Originally Posted by
urbanknight
Actually, you're still looking at it too simply. If you're setting up the bike to have the same handlebar height, you would then be making the effective head tube the same length. Whether you have that length in head tube or in spacers, it still continues backward at the same angle. But even if we assume for a moment that you would leave the handlebars at different heights, you're talking about a difference less than 5mm unless you have some crazy length head tube.
You gotta look at the entire bike set up, not just what the bare frame looks like on a piece of paper.
Anyway, that being said, your advice to the OP makes perfect sense to me.
Post #7 tells me about spacers, the 25mm spacers on the op's bike accounts for about 7mm reduction in reach, in other words the best part of the next size stem length should he remove the spacers, the info lacking is the height of the headset above each frame which I simplistically took as equal on both bikes, however my own bikes range between 15 and 20mm which accouns for another mm or 2 reach adjustment. by reducing stem length you reduce height as well as reach particularly with the stem flipped up as the op says, which also effects the number of spacers required and therefore reach again.
Of course I have also assumed that handlebar reach is equal on both bikes which is unlikely to be the case, I find it surprising how many people rattle on about how stem length effects handling when no one blinks if you tell them you use 70mm reach bars or 90mm reach bars. I have also assumed the length of the hoods is the same which is likely to be wrong. I have also assumed that the stem angle on both bikes is the same which may not be the case.
All in all though the more info you take into account the closer you will get with an estimate of set up on the new bike. With my assumptions and the knowledge that in reality you may not notice just a few mm of differene anyway, the set up I posted will get the op pretty close. The calculation comes out at +-about 2 or 3 mm on both reach and height - but like I say some of the assumptions will be off.
By the way OP on the 56 frame suggested as being closer in post 8 would require you to use a 120mm stem on 35mm spacers to get a similar fit. IME I find bikes ride better with less spacers and 35mm is getting up there. If you post a picture up here of a small frame using 35mm spacers and 120mm flipped up stem, you will spend the rest of the day reading comments telling you to get a larger frame. Again, although it seems some people are saying im not thinking about this correctly - I am. and the numbers I have posted are calculated, and correct.
As a side note however, if you can survive riding a lower front end then the 56 would allow you to flip the stem flat and get lower without using a 90mm stem which you would need on the 59
Hope this has helped