gravel" (smooth offroad surfaces, whether dirt, gravel sensus stricto, compacted sand) and the new buzz word for that is "Allroad". 35mm tires or wider is very common among endurance road bikes - the current max is 40mm for the Specialized Roubaix SL8.

On the gravel side of the market, there's a split between "race gravel" (Canyon Grail, Specialized Crux, 3T Racemax, Salsa Warbird) and "adventure gravel" (Canyon Grizl, Specialized Diverge, 3T Ultra, Salsa Cutthroat). Race gravel are in fact having a riding position that are very close to endurance/allroad bikes, but can take even wider tires, and have transmissions that are more suited to offroad use (often single chainrings with clutch derailleur, lower ratios, but not that far off from road bikes), have more mounting points and are more sturdy (about 1kg/2lbs weight penalty), because designed to be used on much rougher surfaces.

On swapping forks: if the bike is rated one section, there's no reason to swap the fork if you remain within the rated boundaries. Swapping forks is complicated and not something that is recommendable on a regular basis (you'll have to disconnect the brakes for example, which would mean with hydraulics to replace the olive and purge the system each time). But what you can do easily is swapping wheels. In gravel, there it's not uncommon to have two ratings for tire widths: one with standards "road" rims (28"/700c), and one with smaller rims (27.5"/650b), but with even wider sections (typical values: 42mm for 28", 55mm for 27.5"). But the most common for those with a gravel bike is to remain with 28" wheels, with conventional road tires on the road wheelset and 40-45mm on the offroad wheelset — going above 50mm in gravel is only good for some niche cases.

On "cross country": cross country in biking jargon is a branch of mountain biking, that is considered to be the less extreme in terms of "technicality". Gravel bikes are capable of doing to the less technical stuff of cross country. But if you meant in a more literal sense (secondary roads too rough for a conventional road bike), gravel bikes are the current answer for that use case (current cyclocross bikes are limited to the UCI discipline, the leisure/long distance moved to gravel bikes).

So in short, if your idea is to go beyond the rated values because of the "cross country segments", going to a gravel bike is an alternative worth considering. After that, there's another discussion that can start on whether it's better to have one set wheels with tires suited for "hard pack gravel/tarmac", or two set of wheels (one with road tires, and one with more offroad tires) — with clearance around 40-45mm, it may not be necessary to have 27.5" wheels though. However I should add that in some regions, a gravel bike is a good compromise (the ones with a good network of secondary/tertiary roads), in other regions a bad compromise (the ones where the secondary/tertiary roads are not developed enough, and going offroad would require a proper MTB).

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    My worry about changing wheel sizes is pedal strike. Changing to a lower effective BB height takes some getting used to, and the lower setup is for rougher ground where there's more to hit. You get some height back from the fatter tyres, but it's unlikely to be more than half of what you lose on the diameter. It was an mtb that I hired the other day with about 20-30mm less ground clearance than mine, and far more pedal strike.
    – Chris H
    Apr 8 at 7:52
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    But +1 for swapping wheels if going onto rough stuff. I tend towards the "rural areas" interpretation of "cross country" rather than the mtb meaning, when I read the question, but it could be either. Anyway if the country roads are anything like as bad as some here in the UK, off-road wheels could be desirable. I've certainly wished I'd fitted my gravel wheels for road rides - and also wished for good honest gravel rather than hard-edged potholes and loose mud slipping against the paved surface
    – Chris H
    Apr 8 at 7:56
  • @ChrisH on the lower BB height: that's probably why the trend is more to go towards 45mm-50mm on adventure gravel but with 28" wheels, rather than going 27.5", but some manufacturers are still keeping the option when designing the frames to go wider with 27.5" rims if the wider width is required. But a gravel with 40-45mm tires is already very capable, without needing to go to 27.5" wheels. My gravel bike for instance is rated with 47mm on 28", and 2.1" on 27.5", but I feel that I'll never feel the need of using 27.5" wheels - and I use it with semi-slick 42mm tires in road club rides.
    – Rеnаud
    Apr 8 at 8:08
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    I agree. My gravel tyres are only 37mm. The frame will take 42 or maybe 45, but not with my mudguards. At some point I'll upgrade my gravel tyres, slightly bigger and with a bit more tread on the shoulders, and relegate the current ones to commuting
    – Chris H
    Apr 8 at 9:37
  • Other than adjusting cable/hose length (which has some leeway), is there a reason that swapping the fork would require disconnecting the brakes?
    – RLH
    Apr 8 at 16:56

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