OK so apologies if this easily found from past threads - my first post.

I know in general terms, a heavier rider will put out higher watts, but the watt / kg ratio will likely be impacted. eg me - 100Kgs at 250w =2.5 .

I also get that, say a 50 kg rider with same 250 watts would get a watt/kg ratio of 5.0; - and finally - to keep a high watts / kg ratio for a long time is usually more difficult for heavy riders …

But here is my question - if two riders of DIFFERING weights have the same watts/kgs ( eg 2.5) - does the lighter rider get a faster speed because the heavier rider’s power is offset by their weight? and so in that sense a lighter rider benefits more from the ratio than a heavier rider - even though the lighter rider may not be able to generate the watts of the heavier rider / what they used to when they were heavier?

i ask as i can see myself going 27-30km/hr , but i am slower than others that I think I see at the same ratios, or lower ( and so i am assuming they’re lighter than me - or cheating on their weight).

It depends. (yay! ) I therefore reference you to the Zwift Insider: Speed Tests: Steady w/kg Across Various Body Weights | Zwift Insider
This may not seem right, because normally heavier riders are faster on flats and lighter riders are faster on hills. But the difference is that, as you said, it is harder for heavier riders to output high w/kg, and it is harder for lighter riders to output high raw watts. Comparing same watts or same w/kg across weights assumes that a heavier rider can do high w/kg or that a lighter rider can do high raw watts, which usually is not the case.

On the flats I have a difficult time. I can do 46-48min ADZ but must do 3.5w/kg or more to not get stuck at the back or dropped by the 170 strong Coco group on Tempus.

Even worse it feels like riding through mud in comparison to going up ADZ. I have to put out high watts/kg just to try and get mid-way through the Coco group. If I ease off slightly I get pushed to the back again.

I am 100 kg…in a Bot ride on flats I can stay on the back at 1.3-1.4 w/kg…(Target is 1.8)…But that is boring so I push on the front to keep my avg up around 1.7-1.8. I also have an advantage on downhills and rollers where I do not shift for the little uphills…just stand and crank 400 watts and rocket out the front …soft pedal until halfway up the next roller when they catch me…most fun!

So to summarise (kind of lol ) , if we go back to the question - let’s not worry about it being harder / easier… if two riders have the same watt /kgs… then I was wondering if the lighter one would be faster (less power needed to move less mass in the ratio etc.) … BUT based on the link you shared (thank you!) it seems regardless of hills or flats, a heavier rider at the same w/kg IS faster… so then my experience of same w/kg going faster than me is heavier riders, NOT light riders …interesting… it also suggests than even a 1w/kg improvement / difference - (yes that’s a lot of effort to change ) - makes a huge difference IF in doing so you are now also your lighter… e.g. if you go from 2w/kg 100kgs to 3 @85 kgs - and drop weight in doing so, then you effectively ramp up speed even though you lost weight and potentially - power(watts).

Thanks for this excellent link. It confirms, with some basic analysis of results:

bike + equipment adds approximately 9 kg to your weight, no matter your weight. So heavier riders at the same W/kg will climb slightly faster since the bike is a lower fraction of their mass.

wind resistance is approximately proportional to the square root of mass. So at the same W/kg, riders at higher mass require more power than lighter riders, but not enough added power to eliminate the speed advantage. Rolling resistance is still significant, however, and this is proportional to rider mass.