https://www.merida-bikes.com/en-au/bike/3110/scultura-endurance-5000
I have just booked merida scultura endurance 5000 and wondering whats the reasoning to provide wide 32c tyre. Wouldn't it be too slow for a carbon frame aerodynamic bike. The cheaper scultura models have 25c.
What can be possible tyre upgrades to make my daily commute faster on this bike.
The Merida Scultura Endurance 5000 is an endurance bike. It is not an aero road bike, by which I mean something like the Specialized Venge or Cervelo Soloist that's designed to maximize aerodynamics. Now, many endurance bikes have some aerodynamic tubing, although I'm not sure if the Scultura has that design feature.
Endurance bikes are designed for average riders to go long distances comfortably. This is probably why they specced 32mm tires, although I'm not sure what the current trend is (at one point, 28mm would have been fine for endurance bikes). 32mm tires should make for a pretty comfortable ride.
Tire rolling resistance is complex. But briefly, wider tires at an appropriate pressure are not higher in rolling resistance than narrower tires. (You'll sometimes hear that wider tires are faster than narrower tires; I think this is a misstatement, but for sure running your tires at too high pressure will be slower.) You can design a fast-rolling 32mm tire, e.g. the Continental GP 5000 and the Schwalbe Pro One have 30 and 32mm versions.
In terms of aerodynamics, it's true that higher frontal area equals increased drag. However, you would also need to consider the interface between the tire and the rim. Aero wheels will be designed around a certain width of tire, often 25mm, but some are designing for 28mm. Some aero gravel wheels are designed around gravel width tires, although this is considerably more challenging (for one, gravel tires are really wide, and knobs will also introduce turbulence before the airflow hits the rim, which raises drag). In any case, I don't think the Scultura 5000 has aero wheels. I'm not able to quantify what I think the aerodynamic penalty of a 32mm tire vs a 25mm tire would be, but for the use case of an endurance bike at long slow distance speeds, I don't think the penalty is meaningful.
When we are considering an aero wheel, I think I've heard that the penalty for a tire that's a bit wider than the rim versus an optimal width tire is something in the mid to high single digit watts at high speed (in the region of 28 mph). That penalty is definitely meaningful if you are in a race and you are trying to, for example, catch a breakaway group. You will be well over your threshold power, and in that use case, every watt is precious. In the use case of a casual rider at a much slower speed, that's less relevant, and they also need to consider comfort.
Edited to add: The original question asked about tire upgrades. Per the FAQ, we are not a shopping guide, and we tend to be careful if we recommend products. Objectively speaking, Bicycle Rolling Resistance does test tires for rolling and puncture resistance, plus grip. The latter two are lab tests that can be hard to translate to real-world performance. That said, the rolling resistance test is probably reflective of real world performance. The Maxxis tires tested there are all pretty slow. I mentioned the Continental and Schwalbe models because they are excellent all-round performance tires. That is, they would be excellent on a fast road bike. However, they don't maximize puncture resistance. They aren't fragile, but for commuting, the tradeoffs are different. You might want to favor cost and puncture resistance. Alternatively, you might live where there are really good roads and you're light, and you might even favor the performance tires. All that can be said for sure is don't switch to time trial tires.
Endurance riding is what I do, and the difference between 28 and 32mm tyres is significant for a few reasons:
The pace doesn't suffer much. Until I bought something lighter recently also a little more aero) my endurance bike was a tourer, and with 28s amd mudguards maintaining 30km/h true average for over an hour was very doable, subject to junctions and traffic.
In your case of commuting, for typical rush-hour conditions, tyre choice will make no difference. Consider how much you can actually go flat out, because it's only on those bits that you could benefit from greater speed.
Besides rolling resistance and aerodynamics (that are often overrated), another point that is often neglected is that "comfort" can translate into higher speeds if the surface is not perfectly smooth tarmac. This might be relevant in the case commuting, as you have less freedom in term of choice of starting point and arrival: a more comfortable ride can open the possibility of using some segments that are in less good condition without suffering (for example: taking a shortcut in a cobblestone road).
Also, if you commute has an urban component, you may not also achieve the speeds where the aero advantage of a 32mm tire vs 28mm will be noticed.
A side note, as the question is written the main motivation is to go faster on a commute: endurance road bikes are only better commuters in some niche cases (long commute on countryside roads) to my opinion. But in other cases, it might to be the best compromise (for commuting: maintenance requirements, puncture resistance, ability to carry stuff, clothing and shower at arrival should also be taken into account). You may be interested in this question: How feasible is an expensive road bike for commuting?
