I have a gravel 1by bike with 42t and a 11-42 cassette. I also have a road bike with 50-34t and then 11-34 cassette. My question. When going uphill in easiest gear in both, they would both be a 1:1 ratio, but is one effectively an easier gear(i.e less effort) than the other because of the different number of teeth? cheers
No, both gears will be identical. The absolute number of teeth does not matter, only the ratio does. Both bikes have a lowest gear ratio of 1:1, so from the gearing alone both will be equally "hard".
However, since the gravel bike's tires are probably bigger, the distance traveled in one wheel rotation is longer than on the road bike. This means that even in identical gear ratios (e.g. both 1:1), the gravel bike will be slightly "harder", particularly considering that the gravel bike is probably heavier.
As said previously, the ratio is the important metric, not the number of teeth. Tires (tread and pressure) can be a important differentiating factor between the two bikes. The gravel probably has larger tires, which impact the outer diameter (as explained) and the surface in contact with the road.
They are also meant to be run at different pressures. Road bikes inflated are typically at high pressure (>6bars), while gravel bikes should be inflated at much lower pressure (2.5bars-4bars). That alone has an impact on the rolling resistance.
Gravel tires also have (deeper) treads, which improve traction on loose surfaces, at the cost of rolling resistance on hard surfaces. The effect of rolling resistance is more felt in uphill than on flat terrain, because it adds to an already existing effort.
So with that, the road bike should be easier on hard surfaces, while the gravel will be easier on loose surfaces because of the additional grip.
Doesn't matter for easier pedaling, but matters for wear
Since nobody has mentioned it yet - with bigger gears,
- the chain runs smoother as the gears are closer to circles,
- the chain links have to bend for a smaller angle,
- the force on the chain gets proportionally lower,
all effects that reduce wear. On the other hand, the chain travels over more teeth in the same amount of time, which might increase wear, but I'm pretty confident the wear-reducing effects dominate, and thus bigger = longer lifespan.