I replaced my 26″ wheel commuter bike frame this week with a newer one. All parts swapped over and new tyres bought – Schwalbe marathons replacing some worn MTB tyres. First ride into work on Monday felt terrible – really hard to accelerate away from lights and a short steep climb on gravel nearly had me off. I assumed it was the tyres, and puncture resistance is good but holy hell I wasn’t putting up with that feeling so put the worn MTB tyres back on. Yesterday was a bit better – but still the bike is noticeably harder to accelerate and climb on. Bike setup is a singlespeed which I guess highlights the differences, on a geared bike I’d just choose a different gear until it felt comfortable again and wouldn’t notice I was in a lower gear than before. The only thing I can think is that because this bike is a later model it is suspension adjusted for a longer travel fork and so fitting the same length fork as my old frame has resulted in the head and seat angles being a bit too steep. So now I’m wondering if the steep seat angle can effectively reduce my power output because it really feels like I’m in a higher gear. I know about KOPS, but thought that KB has discredited it – but I can’t think what else it can be? Both frames are steel
Both about the same actual TT length
Newer frame is slightly lighter
Commute is on the road, both ways so no difference from wind etc.
All parts are the same apart from the frame.

Move saddle back to get the same kops position as before, shouldn’t feel any different pedalling wise then, adjust for reach by changing stem length

Already fitted a layback post and it hasn’t helped much as the difference is pretty marked. I measured the head angle of the old frame before I stripped it and it was around 69 degrees, measured new frame last night and it was 73 degrees.
Old frame would have had a 71/73 angle combo so the seat angle would haver been something around 71 degrees. New frame I think should be 71/74, which means the seat angle is approx 76 degrees – 5 degrees different.