I rode a giant for 7 years on a terry falcon saddle.

I recently broke down and bought a cannondale synapse and set the bike up almos identically to the giant. The saddle setback, sadde height is exact. I am getting some chafing on my right ass cheek. (same model saddle I've done 50k on) what could be causing this?
I also have a new set of shoes I have set up with the ergon tp-1 cleat tool. I can figure out what could be causing this. Saddle to bar drop and reach is nearly identIcal.
Help is appreciated.

Is there any way to slide your saddle slightly to the left or right in the cradle? I ask because I had an issue similar to yours once and it turns out that I had the saddle slightly slid to the left in the cradle and I needed it even. That little 1.5 -2 mm made all the difference.

Also, if you have a round seatpost, perhaps you have it turned just ever so slightly off to one side maybe?

I can't shift it left or right, but I can certainly rotate it. If my right side is chafing, should I rotate to the left?

That would really depend on if your original placement is off to the left or right to begin with...Make sense? Look down at your saddle from the front of your bike and see if it look completely lined up with the top tube first. If it is is, then play with the side to side turn of the post just slightly one way and then the other during subsequent rides and see what feels better.Or, if it isn't completely lined up with the top tube, then move it until it is. Does all that make sense?

unfortunately, you've eliminated all the non personal possibilitites, so...how can i put this delicately Danielle, have you perhaps put on a little posterior weight?

Nope. I ride 40 miles a day and am fit.

ha! good for you!

^^^ Fishing for pics.

Is it possible to try the old shoes and the old pedals on the new bike?

I had set up the cleat on my new shoes just off my 2mm and it was very painful after a couple of days riding like that.

Also, what is the relative position of the handlebars compared to the old bike.

Same pedals. Reach to hoods is within 5mm. What is the best way to get cleat position matched up to old shoes? Trial and error just doesn't cut it. When you change the cleat on one shoe it throws te other off. Is there a way to methodically set up cleat position?
My gut instinct tells me this is a cleat issue....but I don't know how to go about it methodically....

I guess I didn't read close enough the first time because I didn't know you had new shoes. Your stack height could be different between the two pairs of shoes. In terms of setting the cleats up in the right position, visually match them up to the old shoes. Sometimes, the cleat mounts are at slightly different points between various shoe manufacturers so that may not work. When I buy different shoes from another manufacturer, I simply always line my cleats up right over where the ball of my foot is no matter what. I have never had any further issues when doing that.

Super obvious and probably wrong, but did you check crank arm length?

Crank length the same

What does q factor have to do with saddle comfort? How is it measured and how can you match it up?

Yeah, cleat positioning was my first thought, but I don't have great ways to check to make sure it's exactly the same.

Check the width of the cranks, side to side where the pedals attach. Wider will of course put your knees farther apart, changing how you interface with the saddle. Measure from the outside of the crank arm to the centerline of the seat tube, both sides.

^^ Bingo. This is the Q factor. It normally ranges from 155 to 170mm. The way you adjust it is with the cleat, but some pedal spindles can also be shimmed if you're too narrow. (No help if too wide.) It only really becomes a problem if you can't move the cleat in or out (EDIT: in/out means from left and right as you sit on the bike. in/out from the crank.) any further and need to. Hopefully that doesn't happen because you'd need a new crank.

Do you get the same issue when you use your old shoes on the new bike?

Also 5mm is actually quite a lot of difference for reach (at least for me).

"---" 5mm

"----------------------------------------" 5cm

What are you? The princess and the pea?

I can tell 0.5cm difference in reach and 0.2cm difference in saddle height.

I guess you are not as sensitive.

Wow, you are sensitive.

when its 2mm too much, you can tell.

No. I don't write for Bicycling.

Yeah, werry, werry sinsitive. Oh My!

Bull puppies.

not in reach but certainly in saddle height.