fancy sticking an x7 double 28-42 on the cross bike and keepign a closer ratio cassette out back. other wise its standard compact and 11-32 out back

GXP ones showuld work as they only locate against one bearing and float in the other, but it’ll leave a 7.5mm gap on the drive side and screw up the chainline.

Why not just run spacers?

trying to keep the q the same as on a road bike

Nope, q factor on a ht2 chainset is goverened by the length of the axle (err, actually a ‘spindle’ technically)attached to the crank, not the width of the BB it spins in. So if you fit the bb with no spacers you will just get near enough the same q factor minus maybe a mm or 2, and about 6-7mm side-to-side play.

So if you fit the bb with no spacers you will just get near enough the same q factor minus maybe a mm or 2, and about 6-7mm side-to-side play.

Not in SRAM/Truvative GXP ones you wouldn’t.

They trap the NDS bearing between the LH crank arm and a step on the spindle, the spindle just floats on the DS bearing.

Actualy a pretty good system as the DS bearing takes the load from the riders weight (same as the NDS) plus the load from the drivetrain, so isolating it from side loads allows it to spin freely and shares the wear between the two sides evenly.

OP,
Have you measuered/reserached the Q factor or each chainset? They might be the same despite differing BB widths.

i guess the question is more based around the spindle length. Will i end up with a 7.5mm gap due to not using the spacers, or will the chainline be out due to having 2.5mm of spacers on teh drive side that would not be there on a road chainset.

will fire the question to cy as well see if he knows

ta for response so far