Importance of tire width

Question

How much of an impact does tire width have on the performance of a bicycle?

I am in the process of buying my first real bicycle and am having trouble deciding between a more traditional road bike with 25mm tires versus an "adventure" bike with 32mm tires. The manufacturers description for the second specifically mentions paths and trails with variable terrain while the road bike only mentions different weather conditions.

Most of my local riding would be on paved trails where I wouldn't expect any problems with the road bike. However, there is a possibility that I would also like to do some packed dirt canal towpaths that are a little further away. Ideally one bike would be good in both locations.

Is it a terrible idea to try and use a road bike anywhere but pavement? How much of a difference does a wider tire make while riding on pavement?

Answer 1

1. Tire width has a large impact on bike performance but should be considered alongside tire qualities such as suppleness and proper inflation.

Very generally: A wider tire can provide more suspension.

When anyone asks me for recommendations on bicycles, I immediately encourage them to consider a bike with wider tires.

2. It's not a terrible idea to take any bicycle wherever you want or need to go within your riding skill limits as there are unique challenges with different surfaces and obstacles. Wider tires generally allow wider applications.

3. With proper inflation, on pavement, a wider tire will be just as fast as a skinnier tire and may even allow you to ride more efficiently, quickly and confidently through turns or when rough surfaces, cracks or potholes appear.

Details...

The primary and most notable difference between two identical tires (same tread, suppleness etc.) of different widths will be the amount of suspension they provide over bumps, cracks, rough surfaces and other irregular terrain.

A lesser but notable difference will also be the size of the contact patch where they connect with the riding surface.

A skinnier tire (with equivalent inflation) has less capacity to deform so can provide less suspension and insulation from irregular surfaces. It also provides a slightly reduced contact patch to grip the road, potentially diminishing the bike's 'sure-footedness' when cornering or braking.

I think aerodynamic differences and weight are not notable concerns given your tire sizes and application.

The only caveat is that any tire you choose should be properly inflated for the weight the bike is carrying. Too much pressure and there is no suspension from bumps. Too little pressure and bumps could cause flat tires, wheel damage or an accident.

Knobs or varying tread patterns and various designs and types of tires change considerations somewhat but even a nice, wide, good quality tire is important for a high-end, fully-suspended downhill race mountain bike.

A bike compatible with wider tires will usually have room for fenders and you can always put thinner tires on if you want to run your own experiments.

Answer 2

25 mm would be at major disadvantage on dirt canal towpaths.

32 mm with touring or road type tread is only at minor disadvantage on the road. Slightly more rolling and air resistance but you pick up softer ride, more traction, and less pinch flats.

You can put smaller tires on the adventure bike but I doubt you could put 32 mm on the road bike.

Answer 3

Tire sizing can be pretty important.

The first thing to note is that tire sizing that you can run on a bicycle is a function of the rim (the width of it) and the frame (the tire needs a few mm to clear the frame so that it doesn't rub the frame). A rough rule of thumb is that you won't be able to more than 1 or 2 tire sizes up on a road bike from whats originally spec'd (that being said, there are a lot of road bikes which violate this).

The second thing to note is that an air filled tire absorbs shocks through its deformation. As Sheldon Brown notes, a properly inflated tire will absorb bumps, have low rolling resistance, not pinch flat (if you have a tube) and keep you in control. The proper inflation of a tire is a function of the size of the tire and the load (weight) it has to carry. For example, on a 26x2" tire, one person may use a pressure like 40 PSI whereas on a 700x20 tire, they may use a pressure of 100PSI+ for cruising around town. A larger tire will use a lower pressure than a smaller one to be properly inflated (and the lower pressure is usually more comfortable). A heavier load or one over rougher ground requires a larger tire. So, fat people shouldn't really be using 700x20 tires, for example (*).

---

Now onto the actual questions.

1. Is it a terrible idea to try and use a road bike anywhere but pavement?

Depends on the road bike. Some are better at going on fire roads and other surfaces without significant drops than others. A larger tire size is helpful. Cyclocross bikes tend to be quite good at this sorta thing too.

2. How much of a difference does a wider tire make while riding on pavement?

Depends on the tires. A larger slick tire can be better on pavement than a smaller knobby tire. Unless you're a racer, you probably won't see a penalty with buying a bike that ships with 25 mm tires vs 32 mm tires in performance; in fact, you'd probably get a bit more comfort out of it (bikes designed for bigger tires generally tend to be more comfortable as well).

Note that there are other factors which go into which bike to pick, and the best way is to get a test ride in conditions you'd ride in. That being said, walking paths near canals tend to be pretty smooth typically, so I wouldn't fret on a road bike.

(*) There are obviously other issues to tires for heavy loads; a tougher built bike is better in this case, particularly high spoke and well built wheels.

Answer 4

Apart from comfort/suspension, another consideration for dirt (unpaved) roads is getting flat tires (I road recently with someone who will only ride his road bike on paved roads, to avoid flats).

But I note that, for example, Marathon Plus are available starting at size 25.

I have a "hybrid" bike with 32mm wheels (and disc brakes). A road biker once pointed out my wheels and commented that they look robust, unlike his, and that I wouldn't have trouble with them: from which I inferred that road bikers find their wheels fragile! It's true that I am care-free about the ability of my wheels and tires to survive pot-holes at speed (which matches the footnote of Batman's answer).

In summary there may be a difference of more than only the wheel width: a bike with narrow wheels might be optimized for weight and wind resistance, at the cost of being relatively fragile; a bike with wider wheels might be optimized more for robustness/endurance. Road racers might notice whether their bikes weigh slightly more, recreational cyclists might be happier with something slightly sturdier.

The "adventure" bike you linked to is made of "lightweight and durable aluminum", whereas the road bike (from the same manufacturer) includes "composite" (I presume that means carbon) components. You don't intend to fall over but you presumably will a few times (e.g. apparently everyone does, when they first learn to clip their shoes to the pedals). I think I read that an accident involving carbon components is cause for concern: they might need replacing? Whereas less concern with aluminium.