Originally Posted by
rifraf
The Moultons one size fits all frame, has a relatively short cockpit. The effective top tube is only 55.5cm which makes for a very upright position for my 5" 11' height and my inseam of approx 87.5cm or 34 inches when I do the book between the legs thing and mark against the wall.
Your one-size-fits-all frame sounds like it's about a 56cm. If you walked into a bike shop, they'd probably put you on a 56cm or 58cm frame. There's no genius here: you just got lucky.
Comparing Moulton to the Ogre, the Surly's smallest size frame has a ETT of approx 57.6cm. The size large frame which I've taken loads of advice on before whipping out the credit card is much larger with an effective top tube of 616.3 so the stretched riding position is going to be a shock and take some getting used to after the Moultons very upright position.
Effective top tube isn't the whole story. Keep in mind that mountain bikes tend to use zero- or minimal-offset seat posts and shorter stems than a road bike of the corresponding size. On a road bike, my theoretically ideal top tube length is 545mm... but that theory assumes I'm using a 110mm stem and a seat post with 25mm of setback. Taking this into account, the distance from the seat post to the bars is: 545+110+25=680mm.
My mountain bike has a 587mm ETT, which seems impossibly long when compared to the "ideal" 545mm! Unlike the road bike, the mountain bike came equipped with a zero-offset seat post and a 90mm stem. So the distance from the seat post to the bars is: 587+0+90=677mm. Pretty darn close to the "ideal", despite the seemingly long ETT!
Additionally, the mountain bike frame has more "stack" than the road frame, so the riding position is decidedly more upright even though the reach to the bars is about the same.