oddly enough, I bought a Fenix SL last year, it was a sweet bike. I sent it back after a couple of rides, back pain, it was too long. go by the numbers, mate. strictly by the numbers. check the measurements of your cannondale, ETT, stack, reach. then find the Fenix that best matches those numbers, not easy, as there are large gaps between sizes. I think you want your ETT to be within 5mm of your cannondale. factor in your stem length, as well, that affects your wiggle room. if you can't make up the difference with 10mm longer or shorter on the stem, I say walk away. ETT on the Ridley I bought myself was 10mm longer than the bike it replaced, but a shorter stem did not compensate, maybe they don't measure center-to-center, I don't know. Ridley claims 545mm ETT for the small frame, same as my Salsa Fargo, so I thought I was good to go. but my Fargo does not hurt my back.
after they refunded me for the Fenix, I bought an Orbea Avant, same spec as the Fenix, just as sweet to ride and better sized for me.
my wife has an XS Fenix SL, which has the same ETT spec as her first roadie, but she is using a 1cm shorter stem. she does not have a ton of miles on it yet, but she says it fits...
if you don't have it, hopefully cannondale has your geo chart in the online archives... good luck!
Last edited by kevrider; 06-25-19 at 05:20 PM.