so I bought a brooks, and to my dismay, the rails on the brooks are super short, and in a weird position such that the furthest back position on my setback seat post is still about 2 cm further forward than my regular position. is this a big deal? can I just get a longer stem? this is for a touring bike, with some training and cyclocross mixed into it

Yes a 2cm difference is a big deal. Now the question is, is your current saddle position right where you want it to be?

Moving the saddle forwards will place more weight on your hands/shoulders/arms. 2cm forwards is quite a change. Nominally I wouldn't be moving your weight forwards on a touring bike. How much clamp setback is there on your current seatpost? A typical standard seatpost has about 25mm of clamp setback. Some have zero setback, some seatposts can have 40mm of setback or thereabouts.

Anthony

you're on the money. my setback seat post has 25 mm offset from the seat tube. so what does this mean, I have to get a 45 mm setback seat post?

something else to consider is that i was fitted on the romin evo saddle, which yielded a 7.3 cm setback from the bb. I'm using 7.3 as a frame of reference for the brooks as well (I realize the saddles differ in length by about 4 mm, and that the fit is totally different).

Yes, nominally you want to find a seatpost with 45mm of offset on the clamps to get the same fit. The different saddle lengths and designs throws a small spanner in the works.

Anthony

why cant i just get a longer stem? the more forward saddle position will simply rotate my pedal stroke sequence to a more aggressive angle (downstroke and upstrokes start at different crank positions), wouldn't it?

where the hell do they sell 45mm setback seat posts?

The further forward your saddle is, the more weight on your hands.

You get a seat post with a Head design offering more rearward Saddle position..

Alternate kludge that works : Plain Low cost seat Post . And Brompton's saddle adapter pin

(it offers a Horizontal tube on a typical seat post angle )

you then Use a Regular saddle clip It will be rotated so as to sit above the SAP. (I've done this on a Bike , myself)
adjustable set back distance that way..


On the delux end There is the Nitto Nickel Plated Chromoly seat post , Riv Bike sells those (only in 27.2mm)

Nitto Lugged seat post 27.2 x 250 - 11048

There is the SR MTE-100, an adjustable setback MTB post (with quick release so you can easily adjust the seat position). Goes from about 20 - 80 mm setback. I have one set at 65. Most I have seen are 26.6 diameter which shimmed out nicely for me to 27.2 using garden sheet aluminum from Home Depot. These are long out of production but google them. They are still to be had.

The forward rotated position you talk of is something I do - on my fix gears where I may be riding long distances upwind and don't have the option of gearing down. Definitely NOT what I would choose for touring. There is a lot more weight and pressure on my hands and this is with changes probably half the 2 cm you are talking.

My take on seat position is that it is the most "sacred" measurement on a bike. I won't blink at spending real money to get it right if that bike is going to get any serious use. 2 of my bikes sport custom posts. A third was in line until I stumbled on the MTE-100 (for $15!). "(T)ouring bike, with some training and cyclocross" sounds serious to me.

Ben

one of the things contributing to the problem was that the seat post mast was occupying a lot of real estate on the saddle rails. I went to the shop today, and found a 31.6 (yes it's a PITA 31.6 diameter, not the typical 27.2) with a mast that's much smaller, with the typical 25mm setback. Right now, I am only 5-8 mm away from the measurement of my fore/aft on the road bikes, with the brooks slid all the way back. I think that's good enough.. I hate to go through the trouble to find something that nobody uses, and costs a hundred dollars..

Seat Post sizing Shims abound ,, Then You would Buy one with a 27.2 ID. and your oversize mm OD.

a custom Machine shop project and the center can be closer to one side than the other .ie, eccentric ,

BTW 31.6 is just a hair under 1.25"

No. The purpose of saddle position adjustment is to keep your knee at the correct fit relative to your pedal when the crank is at 180 degrees.

FWIW, selle anatomica has a longer adjustment range to their rail/frame design

Way back (74) Brooks and Campagnolo (1045/a) made a narrower spaced [20 vs 36mm] rail saddle and the seatpost to go with it.
(2x the adjustment range)

at auction, now, they cost a small collector's fortune.