Hi, hoping to get some insight from the experts out there who can explain to me why touring frames have generally slacker seat tube angles than road frames even though both frames will be ridden on mostly paved roads.

When comparing frames of equal size, road frames seem to have seat tube angles between 73 degrees and 74.5 degrees while touring frames are sold with seat tube angles between 71 degree and 73.5 degree. In both cases, smaller frames have a steeper seat tube angle and larger frames the slacker. For the sake of argument, a 55 cm Brand A road frame will have a seat tube angle of 74 degree while a 55cm Brand A touring frame will have a seat tube angle of 72.5 degree. Shouldn't both types of frames have the same seat tube angles as that would determine pedaling efficiency? That is, shouldn't your seat location relative to the bottom bracket be the same for both types of frames? I've read explanations stating comfort and stability as reasons but isn't this a case of the longer chainstays and lower bottom bracket drop touring bikes have compared to road bikes?

In keeping the question focused, I'm hoping replies will omit discussions regarding the front end of the bike; namely head tube angle, fork rake, trial and stem length etc. as they affect more the steering, stability and overall handling of a touring bike rather than seat tube angle and pedaling efficiency.

Thanks.